Development of digital colorimetric detection technique for arsenic (iii), arsenic (v) and total inorganic arsenic

Arsenic is one of heavy metals that are associated with the main threats to human health. Therefore, determination of inorganic arsenic on sites is very important. Although arsenic field kits based on Gutzeit method have been extensively used for arsenic determination in the fields, however the major drawback of this approach is poor reproducibility causing a considerable determination error as the measurement of the coloured complex formed is done by the naked eye. Thus, enhancement of the accuracy and precision of the arsenic detection method is required. In this study, a simple and rapid colorimetric quantitative method was developed based on a colour complex formed by silver ion impregnated on a filter paper with arsine gas produced from arsenic ion reduction in the sample by hydrogen generated from zinc and sulfamic acid reaction. The images of the color compounds were captured and digitised into Red (R), Blue (B), and Green (G) colour values. Experiments with incorporation of image processing technique into the colorimetric method were conducted to determine the significant factors and optimum conditions for detection of arsenic (III), arsenic (V) and total inorganic arsenic in water samples. Mathematical models were developed for estimation of arsenic (III), arsenic (V) and total inorganic arsenic. Besides that, determination of arsenic (III), arsenic (V) and total inorganic arsenic in the real water samples and spiked tap water samples were also performed using laboratory instrument and the newly developed method. The significant factors influenced the detection of arsenic (III), arsenic (V) and total inorganic arsenic were found to be mass ratio of sulfamic acid to zinc powder followed by reaction period and mass ratio of sulfamic acid to zinc powder-reaction period-drying period of silver nitrate impregnated filter paper interaction. The optimum conditions to determine arsenic (III), arsenic (V) and total inorganic arsenic were: 1.00 g of sulfamic acid, 0.50 g zinc powder and 5.0 minutes of reaction period; 3.00 g of sulfamic acid, 1.50 g of zinc powder and 5.0 minutes of detection period; and 1.50 g for sulfamic acid, 0.75 g zinc powder and 5.0 minutes of detection period. From the interference study, it was found that the presence of various ions did not give significant effect on the arsenic determination. The method detection limits of arsenic (III), arsenic (V) and total inorganic arsenic were relative low i.e. 2 μg/L, 3 μg/L and 2 μg/L respectively. The accuracies and precisions of the methods for arsenic (III), arsenic (V) and total inorganic arsenic determinations in water samples were high as the relative standard deviations (RSD)s and the relative biases (RB)s for detection of arsenic (III), arsenic (V) and total inorganic arsenic in ground water and lake water samples were found in the ranges of 3%-15% and 4%-12%, respectively. The recoveries of arsenic (III), arsenic (V) and total inorganic arsenic in spiked tap water samples were high (90.30% to 104.40%) and comparable with that of (97.65 to 99.50%) HPLC