Online testing method of carbon and oxygen isotopes of calcite and dolomite in mixed sample

The invention provides an online testing method of carbon and oxygen isotopes of calcite and dolomite in a mixed sample. The online testing method provided by the invention comprises the following steps: preparing a carbonate sample with the particle diameter range r being more than or equal to 76 microns and less than or equal to 154 microns for later analysis and use; reacting phosphoric acid with sample powder at the constant temperature of 25 DEG C; extracting CO2 generated by reaction stage by stage to carry out analysis of carbon and oxygen isotopes so as to obtain carbon and oxygen isotope values of calcite and dolomite in the mixed sample; and correcting the obtained carbon and oxygen isotope values of calcite through a correction formula. By utilizing the online testing method of carbon and oxygen isotopes of calcite and dolomite in the mixed sample provided by the invention, measurement of carbon and oxygen isotope values of calcite and dolomite in constant samples and micro-samples can be realized; a single diagenetic fabric can be used as an experimental analysis unit; the blindness of traditional whole-rock analysis is avoided; and simultaneously, the online testing method provided by the invention has the characteristics of high precision, test rapidness, accurate result and the like.