Science method

Analytical Chemistry Instrumentation - Science method

Explore the latest questions and answers in Analytical Chemistry Instrumentation, and find Analytical Chemistry Instrumentation experts.
Questions related to Analytical Chemistry Instrumentation
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105 answers
Potassium Sorbate added to cheese with low pH due to the presence of lactic acid; does lactic acid act the same as HCL to convert Potassium Sorbate to Sorbic.
Also, potassium Sorbate added to brine ( saturated water with salt 10% at 4 C degrees)
How you think these conditions will affect the equilibrium between potassium Sorbate to Sorbic acid.
The problem in food industry labs they rely on outside labs to test and analyze samples for all out of ordinary tests and I've been trying to find a lab to analyze Potassium Sorbate separate from Sorbic acid but they only test Sorbate by HPLC which doesn't give an idea how much of each component is in that sample.
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Agree with Matthew Wheal .
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35 answers
Hello,
I'm quantifying residual monomers in a complex mixture via HPLC/UV with a 1 point calibration. To process the data im using Chromeleon 7.2.
At the moment im confirming the identity of the analytes by retention time. I want to add a verification by UV-spectrum. I saw that I can add reference spectrum in the processing method.
Is it possible to extract the UV-spectrum from the calibration to use as reference?
Thanks for your help
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I am no native speaker (sorry for that, indeed). Maybe the author of the manual is also a German and yes, there are typical errors when Germans use the English language. What is meant is obvious for a non-native speaker like me: you can choose every single peak you want as source for the reference spectra ...
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50 answers
The equation of the plate height is given as H = σ^2/L where σ is standard deviation in a normally distributed curve (representing width of analyte peak) and L is the length of the column. Why is the peak width represented as σ^2 and not 2σ?
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Dear M. Farooq Wahab,
From the following relations we could answer to your question:
(1) no. of theoretical plate: N = L/H = Lx/ sigma^2 = L^2/ sigma^2
The variance of the solute peak, which can be obtained by a straightforward graphical procedure, has units of seconds squared and is usually designated as τ^2 (Skoog, Instrumental 7th ed. page 703):
(2) τ = sigma / L/tr = w/4 => sigma = L w/ 4 tr
If you insert Eq. 2 in Eq. 1 you can reach:
N= L^2/(L w/4 tr) ^2
you solve and
N=16(tr/wb)^2
Kind regards,
Ali
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24 answers
How to deal with this problem?
Example I have 10 sample, and I use duplo method. And we have a target for our sample's CV is under 5%
In the 7th sample, the coefficient of variance is more than 5%, but it happened only in the 7th sample. In this case, another sample is fine (CV less than 3%).
Do you have any idea what is going on?
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Flow measurement can be performed with different methods. Accuracy of reading may depend on different factors like samples water etc.
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16 answers
I need to carryout Py-GC-MS analysis for biomass sample but can't find an analytical facility for the same in India. Please help me.
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@ Tapas Kumar Patra I want to know that in GC-Ms facility in your institute is CO gas is used as carrier gas?
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105 answers
The pyrolyzer system cleaning every month, change the ferrule of reactor glass tube and septum thermogreen. 
after bleeding of the column I have this problem. I dont know if the problem is the other glass tube that connected direct with column or the ferrule of the column.
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I experienced the same problem. Changing the septum, o-rings, and the liner did not help in our case. After a thorough diagnosis and leakage test, I realized that the graphite ferrule at the injector side was broken. I changed it with a new one, and the problem was solved.
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15 answers
I am trying to do CHN analysis on a bio-oil sample, but my results seem odd. My CHN results were about 10% H, 11 % C and 0% N. This would leave about 79% oxygen. I think the numbers may be odd due to the volatility of the sample. Is there an accurate method to easily do CHN on volatile samples? Or do these numbers seem reasonable? Other papers seem to have about 50% carbon for the bio-oil.
Thank you,
Michael
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Dear M. Behrens,
I did CHNS of condensed volatile oil of biomass. It has been analysed in a leco elemental analyser. The sample preparation is the main difference. The sample preparation was as follow:
MATERIALS
Tin Blades
Tungsten oxide
Shaper for shaping tin foil to hold the oil with the tungsten oxide
Tablet Forming Press
Analytical balance
Spatula
PROCEDURE
Weigh the Tin Blades and Tare the Scale
With both blades on the balance add approximately 0.1400 g of tungsten oxide to the shaped blade
Tare the balance
Add 0.050 g to 0.1000 grams of dehydrated extract over tungsten oxide
Wrap the blade with the material taking care not to lose material
Wrap the second tin blade over the first to reinforce the seal.
Place the tin package with the sample in the hand press
Beat the press piston sparingly to form the insert
Identify the sample
Ready to analyse.
I hope it helps.
Kind regards
P.S. I add pictures of sample preparation
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20 answers
After performing boehm titration using HCl,NaOH, Na2CO3, and NaHCO3.  I want to know the formula to calculate functional groups.
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I have been having the same challenge but I think the attached document can help. it has the equations but needs logical substitution
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8 answers
Who has experience with the new AriaMx Real time PCR machine from Agilent? While the machine itself seems to work well, the evaluation software is severely crippled and it contains a whole lot of errors.
We complained several times more than 5 months ago but the new software version 1.2. that came up recently not only did not repair anything but on top it became extremely unstable!
I am extremely disgusted that we as customers are used as beta-testers for an obviously flawed product.
Please see the attached file with a list of the most obvious problems and give me feedback about your experience with Agilent. Maybe if more users voice their concern in public, Agilent finally will listen. 
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Thank you for sharing good information!
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12 answers
Hello, I need recommendations about the "CO2 analyzer" for the gas phase in reactors for AOPs. Portable indoor analyzers can be a solution? Someone studies used portable analyzers, but I don't know the accuracy of these types of equipment.
Thanks for the future answers!
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You can use the techniques lister by Bruce or store the gas in a special bags and determine CO2 by GC-TCD. Depending on the outlet gas composition there are also dedicated sensors.
Regards
GB
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18 answers
Hi All,
After our preventive maintenance, when running standards, we can no longer see fluoride, chloride, bromide, nitrate, sulfate and phosphate peaks in our chromatogram. The suppressor has just been recently replaced and we had a good run last time before the maintenance, the backpressure is not too high and is historically typical at 1900-2000 psi for a 1mL/min run, we have already primed the system before use and we are using a deionized water with a resistivity of 18.2 megohm.
The standard we are running is a mixed standard from accustandard, containing all the mentioned anions above. Although the EGC KOH cartridge has just expired last April 2016, we checked the pH of the waste coming out from the column line and it is pink or basic. Personnel who used the equipment last time also reported that he was able to use an expired EGC KOH cartridge,
Id like to ask why are we not seeing sample signals during our run? Have you experienced this?
The service personnel calibrated the detector via a meter and checked it by bypassing the column and directly injecting 10ppm HNO3 to the conductivity detector to check if a signal will appear. A signal did appeared, however was it proper? What are the risks?
Please help!
Best Regards!
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Hi,
I am setting up an IC version ICS3000. There is a Na peak in blank (DI water). I already checked blanks by another IC but it did not show Na peak like ICS3000 (using the same eluent and DI water) . It means that DIw was not contaminated by Na+.
Then I changed new column and suppressor but it still showed Na peak in blank (same eluent and blank).
I checked Dtector and Pump also.... They did not have any problem.
Do you know any posible problem in my case?
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165 answers
I have experienced (-) negative values for a particular element in AAS or ICE-AES analysis.
1. What does this really mean and how could it happen? Can we explain it using the calibration curve?
2. I further have observed that there is the same (-) value for a particular element in different samples and changing (-) value for a particular element in different samples. How can it be explained.
eg.
For Mn: Std are 0.3, 0.5 and 1 ppm in 0.1M HNO3
The samples in 0.1 HNO3 and calculated concentration is -0.035 for all (50) samples
For Ca: Std are 0.5, 1 and 1.5 ppm in 1M HNO3
The samples in 1M HNO3 and calculated concentrations are -0.157, -0.181, -0.199 (changing but (-)so on for all (30) samples.
Thanks in advance
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Your calibration is statistical; you are fitting a curve to a series of calibration points. It has error associated with the curve. When you get down to a low enough concentration, and you have calibrated correctly, then you can, statistically, get negative numbers. This is normal; in fact, any decent auditor would applaud you for doing your job correctly. As long as you are not getting large negative numbers then the data is telling you that the element(s) you are measuring are not present at your detection limit. This is also why you determine, and use, a lower limit of detection (LOD) and a lower limit of quantification (LOQ). These indicate the point at which your calibration is no longer valid; you shouldn't report values below your LOD.
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49 answers
I am trying to analyze Lead in water samples using an atomic absorption analyzer. I tried without modifier but i get really low absorbance levels. I guess I need appropriate matrix modifier to increase the signal.
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Note with using matrix modifier the furnace temperature program must be changed ashing and atomization temperatures must be increased
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234 answers
I am planning to do a research on the levels of mercury in waste water; mercury is known to be a persistent, bio-accumulative toxin, indicating that its toxicity does not diminish through decomposition or chemical reaction, and that it is absorbed faster than it can be excreted. Recently, efforts to minimise the release of mercury, and to track its migration when released, have demanded more sensitive analytical techniques for its measurement.
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I think ICP-MS
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15 answers
What about the calibrant used during CI-MS tuning? I'm just switching from EI to CI. Is it necessary to change the calibrant from PFTBA to PFDTD?
Thank you in advance for your suggestion.
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Yes, we use 69, 219 and 502 m/z but with 69 being not very intense.
A further approach is to simply perform a EI tuning (without methane) but with a CI volume and to copy the parameters from the EI section to the CI section. This works on our instrument, i don't know if it will work on Your machine.
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18 answers
Any instrument or method that can measure lifetime of film samples?
Thanks
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Thanks @Mohammed Mohammed . Really appreciate it!
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30 answers
I am analyzing complex samples by Acquity UPC2 coupled to HRMS and I am having trouble with the carry-over effect of polar compounds - sugars. I´ve tried changing the initial wash solvent (MeOH/IPA 1:1) to more polar one (MeOH/H20 up to 1:1) and increased its volume without any success. Anything else I can do?
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Does anyone know of a Acquity UPC2 users forum?
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30 answers
Hi,
Am using Electrochemical workstation 660E,
Am not able to get X and Y axis values, have tried from rebooting the system to deleting the regedit includes deleting old data.
if someone faced the same issue please let us know.
please find the attached files.
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Dear Pankaj
It was not about the separator (Comma, Tab, Space ), that was about the potential voltage on x-axis and current on y-axis which disappeared on my system but when i used the same .bin file into other system it was showing the values of X and Y axis.
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10 answers
We are searching for a service manual for an Agilent LC/MSD SL. The MSD unit is about 15 yrs old. Need to know proper part #s and diagrams for service to get it back online. Currently have a vacuum leak. Thanks
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I am looking for the same manuals, if someone is willing to send them, please message me.
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104 answers
FTIR spectra were generated for 0.1 M H2SO4 and 0.1 M H2SO4 which had a soaked polymeric membrane. At first, I thought the spectrum of the latter was a mirror image of the former, but that's not the case. Looking at the spectra at 860, 1010 and 1160 cm-1, supports this observation.
The absorption bands from 1310-1910 cm-1 and 3500-4000 cm-1 were caused by H2O molecules present in the branched polymer (30% PEI in H2O). The issue here is, the doublet at 2360 cm-1, which supposedly represents absorption by CO2 seems to be oriented at different directions for the two samples. What could be the possible phenomenon behind this effect?
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Simple: The CO2 content of the air is different. If the CO2 content decreases after the background measurement, the corresponding peaks are negative in the absorbance spectrum otherwise if the content increases you get the usual positive peaks.
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40 answers
I have a solution of both Peroxydisulfate (S2O82-) and Hydrogen Peroxide, and most methods used to detect Peroxydisulfate (S2O82-) interfere with H2O2 because of the similar O-O bond. How can we quantify one without the interference of the other?
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Dear Ali,
there were several papers in which detection of peroxydisulfate and peroxymonosulfate was achieved by ion chromatography and HPLC, probably by this you could distinguish between h. peroxide and PS.
Please see:
Moreover, one chapter in this review is devoted to the determination methods of PS:
Regards,
Stan
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27 answers
We've started a project looking at some OTC botanical tinctures, which are already dissolved in either glycerol/water or glycerol/ethanol. I need to get them dried down for our analysis, and that is proving to be difficult. Does anyone have experience removing glycerol from a sample? Either rotovapping, or lyophilizing, or some other method? Thanks for your help!!
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Those interested at this discussion may possibly want to check also this other RG thread: https://www.researchgate.net/post/What_is_the_easiest_quickest_and_cheapest_method_to_separate_water_from_dilute_glycerol_solution
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28 answers
Thanks in advance for your replies.
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Hello!
I'm trying to plot a chromatogram in .SMS format. I've tried some programs and all the others. TXT or .CSV or some other ASCII file. Please, does anyone know of any software that can open this kind of file in .SMS?
Thanks!
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63 answers
I have approximately 160 UV-Vis spectra collected on an Agilent UV-Vis which are saved in an SD file (which seems to be proprietary). Does anyone have experience translating blocks of data in these files into a useful CSV (or other spread sheet readable) format?
I am aware that after collecting each one, these can be exported one by one, however, it will be nearly impossible to do this as many are nearly the same so selecting each one is non-trivial.
(I just added an example  file7/3/2016). Not sure if it shows up.
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Hi Mustafa,
as you can see from the Spectroscopy Ninja website (e.g. https://www.effemm2.de/spectragryph/down2.html), I give a free Spectragryph license to academic, private and non-commercial users upon request. Your licensed version is just one email away:-)
All the Best,
Friedrich
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28 answers
I have until now been been slightly unruly using adhesive foil plates to seal 96 well sample plates ready for loading onto our HPLC (Alliance 2795). Whilst this is adequate for my needs and I don't mind cleaning the injection port once in a while I'm probably getting leeching of materials from the small amounts of adhesive which find their way into the injection port or perhaps even the injection loop. I'm monitoring my samples via MRM so this slight contamination isn't a problem but I would rather have a method which keeps my system as clean as possible. Does anyone have any recommendations for films that seal 96 well plates that are neither foil nor use conventional adhesive and aren't strong enough to damage the needle or mechanism? Thank you.
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Hi Roland,
The Zonefree Sealing films are available from Alpha Laboratories (cat # ZAF-PE-50 ) or from sigma (cat # Z721646). I've used these now for 3-4 years without issue BUT only with MeOH or MeCN so I've no idea how they would react with stronger/different solvents.
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36 answers
I am very new to gas chromatography. This past month or so is my first time using the machine. I am trying to recalibrate using known standard for what I am testing. Made some dilutions and am sure of their concentration. Concentrations are 0.01, 0.025, 0.05 and 0.25 mg/ml. At first, the three smaller concentrations were very close, but the high concentration was always off, being ~0.3 mg/ml. We have tried to calibrate several times and now it seems most if not all standards are off by 15-25%. What is wrong? What are some common reasons this could happen? We plan on replacing consumables (liner, ferrules, seal, column etc.) as soon as supplies come in.
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You and your organization are a victims of the nonsense spread by instrument makers that instruments are answer machines. THEY ARE NOT. Instruments are just tools for the skilled craftsman to use to ply their skill.
A properly set up lab has a professional analytical chemist experienced in the technique.supervising the technicians who tend an instrument. The instrument and analytical method needs to be set up by an analytical chemist who is well versed in that technique and instrument.
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36 answers
I have a new molecule for which I have initially developed an isocratic LC-MS/MS method (Synergi Fusion column, H2O/ACN 20/80 (+0.1% HCOOH)). Analysis of this method gives limited sensitivity because of broad peak shape (but it was sufficient for the time being), and with no traces of carry-over.
Later on I needed a more sensitive method, so I switched to a gradient method to sharpen up the peak. Now I have great sensitivity but a carry-over of 50%!
Gradient:
A: H2O+0.1% HCOOH
B: ACN + 0.1% HCOOH
t        %A      %B
0       90        10
3       90        10
3.1    20        80
5       20        80
5.1    10        90
8       10        90
Rinse solvent: ACN
Injection of a standard solution followed by a series of blanks showed that the peaks decrease somewhat evenly by about half, after each injection. It will be impractical to therefore injection 10 blanks after each standard solution and sample.
Injection of a completely fresh blank vial (injected as a 'sample) after injection of a standard gave a peak, suggesting that the analyte does not stick to the outside of the needle. Use of an external wash vial showed no improvement in the carry-over. So the problem must be somewhere in the system.
I tried a number of things already, none of which had any effect:
- Tried a different column (Synergi Polar instead of Synergi Fusion)
- raise the gradient to 100% ACN and keep it for an extra minute
- rinse solvent: ACN/H2O 50/50, and MeOH/H2O 50/50 + 1% acetic acid
- used an external wash vial with ACN/THF 90/10
I then went back to using the isocratic method, and no carry-over was observed. But it is not sensitive enough, so I really need this gradient method to work.
What other rinse solution combinations could work? Perhaps something more similar to the mobile phase?
- H2O/ACN 20/80 + 0.1% HCOOH ??
- H2O: ACN: MeOH: Isopropanol (25: 25: 25: 25 V/V) ??
The LC-MS/MS system is an Agilent Series 1290 Pump and Autosampler, with an API 5500 MS
Any help would be appreciated!
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Thanks for all your input!
In the end it turned out to be very strong carry-over due to the physical/chemical properties of the analyte. The analyte showed very strong affinity to virtually all column phases, which means residual amounts remained stuck on the solid phase of the column which kept on eluting in small fractions with each subsequent blank run. I have found a highly deactivated C18 column that showed minimal carry-over with which the analysis could be adequately performed.
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93 answers
I need to get a calibration curve for pure creosote sample. I have the pure creosote solution. I need to prepare different concentration in the range of 1 to 10 ppm. How do i prepare from the pure sample ?
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I want to make 2ppm 20 ml solution from 20ppm, How to calculate it
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72 answers
Just wondering about their expense to make. Does liquid propulsion cause excess interference in IR?. A multifunctional HPLC that checks for impurities would be more valuable. Does the liquid sample need to be stationary to be ananlytes by IR?.
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Flow through cells are cheap. There are selected bands in the IR that are not swamped out by conventional eluants; depending on what you're looking for it could be useful.
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16 answers
Good day all,
I am using hydrothermal synthesis to prepare a certain MOF and due to repeated synthesis and exposure to atmosphere there is a green layer that doesn't come off even when washed with concentrated HF. Is there anyway that i can clean this? Any input will be appreciated.
Thank you all for your time.
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Thank you all for your suggestions.
For those who face similar issues - conc. HCl, DI and sand paper was used to clean the autoclave.
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77 answers
I want to seek the opinions of experts in the field of environmental science. I intend to determine elemental contents of some freeze dried plant samples collected after an experiment. Since I want a non destructive method of determination of these elements, mostly transition elements. I am being sceptical about the use of XRF because I have been used to the use of conventional method of total digestion and analysis by either A AS or ICP MS. So, I want to hear opinion of people that have used XRF concerning the reliability and reproducibility of results. Is it better than normal conventional element analysis and how reliable are the results from XRF? Thank you all
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XRF is not better than normal conventional element analysis but much faster and enables you to analyze the elemental range from Na to the  transuranic elements. The d-block transition elements work very well with detection limits in the lower ppm range (based on dry matter).
How reliable are the results from XRF: The answer is quite simple, it depends very much on Your sample prep, a general answer is not possible. To have a start point I would recommend to start  with freeze-dried samples as loose powder and a fundamental parameter based XRF quantification. You could give some of Your samples to an XRF lab to test it if it fits Your needs, analyses are cheap.
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36 answers
I have Raw graph of the EDX analysis.
how can I convert Graph A to B??
 Do u have link for download??
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Hi there,
It is important to have text file data " for raw data peaks" and use the ORIGIN PROGRAM to do it. See link : http://www.originlab.com/
Regards, 
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24 answers
I am developing a new method for phenolic compounds (especifically: chlorogenic acid, caffeic acid and vainillinic as well). RP-Column C18 (Venusil XBP C18 250 mm x 4.6 mm x 5 um). My mobile phase system includes:
ACN (A) and acetic acid 0.5% in ultra-pure water (B). I have set the wavelenght to 320 nm. My flow rate is 1.000 ml / min and my column temperature is 25 °C. It's a Knauer machine equipped with a quaternary pump and a LPG system and a degasser system, too.
I have flushed my column with isopropanol for around 1 hour till I see no peaks or drift in the baseline. Then, I made baseline with 10 % ACN and 90% of acetic acid solution (0.5%). When I sample with a blank (the same mobile phase) I get it with noise and peaks in my "baseline".
Any help would be appreciated.
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Typically you get that kind of noise out of a UV detector when you either have a saturated reference channel or you have bubble formation. Not familiar with your system, so I have no idea as to how you are mixing the ACN and H2O (low pressure, high pressure, etc), and therefore I have no idea if you could have bubble formation. 
I question the need for a 100 minute separation for something that is relatively simple. Your gradient certainly can be significantly faster. I also question the choice of ACN. You know for certain that the phenols are highly soluble in alcohol; why not use methanol rather than ACN for the separation? 
Have you checked the pka of the compounds? Are you certain that acetic acid is your best choice? I would have probably leaned more towards formic acid or TFA for this analysis.
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135 answers
Please can any one help me?
I fabricated four aluminum matrix composite with SiC and MgO, and I need the best method to find the exact chemical composition after casting.
What is the best method to analyze the chemical composition of metal matrix composites?
I used EDS, but the Si did not appear.
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XrD will not show clear peaks under the following circumstances. (1) Low volume fraction, (2) poor distribution and (3) poor bonding of reinforcement particles with the matrix. Generally in situ composites show clear peaks in XrD compared to aluminum composites prepared by other techniques. Etch the surface of the aluminum composites prior to taking XrD. Etching would expose the particles and improve the peaks in XrD. Generally, XrD can only confirm the successful reinforcement and can't compute composition exactly. Optical emission spectrometry (OES) can be used to find the composition of composite after casting. However, it is not a usual practice. Because metal matrix composite is always written as Matrix/X. Vol% Reinforcement. No one writes in terms of elements just like the composition of matrix alloy.
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20 answers
HPLC Shimadzu Modes PDAD
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In the Left side of the toolbar, change the  real time batch to acquisition mode, there you can switch to single injection mode
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12 answers
I´m working on determination of lactose as allergen in dairy products by GC/FID. After extraction and evaporation, the sample is dissolved in pyridine and further derivatized with TMSI/TMCS(2:1). I´ve been  noticing problems with reproducibility of peak areas from the beginning, Even if I provide repeated injections from the same vial peak areas are getting higher and higher, than unexpectedly a little smaller, than higher again. I´ve read that these agents may plug the syringe, therefore I flush the syringe with acetonitrile after every injection. I can´t see any trubble with the injected volume, which  is 1ul, but the problem persists. Rezex rxi-5ms column, temperature program up to 320, injector temp.250, split ratio 1:80    Could anybody help where can be the problem?
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1. Use splitless (by reducing of course your compound 's on-column amount!) - avoids variations by split which can be less reproducible.
2. Avoid Liners with glass-wool. Use deactivated empty liners.
3. Increase injection volume up to say 2 uL and reduce the amount of samples by a factor x- as you do not want to go beyond the dynamic range.
4. Use lower injection port like 220 C, as you wish to avoid thermal breakdown at injection port.
5. After derivatization reactions with TMSI/TMCS(2:1), make sure to centrifuge well and avoid white particles/ crystals that these compounds invariably form, and take very little.
6. Make larger volume reactions to avoid handling variations, clean syringes with 2-3 washes or more to avoid carry over, do not store derivatized samples more than few hours. Change liner and septa every 24 hours if you keep running it all the time. If few samples, then not an issue.
7. Change a new column syringe, liner, septa, and see if the problem persists.
" if I provide repeated injections from the same vial peak areas are getting higher and higher, " is also seemilngy a "carry over" issue from syringe, septa, liner, columns! So wash and clean well, and run blanks in between every samples! : )
Also, what magnitude (x times) of variation you see? Calculated CV/ RSD as well?
I guess problems would be in points 1-4 and if you can address them one by one, I see the problem going away!
Thanks,
Biswa
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56 answers
Im currently running the HPLC. After autopurging, i normally wash the column using 100% acetronitrile for about 10-30 mins then I would perform the baseline check and every time I run the check it would show "FAILED" few seconds right after I clicked "RUN". Why did this happen? Im sure my mobile phase is not contaminated. Im using C18 column, solvent A: 1%acetic acid: MilliQwater and solvent B is 100%acetronitrile. Normally before I start the analysis I would wash the column again using the initial percentage of acetronitrile I use for my elution gradient program and I wash it for about 10 mins. 
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It fails because your drift has exceeded your limit. You have not equilbrated the column. You do not have a stable baseline ready for testing.
A few comments as I think this may be your very first time using HPLC.
(1) Please do not wash the C18 column with 100% ACN. Instead, use a solution which contains an aqueous percentage (i.e. 2 or 5%) and the same acid you are using for the method (acetic, in your case). This will do a better job of stabilizing the support and washing it. Additionally, you may need to wash your column down with other solutions (e.g. Methanol / water) because the purpose of a wash solution is to remove ALL material (samples) which may have accidentally absorbed onto the support over time. The correct solution should be comprised of liquids which will dissolve 100% of any and all samples used (not 99%) so this usually means that you use a stronger solution than found in your mobile phase (experiment to find out which solvents work).
(2) Next, after you column has been properly washed down you will need to slowly condition it in the initial condition mobile phase. The initial condition mobile phase is the mobile phase composition that you will start your initial hold with, before starting the gradient. For a C18 column, it would most likely not be 100% organic (as noted before), but a mixture of organic and aqueous solution. This mixture should be run through the column until such time as you achieve a nice stable, flat baseline (with no drift) while monitoring the detector. Once this has been achieved, you can make an injection and start the data acquisition.
If you could provide us with some basic chromatography information (column dimensions, flow rate, detection wavelength and bandwidth, detailed gradient program, injection volume, injection solution...) we may be able to provide additional comments, but the answer to your question is "drift".
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18 answers
I'm  working in ICP-MS and the sensivity is not good. I've tried many things, but problems seems to be in the exit slit of the equipment. I never did this maintenance before, there is any care or special procedure to do this? I have to disassemble to check it and/or change it, but don't know how exactly to do.
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You haven't given us any information, so the best we can do is guess. 
What element? How much loss in sensitivity? Any changes in conditions? Etc. Etc.
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36 answers
The pump was not in use for over a year. Electronics work good and can be operated directly from the instrument or through the software. 
It has not been pumping any solvent (Acetonitrile:Water; 50:50) through any port. Has 4 ports. I checked for the firts being blocked but it was not and even if tried with direct tubing, there is no flow. 
Trying to get solvent by reverse suction using a syringe also did not work.
Any comments/suggestions?
Thanks
Reji
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I am using Dionex P680 Pump, yes, it has two 2 pistons. @Marcos Steola
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I am currently using for the first time ICP-AES and we have encountered some ignition problem, the plasma went off suddenly and since then we haven't been able to ignite it, we get a message popping up on screen , which say magnetron voltage is too high. Can someone please highlight some of the problem they have encountered while using Agilent ICP-AES 4200 and how did you solve them?  
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We have a Perkin Elmer ICP-OES (5300 DV). I was warming up the ICP to analyze the samples and the torch was on for atleast 45 minutes. All of a sudden it went out. I tried starting it again but it won't. When trying to start the torch, I could see a spark for 1-2 seconds, but no sustained plasma. I replaced the torch, cleaned the RF coil and also checked the argon flow but in vain. Am missing out on something? Any suggestion would greatly help. Thanks!
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For example, in the UV calibration There are various parameters for calibration as per IP and suppose instrument fails to comply with any one part e.g Resolution, Is it that the instrument should totally be abandoned from its use or can be used till the problem is rectified. How to define it on SOP.
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Not only do you have to discard all the results generated after the failure, but also all the results generated before it as far back as the last time it passed.
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 is the bigger LRI (Linear retention index) or RI (retention index) means bigger concentration or peak area or percentage of peak area for GC MS measurements?
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>  Retention (= the time that compounds stay in a  column!) indices can NOT be related in any ways to their Concentration (=amount!).
Except if the column is overloaded, then the retention times shift a little.
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My group is working on several scientific instrument designs. In keeping with the open source ethos we would like to share them - but would prefer to put it the literature rather than using our website or one of the OSH repositories -none of which are quite appropriate. I have looked at PLOS One that has published some open source software tools (but not hardware yet) and at the Review of Scientific Instruments (that only does hard core new stuff - irrespective of price). They often publish tools with OS software as well. For our most innovative work they both would work - but I am also looking for locations to develop basic tool sets and add that to the literature so that we can all reduce our experimental research costs...the basic stuff we all need but currently pay enormous sums for - e.g. environmental chambers. Any good appropriate journals?
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The link given by Nicolas Guarin-Zapata is not working anymore.
But now there is the Journal of Open Hardware ;-)
"The international peer-reviewed Journal of Open Hardware publishes papers and reviews on technical, legal, economic, and sociocultural aspects of open hardware design, fabrication, and distribution. Its primary goal is to promote research and development of professional, academic, and community-based open hardware projects"
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Hi Everyone,
I work in a lab for a pharmaceutical company. The brand new column we purchased can only last 16 injections (a week) shown by lowered peak separation index and badly shaped peaks.  
Here I list the parameters and any help will be greatly appreciated!
A polar compound is being tested so 100% aqueous mobile phase is used. Temperature 30C, Flow rate 1.0ml/min, pH 6.6, UV detection 210nm. Pressure 115 bar. Solvent A and B: 0.2% potassium dihydrogen phosphate and 0.1% TBAH (tetrabutylammonium hydroxide solution). Equipment: Agilent 1260 infinity. Column used: Thermo Hypersil Gold C18 AQ 4.6mmX250mm 5um.
Question: Anything we can change to lengthen the lifetime of the column? Are there other column recommended for TBAH which is believed to be a damaging agent? 
If anyone had similar experience and happened to fix this please offer your insight. Thank you so much!
Simon
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It is likely you have a non-polar compound in your sample matrix which is being completely retained by your column.  I would reverse and wash the column with 100% IPA in order to extend the column's  lifetime.
You might want to add a column wash step at the end of an injection sequence.
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The connection of autosampler in CP-3800 GC is ok, but the autosampler is not working. That mean there is probably a communication problem CP-3800 GC. Is anybody knows the solution about this? Thanks.
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Hi Asaduzzaman, I agree with John, I suggest review the link between software GC and autosampler, when on the GC and software so the autosampler is on too, if not hapen reset the autosampler, on and of and reconection. 
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Which brands of HPLC is more robust and better-Shimadzu (LC-20AT semi-prep or Agilent (1260 Infinity II)? I am thinking to get one extra and your suggestions will be appreciated.
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Hated Shimadzu software in 2002. Agilent can be customized to do anything you like nowadays for calculations and reporting. Lots of users worldwide, and extremely durable engineering.  Our 1260 Infinity system has been analytical workhorse for vitamins and caffeine and special projects over 2 yr. Only problem was needed pump seals replaced (easy!)
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Can I separate toluene and CO2 using an MXT capillary column? My detector is an FID with methanizer and everytime i run a mixture of CO2,toluene and dry air, I always get two peaks. The first peak is occurs at 13 minutes while the second one is at 18 mins. But i got confused because when I ran it empty, even for several time, I could still get two peaks. I checked for leaks in the column connections using Snoop and there seemed to be none. Thanks for your guidance
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Do you have an idea about your dead time? Is 13 min gross or net retention time? I suspect that 13 min might be your injection peak, which would be very late for a typical capillary GC that's optimized to run BTEX. At 200 °C CO2 surely comes with your injection front (as it would at room temperature anyway).
What is your flow rate and your column dimensions? And how do you inject? Some gas volume with a syringe directly on column?
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HI,
I am currently purifying a protein(64kDa) with rosetta gammi 2 expression. BUt, i notice a yellow colour in my fractions. It was previously not colored but, recently it is eluting in low imidazole concentration(10mM) and it is colored. I have done mass spec and the size is correct but, upon doing biochemistry there is no activity. What do i do?
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If your protein has more number of tyrosine and tryptophan, it will show a tinch of yellow. Also if it is very high concentration, it would be added the color.
Do the protein known to have any cofactor or metal ions ??
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I was using an Aminex HPX-87H column in an Agilent HPLC to detect tricarboxylic acids from Krebs cycle. Now I gonna use UPLC systems (LCT premier and Synapt) to detect it and I'm looking for an equivalent column (2.1 x 100 or 150, ionic exchange and polymer-based matrix) 
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Thanks!! let me check all the suggestions, carbomix  seems to be the best
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We have repeatedly observed dramatic and often sudden losses in the sensitivity of our qTOF-MS during long series of measurements in positive mode. Starting from this situation, measurements in negative mode run with normal sensitivity. After operating in negative mode for a while, polarity can be changed into positive mode again and the sensitivity is normal again. It seems as if negative mode operation would cure the problem.
I know from two colleagues who have experienced the same.
Is there an explanation for this phenomenon?
Is the phenomenon limited to specific MS-types or components?
Can this problem also occur with swapped polarities, e .g. sensitivity lost in negative mode is recovered by operation in positive mode?
Thanks in advance for your help.
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The general and simplistic answer is likely because of the electrochemistry that may occur in the ESI probe. You don't specify what samples you normally work with, but, for example, loss of sensitivity (and possibly even clogging of the capillary) is well known to occur due to electrochemical deposition of easily reducible metals (Fe, Cu, Ag, Hg) while electrospraying their salts in the negative mode. Reversing the polarity will re-oxidize the metals and put them back into solution. I've had to deal with solutions with high Fe(3+) content, and it's an occasional nightmare when you see the elemental iron actually building up on the tip of the capillary. Of course, you're citing a situation in the positive mode, but I'm pretty sure the problem is related. For more on the subject, see for example Henderson and McIndoe, Mass Spectrometry of Inorganic, Coordination and Organometallic Compounds, Wiley, 2005, pp. 117-119 and refs. therein.
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Hello,
 I try to develop a method for determination of PITC derivatized amino acids in cockroach but immediately i established my conditions for the separation (amino acids standard) which gives the perfect separation as evident in the chromatogram i have, the next step (qualitative analysis; identifying each peaks) is not clear to me.
I used Agilent 1260 Infinity Binary LC system equipped with a degassing unit, a quaternary pump,  and infinity diode array detector (G4212B). The column temperature is 33 oC, wavelenght 254 nm, flow rate  0.5 mL/min, column is Agilent extend- C18 columns (25 cm × 4.6 mm i.d., 5 μm), injection volume is 20 μL, Standard concentration is  1.25  μmol/mL . The system was linked to a Lenovo desktop for recording chromatograms, using a ChemStation edition software. The mobile phase is Acetonitrile : water (60:40) and 0.14M sodium acetate containing 0.05 percent TEA adjusted to pH 6.5 using glacial acetic acid.
My question is do i need to separately collect each peak and go for GC - MS for qualitative analysis? N.B we have no LC-MS.
if yes, remember each will contain water because of the mobile phase and can that work for GC- MS?
Any other way to carry out the qualitative and quantitative analysis?
Thanks
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Why are you re-inventing the wheel when Waters already has PITC methods for amino acid analysis called PICO-tag and Accu-tag?
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I will be working with very small peptides and I may not be able to visualize them on a gel, therefore I will have to use MS for analysis.
As a result, can anyone suggest an institute or company that I could get my peptides analyzed by in Ireland?
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Finding local (or international) service providers is quite easy on the Scientist.com platform:
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We are using Shimadzu GC2010 and GC2010 Plus GC-FID with Supelco SP-2560 Capillary column.  Lately we we have been running batches of between 30 and 100 we have noticed a significant shift in retention times. The shift in rentetion times for the smaller batches is not as significant for the larger batches. For a quick example our internal standard retention times started at 13.380minutes for sample 1 and then after 46samples have ran it was at 13.334 minutes. Is there any possible causes for as to why we are getting such a significant decrease in retention times in such short number of injections?
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Peter has, as usual, hit the nail squarely on the head. Your retention times are shifting more for heavier compounds than for lighter; you are seeing phase degradation. Oxygen and moisture are especially hard on polar phases, and this sounds suspiciously like what happens when a polar phase begins to degrade.
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My lab is looking at purchasing an ASE system and I'm curious about people's experiences. Do you find it easy/hard to maintain? Is it worth the money? Any insight would be greatly appreciated! Thanks!
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We have 3 Dionex ASE systems (2 x ASE-200 + 1 x ASE-300) and one Buechi SpeedExtractor and work with some of them since nearly two decades in the field of contaminants analysis.
It almost completely replaced our soxhlet systems and saves us a lot of time and solvent. A big advantage is also the closed system of the ASE, therefore it is easier to avoid contamination effects e.g. from phthalates.
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How high is TOC?
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Thanks a lot for your help
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I am looking for an example of quantitative analysis. Does somebody come across the situation that you cannot find the standard substance to make calibration plot when you want to make a quantitative analysis of an analyte?
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The major problem for protein quantification could be the less of sensor. If there is a special sensor for the target protein, quantification of the protein can be done. 
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Dear all,
I am new with chromatography, I put my hand on old Beckman coulter 126 equipped with 166 detector UV / VIS. The instrument was not used for Approximately 12 years and now I am starting to check before to start my new research project.
To test I have started to clean everything without column and I flush for several times at high flux rate (10ml / min) Mobile phase (H2O: CH3COOH and CH3COH: CH3COOH 99: 1 everyones), previously degassed via ultrasound bath.
After this operation I plugged my column, an other old pieces, (phenomex moon 5u C18 250mm), after some problems I was able to eluate my sample test (Anthracene in Methanol) at the same time.
So I started to check the integrals under the peak for different Concentrations of my sample. Unfortunately I have problem, I am not able to build a calibration curve, the behavior of integrals is not linear and not reproducible.
Then I started to check every things, and I observed that Rheodyne system has some troubles, when i put my sample, some drops go out as it is obstruited. I have also observed that any drops flow out from the waste capillar when I put quantity of solution more than 20microliter.
What can I do? I am thinking to disassemble Rheodyne system and check, but I am not so very handy if you have tutorials about disassembling of Rheodyne, some tips or some alternative solution, It could be very useful!
Thank you
Valentino Russo
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Here is a link to the manual for the Rheodyne 7125 injector valve. For a quick fix I would suggest disconnecting the valve and immersing it in a container of distilled water and placing it into an ultrasonic bath for a few minutes. Flush the valve as per the manual and then try using it again. You might need to rebuild the valve; you can do this using a 7125-999 Rhebuild kit see 2nd link.
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hi, i am using a TD-GC-QTof (Clarus 680 Perkin Elmer) with an accessory that enables the sampling of atmospheric sample, the analytes are collected directly in the trap. today I had a bug in the software running the GC-MS, and then I got the following problems:
- High ratio m/z = 18/28, more than 80%
- I lost the bleeding (flat baseline), even in the noise there is no m/z=207.
- The baseline doesn’t follow the oven temperature program So I checked for leaks, but there wasn’t any. Any ideas?
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If it is no longer under warranty then you have to pay for repairs.  Get a service contract.
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Is there anyone who has a Waters Acquity UPLC with Tandem Mass Spectrometry in his/her lab? Have you ever struggled with decreased sensitivity for your usual analytes? I want to know your experience about getting the sensitivity back to normal, how did you fix it?
It is the same instrument, the same column type, the same mobile phase combination, the same parameters used, every thing is the same. However, one day the instrument started to loss sensitivity toward my analytes, giving such a decrease response that if I compare the response to those from the day before that crazy day, they look like they are unrelated at all!
I tried a different column (similar part number), newly made mobile phase, replaced the sample cone, and replaced the inline filter. Yet, no improvement to mention.
I wonder if someone has a similar experience in the past and was able to solve it, to share with me what was the problem.
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Did you clean your mass spectrometer?
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Dear all,
I use pH meter HI 98 129 to measure pH, but after the stability symbol on the top left of the LCD disappears, the reading pH continuously increases by 0.5 to 1 pH.
So why is the reading pH not stable? and how to fix it?
Many thanks in advance! 
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Many thanks all!
I think it is due to the electrode glass. I calibriated it at two pH points (6.86 and 4.01) and at constant room temperature. However, after calibrating it at pH 4.01, the pH value decreased to about 3.8. 
I measured the pH of kaolin suspensions with different salt concentrations, so what should be noted when measuring the pH of these suspensions?
Thank in advance!
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Separation of epoxides using a B-bex column with acetonitrile as solvent and deterctor FID. The conditions are: oven temperature-max 70 ° C, injector 280 ° C, detector 220 ° C, pressure 38 psi. I used the method around 30 injections, all normal, when finishing one of them, the baseline jumps and generates a lot of noise, from there, in all the chromatograms the baseline shows the temperature ramp that I use. What happened to the column?
Blue line - normal chromatogram. Green line - first time it appears.
Purple line and aquamarine - chromatograms after the jump
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First off, do you mean a b-DEX column? That is a chiral phase, and has to be handled with great care. 
You claim to be running an analysis in acetonitrile but you show that your maximum temperature is well below the boiling point of the acetonitrile. As is obvious to anyone with any experience in chromatography this would simply not be possible. If this is the actual case then you need to completely change your analysis. If you truly are using ACN as your solvent (a very poor choice for GC, by the way) then you are building up solvent all through your system and you are probably flooding your detector. This is consistent with the chromatographic traces that you have shown.
Secondly, 220C for a FID is WAY too low. You will get all kinds of crazy things happen. Raise your detector temperature up to no less than your injection temperature. 280 C as an injection temperature for a maximum oven temperature of 70 C is WAY, WAY too high!!! Lower your injection temperature.
You are in a university environment. You clearly are in need of some very basic GC training. Surely your university has someone who actually knows something about GC? You should consult them.
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Hello,
We are using an agilent 7890B GC and a QQQ 7000c from agilent. I recently started working with this apparatus but it has been installed in 2015. It is supposed to give Gaussian peaks for all the eluting peaks even the heavy weights like benzo[ghi]perylene. The peaks nowadays only give Gaussian peaks for naphthalene and a few others and start tailing after the first 6 components. it looks like only the heavier PAHs tail but I cannot pinpoint the problem in my GC.
I tried to change the Column (30m DB-EUPAH), changed the inert silica column that follows the chormatografic column (1.30m inert silica), we changed the liner and septum and checked for leaks in the system. we had maintenance of the QQQ in December 2016 but the tailing was the same before and after the maintanence so I am assuming that the tailing must be somewhere inside the GC system.
the only thing I can think of are cold spots but how do you figure that out?
any other idea's?
kind regards,
Rochelle de Wit
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We found that dirty flow cell windows were not amendable to solvent/sonication cleaning and instead did a light polishing with 1 um diamond grit.
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can I get suggestions regarding kieselguhr cholesterol column packing for cholesterol oxidase protein purification?
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Dear all,
we are working with an analytical HPLC system using G1315A DAD. For our analysis we are using 210 and 278 nm as Signal wavelength. So far the system was running fine and the noise signal of the UV detection was in a range of up to maximum 5 absorption units.
Recently we observed that the signal at 210 nm suddenly became very noisy with about 100 mAU frequency (see screenshot). 278 nm does not show this behavior. We tried to exchange the solvent (which is 5/95 AcN/water - solvent A and water/AcN - solvent B each with 0.1% formic acid), cleaned the flow cell, kept the system running over about 3 days with solvent A flow and exchanged the flow cell outlet tubing without any improvement. When we do an analysis, we can see no peak signals for 210 nm but for 278 nm we see the typical signals.
Do you have any idea what could be the reason or what needs to be exchanged? Our idea was that it's "just" the flow cell, but before ordering this, I wanted to make sure, if I forgot anything else.
Thank you very much in advance.
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I agree with John R Carney. The noise is so high, that there is nearly no light intensity at your wavelength. Your HPLC-DAD stystem makes a base-Zero before each run, so you can't see the light intensity directly. Diagnostics of the DAD in 'Instrument Verification' will help!
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In our lab, we have an HPLC system (Agilent) which is attached to an FLD detector. The FLD detector is connected to the system and gives peak area measurements in mVolts.
How can I convert from mVolts to mAu? I can't find the conversion factor anywhere and explanation is not clear. I would really appreciate any help regarding this. Thanks much!
Regards
Mizan
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The reason you got the mAu is because it is the "absorbance unit" on the "UV" detector. You will have "0" mAu for something that does not absorb the light at the setting wavelength. For instance, if you put water in the cell and look at the 254 nm and assume that water does not absorb light at this wavelength, the reading will be 0 mAu. If you have acetone which will absorb the light to the max, you will get the reading at the maximum absorbance full scale (normally 2 Au or 2000 mAu. On the other hand, fluorescence detector is the detector that measure amount of light (emission wavelength)  that the compound emit when it was subjected the light at a lower wavelength (excitation wavelength). It light intensity reacts with the detector and give an electrical signal and you measure in mV.  Bottom line, it does not matter what the unit is, All you need is to plot an  xy graph between the concentration of analyte (x) and the detector signal (y) in mAu or mV to make a calibration curve so you can estimate the amount of the unknown.
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I have problem when detecting the 1uL of standard PAH, its either the standard that I used is expired. The peaks coming out is not even distribute evenly and some peaks cant be detected it peaks area, height and etc. The peaks overlap in the first 3 minutes retention time.
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Dear Siti,
standards of PAHs, stored out of direct sunlight, are very stable, decomposition is therefore very unlikely. You can only face of  changes (increase) in concentrations caused by partial evaporation of solvent during long storage.
1) The problems with your column were already mentioned, they can be easily revealed using "less difficult" target analytes than PAHs, eg mixture of n-alkanes, which are available in (almost) every lab. The peaks should be sharp and symmetric.
2) I strongly recommend recheck tightness of your FID, too (remove the thermal insulation on the bottom part of the detector and check right tightening of all fittings).
Any leaks on FID (caused by changes in temperature in the oven) cause drop of detector response.
3) Improper position of the column in the inlet and/or leaks in the inlet are responsible  for peak distortion, too.
hope it helps a bit,
kind regards,
Tomas
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Hi everybody.
I was trying to analyse Ivermectin in a pharmaceutical product, but when I ran the standard it does not appear any peak (I'm using the USP 39 method for ivermectin).
I tried to modify the column and the mobile phase but it didn't appear anyway.
So I decide to check if the ivermectine was disolving correctly in methanol by analysing its UV spectrum and I found that there was no the expected spectrum, instead I got a weird signal (I have attached a photo).
So my question is: could it mean that the standard has degraded? or probably it could be a UV lamp problem?
By the way, the sample looked like it has the ivermectin compared to other analysis from months ago  (obviously I cannot be sure unless I compare it with the standar).
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Yes. Your concentration is far too high. Absorbance > 3 is not valid at all. The strange peaks may be noise of the detector. Your spectrum needs to be below 2, better around 1. By the way, your methanol seems to be too dirty. You need a UV or HPLC grade quality. The signal of methanol should be very low in your wavelength range.
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LC-MS system comprised of QTrap3200 and a Shamidzu HPLC (Autosampler model is SIL-20A). The needle is not going into the well instead going in between two wells and not picking up the sample. Tried to adjust ZHoming but could not do it locally or remotely.
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We control the autosampler thru the software. I use Chromeleon 7 software and I select from the Chromeleon Console> Instruments > Autosampler > Tray Control > 96 wells or 96 deep wells.  After that I make sure I selected the correct tray in the software where my samples are located and under my Data console where I have my sequence, I make sure the "position" of my sample tray is correct and in agreement with the tray I selected in the Instrument software.  I'm sure it must be similar with your sofware, just make sure the location of your samples and the tray you selected are the same.
I hope is just a miscommunication between your actual tray position and the one selected in the software.
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Our autosampler is giving us problems in terms of both vertical and horizontal motion.  It can't, for example, reliably find its home position. 
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Typically auto samplers use a sensor to determine when the home position is reached, and then either use endpoint sensors or step counting to move x,y. I would check your home position sensor; it may not be working properly.
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Hello, ladies and gentlemen,
Now I am planning to design lab-scale flat-sheet type membrane operation unit to separate C3 olefin/paraffin, which are propylene and propane. Since the permeated C3 gases are re-adsorbed onto the membrane, N2 sweeping gas will be used on permeation side. Selectivity of C3 gases measurement is ok using GC, however I have no idea to measure the C3 gases permeated fluxes. Due to limiting conditions in my lab, FID detector in GC is only for use. Anyone knows informative papers, experiences, or anything, please let me know and I will appreciate your support.
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Hello Hyeon-gyu - similar concept to what described was developed in early 90-ties for near-real time continuous air sampling of VOCs using portable GC.  The concept is called "membrane extraction with sorbent interface (MESI)" and was pioneered by Dr. Pawliszyn's group.  One of the recent papers is here:
Segal et al. Development of membrane extraction with a sorbent interface–micro gas chromatography system for field analysis. J Chrom A, 2000, 873, 13-27
This work refers to earlier manuscripts.  There was another paper on breath analysis published in JCA in 2004. 
I hope it helps,
Jacek Koziel
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for sibutramine extraction, can we use the extraction method as follows :
1)extract with methanol or water, followed by
2)acidifying with 5% H2SO4, then
3)basify with 10% NaOH to pH 8-9, and extract with dichloromethane
what is the function of acidifying and basifying?
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excuse me
Do you have research support for answer?
because i want to learn more about sibutramine
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I am trying to separate a fusion protein through HIC and unable to properly resolve the late peak. There are 4 peaks in total that elute out in the developed method but the last peak kind of merges with the main peak. Can someone help provide any suggestion as to how can I clearly resolve it? I am using a TOSOH Phenyl HIC column.
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From the info supplied so far, I think you are using the 7.5 x 75 mm Phenyl-5PW PMMA support with 1000A pore size (exclusion limit ~ 1 M Daltons). Is this correct? If so, this column has an est. void volume of 2.32 minutes.
If you could supply us with the flow rate, then we could calculate the K prime for your most prominent peak at 15 minutes. What is the flow rate?
As previously suggested, often the method can be improved by incorporating some organic phase (MeOH, ACN or even ethanol), per the column manufacturers guidelines (to a max of 50%), using a gradient. This allows you to quickly determine the proper % composition range to use in your actual method. If you have not done so, you should run these initial gradients to begin the method development process for your samples. If you are trying to reduce the chances of protein inactivation/denaturation and wish to stay with purely aqueous compositions, then try adjusting either the molarity of the chosen salts or pH value using a gradient to first retain, then elute each peak.
Do you have an idea what the Mw's of the samples are (Range)?
A much simpler method may exist. If you could share with us WHY you are using this specific method that would be helpful.
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Hello,
I am going through a few problems in the Thermo LCQ-Deca mass spectroscopy. I am using MeOH/H2O solvent system for the most of my analysis.
Recently, there was an issue about the multiplier. It could detect only the positive ions, but not negative. I replaced the multiplier. After replacing multiplier, I found few more issue when doing diagnosis. For example, Lens, Ion detection, RF, API source, and status were failed. I tried to fix all of them.
After that, the diagnosis gives only ion detection fail. I thought it is a calibration issue and tried the calibration. When i run the calibration solution, then i saw all the ion picks except caffeine (m/z 195 in the positive ion mode) but they are off with the recommended intensities. However, i was finished all the steps of the calibration according to the manual. But, finally, i found the calibration failed. I tried factory calibration, but the result is similar.
I would highly appreciate if you give your scholastic suggestion to resolve it. Thanks in advance.
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Contact the manufacturer through the local distributor.
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I ran a column experiment with a tritium tracer and am trying to find out the porosity of the soil. Unfortunately, I discarded the soil inside the column already without measuring the mass used. The tritium arrived at 50% of injection concentration after 98 hours while the flow rate was 5 ml/h with a total column volume of  294 mL. The breakthrough curve itself was very sharp so there was little diffusion or dispersion.
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Nope, sorry. You are measuring two different things. You have the retentivity for the soil for tritium, which is really cool. Unfortunately, while it is indirectly related to the soil permeability it is not a measure of either the permeability nor the porosity.
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When calibrating the flame AAS (AAnalyst400) with mixed-metal standards I receive an error message "No calibration because the signs of absorbance and concentration may differ". This message appears after my final calibration standard (30ppm) has been ran. Initially this only appeared when analysing for Zn, but now appears for every metal. I have tried using freshly prepared standards but have the same result.
Has anybody had this message before/knows how to overcome this issue? 
Any help is appreciated!
Alex
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Dear Alex Riley,
  I agree with both M. Farooq Wahab and Alexander Leiendecker. If all they said were not helpful, try to check the nebulizer again, this time by turning it with your fingers in a 
reverse direction of sucking.  This time, the nebulizer will push out air and you see strong bubbling in the distilled water.  if not, it means the capillary is blocked and you have to change it. But, if you continue, the capillary might open by the air pressure and you will see bubbling. In all cases, zeroing the instrument with good distilled and deionized water is important, in addition to HCL and its correct adjustment.  It might be useful also, if check the instrument with other metals. .  Thank You and
Good luck 
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Hello, everyone.
My laboratory is going to buy a magnetic stirrer or stirrers, having about 1-1.5k euro for that. We have found a very nice (by characteristics) magnetic stirrers (LLG-company, Phoenix - manufacturer) but very cheap. Do you have any experience with these stirrers? Or is it wiser to go with "IKA RCT basic" which are twice as pricey? 
Do you have any other good stirrers in your mind?
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You can not base your decision on the brochures or spec sheets at all.
I would recommend staying away the from any "low cost" hot plate/stirrer unit. I have direct personal experience purchasing several diferent low cost models over the years and I have found many of them to lack the power needed to stir many solutions (they stall easily and are hard to regulate). We thought we were saving money, but in fact it cost us more money because they were of such poor quality that we could not use most of them and still had to buy better quality models. Don't make our mistake.
Strongly advise you invest in good quality models from Corning or IKA. Ceramic tops are my preference as well. They will last a lifetime and have better overall performance. You do get what you pay for (not always true, but in this case, it is).
One other suggestion. If you want to save some money, than consider the purchase of well maintained USED hotplate/stir units from one of the higher quality manufacturers. If you choose carefully (*buy one which offers a return option so you can take it for a "test spin and heat"), you can purchase a used model for a price that is 1/4 or less of the original list price.  We have purchased about half of the ones in our lab as used models over the past decades and probably never paid more than $ 50 USD each for any of them. Also worth checking with the various vendors who sell the better quality ones to see if they have any specials, demos models or promotional discounts too.
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Our lab has a Waters triple quandrupole instrument (Xevo TQ-S). The first quad is seriously hurting the signal intensity in the ESI negtive mode. Has anyone had the experiences in cleaning TQ-S quad?
Thanks!
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Looks like i have very similar problem. After the stepwave cleaning i have very poor or almost no signal in positive ion mode on MS1. Signal is only good short after turning the instrument into operate mode after overnight in stand by and after the switching the ionization polarity form - to + . MS2 signal is excellent.
As there is some fault related to MS1, i cant perform the MRM analysis in positive mode, but i found two ways how to overcome this:
1 - is to increase the ion energy on MS1, from 0.2 to ~1.5 in my case. But i'm not sure this is good in long term.
2 - the other way is to insert additional MRM NEG channel in my existing MS-method which originally has one MRM POS channel.
The second option works so good that you even can't notice about any failure. Signal and linearity is as good as it was with the new instrument.
Anyway i think that this is not reasonable in longer term and some (which exactly) repair or cleaning needs to be done.
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Hello!
I am new to MS, so any info will help. I synthesized a Fe complex with Azidothymidine, and want to run its MS.
I found a protocol for a matrix for AZT-metal complexes that suggests 45M anthranilic acid, 45M Nicotinic acid 55mM diammoniumhydrogencitrate in 45% ACN.
Has anyone tried this before? Any suggestions or other protocols?
What kind of tubes do you make the matrix in? Would regular RNAse free eppendorf tubes do? 
Also, do you think it is appropriate to use pure AZT for calibration? 
Thanks!
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Dear Anna,
take care of the pH-conditions during sample prep (matrix/analyte mixture) - the conditions chosen should retain the interaction between the metal ion and your nucleoside.
We found the matrix ATT (6-Aza-2-thiothymine) quite good for this purpose.  However, it is always recommended to test a wider range of matrices. In several cases, also ionic liquid matrices are well suited for the analysis of low molecular weight analytes, as these matrices usually have fewer background signals compared to crystalline matrices.
As your analyte is certainly in the same m/z range as the matrix it is highly recommended to measure matrix blanks first. You can use this as well as other commonly used matrix substances) also for calibration in the given mass range.
Regarding the tubes: classical test tubes (eppendorfs) usually fit - however, take care with organic solvents ( or use the right tubes) as these can liberate plasticizers under some circumstances. You will find information about compatibility with organic solvents in the respective vendors catalogues.
best regards
andreas
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Hello everyone.
I would like to know which HPLC ( is it possible to use UV-Vis or Fluorescense detector?) method for crude oil analysis do you recommend to me, to replace S.A.R.A analysis, which is so expensive and uses so dangerous solvents. I would prefer a validate method :)
Thank you so much.
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For crude oil actually the best system is GC, GC-MS. Universal column for Alkanes will allow to get fingerprint and etc. By  HPLC (UV-VIS)  you can analyse PAHs. 
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There is only a Aglient 6230 single Tof in our lab, it is may only matched for DAR research for ADC Drugs.
So now, we wanna get a new configuration aim to full characterization of ADC drugs or may proteins.  I just focus on Agilent 6545,6550 and AB Sciex 5600+ and Waters G2-XS but has less knowledge  on Thermo Q-Exactive.
Can someone show me the points how can i get a satisfied one? Tech support, greater performance, lower repairs fees, easier use of the software.
Thanks you all.
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Hi, Eef and WeiBin
We decide to sent out the DEMO sample for a Pre-Run in  supplier  application  labs.
For a fully evaluation, sample pretreatment & instrument performance and supportor skills all will be considered.
Thanks you all, have a good holiday.
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We have a limited budget and the HPLC Sykam S 500 is cheaper than Agilent and other brands. Please share your experience with us. We will order gradient pump S1125 with PDA detector.
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Dr. Milan 
I need more details from you
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We would be interested in 50mm column diameter scale. We are looking at Waters, Agilent, Shimadzu. Any comments on robustness? Customer support? Bad experiences?
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Hi Dean,
there was a similar question about a year ago on RG, I attached the link FYI. In general, every company will tell you that they are the best. We use Agilent 1200 system. However, we never had a bad experience regarding the customer support. From the instrument reliability, we do not have a comparison, but this also depends on the maintenance work you do. Any nice instrument will break down if the maintenance is bad or not existent at all...
You could also check supercritical LC. Rather expensive, but the solvent is CO2 which simply evaporates and you do not need to freeze-dry your samples. Also available in preparative scale.
Good luck, Marcus
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Hello everyone. I need to know how to match the mass spectrum of a structure of N-glycans with fragmentations of it made in the GlycoWorkbench program. We do not find any document or tutorial help us. I can only open the mass spectral fragmentations and make separately but still I can not match both. Aguiar has experience in this or have any document showing me how to do?
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Hi Annia, I would instead use Byonic: the fragments are matched automatically with suggested compositions - much easier.
St John
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I would like to purchase a GC/MS Autosampler all-in-one (liquid, headspace and SPME). Could anyone please share his/her experience with such a platform? how convenient is to rotate between the injection modes?
Thanks, Vered
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Hello Dr. Tzin -  mainline autosamplers for GC-MS have a SPME option and accessories:
(1) http://www.palsystem.com/   (CombiPAL, CTC Analytics)
Also, this article in Nature Protocols (plus several others by Pawliszyn's group) might be helpful:
Sanja Risticevic, Yong Chen, Lucie Kudlejova, Rosa Vatinno, Bruno Baltensperger, John R Stuff, Dietmar Hein & Janusz Pawliszyn. Protocol for the development of automated high-throughput SPME–GC methods for the analysis of volatile and semivolatile constituents in wine samples. Nature Protocols 5, - 162 - 176 (2010) Published online: 7 January 2010 | doi:10.1038/nprot.2009.181
 Good luck with your research,
Jacek Koziel
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I am going to purchase a TOC analyzer for our Geochemistry lab. We experienced acid treatment problems in the past. Please advise me on any rapid TOC method / instrument with out acid treatment (multi stage temperature program etc.).
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From best methods is UV/Persulfate oxidation method and I prefer those instruments with conductivity cells as detector. You still need the high temperature method for higher concentrations, so it depends on your samples concentrations ranges.
At HCWW we use the first method accurately till 50 ppm max.
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I mean, to different times of elution and specific pikes of the chromatogram. Thank you very much!
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I would like to express my opinion.   You should use the fraction collector without using rotating mechanism.   I have previously used such a collector using boustrophedon mechanism safely (our unpublished observation); i.e.,
Further, I have luckily had a good chance to compare the fraction collectors between GE ÄKTA (rotating mechanism) and Shimadzu (boustrophedon mechanism), and I have observed that boustrophedon mechanism is reliable.   Rotating mechanism is non-reliable due to slipping phenomenon, and mis-collections between chromatogram and fraction number frequently have occured (at the University of Tokyo; my unpublished observation).   Mis-fractionation is very regretful phenomenon for both the employee and the employer.
By the way, it is also noteworthy that the collected fraction is delayed as compared to the chromatogram due to the volume of HPLC-line between exit of the detector and the outlet of fraction collector (present above the tubes).   Therefore, it should be done precisely to measure or calculate the volume between detector and fraction collector (calculation is sufficient by using inner diameter and length of the HPLC line).  
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Dear Peter Hastwell, is the genedisc reader commercially available? How the DNA assays are performed on the consumable discs? genedisc project
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Thanks for the information. Raustech’s platform 3rd generation electrophotography sounds very promissing.
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Dear All
I want to measure sulfate radicals concentration using dimethyl sulfoxide. Please, can you provide me with a reference for measurement of sulfate radicals using dimethylsulfoxide.
Regards, 
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Hey Amal Elsonbaty, I also observe oxidation of DMSO by HO2-radikals to DMSO2 in solution. I think there are many possibilities to oxidize DMSO. 
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I am creating a GC to measure VOCs. I want to control a sampling loop and injection onto a separation column using a 6 port valve. I have seen some affordable ones for sale on ebay in the US, but no such equipment is available in the UK, as far as I can tell.
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Thanks all. I've also seen them on eBay, which seems to be the most affordable of all available options. In the mean time I've gone for a simpler option - but I'm still on the look out for a 6 port!
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Dear All,
I was wondering what analytical method I should utilize in order to detect any chemical alteration in an organic sample that is irradiated by X-ray radiation?
Note: The color change was observed as a result of irradiation.
Best,
Sevan
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You can also use IR and near-IR spectra. These methods are cheaper and often more easily applied to such samples.
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These are solid samples. We do not have a microwave machine for analyses.
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I wonder if reduction of the stannic oxide SnO2 with C (anthracite and graphite powder, Mitchell and Parker) into a Sn(l) melt @1000 degree C may be a good start? Then yeah, HCl.
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Hello Everyone, 
I'm working with Agilent 1220 LC system. The openlab software shows that the pump is idle but its shows the pressure is zero. It looks like pump is not building pressure. Can anyone please help.
Thanks,
Sachin
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First of all, make sure you have sufficient solvent in the solvent bottle. Prime the system by running with the purge valve open for several minutes.
When primed, remove the HPLC column and close the purge valve. Point the capillary tubing at a beaker to verify that solvent is being pumped through. Assuming this is working, pause the flow, reconnect the column and test the pressure. 
If you are not getting solvent flow there is a significant air bubble or a leak. The purge should have removed the air bubble, but further purging (with an organic solvent as well to reduce bubble formation) should remove it. If there is no flow, this may mean that there is a pump problem, such as failed piston seals (as Trivikram states), purge valve, check valves, or even a broken piston or piston driver. Check also that the solvent line from the reservoir (and degasser if fitted) is not blocked and that solvent can get to the pump.
If you did get flow at the first check but the system is still not building up pressure, fit a blanking plug instead of the column and try to build up pressure. Each time you do not get pressure, move the blanking plug towards the pump, missing out sections of tubing (eg missing out column oven, missing out autosampler etc) until the blanking plug is on the pump outlet. In this way you can trace the source of any leak. If the pump is still not building up pressure, then again it is likely to be a failed seal, valve or piston.
I hope you can get this working again soon
Richard
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I am looking for a DSC with a temperature range from room temperature up to at least 1000 oC, with a good resolution and the possibility of measuring under different types of atmosphere (such as Ar or N gas). Also we will be working with rare earth (Nd, Sm ... etc) if that is relevant. If anyone has worked with such devices, I would appreciate a short assessment of the performance of the device (and the manufacturer if possible).
Thank you !
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I have worked extensively with both TA Instruments devices and with SETARAM instruments devices, so that informs my response: 
TA Instruments machines are cheaper in up-front cost, but much more expensive to operate in terms of consumables and repairs. Many TA maintenance and repair operations are not easily performed by the user as they require specialized tools or an extremely steady hand which only comes from practice - so you will need a service contract with regular service engineer visits. The hang-down TGAs are extremely delicate and not something I would allow an undergrad or even an early graduate student unfettered access to unless you want your repair costs to balloon - nor would I want multiple users in the equation. They are one-user instruments for best performance - because that way the instrument technician has ownership over taking good care of the instrument. The DSCs are a bit prone to calibration drift and thus relatively high-maintenance but otherwise fairly easy to use. The instruments do produce good data and are generally quite reliable - but when they do break down, expect at least five figures in the repair bill and a service visit. TA instruments machines tend to come with a lot of bells-and-whistles options which affect the look and image of the instrument without significantly affecting the performance like touch-screen interfaces etc. The consumables are in general between 2-5x more expensive than Setaram consumables (being the other brand I'm familiar with). I would say TA instruments devices are the choice if you care more about it looking good and being user-friendly on a daily use basis than about high performance, extreme environments, ease-of-maintenance and operating costs. They make good workhorse instruments, if a bit on the expensive side to run.
I have not worked with NETZSCH instruments before - the general reputation is that they are in between TA and SETARAM in terms of up-front cost, and on par with TA in terms of recurring cost, more versatile than TA but less than SETARAM, and more bells and whistles than SETARAM but less than TA. I have heard that some NETZCH systems can be delicate and prone to breaking easily, but I've also heard that they're otherwise well-engineered. I don't have personal experience with NETZSCH instruments so I can't give an informed opinion about what the deciding factor is there or what the user experience is.
SETARAM instruments in general are a bit higher in up-front investment required, are extremely versatile in terms of atmospheres and samples that can be accommodated, and are both inexpensive and easy to maintain. SETARAM also offers high-sensitivity Tian-Calvet calorimetry in some of its instruments, and is able to accommodate more extreme environments than other manufacturers including offering the only commercial instrument to my knowledge which can measure under pure hydrogen atmosphere up to 1750°C (unsure if your rare earth work is using hydrogen storage alloys - but it might be relevant), as well as having the capability to accommodate other corrosive gasses such as HF and Cl2, and high pressures up to 10K bar (depending on the instrument - their Setsys DSC is the one with the corrosive gas and H2 capability. Labsys is more of a typical workhorse instrument and is a solid choice for routine lab work - it does have a high sensitivity option, but the high sensitivity is not as good as a Sensys or Alexsys would be. Sensys or Alexsys would be the instruments of choice for high pressure DSC at high temperatures). Most routine maintenance and repair is user-doable on a SETARAM instrument, and consumables are the cheapest of the big manufacturers, making a low year-on-year operating cost which to my mind balances out the higher up-front cost. I would not recommend opting for a service contract for a SETARAM instrument as they tend to be low-maintenance so you genuinely don't need it.  As a company, they focus more on the high performance and the ability to handle extreme environments (pure hydrogen, corrosive gasses, radioactive environments, extremely high temperatures or pressures, etc) than on flashy looks or "bells and whistles" type of options. They require a bit more in terms of up-front training only because SETARAM trains users in routine maintenance and replacement of consumable parts - and once you're done training, they're very reliable and straightforward to operate in my experience. SETARAM is the instrument of choice if you want top-end performance, robust construction, and great ease of maintenance, or if you want to work with extreme environments.
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Obviously clean glassware is essential to the success and reproducibility of any experiment, but even more so for single molecule fluorescence microscopy which can be extremely sensitive to stray contaminants that may be indistinguishable from single fluorophores of interest.
Our lab has more or less arbitrary, unquestionable, rules of cleaning, that often take several hours to complete, e.g. for washing sample glass vials it could take 3 x 10 min sonication in soap, then water, then ethanol, then chloroform. As you can see, this procedure takes 2 hours in sonication alone, not counting manual labor in between.
Does anybody know if there are any studies (i.e. not anecdotal beliefs and hand-me-down protocols) investigating this?
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I don't clean my glassware, I etch a fresh surface onto it with 2.5% w/v (5%concentrated HF v/v) in water (prepared in a plastic bottle)! The object to be cleaned is immersed in the dilute aqueous HF solution in a plastic vessel and gently swirled until the surface its evenly wetted. For test tubes, beakers and flasks I pour the dilute HF solution in them, cover (Parafilm M) or stopper, and shake the vessel vigorously for several minutes. The object is then rinsed with distilled water. This leaves hexafluorosilicic acid residues on the glass surface which are easily removed by immersing the object in 5%w/v KOH in 50%v/v ethanol:water for a few seconds and then rinsing with distilled water. This leaves a pure clean evenly wetted glass surface behind. Caution HF especially in the more concentrated forms is toxic, corrosive and causes severe burns. That said, in my younger days, I used to wipe the dilute HF solution around on the glass surfaces with my bare hands, with no ill effects!  If you do the calculations you will find this dilute HF solution is about twice as acidic as vinegar (5% Acetic Acid). This 2.5%w/v HF solution can also be used to remove the white glazed on lettering and graduations on the outside of bottles and other glassware.
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Our UV/vis Spec. measurements are no longer repeatable, after a minute or two the absorbance of the same solution in the same cuvette changes significantly. Sometimes the absorbance is zero or even negative. Is it the light source or the detector?
Our Spec. is an archaic WPA S2000 model with a D2/tungsten S2000L light source, and I don't know exactly when the lamps have been replaced.
The lamp model is Deuterium J05, and I couldn't find the same part in the country, but I hope I can replace it with a similar one. Do you know if there is a model that can be inserted instead?
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I have searched for pulsed deuterium lamps in vain, and pulsed xenon lamp is present.   Deuterium lamp can not be used in visible light, and is used for UV detection.  Pulsed xenon lamp seems to be like a sun-light, and can be used as UV/VIS detection.   Then, you should buy pulsed xenon lamp ? 
Hamamatsu Photonics K.K. (Hamamatsu, Shizuoka, Japan) produces and deals many kinds of lamps,,,
By the way, Mr. Kenjiro Takayanagi (Hamamatsu Photonics Co.) has firstly invented television in 1926.