Doubts about gas chromatography peak area
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1 g of the reagent is added to volumetric flask A with a capacity of 50 ml; then 1 ml is taken from A and added to volumetric flask B with a capacity of 25 ml. Samples are taken from both A and B for gas chromatography analysis. What should be the peak area of the reagent in A compared to that in B? I think it’s 25 times, but why is the result 100 times?
1. Loss or adsorption of reagents during dilution； 2. Caused by the instrument’s “linearity” ； Trace analysis and macro analysis should be selected and processed according to the requirements of the measurement.
It’s not caused by loss or adsorption. What does “linear” mean? Could you be more specific?
At low concentrations, an increase in concentration can follow a linear relationship according to a first-order equation (y=kx+c), which is appropriate for analysis. Otherwise, it is incorrect. When injecting samples, you should first test those with low concentrations and then those with high concentrations, in order to avoid contaminating the samples. This post was last edited by hldj1964 on 2008-11-25 16:18]
The problem now is that one of our experienced colleagues says it should be 100 times; I don’t understand why it has to be 100 instead of 25 times
From another perspective, whether using the internal standard method or the external standard method in gas chromatography, the standard substance used should be as similar as possible to the substance being analyzed. If the concentration differences of the same substance are too large, the same standard material should not be used for measurement.
Get an injection and see the results; whatever anyone says needs to be verified through actual testing. What the several bosses said and what you said pertain to different issues
The actual result is 100 times. . .
In fact, when addressing this issue, one thing that needs to be considered first is whether the injection volume is the same. Even if you ensure that the injection volume is 1 microliter or 2 microliters, etc., it isn’t exactly consistent, which leads to injection errors. Therefore, it’s not sufficient to rely solely on the ratio of the peak areas of the samples from the two analyses； To find out why the peak area ratio is not 25, you can check the area of the solvent peak – what is its area, and are the areas of the solvent peak identical in the two analyses? If they are not identical, by how much do they differ? (Of course, if the solvent peaks are all sharp peaks, then it’s impossible to make a comparison, as the peak areas in such cases do not reflect the actual values.) Alternatively, the peak area ratio can be simply used to attempt to determine changes in solution concentration (of course, this is only qualitative rather than quantitative). The solute peak area/solvent peak area for Sample A can be compared with that of Sample B to see if it is around 25 times; of course, this is only an approximate value. This is why we use internal or external standard methods for quantitative analysis in chromatographic experiments. This post was last edited by rabbit7708 on 2008-11-27 15:10]
The reagent is lost or adsorbed during the dilution process
Could you take 10 ml or 5 ml of the solution, dilute it to 25 ml, and then perform chromatography to see how the ratio changes?