The application of dealginated seaweed as a cation exchanger for on-line preconcentration and chemical speciation of trace metals

Methods for the on-line preconcentration of Cd2+, Cr3+, Cu2+ and Pb2+ and c hemical speciation of Cr3+ and CrO42- using a microcolumn (50 x 7 mm id) pa cked with about 0.34 g dealginated seaweed biomass are described. Prelimina ry batch experiments showed that metal sorption by the biomass is rapid, ab out 90% of the metals in solution is taken up in less than 5 min, and occur s in a wide pH range, 2-7. Maximum binding was obtained between pH 6 and 7 and the effective binding capacities at pH 6, determined from column breakt hrough measurements using a flow rate of 0.8 mL min(-1), were 4.0, 8.7, 9.4 and 8.5 mu mol g(-1) for Cd, Cr Cu and Pb, respectively. Unretained CrO42- was separated from Cr3+ thus making it possible to determine the levels of both species in solution. The analytical procedures developed for metal pr econcentration and chromium speciation were validated by analyses of two La ke Ontario water reference materials, TMDA 51.2 and TMDA 54.2, and a synthe tic seawater sample. Comparison of the results obtained by the proposed met hods with the certified total values using the Student t test at 95% confid ence limit showed that the differences were not statistically significant. Independent confirmation of the accuracy of the chromium speciation results was obtained using the measurement of absorbance of the 1,5-diphenylcarboh ydrazide-chromium complex, before and after treatment with nitric acid, to determine the levels of CrO42- and Cr3+ by difference. The results obtained with the proposed method for the analyses of TMDA 51.2 and TMDA 54.2 for C r3+ and CrO42- were 20 +/- 0.2 and 39 +/- 0.3 mu g L-1, and 162 +/- 1 and 2 99 +/- 1 mu g L-1, compared with 12 +/- 5 and 54 +/- 31, and 132 +/- 12 and 313 +/- 16 mu g L-1, respectively.