On-site analysis for phosphorus and nitrogen in environmental water samples by flow-injection spectrophotometric method

On-site analytical methods for the determination of trace amounts of phosphorus and nitrogen in environmental water samples were investigated by using flow-injection (FI) technique. Detection reactions used for on-site chemical analysis for ortho-phosphate, nitrite and nitrate were examined. For economizing the reagents and cutting down waste arose along with chemical analysis to enhance zero emission, a micro-flow injection (mu FI) technique, in which each flow rate was below one tenth of conventional FI systems and was 50 mu l min(-1), was investigated fundamentally and applied to on-site analysis, and also a micro-reactor such as a miniature column for the reduction of nitrate to nitrite was developed. To realize the on-site spectrophotometric measurement, an easy-to-move and a one-box type chemical analyzer was newly developed. The analyzer is based on a mu FI technique, works with a battery (12V) and can analyze samples rapidly on site with better precision and higher sensitivity than conventional Fl systems. For the sensitive determination of phosphate, an ion association reaction of molybdophosphate with Malachite Green was used. Nitrate and nitrite were determined spectrophotometrically on the basis of a diazotization-coupling reaction, where nitrate was reduced to nitrite was found to be useful for on-site determination of phosphorus as ortho-phosphate at ppb-levels, and nitrogen as nitrite and nitrate at ppb-levels in environmental samples.