Reasons for inverted peaks in gas chromatography
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We are using a Shimadzu 2010plus gas chromatograph equipped with a FID detector, which is primarily used to detect trace amounts of CO, CO2, and CH4. However, a problem has arisen recently: a reverse peak appears for CO2, while the other two peaks remain normal. I have tried various methods, including changing the carrier gas, but with little effect. Eventually, I switched to Ar as the carrier gas; the peak shape became normal, but it was not ideal, with bulges at both the beginning and end. Moreover, after some time, the level of CO2 drops by almost half, while the levels of CH4 and CO remain normal. Dear experts, what’s going on here? Have you encountered this situation before? How to solve it?
To detect trace amounts of carbon monoxide and carbon dioxide by gas chromatography, a methanation converter is required – a small active nickel hydrogenation reactor that converts carbon monoxide and carbon dioxide into methane, which is then detected using a FID; this increases the sensitivity of the response values. I estimate that in your case, either there is no methanation conversion unit, or the catalyst in that unit has lost its effectiveness. Furthermore, if the organic content in the carrier gas and auxiliary gas exceeds the allowable limits, resulting in a high baseline level, this will also have a significant impact on the analysis results.
Looking forward to an answer; I also want to learn * a bit
There must be a methane converter. I just replaced the nickel powder, and the carrier gas is from Beijing Helispectra; everything else worked fine before. The hydrogen is also from gas cylinders, and the chromatography column has been newly aged. I also changed the valve switching time. Now it’s carbon dioxide instead of an inverted peak, but the peak area is extremely small. Why is that?
The negative peak in CO2 may be caused by a high concentration of CO2 in the carrier gas.