A microflow analyzer with an integrated gas diffusion unit

Abstract

This work describes the development of a microflow analyzer with an integrated gas-diffusion unit. Deep ultraviolet photolithography was employed to engrave the channels (width of 500 μm and depth of 440 μm) on two plates of urethane-acrylate (UA) photoresist, and a polytetrafluoroethylene (PTFE) membrane was adapted between the structures designed for manipulation of donor and acceptor solutions. To perform the conductivity measurements, three pairs of electrodes (six copper wires with 0.5 mm diameter) were coupled into guiding channels, orthogonal to detection channel. The proposed microfluidic device presented a total internal volume of 48 μL and supported flow rates up to 1.0 mL min-1 without leakages or membrane damages. Analytical signals for the determination of bicarbonate in mineral waters provided a linear response (R2 = 0.999) for the concentration range studied (20 to 80 mg L-1), a limit of detection (LOD) of 2.3 mg L-1 and a relative standard deviation (RSD) of 2.5% (n = 5). A similar performance was observed for the determination of ammonium in medicinal tablets (R2 = 0,998 (10-40 mg L-1), LOD = 2.9 mg L-1 and RSD = 3.0% (n = 5)). The sampling rates for HCO3- and NH4 + procedures were 15 and 25 injections h-1, respectively. For both applications, results agreed with those obtained by potentiometric titrations (HCO3-) and UV-Vis spectrophotometry (NH4+). In addition, by using a flow rate of only 40 μL min -1 for donor and acceptor solutions, a reduction of approximately 75% in residues generation was estimated by comparing the micro-analyzer with a conventional flow analysis system. These results demonstrate the viability of developing microflow analyzers with an integrated gas diffusion unit and conductometric detection.