Determination of Carbon Content in Total Solids of Latex and Its Stable Carbon Isotope Ratio (δ¹³C) by EA and IRMS in Hyphenation

Hyphenation of EA and IRMS was applied to the determination of carbon content and carbon isotope ratio (δ¹³C) in total solids of latex sample. A portion (0.500±0.100) mg of the dried and transparent latex piece, prepared from fresh latex was analyzed for its carbon content by EA under its working condition. Primary carbon standards of urea, aspartic acid, glucose and sucrose were used separately to prepare standard curves of carbon and good linearities were obtained between values of mass concentration of carbon and their respective peak areas of CO₂. Stability and linearity of the EA-IRMS system were tested, giving stability index less than 0.1‰, and linearity index less than 0.06‰·V^-1, both of which met with the qualifications quite well. A comparison study on 3 calibration methods used to calibrate the initial corrected values of the latex sample and 3 CRMs obtained by Craig correction method was also made. It was shown that: accuracy of the regression method was found to be best among the 3 methods, it could be used for calibration of initial corrected values of samples with different properties or with different compositions of carbon isotopes; the interception method could be used only for calibration of data of samples with their compositions of carbon isotopes close to that of the reference gas; and interferences due to ¹⁷O and fractional distillation of isotopes could not be eliminated by the original regression method, hence it could not be used for calibration of the determined data. It was found by the proposed method that the carbon content of in total solids of latex sample was 81.83% and value of δ¹³C_s-PDB^M found was -26.70‰ (calibrated value by the regression method).