| Summary: | Background: Polydiallyldimethylammonium chloride (poly-(DADMAC) is used in many drinking water treatment plants in most parts of the world as a flocculant to remove suspended solids from raw water. However, it is very important that residual poly-(DADMAC) is monitored because it disintegrates into a carcinogenic compound known as N-nitrosodimethylamine (NDMA) during the treatment of drinking water. Methods: In this work, the gold nanoparticle method is optimised for the detection of poly-(DADMAC), where the gold nanoparticles were stabilised with trisodium citrate and then used in quantifying poly-(DADMAC) by Ultraviolet–Visible-Near Infrared spectrophotometry. The optimised method was able to measure poly-(DADMAC) at low concentrations of 1.000 μg L−1 in drinking water with limits of detection and limits of quantification of 0.3302 and 1.101 μg L−1, respectively. Significant results: The method was applied to two different water treatment plants and the concentration of poly-(DADMAC) found during stages of the water treatment process ranged from 1.013 to 33.63 μg L−1. The average poly-(DADMAC) concentrate concentration that is dosed for coagulation in Umgeni Water plant A was 7.889 μg L−1 while in plant B was 19.28 μg L−1. Residual poly-(DADMAC) concentration in drinking water was within the accepted limit of 50.00 μg L−1, regulated by the World Health Organisation (WHO).
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