Dry Ashing Technique for the Determination of Arsenic in Marine Fish

Abstract

Abstract A dry ashing procedure, followed by the silver diethyldithiocarbamate colorimetric determination of arsenic in marine fish, is presented. The sample is first homogenized and a portion is pre-ashed with magnesium nitrate, using infrared heat, followed by ashing in a 500°C muffle furnace. The residue is dissolved in HCl and the arsenic is reduced by means of zinc and HCl to arsine, which is complexed with AgDDC and determined colorimetrically at 535 nm. At temperatures of 460°C and above, efficient ashing was obtained. The effect of various volumes of ashing aid (50% magnesium nitrate) was also studied. Maximum recovery and precision were obtained when a minimum of 8 ml 50% magnesium nitrate was used. Standard recoveries of inorganic arsenic added to NBS orchard leaves and a sample of dry marine fish tissue gave values of 91–98%. Analyses of a number of standard NBS orchard leaves and marine fish As-1 and As-2 gave coefficients of variation of 7.0, 6.0, and 8.1%, respectively. Results from dry ashing and wet digestion of a number of species of marine fish were not comparable. Levels of arsenic found in different species of marine fish ranged from <0.4 to 27.0 μg As/g wet weight. Crabs were found to contain elevated amounts of arsenic.