No abstract

The determination of trace elements in environmental waters is increasing in contamination studies, owing to the need to guarantee the good quality of water for various purposes. For the determination of Cd in water samples, graphite-furnace atomic absorption spectrometry (GF-AAS) is the chosen method of many analysts because of its relative simplicity, the possibility of automation and the low instrumental detection limits given. However, for complex samples such as seawater, there are important problems: firstly, matrix interference from the salt matrix remains, which causes a deterioration in the accuracy and precision. Secondly, a previous preconcentration of Cd is required, because of the very low concentration of cadmium in the surface seawater.1 Thus, a different preconcentration procedure, e.g., coprecipitation 2 , solvent extraction 1,3 , sorption on chelating resins 3,4 or immobilized adsorbents 5-8 , have been proposed to preconcentrate and separate cadmium from the seawater matrix. However, most of the procedures involve several chemical stages, including a laborious pH adjustment in order to remove any interfering matrix, thus increasing the possibility of a loss of the analyte and sample contamination. Recently, a column of a reversed-phase substrate loaded with hydrophobic molecules, such as bis(2-ethylhexyl)-hydrogen phosphate and 2-ethylhexyldihydrogen phosphate 10 , tris(2,6-dimethoxyphenyl)phosphine 11 and quaternary ammonium salts 9,12 , has been prepared to develop a preconcentration method for trace elements in acidic solutions. These materials were used for the preconcentration of rare-earth elements 10 and Cd 12 in seawater by column techniques. Previously, we 13 proposed a new preparation technique of a dynamically coated column involving C 18 -bonded silica gel (C 18 ) coated with methyltricaprylylammonium chloride (Aliquat 336). The column was applied to the matrix isolation and preconcentration of platinum 13 and zinc 14 in environmental samples. This paper describes a simple and convenient method for the selective preconcentration of trace cadmium from seawater, followed by an atomic absorption spectrometric determination of the element. The precision and accuracy of the method were demonstrated by analyzing certified reference materials. The process of preconcentration is simple, easily yields a large enrichment factor, requires no buffer and results in a low contamination of the blank. Experimental ApparatusAtomic absorption analyses were performed on a Perkin-Elmer (Model 4100ZL) atomic absorption spec- Applied and Environmental Chemistry, Kitami Institute of Technology, Kitami, Japan **Muroran Institute of Technology, Muroran, Japan ***Hokkaido Institute of Environmental Sciences, Sapporo, Japan A dynamically coated column of C18-bonded silica gel with methyltricaprylylammonium chloride was used for the selective preconcentration of Cd from water samples under acidic conditions. The complete adsorption of Cd occurred from seawater with no additional reagent, and was found f...

A highly sensitive method was developed for the determination of cadmium, lead and zinc in natural waters by atomic absorption spectrometry after coprecipitation with 8-quinolinol. Quantitative recoveries of the metals were possible over the pH range 8 -10 when magnesium was present as a carrier ion. The precipitates thus formed were analyzed directly by an atomic absorption spectrometer equipped with a specially deviced graphite furnace and a miniature cup. Reliability of this procedure was confirmed by the determination of the metals in lake and river water samples. For the analysis of a 400-cm3 portion of water sample, detection limits(3ab) for Cd(ll), Pb(II) and Zn(I I) are 0.6, 2.3 and 1.9 ng dm-3, respectively. A corresponding precision of 3 -5% was typical.

An octadecylsilylsilica (C18) column dynamically coated with methyltricaprylylammonium chloride (C18-Aliquat 336) was examined for the preconcentration of trace amounts of Zn in water samples. Zinc was quantitatively retained on the column from an HCl solution at between 0.5 and 3 mol dm-3, or seawater acidified with HCI, ranging from 0.5 to 1.0 mol dm-3. The retention capacity of the Cls-Aliquat 336 for zinc was about 50 µmol g-' from a 1 mol dm3 HCl solution. The Zn retained on the column was completely eluted with 3.5 ml of 0.1 mol dm3 nitric acid, and was directly determined by graphite-furnace atomic absorption spectrometry. The precision and accuracy of the present method were demonstrated by analyzing certified reference materials, such as Coastal Seawater (CASS-2) and Riverine Water (SLRS-3). The total procedural blank was 1.9±0.4 ng for Zn. The detection limit (3u of the blanks) was 2.4 ng dm-3 for Zn based on a 125-fold concentration of a 500-ml sample.

An enrichment procedure for cobalt is described which is based on precipitating this element with 8-quino ino and a carrier metal ion, filtering the precipitates and then analyzing them directly by e ectrotherma atomic absorption spectrometry (EAAS). Submicrogram amounts of the element were coprecipitated quantitatively with magnesium 8-quinolinate from 100cm3 of aqueous solutions of pH 9.5. Quantitative recoveries of the metal from aqueous solutions ranging from 200 to 500 cm3 were also possible. Humic material and organic acids do not interfere with the recovery efficiencies of the method. This method was applied to a tap and river water samples. Using this method, cobalt(II) in natural water at levels below µg dm-3 range could be determined by EAAS using a solidsampling technique.