porapak-Q column, ethanol-water
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Dear experts: I am using a Porapak column to analyze ethanol-water systems, with the following parameters set: column temperature: 180°C, injector temperature: 150℃； Thermal conductivity cell: 180℃ ； H2 flow rate: 35+35 ml/min ； Bridge current: 120mA. This parameter was determined after conducting numerous sets of analyses; we tried column temperatures ranging from 105 to 200, and injection temperatures ranging from 105 to 180. The best spectra were obtained under these parameters, but the water peak and the alcohol peak still did not separate! ! During the subsequent corrections, it was found that this issue had a significant impact on the analysis results! So, I would like to ask everyone how to completely separate the water peak from the alcohol peak – could it be that the quality of the column has declined? please~~
The same conditions can be used to lower the column temperature or reduce the column flow rate
Reply to 2# dalian*aochao: Thank you. I also think that the column temperature is higher than what is mentioned in the literature; however, we have tested various temperature gradients, and it turned out that the peak formation is indeed poor at lower temperatures. Other teachers have suggested lowering the column temperature; I think I should give that a try as well – it’s possible that the problem lies in the poor efficiency of the column. . .
Reply to 3# Lu Xiucai: Precision work requires careful attention to detail. It will be easier to trace things back to their source. First, make sure that there are no issues with the instruments themselves, as well as with the electrical and pneumatic systems, and then gradually improve the conditions. If the column you chose is appropriate, the failure to separate is definitely caused by either an excessively high column temperature or too fast flow rate.
Although I haven’t used chromatography for over 10 years, based on my previous experience, it is best not to use chromatography for determining the water content in chemical materials. At low water concentrations, the sensitivity is poor, and the repeatability is also low ； When the water concentration is high, the chromatographic peak shape shows severe tailing, which can affect subsequent analyses. Although some literature suggests that certain conditions and certain types of columns yield better results for water analysis, in practical work, it is difficult for both researchers and users to achieve good analytical outcomes. At its core, water is a highly polar molecule with strong intermolecular interactions, which results in extremely complex and variable retention behavior of water on both highly polar and less polar columns. Simply changing the temperature and testing conditions makes it difficult to achieve satisfactory results in water analysis.
Reply to 5# qugd: This issue was indeed encountered during the analysis; when the ethanol concentration exceeded 90%, the analysis error became very large.