The Incorporation of a continuous precipitation unit built Into flow Injection manifolds Is presented and discussed, In order to show Its analytical potential in the development of Indirect automatic atomic absorption methods. The precipitate is formed by Injecting an anion (analyte) Into a carrier containing a cation (reagent) and Is retained on a stainless-steel filter. Two unsegmented flow configurations, one of which Involves the dissolution of the retained precipitate, have been tested. Three types of precipitates encountered In gravimetric pro-cedures have been considered In this work: crystalline (calcium oxalate), curdy (sliver chloride), and gelatinous (ferric hydroxide). By continuous precipitation, chloride and oxalate could be determined In the range 3-100) jg/mL and 5-90 Mg/mL, respectively, with a relative standard deviation between 2 and 5%. The sampling frequency ranges between 10 and 50 h~ 1.

To extend the scope of application of atomic absorption spectrometry (AAS) and to increase the sensitivity achievable for elements directly unsuitable for trace analysis, much attention has been devoted to the development of indirect methods for such elements (1-3). The application of these methods to the determination of nonmetal elements and or-ganic compounds involves carrying out a suitable chemical reaction. One of theseis based on the reaction of an anion with a solution of a cation at an adequate concentration to yield an insoluble compound. The cation is then measured either in the filtrate or in the precipitate. Precipitates of analytical interest have very different physical properties, which determine both their analytical applicability and the