On-line complexation of zinc with 5-Br-PADAP and preconcentration using a knotted reactor for inductively coupled plasma optical emission spectrometric determination in river water samples

SALONIA, JOSÉ A.; WUILLOUD, RODOLFO G.; GÁSQUEZ, JOSÉ A.; OLSINA, ROBERTO A.; MARTINEZ, LUIS D.

Concepción-Pucón

Simposio; SIXTH RIO SYMPOSIUM ON ATOMIC SPECTROMETRY; 2000

Universidad de Concepción

Zinc is the 24th most abundant element in the Earth¡¦s crust, and its concentration averages about 70 ug/g in most rock-forming minerals. In mineral deposits of base and precious metals, zinc is associated with Cu, Pb, Ag, Au, Sb, As and Se, and is an excellent indicator of such deposits as well as a good pathfinder. Thus, Zn is widely used for geochemical prospective studies. The average concentration of Zn in river water is in the order of 20 ƒÝg/L, which is taken as the base value for prospective studies. Therefore, powerful techniques are required, and only a few of them show sufficient sensitivity. Among these are electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma mass spectrometry (ICP-MS). Inductively coupled plasma optical emission spectrometry (ICP-OES) is one of the most used techniques for the determination of zinc traces. The most sensitive line for Zn is at 213.856 nm. However, this line exhibits spectral interferences from elements such as Fe, Ni, and Cu. The second most sensitive line, at 206.200 nm, does not exhibit such interferences. However, the determination limit that can be reached (approximately 40 ug/L) is not enough for Zn determination in river water.In order to achieve accurate, reliable and sensitive results, preconcentrations and separations are needed when the concentrations of analyte elements in the sample are too low to be determined directly by ICP-OES. Flow injection on-line preconcentration based on the sorption of metallic complexes on the inner walls of a PTFE knotted reactor (KR) has been successfully applied. The use of the KR as a collector for precipitates has been found feasible in FI on-line precipitation-preconcentration systems. The most widely used reagents for metal preconcentration in KR have so far been diethyldithiocarbamate (DDTC) and ammonium pyrrolidine dithiocarbamate (APDC). Pyridylazo reagents form insoluble chelates with numerous metallic ions. However, we have not found any reference in the literature to the use of these reagents in KR preconcentration. 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) has been used as a reagent in the spectrophotometric determination of numerous metallic ions, although precautions had to be taken in order to avoid the precipitation of the corresponding chelate, such as the addition of surfactant agent. This fact suggested to us that, in absence of a surfactant, 5-Br-PADAP could be a suitable reagent for preconcentration of zinc on KR.In the present work, a method for preconcentration and determination of zinc using a KR is proposed. Zinc was retained under the form of Zn-(5-Br-PADAP) complex. The determination was performed using ICP-OES associated with a FI methodology.An enrichment factor of 42 with a sample loading time of 120 s was obtained for the KR system with respect to ICP-OES using pneumatic nebulization. The detection limit for the preconcentration of 10 mL of aqueous solution was 0.09 ug/L with 2.3% of relative standard deviation (RSD), calculated with the peak heights obtained.The method was succesfully applied to the determination of zinc in river water samples.