Chromatography Forum

Hi all,

Now I have a problem about resolution in a GC method for determination of acetone. I want to detemine acetone in a sample and the requirement is less than 5000 ppm. But i found a small interfering peak in DMSO which I used as solvent. The resolution of acetone and the interfering peak is 1.1(The interfering peak area is about 10,000 and the acetone peak area of 5000ppm is about 250,000). I want to know: is this method can be accepted? or I must separate those two peaks to get a better resolution.

Thanks.

If your samples are well below the 250,000 range, I wouldn't worry about it too much, just note the interference and use a different (better) lot of DMSO next time.

Just note in your report that your blank contains an interference of about 200 ppm calculated as acetone.

As long as your results give values of less than 5200 ppm of acetone then you should be fine, no?

best wishes,

Rod

One thing to consider....

If you are using the DMSO to make your acetone standard, there is a contribution of the contaminant to the response of the acetone. If you are doing a single point calibration at your acceptance limit and the DMSO ratio in your samples and standards is the same, and your samples are at your acceptance limit limit the effects of the contaminant will cancel out. However, if you deviate from those conditions your results will be biased high, and not always by 200 ppm.

If you are using a multipoint calibration and you make the assumption that the contribution of the contaminant is constant, your results will be either biased high or low depending on the portion of the curve you are working with.

Hope this helps.

Jack

Sorry I did not address your question more carefully. I answered before assuming that you might not be reviewing the chromatography but taking the computer results at face value. The computer results might identify the contaminant peak as acetone even though there might be a large amount of acetone ( peak misidentification) and especially if there were no acetone in your sample at all. The parameters of your integration software should be chosen with care so a correct assignment of naming is achieved.

Your present resolution of the contaminant and a 5000ppm peak of acetone appears adequate to properly ID and measure the acetone peak, especially if you personally review the chromatogram to verify the proper peak identification. It is assumed that differing amounts of acetone present in your sample does not affect the retention time or resolution of the interferring peak.

I also assumed that you were within a linear range of measurement as the previous post correctly points out could be a problem if you are calculating from a regression line.

DR's advice is good (as always) and should be your guide.

best wishes,

Rod