Dispersive liquid–liquid microextraction combined with microvolume spectrophotometry to turn green the 5530 APHA standard method for determining phenols in water and wastewater

Abstract

In this work, a new method based on the combination of dispersive liquid–liquid microextraction (DLLME) with microvolume spectrophotometry has been developed as a greener and miniaturized alternative to the 5530 APHA standard method for determining phenols in water and wastewater. The method relies on the oxidative coupling of phenols with 4-aminoantipyrine (4-AAP). In order to preconcentrate the dye formed, the classical liquid–liquid extraction used in the 5530 APHA method (involving 500mL of sample and 50mL of trichloromethane) has been replaced by DLLME (with 5mL of sample, 50μL of trichloromethane and 200μL of acetonitrile). After optimization, the method yielded limits of detection and quantification (0.8 and 2.5μgL−1, respectively) that were comparable with those obtained by the 5530 APHA standard method. Repeatability, expressed as relative standard deviation, was 5.2% (N=6), and the enrichment factor (EF) was 700. The proposed method was applied to the determination of phenols in different water samples and a wastewater with recoveries in the range 90–99%. The greenness profile was established in accordance with the suggestions made by the NEMI (National Environmental Methods Index). The absence of PBT (persistent bioaccumulative and toxic chemicals) and corrosive reagents and a drastic reduction of generated wastes can be emphasized.