The selectivity of the spectrophotometric methods for determination of microgram quantities of osmium (IV) with acidic monoazo dyes Tropaeolin O (TpO) and Tropaeolin OOO-I (TpOOOI) in the presence of concomitant metals, particularly platinum group, heavy and rare earths (RE) has been studied. The tolerance ratios of interfering elements have been established. The selectivity of the interaction of TpOOOI with osmium (IV) relatively to platinum group elements (PGEs) is much better than TpO. It has been established that the influence of interfering ions can be easily eliminated by means of masking agents viz. EDTA, tartrate, citrate, pyrophosphate and fluoride, and thereby the selectivity of the methods of osmium determination with TpO and TpOOOI has been sufficiently improved. The methods have been approved during the analyses of various model solutions containing ruthenium, platinum, palladium, rhodium and iridium and the masking reagents. Also osmium content has been determined in the intermetallic alloy Nd20Os15Sі65. The standard deviations did not exceed typical values for spectrophotometric methods (RSDs < 5 %). Thus the elaborated methods with various masking agents may be used for direct determination of osmium in complex samples without any preliminary separation of osmium in the form of OsO4 as well as without the extraction of matrices elements.
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