A portable device for quick, on-spot, total arsenic measurement over a wide concentration range in water

It is important from a public health perspective, that an on-spot measurement method can quickly distinguish between water sources both below and above the WHO-allowed level of 10 ppb of arsenic (As) in drinking water, because of its toxicity. To that end, a low-cost, colorimeter-based portable device has been developed that works in conjunction with an optimized concentration of a molybdenum-based sensor reagent as a fast method for As measurement. The device, which consists of an IR LED-phototransistor assembly along with the onboard mi-crocontroller, measures the absorbance of the analyte at a wavelength of 890 nm. The absorbance increases in proportion to As(V) concentration. Reagent optimization in the device allows for a very wide measurement range (6 ppb - 1 ppm) for both As(III) and As(V), and hence As, within 10 min of response time. The limit of detection (LOD) and limit of quantification (LOQ) of the device are 6 and 18 ppb, respectively. The device does not give any interference, even on spiking with high concentrations of other common cations (Fe2+, Ca2+, Zn2+, Mg2+, Cu2+, Cd2+, Na+) and anions (SO2  4 , NO 3), which can be present in water. Also, phosphate interference, if present, is completely eliminated by using an appropriate amount of amberlite IRA-96 free-base microporous resin. The performance of the developed device was verified with environmental water samples and compared with both UV-VIS spectrophotometer and ICP-MS, showing high accuracy. Overall, this work demonstrates that there is a reliable, on-site method for quantitative measurement of As, across a wide range.