Gas diffusion–flow injection determination of total inorganic carbon in water using tungsten oxide electrode

A novel gas diffusion–flow injection method has been developed for the rapid and sensitive determination of total inorganic carbon (TIC) in water. The method is based on the diffusion of CO2 across gas permeable membrane from a donor stream containing 0.1 M HCl to an acceptor stream of sodium acetate (10−5 mol l−1 and pH 10). The CO2 trapped in the acceptor stream passes through an electrochemical flow cell contains a tungsten oxide wire and a silver/silver chloride electrode, where it was sensitively detected. The parameters affecting the sensitivity of the electrode such as buffer concentration, pH, flow rate and injected volume were studied in detail. The electrode response was linear in the concentration range from 5 to 100 μg ml−1 CO32− with a correlation coefficient (R2) of 0.998. Precision (R.S.D.) was 1.42% for 20 μg ml−1 standard solution of CO32− (n=10). The detection limit was 0.20 μg ml−1 CO32−. The method was evaluated by the injection of real natural water samples and an average recovery of 100.1% was obtained. The sampling rate was 30 samples h−1. The method is simple, feasible with satisfactory accuracy and precision and thus could be used for monitoring TIC in water.