Issues related to the purity of pure methanol and impurity analysis
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When performing chromatographic analysis to determine the purity of pure methanol, the external standard method is used; when creating the standard curve, the methanol content is assumed to be 1, and the reproducibility RSD remains within 3%. However, in actual analyses, the value for methanol is generally around 1.1, and sometimes it even reaches 1.4 or 1.5. Sampling is carried out using an automatic sampler. The peak area of methanol is unstable. Could the experts please discuss what the cause of this problem is – whether it’s due to methanol itself or the instrument. We are using a Shimadzu 2010PLUS, with a non-polar chromatography column.
The analysis of pure methanol does not involve directly measuring the purity of methanol; instead, impurities present in the sample are analyzed, and the content of pure methanol is calculated using the subtraction method. It’s a problem with how you use your method, not a technical issue.
What I mean is not to directly analyze the methanol purity, but to use the area of the methanol peak in each analysis as a basis to determine whether the injection volume using the external standard method is accurate.
What I mean is not to directly analyze the methanol purity, but to use the area of the methanol peak in each analysis as a basis to determine whether the injection volume using the external standard method is accurate.