N- Nitrosamine Impurities in Ethalfluralin: Determination of an Overlooked Deleterious Source in Pesticides

N- nitrosamines are a class of carcinogenic chemical compound. Considering the large-scale application of agrochemicals globally, the elimination of N- nitrosamines from pesticides should be a priority for manufacturers and regulators. A set of methods was developed and validated for the determination of the toxicologically relevant N -nitrosamine impurity of ethalfluralin (ethyl- N -(2-methylallyl) N -nitroso amine—EMANA) in 33% w v −1 emulsifiable concentrate (EC) formulations. Solid Phase Extraction (SPE) was compared with the “dilute and shoot” approach. Gas chromatography (GC) was combined with Flame Ionization Detection (FID) and mass spectrometry (MS). For MS, two mass filtering modes (Selective Ion Monitoring—SIM, tandem mass spectrometry—MS/MS) and two ionization modes (Electron Ionization—EI, Positive chemical ionization—PCI) were applied. It was concluded that, in the case of samples with high nitrosamine concentration (>90 μg g −1 ), the “dilute and shoot” approach can be applied without compromising the quality of the results. SPE, however, is required to attain the LOQ (0.33 μg g −1 ) with good recovery (97.4–110.67%), linearity (R > 0.99) and precision (%RSD 0.68–1.74). The LOQ supersedes the limit set by EFSA (1 μg g −1 ) in the Technical Active Substance—TAS. The concentration range of the methods is 0.05–110 μg g −1 . The methods were applied for the official surveillance program of the Greek agrochemicals market.