Zusammenfassung
Das Verfahren beruht auf der katalytischen Wirkung des Molybdäns auf die Peroxoborat-Iodid-Reaktion. Durch Zugabe einer definierten Menge von Ascorbinsäure, die das zunächst entstehende Iod sofort reduziert, wird eine Landolt-Reaktion aufgebaut. Der Endpunkt (Verminderung an Iodid) wird potentiometrisch mit der Iodid-Elektrode indiziert. Zwischen der Zeitdauer bis zum Endpunkt (t in Sekunden) und der Molybdänkonzentration besteht die Beziehung 1/t=4,79 [Mo(VI)]+0,598 im Bereich von 0,5–5,0 μM Mo(VI). Wolfram(VI) stört. Molybdän kann nach diesem Verfahren in Meerwasser nach Konzentration am Chelationenaustauscher Chelax-100 bestimmt werden (Standardabweichung 0,52 μg/l für 8,62 μg Mo/l).
Summary
Trace amounts of molybdenum(VI) have been determined by means of its catalytic effect on the peroxoborate-iodide reaction in acidic medium. The indicator reaction is transformed to a Landolt reaction by the addition ofl-ascorbic acid which reduces iodine to iodide. The end-point of the reaction (decrease of iodide) is potentiometrically monitored by the aid of an iodide ion-selective electrode. The relationship between the time required to reach the end-point (t in seconds) and the concentration of molybdenum(VI) was found to be 1/t=4.79 [Mo(VI)]+0.598 in the range of 0.5–5.0 μM Mo(VI). Tungsten(VI) interferes. The method has been applied to the determination of molybdenum(VI) in sea water after its concentration by the chelating resin Chelex-100 (standard deviation 0.52 μg/l for 8.62 μg Mo/l).
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Kataoka, M., Tahara, S. & Ohzeki, K. Catalymetric trace determination of molybdenum(VI) based on a Landolt type peroxoborate-iodide reaction using an ion-selective electrode. Z. Anal. Chem. 321, 146–149 (1985). https://doi.org/10.1007/BF01117753
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DOI: https://doi.org/10.1007/BF01117753