Spectrophotometric method for the determination of trace cationic surfactants using sequential injection

Abstract

This paper presents a sequential injection spectrophotometric method for the determination of cationic surfactants (CS) on the basis of forming a coloured ion-associate complex of anionic dye, Bromophenol Blue (BB) with cationic surfactants, including zephiramine (Zeph), cyltrimethylammonium bromide (CTMAB) and cetylpyridinium bromide (CPB), and causing a red shift of λmax from 585 nm for Bromophenol Blue to 634 nm for CS+·BB− associate. The increased absorbance value is proportional to the concentration of cationic surfactant. Various chemical and physical parameters for the sequential injection spectrophotometric method were optimized. The linear ranges were 6.34–50.8 µg/mL for Zeph, 7.29–32.8 µg/mL for CTMAB and 7.50–40.0 µg/mL for CPB. The detection limits were 0.22 µg/mL, 0.29 µg/mL and 0.25 µg/mL for Zeph, CTMAB and CPB, respectively. The proposed system can be used to analyse 28 samples per hour with a relative standard deviation (RSD) lower than 4.1%. The method was applied to the determination of cationic surfactants in both synthetic and spiked water.