Microfluidic chip-based valveless flow injection analysis system with gravity-driven flows

In this work, a microfluidic chip-based valveless flow injection analysis (FIA) system with gravity-driven flows and liquid-core waveguide (LCW) spectrometric detection was developed. Automated sample injection in the 0.3–6.4 nL range under gated injection mode was achieved by controlling the vertical position of the waste reservoir fixed on a moving platform and the residence time of the reservoir in each position, without the requirement of microvalves or electrokinetic manipulation. An integrated LCW spectrometric detection system was built on the chip by coupling a 20 mm-long Teflon AF 2400 capillary with the microchannel to function as a LCW flow cell, using a green LED as light source and a photodiode as detector. The performance of the system was demonstrated in the determination of [NO2]2− based on the Saltzman reaction. Linear absorbance response was obtained in the range of 0.1–20 mg L−1 (R2 = 0.9910), and a good reproducibility of 0.34% RSD (n = 17) was achieved.