Questions regarding the selection of conditions for detecting high-boiling substances using a gas chromatograph
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Recently, while analyzing high-boiling substances in chlorosilanes, it was found that there are mainly two such substances, with boiling points of 137 degrees Celsius and 144 degrees Celsius (at standard pressure). However, during actual analysis, the conditions were set as follows: 120°C at the injection port, 80 degrees Celsius in the column chamber, and 120°C at the detector. Under these conditions, it is still possible to separate these two substances, resulting in 4 peaks; when using only GC/MS, 3 peaks appear, with two of them being isomers of the same substance. Are such testing conditions not appropriate? Could there be residues in the column? How should the correct conditions be set? The column used was a 25% DC550 polar column, with a TCD detector, for the separation of chlorosilanes. Does anyone have any good communication groups to recommend? My QQ is 791127071
The two high-boiling substances, 137 and 144, are hexachlorodisiloxane and hexachlorodisilane, right? Has the peak time been determined yet? Take an additional step to see if a value of 2 can be obtained; perhaps the vaporization temperature of 120°C is too low, resulting in residues remaining in the column. Increasing the TCD temperature might help. The vaporization temperature for GCMS should be set above 200°C, which would also enable more thorough separation using capillary columns.
Just set it directly to 250 degrees Celsius; increase the temperature of the column chamber a bit more at the end to ensure proper curing
Hello, Mr. Fan. Which part’s temperature does 250 degrees Celsius refer to?
This post was last edited by 277302698 on 2015-10-9 at 17:21. 1. Yes, it’s these two substances, haha. 2. Previously, I tried setting the column oven temperature to 80 degrees Celsius and running the analysis for 2 hours (normally it takes 30 minutes to complete), and no other compounds showed up as peaks. Moreover, with this current method (column oven at 80 degrees Celsius), the reproducibility when analyzing samples is good; in other words, the peak positions remain consistent. Generally speaking, it is recommended to set the column oven temperature to a value close to the boiling point of the sample. I wonder if the boiling point of the sample will decrease after it enters the instrument (with the carrier gas at a pressure of around 0.3 MPa). Could this lead to a decrease in the boiling point of the sample, so that the column oven temperature can also be set lower? 3. During GC/MS analysis, the temperature is relatively high; the column oven temperature is set at 80, the injection port temperature at 180, the ion source temperature at 230, and the auxiliary heating zone temperature at 280. An Agilent 7890/5975 instrument is used, in full scan mode. The chromatography column is a capillary column CP7435, specifically designed for silane analysis.
Generally, the injection port temperature is 30 to 70 degrees higher than the maximum column temperature; it doesn’t matter if the detector temperature is the same as that of the injection port or slightly lower. The maximum column temperature should be 30 degrees higher than the boiling point of the substance being analyzed. Gas chromatography isn’t that delicate – as long as the column isn’t damaged, it’s fine
Due to the low boiling point of chlorosilanes, a programmed temperature rise method should be used when analyzing their high-boiling-point impurities. In the high-temperature area, it is recommended to set the conditions as follows: injector at 200, column box at 160, detector at 200... The temperature should also not be too high, otherwise it may cause instability in the medium.