How big is the error in gas chromatography detection?
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My colleague used gas chromatography to detect a mixture of methanol and methyl ester prepared according to mass percentage. The result was quite different from the prepared mass percentage. Is this an inherent error of the equipment?
Friend, please explain your colleague's operation in detail. 1. The responses of the two on the instrument are different, so it is best to use the correction factor. 2. If it is just methanol and methyl ester, what is your mobile phase, or what is your solute? Please explain these clearly. We can only answer them in detail after verifying them ourselves.
Check whether there is a problem with the standard curve, whether it is beyond the linear range, whether there is any problem with the standard solution, the injector, etc.
Use the external standard method. . . To establish standards.
The question is not clear, and the method used is not mentioned. Is it the normalization method, the external standard method, or something else?
Thank you for your help in analyzing the reason! My colleague did this specifically, using analytically pure methanol and methyl methacrylate by weight 1: 1 Prepare the solution and inject it into the gas chromatograph. The measurement conditions are 50~150°C. Hold at 50°C for 1 minute and then increase it by 5°C per minute. The final measured results are methanol 40.26% and methyl methacrylate 59.7%. Can you help me find out where the problem lies? :) Thanks!
Possible reasons 1. The volatilization loss of methanol 2. The corresponding differences between the two substances 3. The strange thing is: You use methanol as the solvent. Why does methanol participate in the integration and calculation? If you are testing the purity or content of the finished product, there is no need to use methanol in the calculation.
The error should not be that big. 1. First of all, I don’t know if you have calibrated it or if there is a correction factor. 2. When proportioning, be sure to weigh the non-volatile substances first, and then quickly weigh the volatile ones. Also, whether your weighing bottle is airtight, 3. If the configuration is late, it is best to calibrate it immediately. Before injecting samples, check whether the instrument is running normally and whether the baseline is straight. I don’t know if you are using external standard and you are talking about normalization?
The error is not very big, but it also depends on your equipment~~Old equipment is not so good~I have used new ones and they are very good.……
Whether it can be qualitative or quantitative mainly depends on the method.
The calibration factors of the two should be measured using configured samples, and then measured again. If calculated directly based on the chromatographic peak area, there will definitely be a lot of difference! !
I feel that the chromatographic analysis is quite accurate. There should not be such a big error. It is recommended to use imported chromatographic instruments. I feel that the accuracy of domestic ones is a little worse.
The key is which method to use, including area normalization, external standard, and internal standard.
In fact, this is always mainly because the calibration factors of each substance on the detector are different. Generally, chemical analysis is not for scientific research, so the area normalization method is basically used, that is, the calibration factors of all samples are calculated as "1". In fact, if you want to get accurate results, you need to apply the area normalization method. For the product correction normalization method, all the information related to the correction factors can be found. Judging from the analysis results of the sample you prepared, the correction factor of methyl methacrylate is lower than that of methanol. If you multiply the respective areas by their correction factors, the analysis results should be the same as the results of the actual sample you prepared.