Experimentally validated extractive spectrophotometric determination method of osmium(VIII) from environmental samples: sequential separation of osmium(VIII), rhodium(III) and ruthenium(III)

Abstract

ABSTRACT An ethanolic solution of 1, 3–bis(hydroxymethyl) benzimidazole–2-thione (BHMBT), in the presence of hydrochloric and perchloric acid (1 mol L−1), reacts with osmium(VIII) to give pink-coloured complex instantly at room temperature. The coloured species formed is extracted into methyl isobutyl ketone and shows maximum absorbance at 520 nm (hydrochloric acid) and 540 nm (perchloric acid). Excellent linearity with regression equation as y = 0.025x + 0.005 having correlation coefficient R 2 = 0.999 over concentration range of 5.5–30.0 µg mL−1 of osmium(VIII) is achieved with notable molar absorptivity of 4.907 × 104 L mol–1 cm–1. The optimum concentration range is 5.62–29.99 µg mL−1 which is deduced by Ringbom’s plot. Further other features like limit of detection (LOD = 0.15 µg mL−1), limit of quantification (LOQ = 0.48 µg mL−1) and Sandell’s sensitivity (SS = of 0.038 µg cm−2) are determined as well. The stoichiometry of [Os(VIII)–BHMBT] (1:1) complex is confirmed by applying log-log plot scheme. The specificity headed for osmium(VIII) is well studied and proper masking reagents are used where required to improve it. The intra-day and inter-day precision values are found to be brilliant with % relative standard deviation of 0.84 and 0.87 respectively with % accuracy within the range of 99.00–100. The method is effectively used for determination of osmium(VIII) from water samples, binary and ternary synthetic mixtures, simultaneous spectrophotometric determination of palladium(II) and osmium(VIII) and sequential separation of it from other associated metal ions. The method is sensitive and free from interference of associated ions commonly found with osmium(VIII).