P&T VOC identification criteria

[camino]

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!!

[gpronger]

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.