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In this study, a syringe was filled with silica gel loaded with 3-aminopropyltriethoxysilane, for the separation and preconcentration of copper, cadmium and chromium prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS) in seawater. For this purpose, a syringe was filled with 0.5 g of modified silica gel and the sample solution was drawn into the syringe and ejected back again. The analyte elements were quantitatively retained at pH 5. Then, the elements sorbed by the silica gel were eluted with 2.0 M of HCl and determined by GFAAS. At optimum conditions, the recovery of Cu, Cd and Cr were 96-98%. Detection limits (3delta) were 6.6, 7.5 and 6.0 micro g L(-1) for Cu, Cd and Cr, respectively. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only once. Cu, Cd and Cr added to a seawater sample were quantitatively recovered (>95%) in the range of the 95% confidence level. The method proposed in this paper was compared with a column technique. Optimum experimental conditions, reproducibility, precision and recoveries of both techniques are the same, but the syringe technique is much faster, easier and more practical than the column technique. It is a portable system and allows one to make the sorption process in the source of sample. In addition, the risk of contamination is less than in the column technique.

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Silica gels modified with 3-aminopropyltriethoxysilane or 3-mercaptopropyltrimethoxysilane groups have been developed for the preconcentration of copper and cadmium prior to their determination by flame atomic absorption spectrometry. The surface areas of the modified silica gels were determined by the Brunauer-Emmett-Teller (BET) method to be 290 m2 g-l of the amino-modified silica and 410 m2 g-1 of the thiol-modified silica. Batch and column methods were used for the separation and concentration of copper and cadmium. These metals were quantitatively retained on both the modified gels in slightly acidic media. In the batch method, the effects of pH, shaking time and type of buffer on the adsorption of copper and cadmium were investigated. In the batch and column procedures both copper and cadmium adsorbed on the silicas were quantitatively recovered (relative standard deviation of 2-6%) using 2 mol dm-3 hydrochloric acid even in the presence of sodium chloride up to a concentration of 1 .O%.

The preparation and characteristics of thiol-modified silica and its application to the preconcentration and determination of trace amounts of copper and cadmium by flame atomic absorption spectrometry are described. For the preparation of modified silica, the untreated silica suspended in methanol was impregnated with 3-(trimethoxysilyl)-1-propanethiol to obtain thiol-modified silica and the methanol was evaporated under vacuum. The residual silica was dried at 150° C and washed with distilled water until the washings appeared clear. The surface area of thiol-modified silica was 410 m2/ g, whereas the copper capacity was about 0.022 mmolCu/ g silica. Batch and column methods were used for the separation and concentration of the above-mentioned metals. These metals were quantitatively retained on the adsorbent at acidic media. In the batch method, the effects of pH, shaking time and the kind of buffer on adsorption of copper and cadmium were investigated. The shaking time of 30 min was sufficient for a quantitative adsorption of the metals. In the column and batch procedures, both copper and cadmium adsorbed on the modified silica were quantitatively recovered with 2 M hydrochloric acid. Sodium chloride (up to 1%) had no effects on the recoveries.

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The method described uses the separation of As(III) and As(V) species in aqueous samples by means of the anion‐exchange resin Amberlite IRA‐93. The samples were acidified using acetic acid and passed through a glass column filled with pre‐treated Amberlite IRA‐93 resin. As(III) was poorly adsorbed on the anionic exchanger material, whereas As(V) was retained. The arsenic concentration was measured in the column effluent by graphite furnace AAS (GF‐AAS). The retained As(V) was eluted from the column using 1 M NaOH. Prior to the determination of the As(V) concentration in the NaOH eluate, the eluate was passed through a glass column filled with a cation‐exchange resin (Amberlite 200) to remove sodium ions and minimize the Na+ interference with the AAS determination. After calibration the method was applied to the separation of As(III) and As(V) species in two aqueous extracts of arsenic contaminated soils. The results were compared with those obtained from an on‐line separation and determination of As(III) and As(V) in the aqueous soil extracts using a state of the art HPLC‐ICP‐MS system.