Comparison of mild extraction procedures for determination of arsenic compounds in different parts of pepper plants (Capsicum annum,L.)

摘要

Eight extraction agents (water,methanol-water mixtures in various ratios,methanol,a 20 mmol l~(-1) ammonium phosphate buffer,and a methanol-phosphate buffer) were tested for the extraction of arsenic compounds from fruits,stems + leaves,and roots of pepper plants grown on soil containing 17.2 mg kg~(-1) of total arsenic.The arsenic compounds in the extracts were determined using high-performance liquid chromatography-hydride generation inductively coupled plasma mass spectrometry.Whereas pure water was the most effective extraction agent for fruits (87 +- 3.3% extraction yield) and roots (96 +- 0.6% extraction yield),the 20 mM ammonium phosphate buffer at pH 6 extracted about 50% of the arsenic from stems + leaves.Decreasing extractability of the arsenic compounds was observed with increasing methanol concentrations for all parts of the pepper plant.In pepper fruits,arsenic(III),arsenic(V),and dimethylarsinic acid (DMA) were present (25%,37%,and 39% respectively of the extractable arsenic).Arsenic(V) was the major compound in stems + leaves and roots (63% and 53% respectively),followed by arsenic(III) representing 33% and 42% respectively,and small amounts (not exceeding 5%) of DMA and methylarsonic acid were also detected.Hence,for a quantitative extraction of arsenic compounds from different plant tissues the extractant has to be optimized individually.