FLOW-INJECTION MANIFOLDS WITH MEMBRANE FILTERS FOR PRECONCENTRATION AND INTERFERENCE REMOVAL BY PRECIPITATION FLOW-INJECTION FLAME ATOMIC-ABSORPTION SPECTROMETRY

The use of inexpensive, disposable, non-metallic filters in two manifolds for continuous precipitation, as a means of pre-concentration and matrix separation, is described. In one manifold, novel valve configuration and a simple timing device allowed the merging of sample and reagent streams, precipitation, and collection during the "load" part of the cycle. In the "inject" position, the stream switching flushed the dissolved precipitate through the filter. Copper was precipitated as the hydroxide and collected on a disposable cellulose acetate membrane filter. The degree of pre-concentration was shown to be proportional to the volume of sample passed. After sufficient precipitate had been collected, it was dissolved in a stream of hydrochloric acid. Each pre-concentration step was followed by a timed wash step before injection/dissolution of the precipitate. For a sample volume of 11 ml, a pre-concentration factor of 12 was achieved. Calcium (10 mg l-1) was shown to be selectively precipitated in the presence of an aluminum concentration of up to 1000 mg l-1, allowing the successful determination of calcium in the presence of aluminium, not normally achievable by atomic absorption spectrometry with an air - acetylene flame.