MEASUREMENT OF ORGANIC CARBON STABLE ISOTOPE COMPOSITION OF DIFFERENT SOIL TYPES BY EA-IRMS SYSTEM

Element analyzer-isotope ratio mass spectrometers(EA-IRMS) is a rapid and precise method for measuring stable carbon isotope.Pure CO_2 reference gas was calibrated via international standard-Urea,and the δ(~(13)C) vs_(PDB) value of pure CO_2 is(-29.523±0.181)‰.Stability and linearity of the EA-IRMS system,precision of δ(~(13)C) measurement for samples were tested through experimental comparison.Moreover,determination method of organic carbon stable isotope in soil was based on the system.The EA-IRMS system had well linearity when ion intensity ranged from 1.0 to 7.0V,and it excelled the total linearity when the ion intensity was from 1.5 to 5.0V,and the accurate result of δ(~(13)C) for sample analysis could be obtained with precision of 0.15‰.If carbon content in sample is more than 5μg,the requirement for analyzing accurate result of δ(~(13)C) could be achieved.The organic carbon stable isotope was measured in 18 different types soil samples,the average natural abundance of~(13)C was 1.082%,and the organic carbon stable isotope composition was significantly different among different type soils.