Preservation of inorganic arsenic species in environmental water samples for reliable speciation analysis

Preservation of arsenic species in environmental water samples is important to produce representative species-distribution data. However, published literature on preserving arsenic speciation is confusing and contradictory, predominantly because of the reactions of the Fe(II)/Fe(III) redox system and the microbe-mediated arsenic-species transformations. Field filtration, refrigeration and storage in the dark are prerequisites for stabilization of As(III)/As(V). Filtration removes suspended matter and most microbes, refrigeration suppresses most biotic and abiotic reactions, and storage in the dark avoids photochemical reactions of Fe(III) and As(III). There are reagents that inhibit the oxidation of Fe(II), but the efficiency of preservation depends on the sample matrix and its response to these methods of preservation.