Gas chromatography
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Our facility has two gas chromatographs that can be used to analyze the same substance; the results obtained are 100% and 99.75% respectively. Could someone help me analyze why this is the case? Thank you, first. What is measured is mainly a mixture of alcohols and esters; one detector is a TCD detector and the other is a FID detector.
What method is used for the calculation? What is the repeatability of the sampling?
1. Is the method you are using the same one? Sometimes, different methods yield different results. 2. Is the amount of samples introduced consistent? 3. Run a few more parallel samples first.
First, a standard sample for comparison is necessary; it is best to use a normalization method with correction factors, and the injection volume should also be roughly consistent； Furthermore, the detection sensitivity of the thermal conductivity detector is inherently lower than that of the FID, so it is unable to detect certain trace amounts of impurities ； For chromatography columns, different separation conditions yield different results ； Lastly, chromatography sometimes suffers from certain errors due to the presence of substances with high concentrations, especially in some domestic models; this is something that cannot be avoided.
The sensitivity of TCD is inherently far inferior to that of FID. If the column is fine, I think the result is normal.