Determination of ethylenethiourea in crops using particle beam liquid chromatography/mass spectrometry

Several food crops were analyzed for residues of ethylenethiourea (ETU), a suspect thyroid and liver carcinogen present in EBDC fungicides, using a commercial particle beam (PB) LC/MS method. The PB/LC/MS detection limits for ETU in crops (5 ppb, 1.25 ng) are comparable to those obtained by LC with electrochemical detection. Spectra obtained from crop samples containing as little as 5 ng of ETU were matched with the NBS library reference EI spectrum. Isotopically labeled ETU was used as an internal standard for quantitation and determination of recoveries. No enhancement of molecular ion signal intensity from unlabeled ETU was observed upon coelution with the isotopically labeled variant. This MS method permits detection of ETU with increased selectivity without compromising sensitivity.