Preliminary Performance Evaluation of the Gold Nanoparticle Method for Quantification of Residual Poly-(Diallyldimethyl Ammonium Chloride) in Treated Waters in the Umgeni Water Catchment, Kwazulu-Natal (South Africa)

A “real world” study to assess the performance characteristics (precision, accuracy) of the citrate-capped, gold nanoparticle, Ultraviolet-Visible colorimetric method, for quantifying residual poly-diallyl dimethylammonium chloride (poly-DADMAC) in four raw dam and treated potable waters, was undertaken. Using three calibration methods, the method was found to be sensitive (LOQ=2 μg/L), over the linear range 10-30 μg/L. The overall mean within-batch precision (%RSD) was: 7.42 (±7.07) for Method 1, and 7.66 (±7.37) for Method 2; between-batch (reproducibility) (%RSD) was 54.37 ± 30.03) and 35.89 ± 34.89). Statistical data analysis indicated fairly good agreement (no significant difference) for poly-DADMAC levels in 30 samples analyzed by the two methods Method 1 and 2. The residual poly-DADMAC potable water levels (range: <2-8 μg/L), were: on average (±SD) (μg/L), 1.21 (±1.31) for Hazelmere Dam, 1.22 (±0.55) for Midmar Dam, 3.40 ± 3.89) for Inanda Dam, and 3.64 (±3.83) for Nagel Dam. The observed, apparent poly-DADMAC levels, obtained by Method 1, (range: 6-16 μg/L) were, on average (±SD) (μg/L), for the raw water samples: 3.73 (±0.46) for Inanda Dam, 5.73 (±6.57) for Nagle Dam, 6.82 (±9.03) for Hazelmere Dam and 10.12 (±6.94) for Midmar Dam. The study indicated compliance of all treated, potable water for residual poly-DADMAC, to the current international limit of ≤50 μg/L. The relatively high apparent concentration (range: <2-24 μg/L) of poly-DADMAC observed on the raw dam waters was attributed to the presence of Natural Organic Matter (NOM).