ASTM D5622 Standard Test Methods for Determination of Total Oxygen in Gasoline and Methanol Fuels by Reductive Pyrolysis
5. Apparatus
5.1 Oxygen Elemental Analyzer - A variety of instrumentation can be satisfactory. However, the instrument must reductively pyrolize the specimen and convert oxygen to carbon monoxide.
5.1.1 Test Method A - Helium carrier gas transports the pyrolysis products through a combination scrubber to remove acidic gases and water vapor. The products are then transported to a molecular sieve gas chromatographic column where the carbon monoxide is separated from the other pyrolysis products. A thermal conductivity detector generates a response that is proportional to the amount of carbon monoxide.
5.1.2 Test Method B - Nitrogen carrier gas transports the pyrolysis products through a scrubber to remove water vapor. The pyrolysis products then flow through tandem infrared detectors that measure carbon monoxide and carbon dioxide, respectively.
5.1.3 Test Method C - A mixture of helium and hydrogen (95:5 %), helium, or argon transports the pyrolysis products through two reactors in series. The first reactor contains heated copper which removes sulfur-containing products. The second reactor contains a scrubber which removes acidic gases and a reactant which oxidizes carbon monoxide to carbon dioxide (optional). The product gases are then homogenized in a mixing chamber, which maintains the reaction products at absolute conditions of temperature, pressure, and volume. The mixing chamber is subsequently depressurized through a column that separates carbon monoxide (or carbon dioxide, if operating in the oxidation mode) from interfering compounds. A thermal conductivity detector measures a response proportional to the amount of carbon monoxide or carbon dioxide.
5.1.4 Test Method D - Nitrogen carrier gas transports the pyrolysis products through scrubbers to remove acidic gases and water vapor. A reactor containing cupric oxide at 325 °C oxidizes the carbon monoxide to carbon dioxide, which in turn is transported into a coulometric carbon dioxide detector. Coulometrically generated base titrates the acid formed by reacting carbon dioxide with monoethanolamine.
5.2 A technique must be established to make a quantitative introduction of the test specimen into the analyzer. Specimen vials and transfer labware must be clean and dry.
5.3 For instruments that measure carbon monoxide only, pyrolysis conditions must be established to quantitatively convert oxygen to carbon monoxide.
5.4 A system of scrubbers and separators must be established to effectively remove pyrolysis products that interfere with the detection of carbon monoxide or carbon dioxide, or both.
5.5 The detector responses must be linear with respect to concentration, or nonlinear responses must be detectable and accurately related to concentration.
5.6 Selected items are available from the instrument manufacturer.
5.6.1 Pyrolysis tubes,
5.6.2 Scrubber tubes, and
5.6.3 Absorber Tubes.
6. Reagents
6.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
6.2 Calibration Standards:
6.2.1 NIST SRM 1837, which contains certified concentrations of methanol and t-butanol in reference fuel, can be used to calibrate the instrument for the analysis of oxygenates in gasoline.
6.2.2 Anhydrous methanol, 99.8 % minimum assay, can be used to calibrate the instrument for the analysis of methanol fuels.
6.2.3 Isooctane, or other hydrocarbons, can be used as the blank provided the purity is satisfactory.
6.3 Quality Control Standard - NIST SRM 1838 can be used to check the accuracy of the calibration.
6.4 The instrument manufacturers require additional reagents.
6.4.1 Test Method A:
6.4.1.1 Anhydrone (anhydrous magnesium perchlorate),
6.4.1.2 Ascarite II (sodium hydroxide on silica),
6.4.1.3 Helium carrier gas, 99.995 % pure,
6.4.1.4 Molecular sieve, 5Å, 60 to 80 mesh,
6.4.1.5 Nickel wool,
6.4.1.6 Nickelized carbon, 20 % loading,
6.4.1.7 Quartz chips, and
6.4.1.8 Quartz wool.
6.4.2 Test Method B:
6.4.2.1 Anhydrone (anhydrous magnesium perchlorate),
6.4.2.2 Carbon pyrolysis pellets, and
6.4.2.3 Nitrogen carrier gas, 99.99 % pure.
6.4.3 Test Method C:
6.4.3.1 Anhydrone (anhydrous magnesium perchlorate),
6.4.3.2 Ascarite II (sodium hydroxide on silica),
6.4.3.3 Carrier gas, either helium (95 %)/hydrogen (5 %), mixture, 99.99 % pure; helium, 99.995 % pure; or argon, 99.98 % pure,
6.4.3.4 Copper plus, wire form, and
6.4.3.5 Platinized carbon.
6.4.4 Test Method D:
6.4.4.1 Anhydrone (anhydrous magnesium perchlorate),
6.4.4.2 Ascarite II (sodium hydroxide on silica),
6.4.4.3 Copper (II) oxide,
6.4.4.4 Coulometric cell solutions, including a cathode solution of monoethanolamine in dimethyl sulfoxide and an anode solution of water and potassium iodide in dimethyl sulfoxide,
6.4.4.5 Nickelized carbon, 20 % loading, and
6.4.4.6 Nitrogen carrier gas, 99.99 % pure.
