Comparative study of three methods for testing hydrogen and oxygen isotope of karst water samples

Compared with water samples in non-karst areas, water samples in karst areas have higher Ca2+ content, and this characteristics has certain impact on the hydrogen-oxygen isotope test results in water bodies. In this paper, three commonly used methods of high temperature conversion/elemental analysis, i.e. isotope ratio mass spectrometry (TC/EA-IRMS), sample preparation device-stable isotope mass spectrometer (GasbenchⅡ-IRMS) and laser spectroscopy for the detection of hydrogen-oxygen isotopes of water samples in karst areas were applied to conduct a comparative study. The study area is the underground river of Maocun village, located in Chaotian township, Lingchuan county, Guilin City. The underground river outlet, cave drip water and karst groundwater samples were collected and analysed by using the above methods. Testing results show that,for the hydrogen isotope, in general the precision of TC/EA-IRMS is not more than (≤) 0.3‰, while the precision of laser spectroscopy is ≤0.1‰，and both are better than the GasbenchⅡ-IRMS with a precision of 1.4‰. For the oxygen isotope, the precision of GasbenchⅡ-IRMS is ≤0.02‰,laser spectroscopy is≤0.04‰，and both are better than TC/EA-IRMS with the precision of 0.16‰. Therefore, the determination of hydrogen and oxygen isotopes of the water samples in karst area by laser spectroscopy can meet the high precision test requirements of the samples in karst area due to the small quantity of samples and high precision. However, due to the existence of a high temperature gasification chamber in the laser spectrometer, and if the high salinity karst water is continuously tested for a long time, whether the gasification efficiency of the water sample affected by the consolidation of the salt in the gasification chamber needs further study.