Design, fabrication and characterization of an integrated micro ammonia analysis system (IMAAS) with microreactor and in-plane type optical detector based on the Berthelot reaction

An integrated microammonia analysis system (IMAAS) with microreactor and in-plane (x-axis) type optical source and optical detector with ease and precise optical alignment method using microchannels for optical fiber guide by silicon deep RIE process based on the Berthelot reaction was newly proposed and investigated. It is not necessary to do difficult and complex optical alignment process for ammonia analysis than the case of using out-of-plane (z-axis) type optical detector perpendicular to microfluidic devices. The proposed IMAAS with the size of 5 cm × 5 cm and thickness of 1 mm was fabricated using typical and simple MEMS processes. IMAAS was packaged with inlet and outlet tube, and optical fiber connected with in-plane type optical source and optical detector using UV epoxy bonding. Reaction rates from ammonia of the concentration of 16.5 ppm to indophenols at IMAAS were remarkably increased with temperatures from 308 to 318 K on hot plate as a heater. In case of reaction temperature of 318 K, complete reaction time was less than 1 min. Reaction rates were increased with ammonia concentrations from 4.1 to 33.0 ppm at the temperatures of 308, 313 and 318 K. In order to remarkably decrease total analysis system, thermoelectric heater of 2 cm × 2 cm was used as a heater. In case of using thermoelectric heater at the temperature of 308 K and the ammonia concentration of 2 ppm, the complete reaction time of indophenol in IMAAS was in the range of 100-150 s. From these results, IMAAS on thermoelectric heater has advantage for small size and local heating of reaction region in IMAAS than the case of using hot plate heater. Fabricated IMAAS were reproducible and suitable for the determination of ammonia concentrations. For the future works, it was thought these microsystems could be used for other microreactions for versatile species analyses as well as detections for N-containing organic species.