ASTM D5986 Standard Test Method for Determination of Oxygenates, Benzene, Toluene, C8-C12 Aromatics and Total Aromatics in Finished Gasoline by Gas Chromatography/Fourier Transform Infrared Spectroscopy
12. Calculations
12.1 Oxygenates:
12.1.1 After identifying the various oxygenates, measure the areas of each oxygenate peak and that of the internal standard. Fig. 3 gives the elution order of the various oxygenates. From the least squares fit calibrations, Eq 13, calculate the absolute mass of each oxygenate components (Wi) in grams in the gasoline samples using the response ratio (rspi) of the areas for the oxygenates components to that of the internal standard as follows:
12.1.2 To obtain mass % (wo) results for each oxygenate Tables 9-11:
wo = (Wi/Wg)(100 %)
where:
Wg = mass of gasoline sample.
12.1.3 Mass % Oxygen - To determine the oxygen content of the fuel, sum the mass of oxygen contents of all oxygenated components determined above according to the following equation:
where:
wo = mass % of each oxygenates,
wot = total mass % oxygen in the fuel,
Mi= relative molecular mass of the oxygenate as given in, Table 9,
16.0 = atomic mass of oxygen, and
Ni = number of oxygen atoms in the oxygenate molecule.
12.1.4 If the volumetric concentration of each oxygenate component is desired, calculate the volumetric concentration according to Eq 16:
vi = wi(Df/Di)
where:
vi = volume % of each oxygenate to be determined,
Di = relative density at 15.56°C (60°F) of the individual oxygenates as found in Table 9, and
Df = relative density of the fuel under study as determined by Practice D1298 or Test Method D4052.
12.2 Aromatic Hydrocarbons:
12.2.1 After identifying the various calibrated aromatic hydrocarbons in Table 2, including benzene, (Fig. 4) measure the areas of each aromatic peak at the selective reconstruction frequency in Table 6 and that of the DME internal standard. From the least squares fit calibrations, Eq 13, calculate the absolute mass of each aromatic components (Wi) in grams in the gasoline samples using the response ratio (rspi) of the areas for the aromatic components to that of the internal standard.
12.2.2 Uncalibrated Aromatic Components (3.1.5) - The calibration components in Table 2 may not account for all of the aromatic hydrocarbons present in the gasoline sample. For the uncalibrated components (Fig. 4 and Fig. 5) follow the chromatographic fingerprint in Fig. 5 to selectively quantitate each uncalibrated compound using the specified SWC in Fig. 4. Use a SWC of 600 to 900 cm-1 as a guide in detecting the uncalibrated aromatics (Fig. 4 was obtained with a SWC of 600 to 900 cm-1). Use the least square linear fit of 1,2,3,5-tetramethylbenzene obtained using the SWC of 600 to 900 cm-1 for the quantitation of the uncalibrated aromatic components.
NOTE 5 - Consider all peaks between the retention time of indan and the end of the 600 to 900 cm-1 chromatogram (end of GC analysis time) as uncalibrated aromatic components except for the calibrated components in Table 2.
12.2.3 To obtain mass percent (Wa) results for each aromatic hydrocarbon, including uncalibrated aromatics:
wa = (Wi/Wg)(100 %)
where:
Wg = mass of gasoline sample.
12.2.4 To obtain the mass % of the total aromatic concentration Wt, sum the mass % of each aromatic component, including the mass percent of the uncalibrated components:
wt = ∑wa
12.2.5 Report results to nearest 0.1 mass % for the total aromatics and to nearest 0.01 mass % for benzene.
12.2.6 If the volumetric concentration of each aromatic component is desired, calculate the volumetric concentration according to Eq 19:
vi = wa(Df/Di)
where:
vi = volume % of each aromatic to be determined,
Di = relative density at 15.56°C (60°F) of the individual aromatics as found in Table 3, and
Df = relative density of the fuel under study as determined by Practice D1298 or Test Method D4052.
12.2.7 To obtain the volume % of the total aromatic concentration Vt, sum the volume % of each aromatic component, including the volume percent of the uncalibrated components:
Vt = ∑Vi
12.2.8 Report results to nearest 0.1 volume % for total aromatics and to nearest 0.01 volume % for benzene.