Performance optimization of a commercially available iminodiacetate resin for the determination of Mn, Ni, Cu, Cd and Pb by on-line preconcentration inductively coupled plasma-mass spectrometry Original Research Article

The on-line preconcentration performance characteristics of a commercially available iminodiacetate resin (Toyopearl AF-Chelate 650M) were investigated. The method was optimized for several parameters, including buffer pH, rinsing of matrix salts from the resin, elution acid type and strength, and the nebulizer gas flow rate. An ammonium chloride buffer with a pH of 8.80 was mixed with the sample on-line prior to loading. This pH was found to be optimal for Mn, Cu, Cd and Pb, whereas a pH of ≥9.2 was optimal for Ni analysis. Column rinse experiments showed that both buffer and water reduce Na concentrations to <100 μM in the rinse solution within 3 min. It was also determined that using 1 M HNO3 acid for column elution yielded higher intensities for Mn, Ni, Cu and Pb, while 1 M HCl yielded higher count rates for Cd. The change from the optimization solution, with a 0.2% HNO3 acid concentration, to the 10% elution acid required a reduction in the nebulizer gas flow rate of 0.05 l min−1 in order to obtain reduced blank intensity ratios. Calibrations performed using standard solutions (1 ml) with concentrations ranging from 0 to 10 pg ml−1 (ppt) resulted in regression coefficients of 0.990–0.998. Method detection limits of 1.1, 0.08, 0.47, 0.06 and 0.16 pg ml−1 for Mn, Ni, Cu, Cd and Pb, respectively, were obtained. Accuracy was demonstrated by results from runs of the certified standard reference materials (SRMs), CASS-4, a newly available coastal seawater reference standard and NASS-4, an open ocean seawater reference material.