Determination of four fluorescent whitening agents in laundry detergents by solid phase extraction combined with ultra-high performance liquid chromatography

Abstract

A new method was established to determine three stilbene-type disulfonate and one distyrylbiphenyl-type fluorescent whitening agents (FWA351, FWA85, FWA28 and FWA71) in laundry detergents by solid phase extraction (SPE) and ultra-high performance liquid chromatography with a diode array detector (UPLC-DAD). The fluorescent whitening agents were extracted from laundry detergents with 2% formic acid aqueous solution and methanol, and purified by WAX SPE column, and analyzed by UPLC-DAD on a Phenomenex Synergi Max-RP column (150 mm x 2.0 mm), employing acetonitrile-10 mmol/L ammonium acetate as the mobile phase in a gradient elution mode. The fluorescent whitening agents were qualitatively determined by retention time, and confirmed by the ultraviolet spectrum. The results indicated that the target analytes were in the range of 0.05-180 mg/L with the correlation coefficients (r) greater than 0. 999 3, and the method limits of quantification (MLOQ) of target analytes were ranged from 1.5 mg/kg to 15 mg/kg (S/N = 10). The feasibility of this method was demonstrated by the determination of FWAs in samples with spiked recoveries. The recoveries were in the range between 84.9% and 105%, and the precision (relative standard deviation, RSD) ranged from 3.2% to 6.1% (n = 6). Among the 15 samples analyzed, the rate of positive samples was 53.3%, over 1 000 mg/kg of FWA351 and FWA71 were detected. The method is simple, precise and has high recoveries for the determination of fluorescent whitening agents in laundry detergent samples.