Science method
Analytical Chemistry Instrumentation - Science method
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I’m using gradient elution on an LC-MS (Waters 2695) for PPCP separation and analysis. Currently, with my column volume and flow rate, I allow 12-13 minutes for re-equilibration between injections, extending the overall method time to about 36 minutes. Increasing the flow rate slightly to 0.4 or 0.5 mL/min could potentially shorten re-equilibration time and I can adjust that time in between somewhere to allow more effective separation during the gradient steps, or simply decrease the overall method duration. However, I’m considering whether this adjustment could impact column or system performance, such as creating back pressure issues.
My current gradient is set at 20% methanol from 0 to 2 minutes, then linearly increases to 80% at 8 minutes, 95% at 9 minutes (held isocratic until 20 minutes), followed by a return to 20% methanol at 23 minutes, with a 13-minute re-equilibration period.
We'll have vials in which we expect H2 generation to occur. Over the first few days, the amount of generated H2 is expected to be at ppb level.
GC (+ TCD) detector is best when your H2 level is in the ppm range.
GC-MS is difficult as the ionization energy of H2 is high and the M/Z ratio will be small (2).
FID is not reliable as hydrogen flame is used
Other fancy methods (e.g., Raman-based and optical methods) are quite expensive.
What are your suggestions?
Thanks
After performing boehm titration using HCl,NaOH, Na2CO3, and NaHCO3. I want to know the formula to calculate functional groups.
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!!
Dear researchers,
I would like to ask you whether the retention of analytes of interest on the C18 column can be slightly affected by buffer concentration.
I have analyzed a mixture containing sulpiride (weak base) and diclofenac (weak acid) at 250 ng/mL on the C18 column with mobile phase A: ammonium formate and mobile phase B: methanol.
I have observed that when the concentration level of ammonium formate increased from 2mM, 5mM, to 10mM, the retention time of sulpiride slightly decreased from 6.72 min, 6.52 min to 6.46 min respectively, whereas that of diclofenac slightly increased from 10.04 min, 10.17 min to 10.28 min respectively.
As far as I am concerned, for a basic compound such as sulpiride, an increase in buffer concentration (ammonium formate) can result in a decrease in silanol activity so a positively charged compound such as sulpiride can have a slight loss of retention due to the ion exchange interaction between the compound and silanol group during a loading step. Consequently, the retention time of sulpiride was slightly decreased with an increase in buffer concentration.
However, for an acidic compound such as diclofenac, it is quite difficult to explain this phenomenon. In my opinion, it seems that when the concentration level of ammonium formate increases, the pH of the mobile phase slightly increases so the charged state degree of diclofenac slightly increases either. As a result, the energy configuration of diclofenac diffusing inside the pore of the C18 column is lower at a higher concentration level of ammonium formate (10mM) so it will have more interaction surface area with the C18 column, leading to more retention. However, this explanation seems not to be convincible because the higher charged state degree of diclofenac is, the more soluble is and the less retention is.
However, for the retention behavior of sulpiride and diclofenac, the above explanations are just my own opinion. Of course, I am not sure whether they are right or wrong.
If someone here can help me clear the retention behavior of sulpiride and diclofenac, I am really happy to listen to your valuable suggestions.
Thank you so much in advance,
Hello,
When working with methanol, I noticed that I could never take the exact volume of methanol with micropipette.
Is there any other tool or method that could solve this problem?
Many thanks for your concern,
I have powdered diphenylcarbazide and I want to make 0.5% w/v solution of diphenyl carbazide. Since it is dissolved in acetone.
Does it mean 0.5 g in 100 mL acetone? Is there any need to add distilled water?
In literature it is prepared by dissolving in acetone and then 200 mL distilled water was added.
Thanks for your guidance
Hi, I'm working on my bachelor's final year thesis which is based on being able to detect the presence of saliva in crime scenes. My first step was to confirm that with the settings I have I am able to detect the presence of tryptophan. This was a 0.5g in 100ml solution of 5mM KCL and 2ml of this was placed in a cuvette and scanned for, which was successful - it result in an emission peak around 350nm.
I further tested swabbed dried saliva with a PBS swab off a lab-grade glass slide and placed it in a cuvette with 2ml of 5mM KCl and ran the tests. The results were way off the intensity scale.
So I tested for the range of dilutions to see in what range the readings wouldn't go off the scales, and dilutions of 1 in 100, 250, 500 and 1000 seemed to have worked. But unfortunately, the intensities of all of these were varying there was so linear relation like one would expect since its decreasing dilutions. I decided that I'll perform my tests from scratch and zeroed the instrument with KCl since that's what my samples are diluted in, and then ran the control again to see if any peak appears (since if you zero the instrument with a certain chemical, if you scan for it, nothing should appear), and a peak showed.
I then contacted Agilent hoping they'd be of some help. They said I was overloading/maxing out the detector, which I am unable to understand since I have diluted this to a small amount. And from previous papers that have performed similar experiments, they haven't needed to even dilute their samples.
I then tried varying the settings such as the PMT voltages, emission and excitation slits and performed tests with tryptophan to see if the peak at 350 would be detected. And failed as all the resulting peaks turned out to be "below threshold".
I am unable to determine how to go about it, and I'm nearing the deadline for working in the lab and I'm nearing the end of all options.
Obviously, since this is the first thesis I'll ever be writing I'm afraid I won't have results and just have various different trial and error methods.
All suggestions and any help I get will be really helpful.
I will be editing this post to add images of the settings I have my instrument on just for extra information. And for reference, I'm using the Cary Eclipse Agilent Fluorimeter with the Scan application.
Thank you in advance. :)
Shaina
I'm trying out column chromatography for separation.
But the product is not dissolved in solvent system that gives the best separation.
Should I try dry-loading or change the solvent?
Could anyone give me some advice?
Protocol for monosaccharide analysis of polysaccharides by LC-MS/method development/solvent used.
My college research team and I are in search of an instrument to evaluate emotional involvement in soccer fanatics...yet we can not seem to find an instrument to use? Any recommendations? What should I do to find a good questionnaire? How can I acquire an instrument (preferable free)?
Additionally, this instrument has to be standardized.
Actually I have a data on fish otolith microchemistry in ppm and I have to convert it into millimoles per mole for further statistical analysis.
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.
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?
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.
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.
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
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.
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!
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!
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
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.
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.
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.
Any instrument or method that can measure lifetime of film samples?
Thanks
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?
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.
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
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?
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?
Thanks in advance for your replies.
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.
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.
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.
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.
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
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?.
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.
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.
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?
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.
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!
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
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?
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.
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?
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?
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
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.
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.
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
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?
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.
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)
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
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?
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?
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!
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?
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.
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!
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
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
can I get suggestions regarding kieselguhr cholesterol column packing for cholesterol oxidase protein purification?
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.
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
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.
+1
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).
Our autosampler is giving us problems in terms of both vertical and horizontal motion. It can't, for example, reliably find its home position.
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.
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?