Spectrophotometric determination of chromium (VI) with ο-hydroxyhydroquinonephthalein and cationic surface-active agent
1979 Volume 28 Issue 11 Pages 707-710
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1979 Volume 28 Issue 11 Pages 707-710
ο-Hydroxyhydroquinonephthalein (Qn. Ph.)-chromium(VI) {Cr(VI)} complex in the presence of excess cationic surface-active agent (cetyltrimethylammonium chloride) (CTAC) could be used for the spectrophotometric determination of a minute amount of Cr(VI). A maximum absorption wavelength of the complex was 560 nm in a weakly acidic medium, where the apparent molar absorption coefficient was 1.64×105. The Sandell sensitivity was 0.00032μg/cm2 Cr(VI) for an absorbance of 0.001 at the wavelength of 560 nm. The calibration curve was linear in the range 0 to 4μg/10ml Cr(VI). The proposed procedure for the determination of Cr (VI) is as follows. To a 10 ml volumetric flask a sample solution containing less than 4 μg of Cr(VI), 1.0 ml of 2.0×10-2 M CTAC solution and 2.0 ml of 1.0×10-3 M Qn. Ph. methanol solution are added, and the pH of the mixture is adjusted to 5.8 by the addition of Sorensen buffer solution of phosphate. The content is diluted to the mark with water, kept at 60°C for 30 min, and the absorbance of the solution is measured at 560 nm against the reagent blank. The reaction is quite sensitive, and the procedure does not require a long time. This method is applicable to the determination of Cr(VI) in steel in much the same way as previous by reported determination of molybdenum(VI). The mole ratio of Cr(VI), Qn. Ph. and CTAC in the complex was estimated to be 1 : 2 : 2 by the continuous variation and the mole ratio methods.
