Discrepancy in infrared measurement results of carbon monoxide in nitrogen mixtures due to variations of the 13C/12C isotope ratio |
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Authors: | Gerard Nieuwenkamp Adriaan M H van der Veen |
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Institution: | (1) Nederlands Meetinstituut, Thijsseweg 11, 2629 JA Delft, The Netherlands |
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Abstract: | Significant errors in the non-dispersive infrared (NDIR) analyses of carbon monoxide (CO) can be made when the 13C/12C isotope ratio in the sample and the calibrant differ significantly. This paper shows that variations in the 13C/12C isotope ratio of 5×10−2 mol/mol CO in nitrogen mixtures on three different NDIR CO analysers may lead to serious deviations in the instrument response, whereas the instrument response using GC-TCD is unaffected. The observed deviations in the assigned amount-of-substance fraction CO for a 13C depleted mixture vary from +2 to −5% relative to the gravimetric amount-of-substance fraction for different NDIR analysers. A GC-MS method has been developed to perform a pre-screening of the isotopic composition of CO in nitrogen mixtures. This method proved to be an adequate tool to measure differences in the 13C/12C ratio. Based on the GC-MS results a suitable measurement technique can be selected, or information about a possible error in NDIR analysis can be given to the producer or user of the calibration gas mixture.
Presented at 3. International Gas Analysis Symposium, October 6–8, 2004, in Amsterdam |
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Keywords: | NDIR 13C Isotope ratio |
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