The N2O correction in mass-spectro metric analysis of CO2

During cryogenic separation of CO2 from atmosphere and soil air for isotopic analyses, N2O present in the air condenses together with CO2. The N2O, having the same molecular masses (44, 45 and 46) as CO2, seriously affects the results of 13 C and O-18 isotope analyses of carbon dioxide, making it necessary to introduce appropriate corrections. A simple method of correcting the measured delta(13)C and delta(18)O values of the analysed CO2 was developed. It requires experimental determination of several parameters of the used mass spectrometer and changes in the computational algorithm. The performance of the method was tested using N2O-CO2 mixtures. The experiments showed that the proposed correction method removes the effect of presence of N2O in the analysed CO2 sample down to analytical uncertainty of the measurement. This method was adopted in routine analyses of stable isotope composition of carbon dioxide in atmospheric and soil air samples being performed in our laboratory.