Direct spectrophotometric determination of alkylphenol polyethoxylate nonionic surfactants in wastewater

A new spectrophotometric method is proposed for direct determination of alkylphenol polyethoxylate, RO(CH2CH2O)nH (where R is alkylphenyl and n is the degree of polymerization), in wastewater. The method is based on the formation of ternary complex, Pb(II)-meso-tetra-(3,5-dibromo-4-hydrooxyphenyl)-Porphyrin (T(DBHP)P)-alkylphenol polyethoxylate (APE). Under optimum reaction conditions, T(DBHP)P reacts with lead(II) and APE to form a yellow ternary complex with the maximum absorption peak at 479 nm. The color reaction is rapidly completed and the absorbance remains stable for at least 24 h under room temperature. The apparent molar absorption coefficients were 0.4-4.3×104 L mol^(-1) cm^(-1) for n=5-50. As little as 0.02 (mu)g mL^(-1) of APE can be detected. The effects of various substances on the determination of APE were also investigated in detail. It was found that all the studied co-existing substances, especially cationic and anionic surfactants, which always seriously interfere in some reported methods, could be tolerated in considerable amounts. The method offered the advantages of simplicity, rapidity, sensitivity and selectivity without any prior separation or extraction.