Smartphone-based digital colorimetric measurement of dimethyl sulfide in wastewater

Abstract A simple and low-cost method for the measurement of dimethyl sulfide (DMS) in wastewater was developed using digital imaging colorimetry based on a smartphone. This method involved the generation of a pink color through the complexation reaction of DMS with sodium nitroprusside and subsequent acidification. A smartphone camera recorded the developed color through a digital image of the colored reaction mixture and color values in the red (R), green (G) and (B) blue color space were obtained through digital image analysis. The G value was found to provide a basis for the sensitive measurement of DMS. Light box parameters (position and distance of the light source relative to the camera) and reaction parameters (NaOH concentration, reaction time and HCl concentration) were optimized. This method exhibited linearity in the working range of 500–6000 μg kg−1 with a Pearson coefficient of 0.996. The sensitivity, which was based on the slope of the calibration line, was calculated to be −0.017 (μg kg−1)−1, and the limit of detection was 222 μgkg−1. Good precision (0.8 to 1.3% relative standard deviation) was obtained. The G value exhibited good correlation (Pearson correlation coefficient = 0.997) with the absorbance obtained from a spectrophotometer. Measurement of the DMS of a wastewater sample yielded a result which was in agreement (98 % recovery) with the results of a reference GC-FPD analysis, validating its capability for an accurate measurement.