New to GC - and I need help!

[gothyka]

Hi everyone

I am trying to make a calibration curve for dimethyl carbonate using a Shimadzu GC - 17 A chromatography. I was wondering if you can help me with the volume of the sample loop..I know I should open it and measure the volume, but being new I am quite afraid to open it.so..do you know the volume of the sample loop?

Thank you very much,

Dana

[chromatographer1]

You need to discover the length of the tubing of the loop and the internal diameter of the tubing. Then it is a simple calculation to determine volume.

loops should be tagged listing their volume. Have your checked your manual?

best wishes,

Rod

[GasMan]

If you are injecting different concentrations of calibration gas using the same sample loop and will be using the same sample loop for your samples, then you do not need to know the actual volume of the sample loop, providing you are using the same temperature and pressure for the sample loop.

Gasman

[ecelias]

Hi everybody!
Please a need a help.

I have been working with gas chromatography recently (GC CP 3800 - Varian with
Galaxie software). I am trying to solve and understand some problems during my analyses.

I am working in a research project for development of certified material reference for emissions and vehicular gaseous, such as CO and CO2.

Right now I am analysing gaseous samples of CO in nitrogen in differents concentratios to make a calibration curve and verify their behaviour month by month.

So, in the last two months, I noticed that I didn't get the same results (peaks areas) neither than the same retention time for the same CO concentration sample.

I am listing my parameters here:
- column: capillary column- Carbobond Fused Silica (50m x 0.53mm)
- Methaniser (convert CO into CH4)
- Injector tempearature: 423,15 k
- split :1/10
- oven temperature: 298,15k/15 min
- Injection flow: 20mL/min
- Pressure: 4 psi
- Detector temparature (DIC): 473,15k

Please a need a help to undestand my problem.

Thanks

Elizandra Elias

[chromatographer1]

A carbon based phase to analyze CO is not a recommended practice.

Your methanizer may not be converting the CO to methane in a consistent manner.

These are the two most likely problems with the analysis as you are performing it.

best wishes,

Rod

[Peter Apps]

If you are working on certified reference materials you need an analysis that gives you low, and very well understood, uncertainties. As Rod points out you have two likely sources of error, and neither of these are likely to be easy to incorporate into an uncertainty budget since they both change with time.

Peter

[ecelias]

Dear Rod,

Thanks for your answer.
I agree with you. I think the methanizer may not efficient. So, in this case, what can I do to get back the methanizer efficiency?

Best regards

Eliz Elias

A carbon based phase to analyze CO is not a recommended practice.

Your methanizer may not be converting the CO to methane in a consistent manner.

These are the two most likely problems with the analysis as you are performing it.

best wishes,

Rod

[chromatographer1]

You can burn out the methanizer passing first oxygen through it at several hundred degrees followed by a reduction step of passing hydrogen through it at similarly elevated temperatures (not recommended unless you have the proper facilities), or (highly recommended) you can replace the catalyst with new catalyst. Agilent sells the material inexpensively.

best wishes,

Rod