A colorimetry based, semi-automated portable sensor device for the detection of arsenic in drinking water

A portable colorimetric device is presented for arsenic ion detection in drinking water. The main purpose of this device – which was developed to complement a commercial water dearsenating station demanding regular (weekly to monthly) regeneration runs depending on its saturation – is to provide regular field measurements and easy, semi-automatic operation designed specifically for untrained, typically illiterate users e.g. the population of developing countries. The device exploits a commercially available, well established reagent kit, which is widely used in arsenic field-testing in many developing countries. The hereby presented custom-designed microfluidic system enhances the user-friendliness, the functionality and reliability of the test-strip based kit. The response for total inorganic arsenic ion concentrations (As(III) and As(V)) is linear in the 5-20 μg/l (ppb) range with a sensitivity of 1 μg/l, thus the device is capable to distinguish drinkable water based on the World Health Organization (WHO) guidelines of 10 μg/l. The average relative standard deviation of the measurements is 8 % in the linear range and it is below 2 % for higher arsenic concentrations (above 20 μg/l). The hardware construction of the device and the custom microfluidic system is presented in detail. The effect of elevated water sample temperature on the kinetics and performance of the device was also investigated in order to reduce the required time for the measurements. Stable and reliable arsenic concentration values were obtained after 60 min at 22 oC (ambient temperature) and after only 25 min at 50 oC water sample temperature, but at a cost of an increased relative standard deviation to 16 %, in the linear range