DETERMINATION OF (ULTRA)TRACE AMOUNTS OF ARSENIC(III) AND ARSENIC(V) IN WATER BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY COUPLED WITH FLOW-INJECTION ONLINE SORPTION PRECONCENTRATION AND SEPARATION IN A KNOTTED REACTOR

A method has been developed for determination of(ultra)trace amounts o f As(III) and As(V) in water by now injection on-line sorption preconc entration and separation coupled with inductively coupled plasma mass spectrometry (ICPMS) using a knotted reactor (KR). The determination o f As(III) was achieved by selective formation of the As(III)-pyrrolidi ne dithiocarbamate complex over a sample acidity range of 0.01-0.7 mol L-1 HNO3, its adsorption onto the inner walls of the KR made from 150 -cm-long, 0.5-mm-i.d. PTFE tubing, elution with 1 mol L-1 HNO3, and de tection by ICPMS, Total inorganic arsenic was determined after preredu ction of As(V) to As(III) in a 1% (m/v) L-cysteine-0.03 mol L-1 HNO3 m edia. The concentration of As(V) was calculated by difference (the tot al inorganic arsenic and As(III)), Owing to the group-specific charact er of the chelating agent, and the use of an efficient rinsing step be fore elution, the interferences encountered in conventional ICPMS from common major matrix, alkali and alkaline earth metals, and chlorides were eliminated. The presence of organoarsenic species such as monomet hylarsonate and dimethylarsinate in water samples had no effect on the results of As(III) and As(V), Thus, the method can be applied to the speciation analysis of inorganic arsenic at submicrogram per Liter lev els in aqueous solutions with high total content of dissolved solids a nd/or high content of chlorides. Using a preconcentration time of 60 s and a sample now rate of 5 mt min(-1), an enhancement factor of 22 wa s achieved in comparison with conventional ICPMS, The time required fo r a single determination was 200 s, The detection limits (3s) was eval uated to be 0.021 mu g L-1 for As(III) and 0.029 mu g L-1 for total in organic arsenic. The precision for 14 replicate determinations of 1 mu g L-1 As-(III) was 2.8% (RSD) with drift correction and 3.9% (RSD) wi thout drift correction. The concentrations of As(III) and As(V) in syn thetic mixtures obtained by the present method were in good agreement with expected values. Results obtained by the proposed method for tota l arsenic in a river water reference material agreed well with certifi ed and recently reevaluated values. The method was also applied to the speciation analysis of inorganic arsenic in porewaters.