Screening and Quantitation of 250 Pesticides in Fruit Juices with Positive/Negative Switching LC/MS/MS

Liquid chromatography coupled with tandem mass spectrometry operated in multiple reaction monitoring (MRM) mode with electrospray ionization (ESI) is widely used for polar, semivolatile, and thermally labile pesticides in food testing. Many contract labs currently perform multi-residue analysis of pesticides using separate positive and negative methods due to instrument limitations especially for methods with hundreds of MRM transitions. This requires twice the sample and twice the analysis time. Recently, the Bruker EVOQ Elite LC-triple quadrupole system has been introduced to the market; thereby providing fast positive/negative switching allowing for simultaneous determination of positive and negative co-eluting compounds numbering in the hundreds. A study using the EVOQ analyzed 250 pesticides in apple juice, cranberry juice, grape juice, orange juice and vegetable juice using only one method with positive negative switching for over 500 MRM transitions. The measurements were conducted by dilute-and-shoot without sample enrichment. The fruit juices were diluted 10-fold and filtered by filter vial prior to injection. An YMC-Pack ODS-AQ, 3 µm, 150 mm x 3 mm (I.D.) column with mobile phases (A) 5 mM ammonium fluoride in water, and (B) methanol were used. The total run time was 18 minutes including reequilibration.