solid-phase extraction

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

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Hi, I would like to know if anyone habitually uses solid-phase extraction in trace analysis of pesticides.
do you think it is a valid quantitative method of extraction?
despite all the precautions I only get low recoveries (<50%).
do you think this technique can be used for concentrations of order of magnitude of ppt?

Thanks
We use the solid phase extraction listed in EPA Method 525.3 for several pesticides at concentrations in the low to sub ppb range and normally get 70%+ recovery. 70% is the lowest recovery allowed by the method and we usually pass that QC at well above that.

One thing that helps is using matrix matching for the calibration standards. We extract the 1L volume of DI Water through the cartridge and process it through elution by solvents and concentration to final volume, with no surrogate or internal standards added, then use that final solvent to dilute our standards with when preparing them in the normal fashion. The small amount of background matrix compensates for any ionization enhancement or suppression in the MS source.

Also, if you are using GC/ECD EPA Method 508.1 has a very similar extraction process.
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