Abstract：Organic carbon is one of the indispensable indexes in multi-target geochemical surveys, land quality geochemical surveys and other project studies. Accurate quantification of organic carbon is an important part of the geochemical survey with great significance. However, the traditional gravimetric method and volumetric method have long processes and slow speed, which can no longer meet the requirements of large-scale and rapid determination of geochemical samples. In this paper, dilute hydrochloric acid was used to remove inorganic carbon in the samples, and a high-frequency infrared carbon-sulfur analyzer was used to determine the organic carbon in different types of geochemical samples. This paper optimized the conditions such as the sample weight，the choice of acids and fluxes and their optimal concentration and dosage by the comparative experiments. Additionally, the first-level geochemical reference materials also are utilized to establish the calibration curve. A hydrochloric acid pretreatment-infrared absorption spectrometry analysis method of organic carbonin geochemical samples was established by this paper. The experiments showed that the blank value of ceramic crucible could be reduced by burning at 1 200 ℃, which could reduce the impact on the results. The test accuracy was high when choosing the sample weight of 50.0～70.0 mg, and solving the problem of the splash when melting. 0.40～0.60 mL dilute hydrochloric acid (1+7) was chosen as it can remove the inorganic carbon and reduce the loss of organic carbon. The results also showed that the fluxing action was preferably when 0.40～0.50 g pure iron filings and 1.50～1.70 g tungsten particles were used as the mixed flux. The calibration curve of organic carbon established by national geochemical standard reference materials showed good linearity (R2=0.998 5). The detection limit of this method is 69 μg·g-1, and the relative standard deviations (RSD, n=12) of the measurement results is less than 8%. This method has been verified by 63 different types of national geochemical standard reference materials (soil, rock, and sediments), and the results are consistent with the standard values. The method provides the advantages of convenient operation with low detection limits, high sensitivity, and reliable results. It is believed that this method is suitable for the determination of organic carbon in geochemical samples.
