Rapid determination of nitrate in drinking water using ion-exchange-enhanced infrared spectroscopy

Infrared spectroscopy is an effective method for the determination of compositions and concentrations of liquids, with advantages of fast response, no-sampling, flexible in use, and is effective for on-line monitoring. However, for trace substances in drinking water, such as nitrates and heavy metals, infrared spectroscopy is not sensitive enough for the quantitative and qualitative measurement. In this study, we improved the sensitivity of infrared spectroscopy for nitrite determination by developing an ion-exchange-enhanced diffuse reflectance spectroscopy, which consists of an accessory based on ion-exchange resin for enrichment and a Fourier transform infrared spectrometer for measurement. Using this method, the limit of detection for nitrate is 1.7 mg/L, which is enough for drinking water sensing. We also verified the quantitative measurement ability of the method. Furthermore, the limit of detection and quantitative measuring range could be adjusted by changing the mass of resin and adsorption time. This study demonstrated that the method is effective to detect trace nitrites in drinking water, can be applied in the field, and is sensitive, rapid, and inexpensive with a wide dynamic range. Practical applications This study demonstrated an ion-exchange-enhanced diffuse reflectance spectroscopy, which is effective to quantitatively measure nitrate in drinking water with concentrations within several ppm. Compared with traditional used methods for water nitrate analysis, our method is rapid, sensitive, and inexpensive and is potential for on-line measurement. The method can be used in drinking water sensing and water processing. By changing the ion-exchange resin, it is also effective to measure other compositions in water rather than nitrate. It can also be used to determine harmful compositions in drinks. Meanwhile, we developed a smart sensor based on this method, which used an Microelectro Mechanical Systems Fourier transform infrared spectrometer instead of V70 in this study. It is now in the test for the rapid determination of nitrate in drinking water by Water Services Company of Beijing.