Development of an innovative optical sensor to detect extremely low levels of chromium in real samples using colorimetric methods

Abstract

The investigation focused on a methodology for concentrating and analyzing Cr(VI) in aqueous samples. This objective was accomplished through the creation of a cellulose triacetate (CTA) matrix-based membrane optode. This optode was constructed by physically integrating a specific chromophore, 1,3-benzenediamine,N,N′-bis(2-furanylmethylene) (BDBFM), known for its selectivity towards Cr(VI), alongside the plasticizer dioctylphthalate (DOP). The effectiveness of integrating Aliquat 336, an anion exchanger, was evaluated in the process of immobilizing both BDBFM and the Cr(VI)–BDBFM complex within the optode matrix. The progressive intensification of the violet color observed on the optodes, directly correlating with the amount of loaded Cr(VI), highlights the potential of this method for colorimetric screening of Cr(VI) in aqueous samples. The developed optode was also employed for the determination of the total chromium content by converting Cr(III) to Cr(VI) via oxidation using 0.1 M hydrogen peroxide. The concentration of Cr(III) can be quantified by subtracting the amount of Cr(VI) from the total chromium content. This optode enabled the quantitative detection of Cr(VI), even at levels as low as 2.85 ng mL⁻¹. The suggested sensor displayed a low detection limit, fast response time, cost effectiveness, ease of preparation and also remarkable selectivity regarding some anions and cations. Regeneration of the optode can be easily accomplished by employing 0.05 M HNO₃, while demonstrating remarkable reproducibility and reversibility in its response, with a relative standard deviation (RSD) below 1.9. The suggested method was effectively utilized to measure chromium levels in a diverse range of samples, such as food, water, and environmental, and biological samples.