REFRACTORY METHYLATED ARSENIC COMPOUNDS IN ESTUARINE WATERS - TRACINGBACK ELUSIVE SPECIES

Water from the Tagus estuary, Portugal, was concentrated and purified through evaporation, solvent extraction, ion exchange and HPLC, and pe aks of refractory arsenicals were detected by difference between total arsenic (GFAA) and hydride-forming arsenic species (HG QF AA). DCI ma ss spectra of these fractions presented peaks at m/z 139, 157 and 159; the proportion of m/z 157 and 159 peaks, approx. 3: 1, suggested a ch lorinated moiety. DCI MS/MS daughter-ion fragmentation of these peaks seems compatible with dimethylarsenic (cacodylic) acid and structures of the type Me2As(O)Cl or Me3As(OH)F. The refractory character of thes e fractions, however, cannot be explained by these structures. Further work with mixtures of halogen and arsenic species injected in the HPL C system showed that fluoride and iodide can shift DMA (dimethylarseni c) and TMAO (trimethylarsine oxide) to shorter retention times but not to Rf values similar to refractory arsenicals. These latter are attai ned by mixtures of sodium chloride + arsenobetaine, and sodium fluorid e and chloride + arsenocholine. We suggest that peaks at m/z 139 and 1 57 correspond to fragments of a heavier refractory molecule mainly for med by halogenated betaines including chloro-arsenobetaine and chloro- and fluoro-arsenocholine.