peak does not get quantified in chemstation

[kevinetr]

Hello,

I am analyzing VOC's using GC/MS and chemstation software. Occasionally, when the quantitation report is produced, a peak will be visible on the chromatogram, but the software does not quantify it. I can go into the data analysis program and identify the compound using the mass spectra library, but I cannot figure out a way to get the software to label the peak and quantify it. It does not appear to be a problem for any specific compound, as it has "missed" a number of random compounds. I have tried changing qualifier ions and retention time windows, and lowered the reported detection limit but these tactics did not resolve the problem. Also, based on the peak size it does not appear to be related to analyte concentration being too low, or below calibration levels. Any help would be greatly appreciated. Thanks.


Kevin

[Bruce Hamilton]

Well, perhaps you haven't been talking nicely to your computer and Chemstation, and they are becoming petulant....

Anyway, lets assume that the software is feeling good, then the problem is that it doesn't consider your peak as a "peak". There are lots of reasons, and an initial list is below, however the first step is expand up some chromatograms and look closely at the baseline integration points of peaks that were missed compared to those that were integrated - looking for slight differences, or failure to catch start of peak.
Some checks...
Retention time shift - it's not in the peak window, could depend on how you've told Chemstation to detect and integrate non-calibrated peaks, or even the calibrated peaks, check reference peak behaviour compared to both missing and detected peaks.
Integration settings, including timed events, eg threshold/slope sensitivity/peak width settings. They can cause relatively-large peaks to be missed..
Could be that it's ignored because it has a sharp noise spike embedded in the peak, thus not meeting some criteria.
Could be that the peak shape is distorted, and the software treats it as baseline or sharp noise spike, peak width setting is a big issue here
Could be eliminated by some peak valeey ratio of peak size setting.

Please keep having fun,

Bruce Hamilton

[Steve Reimer]

Make sure that the "report non-target peaks" is turned on in the quant report options." Otherwise the report will ignore anything not identified as a target peak.