ASTM D5845 Standard Test Method for Determination of MTBE, ETBE, TAME, DIPE, Methanol, Ethanol and tert-Butanol in Gasoline by Infrared Spectroscopy
11. Procedure
11.1 Equilibrate the samples to between 15 °C and 38 °C before analysis.
11.2 Follow the manufacturer's instructions for establishing a baseline for the instrument, introducing a sample into the sample cell and operating the instrument. If the instructions call for a non-oxygenated gasoline to be used in establishing the baseline, use a non-oxygenated gasoline that is different from the non-oxygenated gasolines used in the preparation of either calibration standards, validation of qualification samples, or quality control standards.
11.3 Thoroughly clean the sample cell by introducing enough sample to the cell to ensure the cell is washed a minimum of three times with the test solution.
11.4 Establish that the equipment is running properly by running the quality control standards prior to the analysis of unknown test samples (see Section 10).
11.5 Introduce the sample in the manner established by the manufacturer. Obtain the concentration reading produced by the instrument.
12. Calculation
12.1 Conversion to Mass Concentration ofOxygenates - If the instrument readings are in volume % for each component, convert the results to mass % according to Eq 1:
mi = Vi(Di/Df)
where:
mi = mass % for each oxygenate to be determined,
Vi = volume % of each oxygenate,
Di = relative density at 15.56 °C of the individual oxygenate as found in Table 2,
Df = relative density of the fuel at 15.56 °C under study as determined by Practice D1298 or Test Method D4052.
If the density has not been measured, an assumed density of 0.742 should be used.
12.2 Total Mass % Oxygen - To determine the total oxygen content of the fuel, sum the mass % oxygen contents of all oxygenate components determined above according to Eq 2:
Wtot = ∑[(mi x 16.0 x Ni)/Mi]
where:
Wtot = total mass % oxygen in the fuel,
mi = mass % for each oxygenate,
16.0 = atomic mass of oxygen,
Ni = number of oxygen atoms in the oxygenate molecule, and
Mi = molecular mass of the oxygenate molecule as given in Table 2.
