Determination of Oxadixyl in Wines by Liquid Chromatography-Tandem Mass Spectrometry: Single-Laboratory and Interlaboratory Validation Study

A direct injection LC/MS/MS method for the determination of the pesticide oxadixyl in wines was developed and validated. A sample divert valve was used to deliver the fraction that contained oxadixyl to the mass spectrometer's electrospray ionization source. Oxadixyl was monitored and quantitated using two transitions in multiple reaction monitoring mode. The method demonstrated recoveries of 99.2 +/- 2.0 and 96.7 +/- 5.2% for red and white wines, respectively, a linearity range of 2-20 mu g/L, LOD at 0.7 mu g/L, LOQ of 2.0 mu g/L, and precision values of 8.2% (RSDr) and 6.2% (RSDR). Direct injection of the wine onto a C18 ultra-performance LC column allowed automation and high throughput screening. Benefits of this approach include minimal sample preparation, short (3 min) run times, and the use of matrix-matched calibration standards, which minimize the matrix effect due to interferences from wine phenolics, sugars, and various other components. The method's performance characteristics were not statistically different for white and red wines. An additional interlaboratory validation study involved 12 laboratories and demonstrated good data agreement with HorRat values ranging from 0.23 to 0.52.