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

Abstract

A simple method for determining the ä13C of TDIC (Total Dissolved Inorganic Carbon) in natural waters was developed and tested. The proposed method is based on chemical and physical stripping of CO2 from water samples. The sampling apparatus consists of a glass bottle (ca 100 ml) totally filled with water sample in the field and sealed by gas-tight rubber/teflon plug. In the laboratory, 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 species present is CO2 both as dissolved and gaseous phase. Then the bottle is connected to a vacuum line to extract CO2 gas and to purify it by means of standard techniques for CO2 purification. In order to test this method, several sea water samples were prepared and analysed, as well as a series of standard solutions of Na2CO3 at known isotopic composition of carbon. The accuracy of these measurements was ± 0.2 ‰ vs V-PDB and their reproducibility was better than 0.2 ‰ vs V-PDB.