The speciation of arsenic in biological tissues and the certification of reference materials for quality control

Arsenic is an ubiquitous element. Its toxicity, environmental mobility and accumulation in living organisms usually depend on the form in which the element is present. Information on the chemical forms is important for understanding the role of the element present as well as revealing its environmental cycle. This requirement stimulates the need for information on the speciation of arsenic and the development of suitable analytical methodology. It is well known that seafood can contain considerable quantities of naturally-acquired arsenic and developments in speciation have focused on seafood samples. It seems that the major arsenic species in fish, crustaceans and molluscs have the tetraalkylarsonium structure (R4As+) and the species in marine algae and bivalves have the trialkylarsine oxide structure (R3AsO). However, the concentrations are still low enough to require a sensitive analytical method based on the isolation, identification and quantification of the individual arsenic-containing species. This review will discuss the accepted techniques for the speciation of arsenic in biological tissues and the need for quality assurance of speciation analyses. Quality control will be discussed, focusing on the use of certified reference materials. As well as validation of methods, reference-material certification involves the participation of several laboratories, enabling the evaluation of state-of-the-art analytical techniques. The certification process of a candidate oyster-tissue reference material for different chemical species of elements (including arsenic species) is discussed. (C) 2003 Published by Elsevier Science B.V.