Bad responses of urinary metabolites

[chandra]

Hello to everybody

In some urine chromatograms i observed only few peaks with very less response but the peak area of Internal standard is very good.What could be the reason of this kind of chromatograms. When i repeated the extraction and derivatization process in triplicate, i got the same result.Interday and intraday results were also the same.What could be the reason for very good response of Internal standard but the response of other metabolites are very less or negligible.Please help.

Thanks
Chandra

[Don_Hilton]

Perhaps the urine samples were diluted by the subjects drining more fluids? Or the metabolite levels were low for some reason? Most often we assume low results from samples means low concentrations of analytes in the samples unless there is reason to suspect a problem with the method. The only information you have given regarding the performance of the method is that the internal standard looks good - so we have no reason to suspect the method. If there is more information that would provide more detail on what is going on, then it would be helpful.