Study of flow extraction by thermal-lens microscopy in microfluidic chips using cobalt (III) tris-(2-nitroso-1-naphtholate)

The flow extraction of complex of Co with 2-nitroso-1-naphthol on the liquid-liquid interface of a water-toluene two-phase flow with thermal-lens detection was studied on a microchip with a complex-shape microchannel partially modified with ODS. The controllable range of flow rates of aqueous and organic phases for establishing a stable liquid-liquid interface and the optimum flow rates for carrying out the extraction processes (6 and 0.05 μl/min, respectively), were determined as well as optimum detection position in a microchannel. The method of the abruptly dropping flow rate of the organic phase (in initial flow rate of 5 μl/min) to the optimum with a constant flow rate of aqueous phase was proposed in order to initiate the extraction processes through the liquid-liquid interface which resulted in the reduction of time of analysis and increase of the sensitivity and reproducibility of determination. The calibration for complex of Co showed good linearity in the range of concentrations of 2.0 × 10-7--8.0 × 10-6 М with a limit of detection of 3 × 10-8 М and the standard deviation in this range of no higher than 0.03.