A highly reproducible solenoid micropump system for the analysis of total inorganic carbon and ammonium using gas-diffusion with conductimetric detection

In this work, a simple, economic, and miniaturized flow-based analyzer based on solenoid micropumps is presented. It was applied to determine two parameters of high environmental interest: ammonium and total inorganic carbon (TIC) in natural waters. The method is based on gas diffusion (GD) of CO2 and NH3 through a hydrophobic gas permeable membrane from an acidic or alkaline donor stream, respectively. The analytes are trapped in an acceptor solution, being slightly alkaline for CO2 and slightly acidic for NH3. The analytes are quantified using a homemade stainless steel conductimetric cell. The proposed system required five solenoid micro-pumps, one for each reagent and sample. Two especially made air bubble traps were placed down-stream of the solendoid pumps, which provided the acceptor solutions, by this increasing the method's reproducibility. Values of RSD lower than 1% were obtained. Achieved limits of detection were 0.27 mu mol L-1 for NH4+ and 50 gmol L-1 for TIC. Add-recovery tests were used to prove the trueness of the method and recoveries of 99.5 +/- 7.5% were obtained for both analytes. The proposed system proved to be adequate for monitoring purpose of TIC and NH4+ due to its high sample throughput and repeatability. (C) 2013 Elsevier B.V. All rights reserved.