Liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for the analysis of neonicoitinoids or their metabolites have been developed for a wide range of sample matrices including atmospheric sorbent materials, bee pollen, food commodities, soil, surface water, and urine. Neonicotinoids and their metabolites are often analyzed using a chemical class-specific approach to obtain better recoveries than with multiresidue pesticide methods. Liquid chromatography-high resolution mass spectrometry has also been used to identify new metabolites of neonicotinoid insecticides particularly where standards are not available. Electrospray ionization in positive ion mode is the most common ionization method. Reversed phase liquid chromatography with stationary phase sorbent choices including specialty-bonded C18 to silica, phenyl or biphenyl, and pentafluorophenyl bonded in a silica surface were commonly selected to provide additional selectivity for the separation to address the wide range of neonicotinoids commercially available. Gradient elution with acetonitrile as the organic modifier and 0.1% formic acid as a mobile phase additive is the most common choice, although a methanol gradient with 0.1% formic acid could also be used to obtain the required selectivity and MS sensitivity. The sample extraction and clean-up approaches varied with sample type. For liquid sample matrices the most common method of sample pre-concentration and clean-up is solid phase extraction (SPE). Neonicotinoids or their metabolites were extracted from solid sample matrices using liquid-liquid extraction, pressurized solvent extraction, QuEChERS (quick, easy, cheap, effective, rugged and safe), solid-liquid extraction, or ultrasonic extraction. When additional clean-up was required the preferred approaches included QuEChERS or modified QuEChERS or an extraction method followed by SPE. To obtain adequate recoveries and sufficient selectivity and MS sensitivity for metabolites of neonicotinoids, generally both sample preparation and liquid chromatography-mass spectrometry parameters were further optimized.
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