Centrifuge-Less Mixed Micelle-Mediated Cloud Point Extraction-Spectrophotometric Determination of Vanadium Using 4-Nitrocatechol and Cetylpyridinium Chloride

A novel, environmentally friendly cloud point extraction (CPE) method based on 4-nitrocatechol (H₂L) was developed in this study to spectrophotometrically determine trace vanadium. This method utilizes a mixed micelle-mediated system comprising a cationic surfactant (cetylpyridinium chloride, CPC) and a nonionic surfactant (Triton X-114). In contrast to conventional CPE, the present approach does not employ centrifugation to separate the two phases. The distinguishing characteristic of the extracted species, (CP⁺)[V^VOL₂], is its ability to absorb light across the entire visible spectrum. The measurement at 670 nm, where the complex displays a local maximum, is advantageous for two primary reasons. Firstly, the blank exhibits virtually no absorption, a property that engenders stable and reproducible results. Secondly, selectivity is high because almost all other metal complexes have absorption bands at shorter wavelengths. The proposed method has the following characteristics: a linear range of 2-305 ng mL^-1, a limit of detection of 0.6 ng mL^-1, a molar absorptivity coefficient of 1.22 × 10⁵ M^-1 cm^-1, a Sandell sensitivity of 0.42 ng cm^-2, and a blue applicability grade index (BAGI) of 67.5. Its efficacy was demonstrated in the analysis of mineral water, a spent vanadium-containing catalyst, and a dietary supplement.