Abstract
Plant tissue analysis methods were evaluated for six explosive compounds to assess uptake and phytoforensic methods development to quantify explosives in plant to obtain the plant data for the evaluation of explosive contamination in soil and groundwater. Four different solvent mixtures containing acetonitrile or methanol were tested at variable extraction ratios to compare the extraction efficiency for six explosive compounds: 2,4,6-trinitrotoluene (TNT), pentaerythritoltetranitrate (PETN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2-amino-4,6-dinitrotoluene (2ADNT), and 2,4-Dinitroanisole (DNAN), in Laurel Willow (Salix pentandra) stem and range grass Big Bluestem (Andropogon gerardii) using LC-MS/MS. Plant tissues were spiked with 500 ng/g of explosives and extracted using ultrasonically-assisted solvent extraction. With the ratio of fresh plant mass to solvent volume of 1:20 for willow and 1:40 for big bluestem grass, results indicated that all explosives in willow except HMX were extracted at higher than 73.3% by using 20 mL of methanol, 50:50 (v/v) methanol:water, or acetonitrile, whereas HMX was extracted with the highest recovery of 61.3% by 20 mL of acetonitrile. In big bluestem grass, the most effective solvents were 20 mL of either methanol or 50:50 (v/v) methanol:water for PETN extraction with a recovery of higher than 101.2% and 20 mL of 50:50 (v/v) methanol:water for HMX, RDX, TNT, 2ADNT, and DNAN extraction with a recovery of 83.8%, 104.4%, 97.5%, 80.7%, and 108.2%, respectively. However, unlike methanol and acetonitrile, 50:50 (v/v) methanol:water provided no problem of leading or split peak in chromatogram; therefore, it was preferred in the test and performed a method validation. Results indicated that 50:50 (v/v) methanol:water provided good repeatability and recovery and method detection limits at 0.5-20 ng/g fresh weight or 8.8-61.3 ng/g dry weight. Overall, results suggested that solvent extraction efficiency of explosives in plant was influenced by plant species and solvent used, and method presented here was believed to provide the preliminary data with respect to the analysis of simultaneous explosives in plants with LC-MS/MS.