Chromatographic peak order
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When the boiling point and molecular weight conflict in the peak order of gas chromatography, which order is dominated by the boiling point or the molecular weight?
This post was last posted by * Edited by lihuagong on 2017-1-17 10:33 Of course it is the boiling point. However, the polarity and adsorption properties of the chromatographic column and the medium to be separated need to be considered.
If the molecular structure in the sample is consistent, the peak order can be determined based on the boiling point or molecular weight. For example, petroleum products. Most of the samples we analyze daily have different structures, which are greatly affected by the properties of the column. It is rarely accurate to infer the order of each component based on boiling point and molecular weight alone.
This post was last edited by qugd on 2017-1-19 10:32. The question the poster should ask is about gas chromatography. For gas chromatography, the peak order of the separated components has a great relationship with the characteristics of the chromatographic column, the retention characteristics of the separated components on the chromatographic column, the type of carrier gas during separation, and the temperature of the chromatographic column. The characteristics of the chromatographic column and the retention characteristics of the separated components are the main factors affecting component separation. It is best for the poster to check the gas chromatography volume in the Handbook of Analytical Chemistry, which contains very detailed data. When the molecular weights of the separated components are the same or similar, but the molecular structures and properties are different, some experimental conditions need to be defined before the judgment can be made. Typical examples of this separation of complexity are: Separation of benzene series, separation of isomers, separation of cis-trans structures, separation of acids and esters with the same carbon number, etc., must have accurate conditions to make judgments.
Judging from my personal work experience, the theoretical things make sense to a certain extent, but there are always surprises. For petroleum product analysis, it is also important to look at the valve program flow path. This is the main thing. On this basis, there are standard materials for characterization. Otherwise, the deviation will be large. Work verification is very important. Theoretical stuff is the basis.