Biopolymer Test Kit for Colorimetric Detection of Chlorine in Water

Abstract

The objective of the study was to fabricate the colorimetric sensor of biodegradable material for free chlorine determination. The colorimetric reagent of N,N-diethyl-p-phenylenediamine sulfate (DPD) was entrapped in the hybrid biopolymer film of agar (AG) and tapioca starch (TAS) and it was coated on the plastic micro-PCR tube. The pink product obtained from the reaction between DPD reagent and chlorine could indicate the presence of residual chlorine in the water.  The condition for the sensor film synthesis was optimized by the digital image analytical technique with mobile phone application. The results were showed that Red-Green-Blue (RGB) intensity of reaction product was not changed, even through the DPD reagent was added over 0.2 g/mL. The addition of 16 g/L EDTA in the buffer solution could reduce the interference effect from some metals, especially Fe³⁺, contaminated in water sample. The water pH could be maintained for best analysis at the volume ratio between buffer and DPD solution of 0.5:1. The incubation of colorimetric film at 60 °C and 60 minutes provided the best sensor performance with fast analysis of 1 min reaction time. In conjunction with the digital image colorimetry (DIC), the developed test kit did not provided only the qualitative information, but the rapid quantitative analysis could be also fulfilled. A wide linear range of 0.3 to 15 mg/L chlorine concentration with good linearity (R² > 0.99) was achieved by this coupled technique. The application of biopolymer film to various kind of real water samples showed the good performances, which were comparable with the standard spectrophotometry (no significantly different results at 95% confidence level). These could promote the use of biopolymer test kit as the environmentally-friendly analytical method for chlorine in water.