A flow injection analyser conductometric coupled system for the field analysis of free dissolved CO2 and total dissolved inorganic carbon in natural waters

Abstract

A flow injection analyser coupled with a gas diffusion membrane and a conductometric microdetector was adapted for the field analysis of natural concentrations of free dissolved CO2 and dissolved inorganic carbon in natural waters and used in a number of field campaigns for marine water monitoring. The dissolved gaseous CO2 presents naturally, or that generated by acidification of the sample, is separated by diffusion using a hydrophobic semipermeable gas porous membrane, and the permeating gas is incorporated into a stream of deionised water and measured by means of an electrical conductometric microdetector. In order to make the system suitable and easy to use for in-field measurements aboard oceanographic ships, the single components of the analyser were compacted into a robust and easy to use system. The calibration of the system is carried out by using standard solutions of potassium bicarbonate at two concentration ranges. Calibration and sample measurements are carried out inside a temperature-constant chamber at 25 °C and in an inert atmosphere (N2). The detection and quantification limits of the method, evaluated as 3 and 10 times the standard deviation of a series of measurements of the matrix solution were 2.9 and 9.6 μmol/kg of CO2, respectively. Data quality for dissolved inorganic carbon was checked with replicate measurements of a certified reference material (A. Dickson, Scripps Institution of Oceanography, University of California, San Diego), both accuracy and repeatability were -3.3% and 10%, respectively. Optimization, performance qualification of the system and its application in various natural water samples are reported and discussed. In the future, the calibration step will be operated automatically in order to improve the analytical performance and the applicability will be increased in the course of experimental surveys carried out both in marine and freshwater ecosystems. Considering the present stage of development of the method, it can only be applied for studying of the carbon cycle in oxic environments.

Flow injection analysis as a tool for enhancing oceanographic nutrient measurements—A review

“…Similarly, Martinotti et al [167] have described a dual GD-FIA system for the determination of both DIC and free CO 2 using conventional conductimetric detection which was effectively used for the determination of both parameters in fresh and marine waters. Faber et al have also reported a GD-FIA probe system that used spectrophotometric detection for the determination of p CO 2 in sediments and overlying waters [168].…”

Membrane-based Separation in Flow Analysis for Environmental and Food Applications

“…Successful applications of this hyphenation can be observed in: the determination of bromide and sulfide in tap and wastewater by spectrophotometry (50,55); chlorine dioxide in water by fluorescence (47); and ammonia and inorganic carbon in water with an acidbased indicator by spectrophotometry (42,44), conductimetry (36,38,56,58) and fluorescence (41,49). Due to the high selectivity of GD membranes, most of the methods combine membrane-based separations with non-selective detectors such as spectrophotometric and conductimetric detection where the color change of acid-base indicators or conductivity changes are measured (36,38,40,42,44,48,50,(54)(55)(56)58,59). Fluorescence and chemiluminescence detectors are usually chosen when lower detection limits are intended as these are sensitive techniques (37,39,41,43,47,49).…”

Extraction of Dissolved Inorganic Carbon (DIC) from Seawater Samples at CEDAD: Results of an Intercomparison Exercise on Samples from Adriatic Sea Shallow Water

“…Each sample consisted of Figure 1 General scheme of the line for DIC extraction from water samples installed at CEDAD 250 mL (from which 60 mL were used for AMS analysis at CEDAD) of seawater sampled with a benthic chamber and Niskin bottles, poisoned on-site with HgCl 2 to stop biological activity, and stored at 4 C until processing. All samples showed a DIC concentration of ~ 2500 µmol/kg as determined by a flow-injection analyzer conductometric coupled system developed by RSE (Martinotti et al 2012). Thirteen samples were also sent to ETH Zurich for an independent analysis of the 14 C concentration in the DIC.…”