Abstract
The on-site and simultaneous determination of anionic nitrite (NO2-) and nitrate (NO3-), and cationic ammonium (NH4+), in industrial and natural waters, presents a significant analytical challenge. Toward this end, herein a 3D-printed micro-reactor with an integrated heater chip was designed and optimised for the post-column colorimetric detection of NH4+ using a modified Berthelot reaction. The system was integrated within a portable and field deployable ion chromatograph (Aquamonitrix) designed to separate and detect NO2- and NO3-, but here enabled with dual LED-based absorbance detectors, with the aim to provide the first system capable of simultaneous determination of both anions and NH4+ in industrial and natural waters. Incorporating a 0.750mm I.D. 3D-printed serpentine-based microchannel for sample-reagent mixing and heating, the resultant micro-reactor had a total reactor channel length of 1.26m, which provided for a reaction time of 1.42min based upon a total flow rate of 0.27mLmin-1, within a 40mm2 printed area. The colorimetric reaction was performed within the micro-reactor, which was then coupled to a dedicated 660nm LED-based absorbance detector. By rapidly delivering a reactor temperature of 70°C in just 40s, the optimal conditions to improve reaction kinetics were achieved to provide for limits of detection of 0.1mgL-1 for NH4+, based upon an injection volume of just 10μL. Linearity for NH4+ was observed over the range 0-50mgL-1, n=3, R2=0.9987. The reactor was found to deliver excellent reproducibility when included as a post-column reactor within the Aquamonitrix analyser, with an overall relative standard deviation below 1.2 % for peak height and 0.3 % for peak residence time, based upon 6 repeat injections. The printed post-column reactor assembly was integrated into a commercial portable ion chromatograph developed for the separation and detection of NO2- and NO3-, thus providing a fully automated system for the remote and simultaneous analysis of NO2-, NO3-, and NH4+ in natural and industrial waters. The fully automated system was deployed externally within a greenhouse facility to demonstrate this capability.
Published Version
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