A compact hydrodynamic sequential injection system for consecutive on-line determination of phosphate and ammonium

Abstract

A simple and compact microfluidic hydrodynamic sequential injection system with a colorimetric detection has been developed for the consecutive determination of phosphate and ammonium in water samples based on molybdenum blue and Berthelot methods. A light-emitting diode as a light source and light dependent resistor light sensor were mounted onto the acrylic microfluidic unit for on-line sample and reagents mixing. This portable and miniaturized analytical system was operated automatically by computerized control switching of solenoid valves. Under the optimum operational condition, a linear calibration graph of phosphate and ammonium (as phosphorus, P, and nitrogen, N) in the range of 0.2–3.0 mg P L−1 and 0.3–4.0 mg N L−1, were achieved with a sample-throughput of 12 h−1. Limit of detection values for phosphate and ammonium were 0.18 and 0.27 mg L−1, respectively. The developed system provides a good precision with relative standard deviations of 2.9 and 4.1% for 11 replicated injections of 1 mg P L−1 and 2 mg N L−1, respectively. Percent recoveries of the analysis of phosphate and ammonium were obtained in the range of 93.5–109.4 and 92.4–107.0, respectively. The developed system offers a compact, durable, cost-effective instrument, with low reagents consumption, that is suitable for monitoring water quality.