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El-Shahawi, M. S., et al. Analytica Chimica Acta 534.2 (2005): 319-326.
Tetraphenylphosphonium bromide (TPP·Br) has been demonstrated as an efficient ion-pair reagent for the selective extractive spectrophotometric determination of chromium species in aqueous media, particularly in complex industrial matrices. In the referenced study, TPP·Br was employed to form a stable ion-associate with the chloro chromate anion (CrO₃Cl⁻) under strongly acidic conditions (pH ≤ 0), enabling effective phase transfer into an organic solvent (chloroform).
Upon mixing chromium(VI) with TPP·Br in 1 M HCl and subsequent extraction, a yellow-colored complex ion-associate was quantitatively transferred into the organic phase. The extracted complex exhibited a single, well-defined absorption maximum at 355 nm, while the reagent blank showed negligible absorbance in the 300-600 nm range, ensuring high analytical selectivity. Key analytical parameters-including Beer-Lambert linearity range, molar absorptivity, Sandell's sensitivity, extraction constant (K_ex), distribution ratio (K_D), and overall stability constant (β)-confirmed the robustness and sensitivity of the method.
Importantly, chromium(III) could also be accurately determined following prior oxidation to chromate using hydrogen peroxide in alkaline medium, allowing for total chromium analysis. The method was successfully applied to real electroplating wastewater samples, highlighting Tetraphenylphosphonium bromide as a reliable reagent for chromium speciation and trace analysis in environmental and industrial analytical chemistry.
