PCBs

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afcollart
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PCBs

Hi,
I analyse PCBs in human serum with a GC/MS. I use an liquid-liquid extraction and then a SPE extraction. My curves for each PCB is beautiful but my canadians controls are too low.
Are you an explanation ou a solution for this problem ?
Thank you
 
 
 

Greg Pronger
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Sorry, but I am not familiar

Sorry, but I am not familiar with teh term "Canadian" regarding control samples.
 
Greg

afcollart
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Canadians controls are

Canadians controls are external controls what come from Canada.

Greg Pronger
Greg Pronger's picture
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I am assuming that this is a prepped, spiked sample, or reference material.
Second, I will assume that you are confident in the concentrations of your calibration (that you are quantitating a second source standard and it is coming out fine (I would call this an ICVS or Initial Calibration Verification Standard).
If this is true (we've verified prep), then it has to be analyte lost in prep.
When having trouble with prep recoveries; work from the last part of the procedure to the first. What you need to do is determine which specific step is causing the loss. However, you're concentrating your extract, prepare the same volume of solvent (or solvents if your prep has more than one), spike it and then concentrate it. If it comes out fine, then go to the prep step just before it. What you'll end up with is a set of recoveries reflecting the amount of analyte loss at each point in the process. This way you'll know what to fix. This may be a tedious process, but when I have had inexplicable recovery problems with prep, it has been about the only way for me to solve them.
If there is more to the issue, feel free to post more details.
Greg P.