Exploiting an automated microfluidic hydrodynamic sequential injection system for determination of phosphate

A microfluidic hydrodynamic sequential injection (HSI) spectrophotometric system was designed and fabricated. The system was built by laser engraving a manifold pattern on an acrylic block and sealing with another flat acrylic plate to form a microfluidic channel platform. The platform was incorporated with small solenoid valves to obtain a portable setup for programmable control of the liquid flow into the channel according to the HSI principle. The system was demonstrated for the determination of phosphate using a molybdenum blue method. An ascorbic acid, standard or sample, and acidic molybdate solutions were sequentially aspirated to fill the channel forming a stack zone before flowing to the detector. Under the optimum condition, a linear calibration graph in the range of 0.1-6 mg P L-1 was obtained. The detection limit was 0.1 mg L-1. The system is compact (5.0 mm thick, 80 mm wide x 140 min long), durable, portable, cost-effective, and consumes little amount of chemicals (83 mu L each of molybdate and ascorbic acid, 133 mu L of the sample solution and 1.7 mL of water carrier/run). It was applied for the determination of phosphate content in extracted soil samples. The percent recoveries of the analysis were obtained in the range of 91.2-107.3. The results obtained agreed well with those of the batch spectrophotometric method.