Development of a simple visual and image-based colorimetric analytical method for Mn2+ using solid-phase extraction with sedimentable dispersed particulates

• A simple colorimetric method for Mn 2+ determination was developed. • MnO 4 − adsorption was achieved with adsorbents bearing trimethylaminopropyl groups. • Accurate analysis could be completed within 1 min in a single vessel. • A 10-fold increase in sensitivity compared with the standard method was observed. • The method can also be used for simple chemical oxygen demand measurements. A simple analytical method for screening Mn concentrations is useful for environmental water management. Herein, a simple analytical method for Mn 2+ based on visual and image colorimetric analysis was developed by considering the adsorption of MnO 4 − , a colored substance, on sedimentable dispersed fine particles. The analyte could be determined by the visual or image analysis of the colored precipitates in a sample vessel. The extraction of MnO 4 − was achieved using fine silica gel particles modified with trimethylaminopropyl groups as an adsorbent. The established method can determine Mn 2+ concentrations within approximately 1 min by simply adding the water sample to a tube containing the reagents and adsorbent particulates. The calibration cure shows good linearity in the range of 0.1 to 1.0 ppm. The limit of detection of image colorimetry using a light box and camera was 0.05 mg/L (3σ). The method was used to analyze Mn 2+ in groundwater, and the results were cross-checked with the values obtained by atomic absorption spectrometry. Finally, the proposed method was successfully applied to the simple measurement of chemical oxygen demand using MnO 4 − as an oxidizing agent. The analyttical time for COD is just over 3 min.