A urethane-acrylate microflow-analyzer with an integrated cadmium column

This work describes the construction and evaluation of a microflow-analyzer with an in-chip cadmium column used to determine total nitrate and nitrite ion concentrations in freshwater. Deep UV photolithography in urethane-acrylate photoresist was used to create channels (390 μm deep and 410 μm wide) and a chamber (1.00 mm × 0.65 mm × 20 mm) where cadmium granules were manually packed before the device was sealed. No clogging or leaks were observed for flow rates greater than 2.0 mL min− 1. The efficiency of converting NO3− to NO2− was estimated at 97.5% by propelling 2.7 μL of nitrate and nitrite working solutions through the column at 40 μL min− 1. Based on the peak heights, a linear response (R = 0.994) was found for the concentration range studied (0.23 to 2.26 mg N L− 1 as NO3−), providing a limit of detection of 0.15 mg N L− 1. Considering the determination of total NO2− and NO3− in six freshwater samples, no significant differences (95% confidence level) were obtained by comparing the results for the proposed device with the reference spectrophotometric method. In addition, a 24-fold reduction in the residue generation was estimated for the procedures using the micro-analyzer when compared to a classical flow injection analysis (FIA) system. This performance meets Brazilian regulations for quantifying NO3− in freshwater and follows the principles of green chemistry.