No abstract

Cassava has been found to contain cyanogenic glucoside, which is hydrolyzed to cyanide as a waste product during cassava processing. This cyanide content is found to vary in the various parts of the cassava plant. Powdered cassava leaf has been utilized to pack cyanide mild steel specimens using BaCO 3 and BaCl 2 as energizers. The microstructures of the treated specimens were examined; these revealed a case formation resulting from the diffusion of C into the specimen. The diffusion proceeded from the case to the core of the specimen with increase in treatment temperature and time. The cutting time of the case-hardened steels was investigated and correlated with pack cyaniding heat treatment. The specimens were found to be more resistant to sectioning with increasing temperature and time.

The flow injection introduction of samples that would be difficult by conventional nebulisation owing to dissolved solid content, viscosity or quenching effects on flame reactions is demonstrated. The various ways of achieving sample dilution by control of volume injected, tube dimensions and flow-rate are discussed and a manifold described for producing solutions for calibration purposes and diluting off-range samples. The important characteristics of the nebuliser and instrument for flow injection work are evaluated. A simple manifold for investigating interference effects is described and its use illustrated for some well known effects. The possibilities of achieving pre-treatment by solvent extraction and extension to include indirect methods are discussed and the role of flow injection procedures in the method development for, and the extension of the range of application of, flame atomic-absorption spectrometry is critically evaluated.

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 1-1) was shown to be selectively precipitated in the presence of an aluminium concentration of up to 1000 mg 1-1, allowing the successful determination of calcium in the presence of aluminium, not normally achievable by atomic absorption spectrometry with an airacetylene flame.

Nylon membrane, 0.45-pm pore. 24 m m f.d.(3) Stainless steel disc. 2 Iun pore. 5 mm f.d.