GC-TCD calibration problem

Chromatography Forum: GC Archives: GC-TCD calibration problem
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Samuel Luk on Sunday, May 2, 2004 - 10:43 pm:

Hi,
Working on CO2/CO/CH4/H2 system with Ar carrier gas. Did calibration manually (i.e. recording peak areas at different vol% of gases). Unfortunately, they don't add up to 100% when doing experiments (sometimes less than 90%, other times exceeds 120%). Any suggestion why? Thnx in advance.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, May 3, 2004 - 05:52 am:

It appears that linearity over the range of measurement is not achieved. Narrow the range of measurement for each calibration mix and your errors of measurement should then be minimized.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Les on Saturday, May 8, 2004 - 05:24 pm:

How exactly are you injecting your gases. Putting the sample under pressure, you'll get more gas in the GC. I inject gases through a needle valve and bubble the vent into water. When the bubbles slow after sufficient purge, I turn the sample valve. If you sample while the bubbles are flowing, the charge is high due to more gas in the loop. Generally I shoot for a charge of about 85 to 110 and normalize the concentrations. If samples charge above the recommended, there may be problems due to areas exceeding the calibration range.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, May 26, 2004 - 08:44 pm:

check all the valves and the connections, it might be leaked. rethighten if posibble.

a big shift in total area/conc reproducibility almost always be due to:
1. a leak in the carrier gas system(valves and lines)
2. a problem with the detectors
3. a change in the injection technique

check all those items, its may helps.

rgds
omar.


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