On-line preconcentration with mono-segmented elution for Cd, Cu, Ni, and Zn determination in soil samples by inductively coupled plasma optical emission spectrometry

A simplified on-line preconcentration with mono-segmented elution for Cd, Cu, Ni, and Zn determination by inductively coupled plasma optical emission (ICP-OES) is proposed. The flow manifold is comprised of a small column filled with AG50W-X8 resin by manual injection. In this system, the eluent is trapped by two air bubbles which generates a mono-segmented elution. The enrichment factors obtained with the mono-segmented elution were approximately two times better as compared to an elution in continuous flow. Precision of the multi-element measurement obtained with the proposed flow system was characterized by a relative standard deviation (n=5) lower than 4%. The feasibility of the system was demonstrated by the determination of Cd, Cu, Ni, and Zn fractions from two soil samples after application of a sequential extraction procedure (SEP). The metals from each fraction were extracted in sequence with strontium nitrate, sodium hypochlorite, and a mixture of ammonium oxalate, oxalic acid and ascorbic acid. The two soil samples contained: 41.2 and 1.52 mg kg -1 of Cd, 3910 and 9.52 mg kg -1 of Cu, 119 and 22.4 mg kg -1 of Ni, and 6900 and 217 mg kg -1 of Zn. The overall recovery rates for Cd, Cu, Ni, and Zn, calculated by comparing the total digestion with the sum of the extraction procedure, were in the range of 83.9 to 109.0%, which are considered good recoveries for sequential extraction procedures.