Cutting-edge approach using dual-channel chromatography to overcome the sensitivity issues associated with polarity switching in pesticide residues analysis.

A fast and sensitive method was validated for the analysis of pesticide residues in baby food. After an QuEChERS-based extraction, the samples were analysed with a dual-channel liquid chromatography instrument coupled to a triple quadrupole mass spectrometer. The method consisted of two independent injections per sample. In the first injection the sample was analysed with a mobile phase optimal for the positive polarity ionisation (water, methanol, formic acid, and ammonium formate), whereas in the second injection the mobile phase was optimised for the negative polarity ionisation (water, acetonitrile, acetic acid). The total number of pesticides was 264, out of which 238 were analysed with the methanol gradient and 26 with the acetonitrile gradient. The dual-channel instrument allowed for sample multiplexing. Thus, sample throughput was equivalent to that of a single-channel system. The limit of quantitation, determined according to the DG SANTE guidance document, was 0.003 mg/kg for 97% of the evaluated compounds. The validation study was followed by a real sample survey. In 42 samples, 16 positives were found.