Rapid screening of agrochemicals by paper spray ionization and leaf spray mass spectrometry: which technique is more appropriate?†
Paper Spray Ionization (PSI) and Leaf Spray (LS) are two new sources of ambient ionization mass spectrometry. In PSI, the sample is deposited on a triangular paper and ions are generated by applying a high voltage on a moistened paper with an organic protic solvent. The LS technique is a variant of PSI, where the paper is now substituted by the matrix itself to be studied, a triangular leaf. Both methods allow rapid and inexpensive analyses compared to traditional API techniques. In this work, both sources were applied to identify and quantify agrochemicals which are widely used in fruits and vegetables. The analytical performance of PS and LS techniques was evaluated from the construction of calibration curves in the positive ionization mode (PSI(+) and LS(+)) using atrazine, diuron and methomyl agrochemicals in arugula, basil, cabbage, lettuce and kale vegetable samples. The concentration ranged from 10 to 1000 ppb. Atrazine and diuron were used as internal standards, not requiring the use of deuterated standards. Both analytical methods demonstrated similar performance for the three agrochemicals with R2 > 0.99, and values of LOD and LOQ ranging from 1.23 to 25.00 and 4.12 to 83.33 ppb for PSI(+)-MS and from 0.03 to 36.00 and 0.11–120.00 ppb for LS(+)-MS. In almost all cases, these values were lower than the established MRLs (Maximum Residue Limits), which are 250 ppb for atrazine and 100 ppb for diuron and methomyl.