STUDY OF THE ANALYTICAL CHARACTERISTICS OF A NEW COMPUTER-CONTROLLED VACUUM EXTRACTION SYSTEM FOR THE FAST HYDROLYSIS OF CARBONATES TO CARBON DIOXIDE FOR SUBSEQUENT ISOTOPIC ABUNDANCE DETERMINATION

摘要

An automated vacuum extraction line for the production of pure CO_2-gas from carbonates is described. The method includes the hydrolysis of carbonates (white marbles) with phosphoric acid, in less than five hours, with a subsequent total extraction time (for a batch of ten samples) of less than two and a half hours. With the new method good precision and accuracy are obtained. Kinetic isotope fractionation effects are eliminated when a reaction time of more than three hours is used. The relative importance of the different sources of variance, i.e. sample extraction and mass spectrometric measurement, is estimated. It is also demonstrated that the variance due to sample extraction is sample specific and more important for delta ~(18)O than for delta~(13)C. Memory effects, expressed as the contribution (in %) of the previous sample to the sample under consideration, are calculated for delta ~(13)C (0.28%) and for delta ~(18)O (0.52%). These results show that memory effects do not influence the results of two subsequently processed samples.