Determination of Trace Chromium in Water by Graphite Furnace Atomic Absorption Spectrophotometry After Preconcentration on a Soluble Membrane Filter

Abstract

A new concentration and determination method has been described for the determination of lower than 0.1 μg L−1 levels of chromium (VI) in water, based on the reaction between chromium (VI) and phenylfluorone (PF) to form an anionic chelate and the collection of the ternary ion-associate of the chelate with cetyltrimethylammonium bromide (CTMAB) (a cationic surfactant) on an organic solvent-soluble membrane filter. Determination of the solution obtained after dissolving the membrane and analyte in a suitable solvent is achieved using graphite furnace atomic absorption spectrophotometry,. The ternary complex (Cr(VI)-PF-CTMAB = 1:2:2) is collected on a 0.45 μm nitrocellulose filter and the filter and analyte are dissolved in a small volume of 2-methoxyethanol (methylcellosolve) acidified with dilute sulphuric acid. The chromium is determined by graphite furnace atomic absorption spectrophotometry under optimum experimental conditions. A good linear relationship exists in the range 0.05 – 0.30 μg chromium in 5.0 ml, with satisfactory reproducibility. The detection limit, defined as three times the standard deviation of the blank, is 0.06 μg L−1 with 20 fold preconcentration. The ions normally present in water do not interfere under the experimental conditions used. The proposed method has been applied to the concentration and determination of chromium (VI) in water samples from several sources by means of direct graphic furnace atomic absorption spectrophotometry; the recoveries of chromium (VI) added to the samples are quantitative, and results found are satisfactory.