Determination of Arsenical Herbicide Residues in Plant Tissues
Paper chromatographic separation of hydroxydimethylarsine oxide (cacodylic acid), monosodium methanearsonate (MSMA), sodium arsenate, and sodium arsenite was achieved with the aid of four solvent systems. Aqueous extracts of plant tissues removed essentially all the arscnicals applied, but mechanoiic fractionation was required before the extracts could be analyzed by paper chromntographic procedures. A standard nitric-sulfuric acid digestion procedure was employed for arsenic analyses, but great care was taken to avoid sulfuric-acid-induced charring by first adding relatively large amounts of nitric acid to drive off chlorides present. Depending upon the amount of chloride present, substantial losses of arsenic as arsine chlorides were observed if the samples charred. Five minutes in fuming sulfuric acid to completely break the carbon-arsenic bonds was another critical requirement for the quantitative determination of arsenic from cacodylic acid and MSMA. The silver diethyldithiocarbamate calorimetric method was useful for detecting as little as 0.6 mg or as much as 20 mg of arsenic per sample.