A highly reproducible solenoid micropump system for the analysis of total inorganic carbon and ammonium using gas-diffusion with conductimetric detection Camelia Henríquez a , Burkhard Horstkotte a,b , Víctor Cerdà a,n a Laboratory of Environmental Analytical Chemistry, University of Balearic Island, CP: 07122 Palma de Mallorca, Spain b Department of Analytical Chemistry, Faculty of Pharmacy, Charles University, Heyrovského 1203, CZ-50005 Hradec Králové, Czech Republic article info Article history: Received 30 May 2013 Received in revised form 30 September 2013 Accepted 3 October 2013 Available online 9 October 2013 Keywords: Multipumping flow system Solenoid micropumps Gas difussion Total inorganic carbon Ammonium Conductimetric detection abstract 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 mmol L 1 for NH 4 þ and 50 mmol L 1 for TIC. Add-recovery tests were used to prove the trueness of the method and recoveries of 99.5 77.5% were obtained for both analytes. The proposed system proved to be adequate for monitoring purpose of TIC and NH 4 þ due to its high sample throughput and repeatability. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Ammonium and carbon dioxide are analytes of special interest in environmental monitoring since they are involved in nearly all biological processes, are transferable between all environmental compartments, such as atmosphere, hydrosphere, biosphere, and pedosphere. Their concentration levels in all compartments are influenced further by human activity. In natural waters, ammonium is an important nitrogen pool. It is the product of bacterial nitrogen fixation, decomposition of organically bound nitrogen, direct nitrogen elimination, and can easily be taken up by phytoplankton [1]. Anthropogenic emissions, especially originated from agriculture, industry, and urban waste contribute significantly to the global budget of atmospheric ammonia with estimation over 50% or 41 Tg of N per year [2]. This problematic has created the interest in effective NH 3 monitoring and analysis in different aqueous compart- ments including groundwater, surface water, and seawater. Carbon dioxide is a key component of the carbon cycle [3] and is involved in the metabolism of all organisms [4]. It plays an important role in the occurrence of the photosynthesis and pH of natural waters [5]. Increasing atmospheric CO 2 through human activity with about 24% over the last 50 years especially decrease the surface seawater pH (ocean acidification) and by this increases the solubility of carbonates, which affects the calcification process of mollusk's larvae [4]. For this reason, the development of methods for free CO 2 and total inorganic carbon (TIC) monitoring in natural waters and seawater is of pressing interest. Gas diffusion (GD) is the separation technique “per excellence” for the determination of volatile species in complex matrix [6], while flow techniques (FT) such as flow injection analysis (FIA) [7], sequential injection analysis (SIA) [8], and multi-syringe flow injection analysis (MSFIA) [9] are the ideal tools to automate GD. Only by this combination, the construction of simple but yet reliable analyzer systems based on GD has become feasible achieving high selectivity, promising sensitivity, excellent preci- sion, and rapidness [10–13]. Solenoid micro-pumps (SMP) are an economic alternative to the syringe and peristaltic pumps typically used for FIA, SIA, and MSFIA. A FT based on SMP has firstly been proposed and character- ized Lapa et al. [14], denoted since then as multi-pumping flow systems (MPFS), although prior and successful use in FT has been reported [15]. SMP provide a semi-continuous flow with a highly pronounced pulsation causing intermediate turbulent conditions in the mani- fold. This improves the mixing efficiency compared to the former Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta 0039-9140/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.talanta.2013.10.005 n Corresponding author. Tel.: þ34 971 173 261; fax: þ34 971 173 426. E-mail addresses: cameliahenriquez@gmail.com (C. Henríquez), burkhard.horstkotte@gmx.de (B. Horstkotte), victor.cerda@uib.es (V. Cerdà). Talanta 118 (2014) 186–194