Improvement of the sample preparation method for AMS measurement of 31Cl in natural environment

The isobaric interference S-36, is a main problem in AMS measurement of Cl-36. The SO42- ion exists in the natural environment with an amount compared with the chlorine concentration. The chemical procedure should have a powerful capacity to remove sulfur from samples. Traditionally, precipitation of BaSO4 is used to separate S from the sample material. The sulfur reduction process should be repeated more than two times for measurement of the sample with a Cl-36/Cl ratio down to 10(-13). The multi-reduction processes take a long time and chlorine recovery is low. In the present work, a new cation-exchange-column method is used. The Ba column is used for separation of S. When the sample solution is passed through the Ba Column, SO42- are absorbed. After removal of SO42- the sample solution is passed through the H column to absorb metal ions and transfer Cl- to HCL Then the HCl solution is passed through the Na column to convert HCl to NaCl. Finally, excess AgNO3 is added to the NaCl solution and AgCl is precipitated for AMS measurement. The chemical process only takes similar to6 h, the time much shorter than the traditional method, and the chlorine recovery is higher than similar to90%. The rainwater, groundwater and seawater samples were prepared with this method. The Cl-36/Cl ratios in those samples were measured in range of 10(-13) - 10(-14). The method can also be used for soil, sediment and rock samples after extraction of chlorine (Cl-36) from the sample materials. Some sediment and rock samples were prepared and Cl-16 was measured. (C) 2004 Elsevier B.V. All rights reserved.