Analytical Chemistry Instrumentation - Science method

While you can change the flow rate during the analysis (or equilibration) phase of the run, it is generally not recommended. Changes to the flow rate directly change the system back-pressure on the system. This changes the detector signal and results in 'drifting' which requires a great deal of time to stabilize (depends on type of detector, column dimensions, change in flow rate and sensitivity). Instead, optimize the analysis method for better throughput. This includes optimizing the flow rate for the analysis method (linear) as well as the mobile phase composition, tubing, flow path, detector cell etc. Equilibration time will 'take as long as it takes'. If your equilibration time is too short, then late eluters, col-elution and/or invalid data may be collected which should be avoided.

Gas chromatography, ultrasonic meters, electrochemical sensors, Raman lidar, and gas-stripping methods are some of the most reliable techniques for measuring hydrogen gas concentrations at ppb levels, depending on the specific application and environmental conditions.

Dear Esteemed Colleague,

Greetings. I trust this message finds you well and thriving in your scientific pursuits, particularly in the area of surface chemistry and characterization. Your inquiry about the mathematical formula for calculating functional groups on surfaces such as carbon materials via Boehm titration is both important and insightful. The Boehm titration technique is a cornerstone in the quantitative analysis of acidic and basic surface functional groups, providing invaluable data for material scientists and chemists alike. Below, I provide a detailed exposition on the formulation and methodology for calculating the concentration of these functional groups using Boehm titration.

Overview of Boehm Titration

Boehm titration is a technique designed to quantify the acidic and basic functional groups present on the surface of carbonaceous materials. This method involves treating the sample with a series of bases and acids to neutralize acidic and basic sites, respectively. The quantity of acid or base that reacts with the sample surface groups is then measured, providing an estimate of the functional group content.

Mathematical Formulation

To calculate the concentration of surface functional groups, the following formula is commonly employed:

�=(�blank−�sample)×��C=m(Vblank​−Vsample​)×N​

where:

Step-by-Step Calculation

Considerations and Best Practices

By adhering to these guidelines and employing the formula with diligence, you can accurately quantify the functional groups present on the surface of carbon materials via Boehm titration. This quantification is essential for understanding the chemical behavior and potential applications of these materials.

Should you require further clarification or wish to explore more about the application of Boehm titration in material science, please do not hesitate to reach out. Your dedication to advancing our understanding of material surfaces is commendable, and I am here to support your research endeavors.

Warm regards.

Check out this protocol list; it might provide additional insights for resolving the issue.

Dear Josh, I'm having a problem very similar to yours. I would like to know if SPE worked well, and if not, how did you resolve it? Thanks in advance.

Back to your original question (and I am done with this thread)... You observed a small (tiny) difference in Rt from small changes you made to the mobile phase composition. No worries, this is normal because no two columns are the same and each may interact to a different degree (or none at all) when you make small changes to the mobile phase composition. Try 20 different C18 columns and you may find some show no change at all, some do. Pick and choose the one that you want for the application (this is what we do in analytical laboratories). The reason for the observed change (change, not "drift") is due to multiple interactions of the solute on the surface of the support. Hard to say if it is electronic or ionization in nature, but it is so small, practically, it does not matter. All chromatographers are familiar with this (no need to 'explain it'). Run enough samples and you will see it. In fact, the one thing that they might question is why you would use a mobile phase of just ammonium formate without an acid (e.g.formic). Why not use a buffer? For LC-MS applications, most would benefit from such a solution to promote ionization and maybe change the separation factor too (depends on samples).

It is likely the presence of water will help to stabilise the metal ions. In the presence of pure acetone the inorganic metal may be insoluble and unavailable to react?

As per above, taking the 0,5 gram and dissolving in pure acetone, then making this up to 100ml, maybe using 50mL acetone, and then using distilled water to complete the volume requirement?

@Shaina Mercy Fernandes

I think there must be some problem with your solvent (water/aqueous buffer in this case). Check the fluorescence of blank solvent. To avoid such interference, always use triple distilled water.

Also check ✔️..

I use HPLC method to check the monosaccharide content.

First of all, you need to read the classical book by MORRIS, Desmonds. The Soccer Tribe (several editions available). Thereafter, you can access the following papers:

- CRISP, R.J.; HEUSTON, S.; FARR. M.J. & TURNER, R.N. "Seeing Red or Feeling Blue: Differentiated Intergroup Emotions and Ingroup Identification in Soccer Fans", in: Group Processes & Intergroup Relations, Vol. 10 (2010), Iss. 1.

- JONES, Marc V.; COFFEE, Pete; SHEFFIELD, David, YANGUEZ, Marc & BARKER, Jamie B. "Just a game? Changes in English and Spanish soccer fans’ emotions in the 2010 World Cup", in: Psychology of Sport and Exercise, Vol. 13 (2012), Iss. 2.

- TEQUES, Pedro; CALMEIRO, Luis; MARTINS, Henrique; DUARTE, Daniel & HOLT, Nicholas L. "Mediating Effects of Parents’ Coping Strategies on the Relationship Between Parents’ Emotional Intelligence and Sideline Verbal Behaviors in Youth Soccer", in: Journal of Sport and Exercise Psychology, Vol. 40 (2018), Iss. 3.

- SABY, Yohan; PUPIER, Yann, GUILLET-DESCAS, Emma; NICOLAS, Michel & MARTINENT, Guillaume. "Longitudinal emotional process among adolescent soccer player in intensive training centre", in: Journal of Sports Sciences, 9 (2019).

I am sorry Andrew, but isn't 100 ppm equal to 0.0001g.? I mean 100/1000000 must be 0.0001.

Correct me if I am wrong.

But as Zoltan writes, it is not that easy to convert from ppm to mmol/mol.

Cheers

There are several other separation methods published for the detection of sorbic acid in foodstuffs. These include HPLC (Saad et al., 2005; FSIS, 2004), spectrophotometric (Campos et al., 1991), micellar electrokinetic chromatography (Boyce, 1999), and CE (Özteki̇n, 2018).

Flow measurement can be performed with different methods. Accuracy of reading may depend on different factors like samples water etc.

@ Tapas Kumar Patra I want to know that in GC-Ms facility in your institute is CO gas is used as carrier gas?

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.

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

Thank you for sharing good information!

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

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?

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.

Note with using matrix modifier the furnace temperature program must be changed ashing and atomization temperatures must be increased

I think ICP-MS

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.

Thanks @Mohammed Mohammed . Really appreciate it!

Does anyone know of a Acquity UPC2 users forum?

Dear Rahu,

Make sure to select sensitivity scale setting to "Automatic" when created this plot. However, you can manually add axial titles in RAW data of CH electrochemical Workstation graphs. You should watch this demo video.

Thank you !

I am looking for the same manuals, if someone is willing to send them, please message me.

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.

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

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!

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

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.

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.

Thank you all for your suggestions.

For those who face similar issues - conc. HCl, DI and sand paper was used to clean the autoclave.

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.

Most HPLC's come equipped with a UV detector (PDA/DAD).  An IR detector is known but not typically used since everything absorbs (thus molecular spectroscopy) including mobile phase solvents like Methanol, Water....

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.

XRD will provide information about the phase composition. You can use XRF in order to get the detailed chemical composition. Also, the use of SEM attached with EDS will provide information on elemental composition.

In the Left side of the toolbar, change the  real time batch to acquisition mode, there you can switch to single injection mode

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

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.

A couple of things. One: have you reduced the injection volume or better yet diluted the sample? Two: I have an Agilent QTOF in which I experienced the sample attaching itself to the plastic lines.... Lastly have you varied the gradient to have more organic in the initial steps?

Hi Nadeen.

I belive you are using a pump with 2 pistons. You describe is look like only one piston is operanting.It is possible check valve remian locked ( I don't know what HPLC pump you are using, but in some models you have 4 check valve. Another way of throuble is piston seal, but this cause leak, if you have some new seal you could replace them. When you dismantle pump you could verify if two pistons are working correctly ( take care in this procedure).

I hope this help you.

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!

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.

>  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.

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"

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.

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. 

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!)

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?

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 ??

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.

Yes, Sepax!  See 1st column in list below;

Why are you re-inventing the wheel when Waters already has PITC methods for amino acid analysis called PICO-tag and Accu-tag?

Finding local (or international) service providers is quite easy on the Scientist.com platform:

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.

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.

Thanks a lot for your help

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. 

Did you clean your mass spectrometer?

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!

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.

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.

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!

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.

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

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.

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.

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

excuse me

Do you have research support for answer?

because i want to learn more about sibutramine