Simultaneous determination of nitrate and nitrite with a paper-based microfluidic device

Microfluidic devices for detecting nitrate and nitrite ion in water samples were developed. Nitrate and nitrite were chosen for their environmental impact, as established in other research. High levels of nitrate and nitrite ions are known to cause eutrophication in small water bodies. In human beings they can increase the occurrence of methemoglobinemia. Paper was chosen as the substrate for preparing these devices as it is easy to handle and cost effective. Hydrophobic (wax) barriers printed on paper define channels through which samples can flow, mixing with reagents.;Nitrite was detected by diazotization in the Griess assay reaction, which gave a pink color. Nitrate was detected by the same reaction after it was reduced to nitrite ion by vanadium (III) chloride within the sensor device. Quantitative measurements were possible based on the intensity of the color formed. The devices were scanned after drying to obtain the color values. The RGB color model was chosen to represent the color reflected from the devices. It was observed that the concentration of nitrate and nitrite was inversely proportional to the green color component (measuring the pink absorbance lambdamax = 540nm). Reflectance spectroscopy confirmed the inverse correlation.;A calibration was developed using nitrite standards and the amount of nitrite and nitrate were determined in drinking water and soil samples. The sensors were able to detect 15-ppm nitrate and 5-ppm nitrite in drinking water samples.