Toward an in situ phosphate sensor in natural waters using a microfluidic flow loop analyzer

In this paper, we describe an automated microfluidic flow loop analyzer toward an in-situ phosphate measurement in natural waters. The system consists of a microfluidic chip and a setup for driving and detecting which form a microfluidic flow loop analyzer with one peristaltic micropump, seven microvalves, three inlets, one outlet and a loop channel which connects them together. The loop channel functions as a mixer, and the mixing process can be monitored continuously. Three reagents can be injected into the water sample at any time. The reagent consumption is 6 μL per sample for one measurement of the phosphate concentration, which would increase the in-situ usage time greatly because of the limited reagents. The analyzer is small, and its power consumption is low (343 mW), which increase the potential of the analyzer for monitoring phosphate in situ. The analyzer has been calibrated, and its performance has been quantified. Because of the continuous monitoring function of the microflow loop, we increase sample throughput to 10 samples per hour. The phosphate concentrations of the water samples have been measured using both normal method and rapid method we proposed. The results show there are no significant differences between our analyzer and reference procedures.