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 pm deep and 410 pm wide) and a chamber (1.00 mm x 0.65 mm x 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 mu L. of nitrate and nitrite working solutions through the column at 40 mu L. 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. (C) 2013 Elsevier B.V. All rights reserved.