Sample extraction for arsenic speciation

The standard method used to determine arsenic species in solid samples is by using an extraction method that minimizes any operationally induced changes in chemical form. However, the use of such methods often results in less than complete extraction, with extraction efficiencies ranging from <1% to 100% for many types of samples. In this study the effect on extraction efficiency of the variables of total arsenic content, sample type and extraction method (methanol/water vs. simulated gastric conditions) were examined. The arsenic content in plant and deer mouse samples from Yellowknife, NT, as well as commercially available hijiki, an edible alga, and their extracts, was determined. Statistical analysis of the results revealed that extraction efficiencies are lower for both plants and mouse tissues that contain the highest levels of arsenic, and this trend persists in plants even when more exhaustive extraction methods (Le., Soxhlet extraction) are used. When the plant data was examined with respect to taxonomic groupings moss appeared to be extracted less efficiently than most other plants, and sedge and cattail appeared to be extracted most efficiently. An extraction method modeling human gastrointestinal conditions, gastric fluid extraction (GFE), was comparable to methanol/water extraction of plants with respect to amounts extracted and proportions of As(III) and As(V) present. However, methanol/water was used more efficiently to extract arsenic from wet hijiki than the GFE method. It is important to include information about extraction efficiency when discussing speciation of arsenic in a sample.