A simple method to determine the δ13C content of total dissolved inorganic carbon

A simple method for determining the δ 13 C of TDIC (Total Dissolved Inorganic Carbon) in natural waters was developed andtested. The proposed method is based on chemical and physical stripping of CO 2 from water samples. The sampling apparatusconsists of a glass bottle (ca 100 ml) totally filled with water sample in the field and sealed by gas-tight rubber/teflon plug. In thelaboratory, we introduce 10 ml of pure Ar as host gas into the bottles and draw out an equal volume of water. About 0.5 ml of 37%extra-pure HCl is then injected into the bottle. Water pH decreases to values close to 1 and, therefore, the only carbon speciespresent is CO 2 both as dissolved and gaseous phase. Then the bottle is connected to a vacuum line to extract CO 2 gas and to purifyit by means of standard techniques for CO 2 purification. In order to test this method, several sea water samples were prepared andanalysed, as well as a series of standard solutions of Na 2 CO 3 at known isotopic composition of carbon. The accuracy of thesemeasurements was ± 0.2 ‰ vs V-PDB and their reproducibility was better than 0.2 ‰ vs V-PDB.