Simple and selective determination of arsenite and arsenate by electrospray ionization mass spectrometry

Arsenic pollution of public water supplies has been reported in various regions of the world. Recently, some cancer patients are treated with arsenite (As(III)); most Japanese people consume seafoods containing large amounts of negligibly toxic arsenic compounds. Some of these arsenic species are metabolized, but some remain intact. For the determination of toxic As(III), a simple, rapid and sensitive method has been developed using electrospray ionization mass spectrometry (ESI-MS). As(III) was reacted with a chelating agent, pyrrolidinedithiocarbamate (PDC, C(4)H(8)NCSS(-)) and tripyrrolidinedithiocarbamate-arsine, As(PDC)(3), extracted with methyl isobutyl ketone (MIBK). A 1 microL aliquot of MIBK layer was directly injected into ESI-MS instrument without chromatographic separation, and was detected within 1 min. Arsenate (As(V)) was reduced to As(III) with thiosulfate, and then the total inorganic As was quantified as As(III). This method was validated for the analysis of urine samples. The limit of detection of As was 0.22 microg L(-1) using 10 microL of sample solution, and it is far below the permissible limit of As in drinking water, 10 microg L(-1), recommended by the WHO. Results were obtained in <10 min with a linear calibration range of 1-100 microg L(-1). Several organic arsenic compounds in urine did not interfere with As(III) detection, and the inorganic As in the reference materials SRM 2670a and 1643e were quantified after the reduction of As(V) to As(III).