A compact multi-parameter detection system based on hydrodynamic sequential injection for sensitive determination of phosphate, nitrite, and nitrate in water samples

Abstract

A miniaturized microfluidic hydrodynamic sequential injection system for multi-parameter analysis with a sensitive colorimetric detection was developed to improve the analytical performance for the measurement of phosphate, nitrite, and nitrate based on molybdenum blue and Griess methods. A homemade colorimetric detection with a light emitting diode as a light source and phototransistor light sensor was integrated into the microfluidic platform to achieve a low cost compact system with low reagent consumption and high sensitivity. Under the optimized working conditions, a linear calibration graph of phosphate (two working range), nitrite and nitrate (as nitrogen, N) in the range of 0.01–0.1 and 0.3–1.0 mg of PO₄³⁻ P L⁻¹, 0.005–0.05 mg of NO₂⁻ N L⁻¹ and 0.01–0.12 mg of NO₃⁻ N L⁻¹, respectively were achieved with a sample-throughput of 10 h⁻¹. The limit of detections were 0.005 mg of PO₄³⁻ P L⁻¹, 0.0026 mg of NO₂⁻ N L⁻¹ and 0.005 mg of NO₃⁻ N L⁻¹. The percentage of recovery for phosphate, nitrite, and nitrate were 90.3–115.0, 90.0–117.0 and 91.3–117.0, respectively, with relative standard deviations in the range of 1.07–4.90%. Capabilities of the developed device for consecutive analysis of multiple analytes were demonstrated to be an excellent choice for water quality monitoring.