| Summary: | The 13С/12С isotopic abundances in carbon dioxide of the external environment and carbohydrates synthesized by the plant differ significantly from each other and vary depending on the growing conditions. The differences in the fraction of assimilated 13C are related apparently to the rate of photosynthetic reactions. To carry out the sample preparation for mass-spectrometric isotope analysis of carbon involved in plant life, we developed a new method of sample gasification and experimental setup. А setup provided concentrating carbon dioxide 100 times with catalytic afterburning of organic microimpurities, and the prepared sample was free from residual impurities able to interfere to a level no higher than 10^-5. The gasification method involves the plant glucose oxidation by yeast with the collecting generated carbon dioxide; the concentration of reagents were matched for it. The collected CO2 was ready for isotopic measurements and the level of residual impurities able to interfere was less than 10^-5. The developed sample preparation technique has been used to study the influence of spectral characteristics of the light medium on the exchange of carbon isotopes between atmospheric CO2 and the plant carbon pool.
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