Of course, we think we’re the best lab to test for your analytes of interest, however, any lab that holds the proper certifications for the tests you want to have done can perform the tests for you. What tests you need to have run depends on the regulatory program to whom you’ll be reporting the results. Different analytical methods have different limits of detection – from high to the low. The cost of the test is usually higher for the lowest levels of detection. As far as matrix type – again you need to see if the laboratory is certified to perform the analyses for that particular matrix. The question of human or animal tissue makes me wonder if you are asking this question for medical reasons. If that is the case you will need to contact your health provider or local health department to provide information on how levels of these analytes affect health.

Thank you,

Columbia Analytical Services, Inc.

You cannot compare areas when running this as you are not comparing apples to apples. The principle for SIM is that you are scanning fewer ions per second than you are for a full scan, thus you have greater signal to noise ratio (not abundances). Hope this helps!

I would suggest you review the EPA’s guide to calibration found at the following location: http://www.epa.gov/fem/pdfs/calibration-guide-ref-final-oct2010.pdf. I think it gives the most comprehensive answer to your question.

The actual reason relates to the time spent monitoring the ions of interest in the two modes. A SCAN mode spectrum typically requires about 1 second to obtain. If one scans from 50-550 M/z, then the dwell time on one mass is about 2 ms. One is monitoring each ion of interest for only 0.2% of the total scan time and data points are spaced at 1 second intervals.

In SIM mode, the fact that you spend the entire time monitoring only the ions of interest means you have longer time to accumulate data for those ions and hence get a larger signal. At the same time, the longer monitoring time provided more opportunity for noise to cancel. The S/N improvement should be related to the relative time spent integrating each ion.

Another problem in fast GC-MS analysis is that peaks are often only a few seconds wide. One needs at least 8 data points to accurately define a gaussian peak. Thus a SIM mode scan can be set up to acquire more data points across a peak and provide a more accurate profile.