The color reaction of 1(2,6dichloro4nitrophenyl)3(4nitrophenyl)Triazene(DCNPNPT)with cethyltrimethylammonium bromide(CTMAB) and cetylpyridinium bromide(CPB)were studied.In NaOH medium,DCNPNPT reacts with quartenary ammonium cationic surfactant(CTMAB,CPB)to form a purplered complex with the molar ratio of 1∶3.The molar absorptivities of CTMAB and CPB are 393×104L·mol1·cm1 and 416×104L·mol1·cm1 by using dualwavelength spectrophotometry.Beers law is obeyed in the range of 0～328×105mol·L1 for CTMAB,0～316×105 mol·L1 for CPB.The critical micella concentration of CTMAB and CPB in the color system was determined.The method was applied to the direct determination of cationic surfactant in water with satisfactory results.
