Determination of the carbon and hydrogen contents of gasoline using a combustion method and the estimation of their measurement uncertainty

• n-Hexane, n-heptane, and isooctane, were found to be appropriate standard materials.
• Both the one-point and four-point calibration methods showed satisfactory results.
• Normalization of the measured values presented improved precision.
• The uncertainty from the 4P calibration was larger than those from the 1P calibration.
• The major uncertainty components were the purity of standards and the injected volume.

An analytical method of determining the carbon and hydrogen contents of gasoline was studied using a combustion method. Four pure organic hydrocarbons were selected and tested as calibration standards. Three hydrocarbon reagents, n-hexane, n-heptane, and isooctane, were found to be appropriate calibration standards. Two different calibration methods – one-point and four-point – were used to calibrate the analysis instrument and both methods showed satisfactory results. The measured carbon and hydrogen values were normalized to 100% minus the oxygen content and these values were more precise than the measured ones. The present paper also presents an evaluation of the measurement uncertainty. The uncertainty estimate for the four-point calibration was larger than that for the one-point calibration. The analysis of the contributions of the uncertainty sources showed that the purity of the calibration standard and the injected volume had a large effect on the overall uncertainty. The other parameters had virtually no influence.