RESUMO
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.
RESUMO
Pyrethrins are natural insecticides derived from chrysanthemum flowers containing a mixture of six components: pyrethrin I, cinerin I, jasmolin I, pyrethrin II, cinerin II, and jasmolin II. In this work, a rapid and sensitive LC-(ESI)-MS/MS method has been developed for the individual quantification and confirmation of pyrethrin residues in fruit and vegetable samples by monitoring two specific transitions for each pyrethrin component under Selected Reaction Monitoring (SRM) mode. Samples were extracted with acetone/water or acetone, depending on the sample type, and raw extracts were directly injected in the LC-MS/MS system. Method validation was carried out evaluating linearity, accuracy, precision, specificity, limit of quantification (LOQ) and limit of detection (LOD) in eight types of fruit and vegetable samples at 0.05mg/kg and 0.5mg/kg (referred to the sum of all pyrethrins). The method based on acetone/water (70:30) extraction led to satisfactory recoveries (70-110%) and good precision (below 14%) for all pyrethrin components in lettuce, pepper, strawberry and potato. The method based on acetone extraction allowed satisfactory recoveries for lettuce, cucumber, tomato and rice samples with recoveries between 71 and 107% and RSDs below 15%. For pistachio samples, satisfactory results were obtained only for some analytes and extracts were also injected using APCI interface, but the lower sensitivity achieved allowed only the validation at 0.5mg/kg. The analytical methodology developed was applied to the analysis of fruit and vegetable samples.
