Development of Membrane Filter Colorimetry for Determining Tap Water Discoloration Using a Spectrocolorimeter

Abstract

In this study, we aimed to develop a novel method to quantify residual colorants in the water supply using a spectrocolorimeter. Cross-tests of color and turbidity showed that standard color solutions of 1–50 color units had a turbidity of ˂0.094 nephelometric turbidity unit (NTU) and turbidity standard solutions of 0.1–5 NTU had color measurements of 0 true color unit, indicating limitations in measuring colorants using conventional methods. Therefore, the samples were diluted stepwise to 1 L and filtered through a 0.45 μm cellulose membrane; then, the residuals colorants were measured using membrane filter colorimetry (MFC) with a spectrocolorimeter to determine the color difference. The color difference exhibited a high correlation with turbidity. Furthermore, scanning electron microscopy/energy-dispersive X-ray spectroscopy and inductively coupled plasma-optical emission spectrometry analyses of the same samples confirmed that the main components of the colorants were iron and manganese; the concentration of these substances in the samples was measured using MFC with the standards Fe2O3·H2O and MnO2. The results confirmed a high correlation between the color difference (△E*ab) and concentration of the samples and standard substances. Our findings suggest that MFC is a promising approach for measuring colorants in drinking water.