Determination of Trace Cr(VI) with Diphenylcarbazide by μFIA-Thermal Lens Microscopy

The optimum reaction parameters for the interaction of hexavalent chromium [Cr(VI)] with diphenylcarbazide in microfluidic chips (μFIA) with thermal-lens microscopic detection were selected. The characteristic feature of the applied flow scheme is the injection of the reagent into the stream containing the test metal, which enables in-field and real-time monitoring of Cr(VI) simply by flowing the sample continuously through the microchip. The limit of detection of Cr(VI) under the selected conditions (signal generating wavelength, 514.5 nm; excitation power, 100 mW; detection position, 10 cm downstream from the mixing zone of the microchip; flow rate 10 μL min-1; injection volume, 1.4 μL) is 15 ng mL-1 (2.9 × 10-7 mol L-1). The linear range is 40 ng mL-1 - 10 μg mL-1 with a relative standard deviation no higher than 10% in the concentration range 0.1-1 μg mL-1. The online monitoring by this scheme provides the possibility of up to 360 analyses per hour.