Direct Determination of Cationic Polar Pesticides in Fruits and Vegetables using Ion Chromatography and MS/MS or High Resolution Accurate Mass Spectrometry

Poster Presentation

Presented by S. Guazzotti
Prepared by T. Christison1, J. Beck2, J. Madden1, J. Rohrer1
1 - Thermo Fisher Scientific, 1214 Oakmead Parkway, Sunnyvale, California, 94088, United States
2 - Thermo Fisher Scientific, 355 River Oaks Parkway, San Jose, California, 95134, United States

Contact Information: [email protected]; 408-393-8441


Polar cationic pesticides such as chlormequat, diquat, mepiquat, paraquat, morpholine, trimethylsulfonium, and propamocarb may occur as residues in food, but may not be included in pesticide monitoring programs due to difficulty in their analysis using generic multi-residue methods. Recently, anionic pesticides determinations methods by IC-MS/MS have been demonstrated using the Quick Polar Pesticides (QuPPe) method. However, a similar approach is lacking for cation polar pesticides.
Here we demonstrate direct determinations of quaternary amine pesticides in homogenized fruit and vegetable samples using cation-exchange chromatography with serial detection by suppressed conductivity and mass spectrometry. These techniques are demonstrated by targeted MS/MS on a triple quadrupole mass spectrometer and by high resolution accurate mass spectrometry (HRAM MS) in full scan and MS/MS.
The targeted MS/MS method was applied to 23 pesticides and demonstrated to be fast, sensitive, and robust with a 20 min run time. Sensitivities for most analytes in a deionized water matrix was established at triple digit ng/L to single digit g/L. Method robustness in food samples was also demonstrated with over 100 injections of a prune sample.
This method was modified for a fast 10 min analysis time using HRAM mass spectrometry and applied to a group of six cationic pesticides. Mepiquat, trimethylsulfonium, morpholine, and chlormequat exhibited good chromatographic resolution with Rs >2. In contrast, diquat-paraquat with the carbon isotopic masses within 2 m/z fully coeluted but were easily resolved in MS/MS by HRAM MS. The method was also developed on a prototype cation-exchange column optimized for the chromatographic separation of diquat and paraquat. The six pesticides had good accurate mass, meeting the SANTE requirements of <5 ppm. The homogenized food samples did not contain native cationic pesticides of interest. Sensitivities were measured in the single digit g/L or less range by spiking pesticides to the samples. Good accuracy was found, with recoveries of spiked in reagents in the standards and the samples within 80 to 120%.