A promazine derivative-oriented chemical sensor for ultra-sensitive chromium determination

Abstract

The study reports a simple and highly selective spectrofluorometric method for trace determination and speciation of chromium(III & VI) species in water using 10-(3-dimethylaminopropyl) phenothiazine hydrochloride, namely, promazine hydrochloride (PMH) as a fluorescence tagging reagent. The method is based on the redox reaction between PMH and chromium(VI) in aqueous H₃PO₄, resulting in the formation of complex [Cr(III)–PMH] followed by fluorescence quenching at λ_ex/em = 300/449 nm. An exceptional value for the limit of detection (LOD = 0.03 μg L⁻¹) is attained with a linear range of 0.1–1.0 μg L⁻¹ under the optimized conditions. A coefficient of variation (CV) of ±2.05% (n = 5) is obtained at 2.0 μg L⁻¹ level of chromium(VI). Chemical speciation of the chromium(III & VI) species is successfully accomplished after the oxidation of chromium(III) to chromium(VI) with H₂O₂ in KOH solution at pH 9.0. The method is validated in environmental water samples with satisfactory recovery percentages (>97.7%) using inductively coupled plasma-optical emission spectrometry (ICP-OES). The proposed and reference methods are subjected to statistical treatment (student's t and F tests) at 95% confidence with no significant difference, indicating the precision and accuracy of the proposed optical probe.