EI and NCI GC–MS and GC–MS/MS: Comparative Study of Performance Characteristics for the Determination of Pesticide Residues in Plant Matrix

Linearity of response and sensitivity (i.e., gradient of the calibration curve) were selected as performance parameters for the comparison of six GC–MS methods that result from all possible combinations of the two ionization (electron ionization, EI, and negative chemical ionization, NCI) and the three mass scanning techniques (full scan, selective ion monitoring and MS–MS). The study involved testing of spiked matrix (tomato) samples as well as standard solutions of 27 pesticides in acetonitrile at a range of concentrations (10–200 μg L−1). The selected pesticides are representative of some of the most common pesticide classes. The performance of each technique was quantified and a comparison made between the different methods. MS/MS was found to perform better as far as linear response was concerned, especially in plant matrix, in agreement with scientific literature. Sensitivity was enhanced with NCI–full scan and EI–MS/MS.