A green and sensitive method to determine phenols in water and wastewater samples using an aqueous two-phase system

A greener and more sensitive spectrophotometric procedure has been developed for the determination of phenol and o-cresol that exploits an aqueous two-phase system (ATPS) using a liquid–liquid extraction technique. An ATPS is formed mostly by water and does not require organic solvent. Other ATPS components used in this study were the polymer, polyethylene oxide, and some salts (i.e., Li2SO4, Na2SO4 or K2HPO4 + KOH). The method is based on the reaction between phenol, sodium nitroprusside (NPS) and hydroxylamine hydrochloride (HL) in an alkaline medium (pH 12.0), producing the complex anion [Fe2(CN)10]10− that spontaneously concentrates in the top phase of the system. The linear range was 1.50–500 μg kg−1 (R ≥ 0.9997; n = 8) with coefficients of variation equal to 0.38% for phenol and 0.30% for o-cresol (n = 5). The method yielded limits of detection (LODs) of 1.27 and 1.88 μg kg−1 and limits of quantification (LOQs) of 4.22 and 6.28 μg kg−1 for phenol and o-cresol, respectively. Recoveries between 95.7% and 107% were obtained for the determination of phenol in natural water and wastewater samples. In addition, excellent agreement was observed between this new ATPS method and the standard 4-aminoantipyrine (4-AAP) method.