Problems when calibrate GC

Chromatography Forum: GC Archives: Problems when calibrate GC
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Juris on Tuesday, September 9, 2003 - 10:15 pm:

We use GC with capillary columns in our laboratoris. We have problems when we calibrate gas chromatographer. RSD for 5 injectins is 4% (injection manual). Linearity for 5 different concentrations is R=0,971. Could you advice what substance better to use for GC with capilar column calibration. To have normal linearity and RSD. We use polar, non-polar and middel polar columns.

Juris


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, September 10, 2003 - 06:20 am:

Review the placement of the column end within the injector.

Do not use a tapered tip needle for manual injections.

Inject slowly, about 1ÁL per 2 seconds.

Most injector designs are optimized for 50 to 200/1 split ratios. Outside that range and your RSDs will increase (RSD=1 is nominal).


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, September 12, 2003 - 12:03 pm:

Manual injections are by nature less reproducible than autosampler. Upon injection, syringe needle dwell time once the septa has been punctured and needle is in heated port must be as identical as possible. Any longer time in the heated port should favor more area/response of the lighter more volatile components of your mix, in effect giving a false representation of your mix. I try to inject as fast and as much like an autosampler would to get good numbers when I am forced to manually inject.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Russ on Saturday, September 13, 2003 - 04:23 am:

Are you using internal or external standard? If external, are you using "solvent flush" technique (can't remember what it is really called). In this, you draw up a small amount of solvent, a small amount of air (or inert gas), the proper amount of the solution to inject, then another small amount of air (or inert gas) so the solution is not in the needle when you inject (some also draw up a small amount of solvent after the solution to inject). Wipe off the needle before injecting.


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