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Thanks

I am interested in the procedures of
5-sulfosalicylic analysis by means of GC-MS.
I want to test the technical product for
determination of impurities.
What method must I use?

Hi,
Ifound a literature reported on analysing my compound using GC column 25QC2/BP-10 (length 25 n, diam 0.25 micrometer). Could somebody tell me what type of GC column is that? and what other equivalent GC columns available now that I can buy ?
Thank you in advance
Catherine

That is an SGE column. The SGE catalog lists it as a replacement for DB-1701, HP-1701, etc. Check their site at http://www.sge.com

Thank you very much Russ for your quick answer.
It is certainly a big help for me.
TrangCatherine

Generally, what it is lowest detection limit for an FID?
I know that it depends on the sample and a lot of other variables but I was wondering if there was a general guideline.

High picograms.

Am attempting to troubleshoot problems with
the HP3393A integrator used with our
CGC-FID system. HP no longer stocks the
Owner's manual for it; our copy has vanished;
am looking to obtain/make a copy we can use
in the lab. Any help would be appreciated.
POC keithk@proaxis.com.

We want to separate oxygen and argon by head-space GC. Can anyone suggest a method? Reference?

Molecular Sieve 5A PLOT capillaries will do it. Resolution may vary, depending on column flow, detector make-up, column conditioning etc. Oxygen-argon separation test chromatogram should be in the Varian-Chrompack catalog among others.

I'm having problem getting reproducible data from a water/acid mixture. Can anyone suggest a good column or method for analyzing a sample which is mostly water and small amount of C2 acid. Thanks you.

Try using CWAX or better yet FFAP (Nukol, CPWax58, or equal) or any of the porous polymer PLOT column for Water/Acetic Acid separations. Acetic Acid tails terribly on most other capillary phases. Run the column fairly hot in any event ca 150 C.

I trust you are using an TCD if you want to measure the water. The response of Acetic Acid on an FID is not great either.

Has anybody experience in analyzing silylated C18-phase extracted (yeast) cell extracts on capillary gc? I´m especially interested in useful internal standard compounds.

Sir,
I would like to know about column & method for seperation of diethyl ether form methylene chloride.

Thanking you,

Vinay

30m SPB-1 (methyl silicone), have the film thickness match the id of the column (beta value of 200-350). Flow 0.7-1.5 ml/min. Isothermal 40-50C.

does t time depend on sample rate--explain
does t time, plate count, and resolution vary with flow rate--explain
will t time, plate count and res vary with temp.--explain
how does the attenuation control help me
I know these questions seem simple to you, but I need to understand this
Thanks

if I double my sample size will my retention time also double
Also if I increase or double my flow rate will my t time, plate count and res. be cut in half
and in what way does temp affect these things
thanks

My areas are not reproducible and my plate counts have decreased. Tf is fine and RT is stable. Do you think the column is aging or there is some other problem?
Thanks,

I'm doing some gas chromatography and I calculated the resolution and the column efficiency... the problem is that I don't know the meaning of these numbers. What is the value for a good resolution? for a great column efficiency?
could you mail me the answer back please.
Thanks.

I am student and am doing a project which involves the quantification of menthol in a range of pharmaceutical products using GC (packed column and capillary column).

I am quite confused about the use of internal standards. I am hoping that you will be able to clarify the reasons for their use, and also give me some advice on the method and analysis of results when using this method. I know this is a lot, so any help at all will be appreciated. Thanks.

Hello Anonymous!

why are you using packed colums, the capillar-colums have a better resolution!

the GC is a relative method. you only get a retention time and a peakarea. You need a standard(e.g. menthol).If the retentiontime of the standard is the same, so the peak in your analysis can be menthol.

external standard: you inject the standard not with the substance you want to analyse. In a second run you inject the standard.

internal standard: you inject both together, the standard and the analyse.

any questions?
florian@phamazie.uni-wuerzburg.de

Anonymous-

I agree with "florian" about the use of capillary columns over packed colums - the resolution is so much better. Packed columns do have their place however.

The idea of an internal standard is to have a consistant, known amount of an (i.s.)analyte that elutes much sooner or later than the analyte you're trying to quantitate. It is best if the internal standard can be added to the sample diluant (this will keep the quantity of internal standard consistant, in my 16 years of experience, spiking each analyte vessel separately isn't nearly as consistant or repeatable by GC or HPLC.)

Internal standard calculations take into account the "ratio" of internal standard to sample analyte. Since the IS is consistant, the ratio or "response factor" can be used to quickly calculate the analyte quantity.

Hope this helps.

I am a student currently learning GC techniques. I have a couple of questions:
When would external standardisation be used as the quantitative method of choice in GC analysis? and what are the requirements for a substance if it is suitable as an internal standard? Any help with this would be greatly appreciated.
Thanx

There are many answers to this question, just as there are many different GC applications. An internal standard may be added at fixed concentration to the sample and ExSTD calibration solutions to correct for differences in injection volume. The ISTD for this purpose should elute somewhere near the sample peak or perhaps be a deuterated version of the sample compound if you have MS detection. Most importantly it should be as inert (non-polar)as possible to avoid adsorption in the sample matrix, injector, column etc. This means it does not have to match the sample compound functionally and herein lies some confusion, even for some experienced chromatographers. We have been talking about relatively simple analyses which would be OK for precision with ExSTD (~2-3% RSD), made even more precise with ISTD (~0.5% RSD).

If the sample peak is subject to matrix adsorption effects these small volume differences may be irrelevant and the analyst may want to compensate for these larger matrix effects by using a surrogate ISTD compound which is functionally similar to the sample compound (deuterated would be good). The problem is that the volumes injected were characterized by just a variance, whereas matrix effects are variance + bias, so you still need ExSTDs to get a handle on this.

Yet another complication is that the ExSTD calibration solutions themselves may need to be matrix-matched. For example if you were analysing for pesticides in fruit you could add extracts of non-contaminated fruit to the ExSTD solutions.

Finally if you have a complex variable sample and non-selective detector, ISTD compounds may interfere, so that would be a reason to use ExSTDs only.

I am currently studying about GC and i would like to know what single point calibration is, we are using a capillary column and also what assumptions are to be made when using this calibration technique? Thanx

hello,
I am looking for a column/method to separate out the following mixture :SF6, HF, and Water.
I need to recover the water!!!
This also has to be FAST as the water will contain 15O which has a half life of 2 minutes!

What is the difference between an internal std method and an external standard method.?

I am trying to run total phytosterols, for quantification:can I add up the area under the different sterol peaks and calibrate against 1 sterol standard