Determination of methylisothiocyanate in soil and water by HS-SPME followed by GC-MS-MS with a triple quadrupole.

Methylisothiocyanate (MITC) is the main degradation product of metam sodium, a soil disinfectant widely used in agriculture, and is responsible for its disinfectant properties. Because MITC is highly toxic and volatile, metam sodium has to be applied in a manner that tries to reduce atmospheric emissions but still maintains adequate concentration of MITC in soil to ensure its disinfectant effect. Thus, monitoring of MITC concentrations in soil is required, and to this end sensitive, fast, and reliable analytical methods must be developed. In this work, a headspace solid-phase microextraction (HS-SPME) method was developed for MITC determination in water and soil samples using gas chromatography-tandem mass spectrometry (GC-MS-MS) with a triple-quadrupole analyzer. Two MS-MS transitions were acquired to ensure the reliable quantification and confirmation of the analyte. The method had linear behavior in the range tested (0.026-2.6 ng mL(-1) in water, 1-100 ng g(-1) in soil) with r (2) over 0.999. Detection limits were 0.017 ng mL(-1) and 0.1 ng g(-1) in water and soil, respectively. Recoveries for five replicates were in the range 76-92 %, and RSD was below 7 % at the two spiking levels tested for each matrix (0.1 and 1 ng mL(-1) for water, 4 and 40 ng g(-1) for soil). The potential of using multiple HS-SPME for analyzing soil samples was also investigated, and its feasibility for quantification of MITC evaluated. The developed HS-SPME method was applied to soil samples from experimental plots treated with metam sodium following good agriculture practices.