Chromatography Forum

We have been trying to do pesticide analysis on fruits and vegetables (Quechers), but with no success. We have the most perfect calibrations, but we get over and under recovery on any commodity we run against the calibration. We believe it's still inteference after the clean up. Are we the only lab in the world who is struggling this much with Quechers? Is the only way of doing this by Matrix match calibration? If this is the case, where do you find a matrix to match, as no two of any commodity is the same?

Yes, you have to use matrix matched calibration to compensate the matrix effect. Some labs use a mixture of representative commodities for matrix matched standards, but most would generate each matrix matched calibration curve for each matrix being analyzed.

If I understand correctly? If I am analysing apples, I calibrate with an apple matrix (?). Where does one find apples that you know has none of your target analytes?

Thanks for the reply.

Most visit organic food markets. I recommend trying to use the same type of apple if possible.

With quechers you often really need to use isotopically labeled internal standards as the method is crude. DIfferent analytes and matrices have different recoveries in the acetonitrile layer from the aqueous or hexane layer depending on the matrix. In some cases less than 60% of the analyte is present in the ACN layer thus the ITSD compensates for this.

Re GCMSLabserve:
About the ISTD
Check the EURL database for pesticide residues
http://www.eurl-pesticides-datapool.eu/default.aspx
There is tab - method validation data. You can list pesticides and there will be general info about extraction method,recovery, ISTD etc. for target pesticide. The most common up to 2012 was TPP (Triphenylphospahte) last year they jump to Chloropiryfos D10. I understand that for some problematic pesticides you need different approach (extraction, internal standard etc.) but for most pesticides in 200+ multiresidue methods you base on one internal standard.
Matrix matched calibration or solvent blanks with analyte protectants are necessary in such analysis.
My last run was 30 samples, 5 commodity groupes...one calibration curve. We are not gods...its all the criteria of acceptance... any documents/guides you base on ?

Best regards
Peter.

GCMSLabserve

Sample preparations by QuEChERS for fruit and vegitable not give good recovery for all pesticides, some analyte are not recovered.
Please try ACN and ethyl acetate and see which one good for you.

For matrix match calibration or matrix based calibration please refer "Method Validation and Quality Control Procedures for Pesticide Residues Analysis in Food and Feed:" SANCO/12571/2013 document. Find below mention link...

1) http://www.eurl-pesticides.eu/library/d ... _12571.pdf


Refer other EURL method (NL-miniLuke-extraction-method, QuEChERS (Ethyl Acetate)) may be it help you

1) http://www.eurl-pesticides.eu/userfiles ... method.pdf

2) http://www.eurl-pesticides.eu/docs/publ ... se&Lang=EN

for Commodity groups and representative commodities as you discuss, please refer Annex A Page 22 of SANCO/12571/2013 document

thank,s