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Adaptation of a flow injection analyser conductometric coupled system for the field analysis of very low levels of free CO2 and dic in marine waters

pubblicazioni - Poster

Adaptation of a flow injection analyser conductometric coupled system for the field analysis of very low levels of free CO2 and dic in marine waters

A Flow Injection Analysis (FIA) conductometric coupled system has been adapted for the field analysis of very low levels of free CO2 in natural waters and used in a number of field campaigns for marine water monitoring. In order to make the system suitable and easy usable for on-line in field measurements aboard of oceanographic ships, the single components of the FIA analyser have been compacted into a robust and easy to use system.

All the measurement operations, including the calibration step, have been automated. The gaseous CO2 presents in the sample is separated by diffusion using a non wetting gas porous membrane (PTFE), and the permeating gas is incorporated into a stream of deionised water and measured by means of a micro-conductometric detector. The calibration of the system is carried out by using standard solutions of potassium bicarbonate at different concentration. The detection limit of the method is 8.64 μmolCO2/kg. Both accuracy and repeatability, evaluated by replicate measurements of a certified reference solution (Dickson, batch 92, 2008), are <5%. The method also allows to perform the direct inorganic carbon speciation in water, without the knowledge of the pH value of the sample and with no need to know the value of the thermodynamic constants of carbonate system in natural waters. The system allows to analyse both actual or acidified samples in order to determine the free CO2 or the DIC (Dissolved Inorganic carbon) contents, respectively. Results concerning performance qualification of the system and its application in experimental surveys, are reported and discussed.

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