The Technicon AutoAnalyzer has been applied to the routine determination of iron, copper, lead and zinc, in the range 0 to 10p.p.m., in a heterogeneous range of 230 substances used in the photographic industry. Conventional colorimetric methods are used. To enable the same calibration standards to be used for all samples, organic and inorganic, it was necessary to devise standard procedures for pre-preparation of samples before introduction into the AutoAnalyzer in solution form. All samples are finally present in the form of a 10 per cent. w/v salt solution; organic samples are ashed, the ash extracted with dilute hydrochloric acid and the extract finally adjusted with sodium chloride to 10 per cent. w/v salt content. Insoluble samples are extracted with dilute hydrochloric acid and the extract similarly adjusted to 10 per cent. with sodium chloride. The intermediate wash solution consists of a 10 per cent. w/v sodium chloride solution. In this manner, variations caused by salt effects are minimised. Reproducibility is & l per cent.
Measurement of the absorptive efficiency of ferric oxide is made by passing a measured volume of air containing a known low concentration of H2S through the sample at a known constant velocity, and measuring the residual HzS which has not been extracted. This last measurement is carried out by passing the air through a paper impregnated with silver nitrate, and measuring the opticaL transmission density of the stain formed. Concentrations are calculated from the sulphide stain densities and the volumes of air passed through the papers. The calibration technique forms the basis of a method of measurement of trace amounts of H2S in the atmosphere, and is unaffected by the presence of SOz.
The usefulness and applications of thermometric methods of chemical analysis are discussed, with particular reference to automated routine volumetric analysis. Titrations have been performed with a constant-deliveryrate syringe burette, and the temperature change of the titrand has been followed by means of a thermistor bridge feeding a recording millivoltmeter. The method is widely applicable and can be made sufficiently rapid to make strict ambient temperature control unnecessary. Consecutive end-points of different components of mixtures may be detected in one titration by using single-or two-component titrants.
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