Chromatography Forum

Hello,

I'm validating a method to analyze VOC with purge and trap and GC/MS detection, with full scan adquisition.

I'm not sure which identification criteria use: mass spectra comparation, or a quantifier and ratio of two or tree qualifiers.

I not sure that a mass spectra of a 0.5 µg/L standard could be accurately compared. All present ions are backgroud, and is ver tedious substract cromatograms for a blank run, and not in all analytes work well.

If measurament of qualifiers ratio is better, how many qualifiers must be measured, and what is the maximun tolerance.

Another question: is neccesary to complay with the BFB calibration criteria for EU reglamentation?


Thank!!

the question is if you are specifically citing the USEPA method. If you're citing the method, then you should be following the method protocol. If you are using it as a guide to be able to run volatiles by purge & trap, then you have more flexibility.

Regarding what criteria to use, our systems (Agilent) do a decent job of background subtracting. Generally, even at 0.5PPB, the ions are present in reasonable rations. There tends to be a fair amount of additional ions due to noise, but otherwise that works. We tend to put 2 - 4 qualifier ions in the method, but then set the criteria fairly wide so that we do not have false negatives and then allow the analyst to drop false positives.