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

摘要

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 CO_2 and NH_3 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 CO_2 and slightly acidic for NH_3. 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 μmol L~(-1) for NH_4 ~+ and 50 mmol 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 NH_4 ~+ due to its high sample throughput and repeatability.