Effect of surfactants on the determination of sulphate in waters

The effects of pure cationic, anionic and non-ionic detergents, industrially prepared detergents, sodium tripolyphosphate, sodium pyrophosphate, soap and NTA, in quantities up to 1000 mg l⁻¹, on the analysis of soluble iron in water using the phenanthroline, tripyridine and biquinoline methods were investigated. The tripyridine method is superior to the other two methods for the determination of iron in the presence of up to 1000 mg l⁻¹ of various surfactants but not for up to 100 mg l⁻¹ of non-ionic detergents. The phenanthroline method can be used to determine iron in the presence of up to 1000 mg l⁻¹ of cationic, anionic and non-ionic detergents, but sodium tripolyphosphate interfered above 2 mg l⁻¹. The biquinoline method can be used for the determination of iron in the presence of up to 1000 mg l⁻¹ of cationic, 100 mg l⁻¹ of anionic and 70 mg l⁻¹ of non-ionic detergents, and 50 mg l⁻¹ of sodium tripolyphosphate.