Preparation and certification of carbon monoxide gas reference material for the quality of CO emission measurements

Carbon monoxide emissions in air are toxic and its monitoring is of great concern worldwide. The monitoring activities should rely on traceable measurement results to the SI units. To serve this monitoring purpose in Saudi Arabia, a primary gas mixture (200 mmol/mol) of Carbon monoxide (CO) in nitrogen has been gravimetrically prepared from pure CO and pure N2 in 5L aluminum gas cylinder based on ISO 6142. From this mixture, three diluted mixtures of concentrations 4.99, 7.49 and 10.01 mmol/mol were prepared also in 5L cylinders and the uncertainty of these gravimetric preparations was calculated. The mole fractions of the three mixtures were verified by GC-TCD in accordance with ISO 6143 and the uncertainty of the chromatographic measurements was calculated. The gravimetrically and chromatographically measured mole fractions together with their standard uncertainties were found compatible indicating good quality of the produced primary gas mixtures. Long term stability of the three gas mixtures was monitored along four years, and the results obtained showed very good stability of the gas mixtures. The relative uncertainty of the GC analytical results was found 0.52%, 0.51% and 0.52% which is small enough and advantageous for the calibration of CO emission measuring equipment.