Abstract :
A simple speciation of chromium oxidation states based only on the difference in reaction rates of Cr(III) and of Cr(VI) has been developed. This speciation, which was carried out in an ammonium 1-pyrrolidinecarbodithioate (APCD)/diisobutyl ketone (DIBK) extraction system, required no sample splitting. At the first extraction, Cr(VI) was extracted into a DIBK phase, and Cr(III) remaining in the sample was extracted secondly after replacement of the phase by fresh DIBK. Inert Cr(III) was extracted directly without the oxidation process. The concentration of chromium in the extract was measured by AAS. In the first extraction, 0.4-0.5% of Cr(III) was extracted and 0.2% of Cr(VI) was carried over to the second extraction. Using artificial seawater, the detection limit (3(sigma)) and the relative standard deviation (n = 5, at 100 (mu)g/L) were 10 (mu)g/L and ca. 4% (concentration factor = 2). Interferences of heavy metal ions were examined; 5-fold cation group (Mn^2+, Fe^3+, Ni^2+, Cu^2+ and Zn^2+) and 1-fold anion group (VO3-, Mo7O24^6- and WO4^2-) exhibited negative errors of 5 and 10% in Cr(III) determination respectively. Validity of the method was checked with the standard reference material JAC-0032 (river water); total chromium was determined as 11.0 (mu)g/L (certified value is 10.1 (plus-minus) 0.2 (mu)g/L).
