A simple, ultra sensitive and selective method for the spectrophotometric determination of Ir 3+ in various synthetic and environmental samples was reported. The analyte ions were collected on a membrane filter in the form of their red complex with 5-(2-benzothiazolyl-azo)8-hydroxy-quinoline (BTAHQ), and the absorption spectra of the colored membrane filters were acquired. Effects of pH value, sample volume, and amount of BTAHQ were examined in order to optimize sensitivity. The interference by

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... common other ions was eliminated using appropriate masking agents. The absorbance is linearly related to the concentration of Ir 3+ in the ranges from 0.1 to 0.8 lg/L, and from 1.0 to 7.0 lg/L, respectively, the correlation coefficients (R 2 ) being 0.9996 and 0.9994. The molar absorptivities were calculated to be 4.81 Â 10 5 and 4.26 Â 10 7 L mol À1 cm À1 at 563 nm, whereas Sandell sensitivity was found as 0.391 and 0.004 ng cm À2 , respectively. The novelty and advantages of the proposed method is the highly sensitivity of the proposed method compared with all previously cited methods for iridium determination. Under the optimal conditions, the detection limit is 0.03 lg/L. The recoveries in case of spiked samples are between 98.7% and 101.5%, and the relative standard deviations range from 1.21% to 1.75%. Ó 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).