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On the semi-micro determination of silica in natural silicates by photometry of β-molybdosilicic acid

β-HPA-Yellow Method

Spektralphotometrische Halbmikrobestimmung von SiO2 in natürlichen Silicaten mit nicht stabilisierter

β-Molybdatokieselsäure

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Zusammenfassung

Die Optimalbedingungen wurden ermittelt und die Einflüsse der üblichen Bestandteile dieser Silicate untersucht. Die Extinktion der Farblösungen (2–8 ppm SiO2, 1500 ppm Na2MoO2 · 2 H2O, pH 1,70) wird bei 370 nm gemessen. Unter den beschriebenen Bedingungen ist die Reproduzierbarkeit der photometrischen Bestimmung doppelt so hoch wie die des Aufschlusses der Proben (max. 40 ppm SiO2, pH 1,00). Von den Bestandteilen natürlicher Silicate stören Al2O3, TiO2 und F nicht, während P2O5, Gesamteisen und Cr2O3 zusätzliche Extinktionen verursachen, für die Korrekturen angegeben werden.

Es wird eine Vorschrift zur SiO2-Bestimmung an 5 mg-Proben gegeben und Analysenergebnisse mitgeteilt, die an geochemischen Referenzproben erhalten wurden. Die Standardabweichung des Verfahrens ist s=±0,5% (4 Proben, 32 Bestimmungen).

Summary

Optimum conditions for the spectrophotometric determination of silica in natural silicates by means of unstabilized β-molybdosilicic acid have been worked out, and the influences of common constituents of these silicates have been studied.

The absorbance of the colour solutions (2–8 ppm SiO2, 1500 ppm Na2MoO4 · 2 H2O, pH 1.70, is measured at 370 nm. Under the conditions described the precision of photometric determination is twice as high as the precision of sample decomposition and preparation of sample solution (max. 40 ppm SiO2, pH 1.00). Among the constituents of natural silicates Al2O3, TiO2, and F do not interfere. P2O5, total iron, and Cr2O3 will cause additional absorbances, for which corrections are given.

An analytical procedure for 5 mg samples is described, and the results of SiO2 determinations on geochemical reference samples are given. The standard deviation of the method recommended is s = ±0.5% (4 samples, 32 determinations).

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  1. Institut für Mineralogie, Ruhruniversität Bochum, Deutschland

    K. Langer

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Langer, K. On the semi-micro determination of silica in natural silicates by photometry of β-molybdosilicic acid. Z. Anal. Chem. 245, 139–148 (1969). https://doi.org/10.1007/BF00454286

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  • DOI: https://doi.org/10.1007/BF00454286

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