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Our company uses gas chromatography to analyze the content of gaseous methanol during the production process. In recent days, no changes have been observed in the manufacturing process, yet the measured level of gaseous methanol is significantly higher (the normal value is around 50 ppm, while it has recently exceeded 100 ppm). We suspect that there is a problem with the chromatography instrument, so we sent samples for analysis at another factory. Using the same sample gas, the results obtained by that factory were lower than those obtained by us. When our chromatograph was used with a standard gas containing 100 ppm of methanol, the results were 88 ppm on the first attempt, 104 ppm on the second, and 90 ppm on the third. We would like to ask: 1. What is the allowable range of variation for the results obtained when analyzing the same gas using chromatography? (Are there any standards or specifications?) 2. Can these three samples analyzed by our chromatograph indicate that it is a problem with the instrument? 3. If it’s a problem with the instrument, can it be determined what the specific fault is? Thank you, experts!
This is related to many factors. Age the chromatography column to see if there is any accumulation inside it ； The injection method causes variations in the pressure per injection in the quantitation tube ； Detector contamination leads to inaccurate quantification. Give them a try; I’m a beginner too, let’s learn from each other
You can search for JJG700-1999 _ Calibration Regulations for Gas Chromatographs; the repeatability is less than 3%. I recommend checking out this website: http://www.bzwz.com/html_news/News_34016.html. It discusses the issue of repeatability in the calibration of gas chromatographs (FID and ECD) – Technology Frontiers – News Center – **Standard Materials Network