Sorption-catalytic determination of cadmium using bromobenzothiazo noncovalently bound to silica and paper

Cadmium (along with Fe(II), Co(II), Zn(II), and Pb(II) ions) decreases the rate of oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with KIO4 conduct ed either without or with Mn(II) as a catalyst. Cadmium(II) is preconcentra ted from aqueous solutions on silica plates or paper filters physically mod ified with a reagent for selective determination of Cd(II), namely 1-[(6-br omo-2-benzothiazolyl)azo]-2-naphthol (bromobenzothiazo, or BET). The modifi er is strongly retained on the both supports at pH 6-10 and does not affect the inhibiting effect of Cd(II) in the indicator reaction. Cadmium is dete rmined by its inhibiting action directly on the sorbents by measuring trans mittance (BBT/paper) or reflectance (BBT/silica) with limits of detection o f 2 x 10(-4) and 0.03 mg/L, respectively. The proposed hybrid combination o f sorption with catalytic detection on the sorbent allows to increase the s electivity factors several times (up to 2 orders) relatively to the determi nation in solution. Tap water samples and soil extracts were analyzed.