Development of an isotope dilution liquid chromatography/tandem mass spectrometry method for the accurate determination of neonicotinoid pesticides, imidacloprid, clothianidin, and thiamethoxam in kimchi cabbage reference materials

A method based on isotope dilution liquid chromatography/tandem mass spectrometry (ID-LC/MS/MS) was established as a candidate reference method for accurate determination of neonicotinoid pesticides, imidacloprid, clothianidin, and thiamethoxam in kimchi cabbage. Their deuterated isotopes, imidacloprid-d(4), chlothianidin-d(3), and thiamethoxam-d(4) were used as internal standards. The combination of HLB and Carb solid-phase extraction (SPE) cartridges was used to clean-up kimchi cabbage extracts. The ID-LC/MS/MS conditions were optimized with fortified kimchi cabbage samples for validation. Imidacloprid in the ERM-BC403 cucumber sample (0.627 +/- 0.026) mg/kg was analyzed with the developed method, and the measured value (0.604 +/- 0.028) mg/kg agreed within their uncertainties. The developed method was employed for the certification of kimchi cabbage reference materials prepared in this laboratory. The measured values of imidacloprid, clothianidin, and thiamethoxam are (0.860 +/- 0.020) mg/kg, (0.524 +/- 0.012) mg/kg, (0.787 +/- 0.014) mg/kg, respectively. The standard deviation of the measured values for ten bottles was < 1%, and the measured values after one year agreed with their first measurements indicating reliable repeatability and reproducibility of the developed method.

Automated summary

A method based on isotope dilution liquid chromatography/tandem mass spectrometry (ID-LC/MS/MS) was established for accurate determination of neonicotinoid pesticides in kimchi cabbage. The method utilized internal standards and solid-phase extraction (SPE) cartridges for sample cleanup. The developed method showed reliable repeatability and reproducibility.