Analytical methods were successfully validated for mancozeb and its metabolite, ethylenethiourea (ETU); each method for the respective analytes was developed and validated in agricultural commodities, animal matrices (bovine), soil, and water. Developing analytical methods to analyze metabolites can require troubleshooting and problem solving, especially if the analytes and/or matrices are difficult to work with and extract. The structures of mancozeb and ETU differ significantly and it was not possible to extract both analytes simultaneously using the same extraction method. Mancozeb is incredibly unstable after addition of solvent, and must be derivitized first before extraction, but after derivitzation, the analyte was easily extracted using the QuEChERS method. In contrast, ETU is very small and polar and has a stable ring structure, but the QuECHeRS method resulted in low recoveries. Instead, a simple extraction with formic acid in water followed by clean-up with C18 sorbent was used for ETU and resulted in acceptable recoveries. Column selection is a critical component of successful method development – due to the significant difference between the two analytes, two different columns were also necessary. A HSS (high strength silica) column was used with mancozeb to provide additional stability and a PFPP (pentafluorophenylpropyl) column was chosen for ETU, which has been shown to retain small, polar molecules well. One radiovalidation for ETU was also performed and produced acceptable results. The methods developed and validated showed acceptable recoveries and relative standard deviations (RSD) based on EPA, OECD, and SANCO guidelines. These methods were also successfully transferred to outside laboratories for Independent Laboratory Validations to confirm the methods efficacy and were also used in field and ecotoxicology studies.

Modifying methods for metabolite analysis: Method development for the determination of ethylenethiourea residues

ACS Fall 2020 Virtual Meeting

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