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Since the retention time of a sample tested using GC will necessarily depend on the column parameters (stationary phase material, oven temperature, flow rate, etc), it follows that the chromatograph will also depend on these factors. How, then, can we compare our results to those published in databases online?

Either the parameters mentioned above should be standardized, or the instrument needs to be 'standardized' (or calibrated) by using a calibration sample and performing some post processing such that for this calibration sample we get identical chromatograph to what is found for the same sample in the data bases.

Which of these actually happen in practice?

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You can use a retention index based on e.g. alkane standards. You run the alkane standards on your column, and compare their retention time to that of your sample to get a retention index. Then, you can compare it to published retention index data.

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  • $\begingroup$ As a comment to Karsten, It can be added that the retention indexes depend on the polarity of the stationary phase and on the temperature. They do not depend on flow rate. Table exist that show the retention indexes R of a lot of substances at a given temperature, plus the rate of changing dR/dT. Using these parameters, you can probably calculate the retention times of all your compounds. $\endgroup$
    – Maurice
    Dec 15, 2023 at 9:04
  • $\begingroup$ @Maurice so then I need to compare retention indices using same or similar stationary phase material? $\endgroup$
    – student1
    Dec 16, 2023 at 0:29
  • $\begingroup$ Yes. You understand the technique. The only trouble is, by reading the tables, that the same product may have sometimes different retention indexes (up to ± $5 - 10$ in retention indexes) for the same column at the same temperature. It only seems to depend on the author of the measurements. I don't know how to explain this strange discrepancy. $\endgroup$
    – Maurice
    Dec 16, 2023 at 10:10

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