ASTM D5441 Standard Test Method for Analysis of Methyl Tert-Butyl Ether (MTBE) by Gas Chromatography
13. Procedure
13.1 Set the instrument operating variables to the values specified in Table 1 or to a temperature determined to be suitable by the evaluation in Section 11.
13.2 When the gas chromatograph has been inoperative for more than 24 h, raise the column temperature to the maximum temperature used in the method and hold for 20 min to remove contaminants from the column. Lower the temperature to the initial method temperature.
13.3 Set the recorder or integration device, or both, for accurate presentation of the data. Set instrumental sensitivity such that any component of at least 0.02 % mass will be detected, integrated, and reported.
13.4 Inject 0.1 µL to 0.5 µL of sample into the injection port and start the analysis. Sample size must follow guidelines discussed in 7.2. Obtain a chromatogram and peak integration report.
14. Calculation
14.1 Identify each peak by matching retention times with known reference standards or sample components as discussed in 12.1. If a computing integrator is used, examine the report to ensure that peaks are properly identified and integrated. It is very important that all oxygenate peaks be separated from hydrocarbon peaks and correctly identified since oxygenates have very different response factors than hydrocarbons and normalization is used for quantification.
14.2 Obtain the integrated areas of each component peak. Multiply each area by its appropriate response factor as determined in 12.2 to obtain peak areas corrected for response differences. Use a response factor of 1.00 for unknown contaminants.
14.3 Obtain the concentration of water in the sample as determined by Test Method D1364, or equivalent.
14.4 Determine the mass % of each component using Eq 3:
mass % component = [corrected peak area x (100 - % water)]/total corrected peak area
14.5 Report the mass % of each component to two decimal places.
14.6 If the volumetric concentration of each oxygenate is desired, calculate the volumetric concentration of each oxygenate using Eq 4 as follows:
Vi = (Wi x Ds)/Di
where:
Vi = volume % of Component i,
Wi = mass % of Component i from Eq 3,
Di = density at 20 °C of Component i as found in Table 2, and
Ds = density at 20 °C of sample under study.
14.7 Report the volume % of each component to two decimal places.
