ASTM D6379 Standard Test Method for Determination of Aromatic Hydrocarbon Types
ASTM D6379 Standard Test Method for Determination of Aromatic Hydrocarbon Types in Aviation Fuels and Petroleum Distillates - High Performance Liquid Chromatography Method with Refractive Index Detection
6. Apparatus
6.1 High Performance Liquid Chromatograph (HPLC) - Any high performance liquid chromatograph capable of pumping the mobile phase at flow rates between 0.5 and 1.5 mL/min with a precision better than 0.5 % and a pulsation of <1 % full scale defiection under the test conditions described in Section 9. See Fig. 1.
6.2 Sample Injection System - The sample injection system shall be capable of injecting 10 µL (nominal) of sample solution with a repeatability better than 2 %.
6.2.1 An equal and constant volume of the calibration and sample solutions shall be injected into the chromatograph. Both manual and automatic sample injection systems (using either complete or partial filling of the sample loop) will, when used correctly, meet the repeatability requirements laid down in 6.2. When using the partial loop filling mode, it is recommended that the injection volume should be less than half the total loop volume. For complete filling of the loop, best results are obtained by overfilling the loop at least six times.
6.2.2 Sample injection volumes other than 10 µL (typically in the range from 3 to 20 µL) may be used provided they meet the requirements laid down for injection repeatability (see 6.2), refractive index sensitivity and linearity (see 9.4 and 10.1), and column resolution (see 9.4)
6.3 Sample Filter (Optional) - A microfilter of porosity 0.45 µm or less, which is chemically-inert towards hydrocarbon solvents, is recommended for the removal of particulate matter from the sample solutions.
6.4 Column System - Any stainless steel HPLC column(s) packed with an approved amino-bonded (or polar amino/cyano-bonded) silica stationary phase4 is suitable, provided it meets the resolution requirements laid down in 9.4.3. Column lengths from 150 to 300 mm with an internal diameter from 4 to 5 mm and packed with 3 or 5 µm particle size stationary phase have been found to be satisfactory. The use of a guard column (for example, 30 by 4.6-mm internal diameter) packed with silica or amino-bonded silica is recommended but not essential.
6.5 HPLC Column Oven - Any suitable HPLC column oven (block heating or air circulating) capable of maintaining a constant temperature (more or less 1°C) within the range from 20 to 40°C.
NOTE 3 - The refractive index detector is sensitive to both sudden and gradual changes in the temperature of the eluent. All necessary precautions should be taken to establish constant temperature conditions throughout the liquid chromatograph system.
NOTE 4 - Alternative forms of temperature control, for example, temperature-controlled laboratories, are permitted.
6.6 Refractive Index Detector - Any refractive index detector may be used provided it is capable of being operated over the refractive index range from 1.3 to 1.6, meets the sensitivity requirement specified in 9.4.2, gives a linear response over the calibration range, and has a suitable output signal for the data system. If the refractive index detector has a facility for independent temperature control, it is recommended that this is set at the same temperature as the column oven.
6.7 Computer or Computing Integrator - Any data system can be used provided it is compatible with the refractive index detector, has a minimum sampling rate of 1 Hz, and is capable of peak area and retention time measurement. The data system should also have minimum facilities for post-analysis data processing, such as baseline correction and reintegration. The ability to perform automatic peak detection and identification and to calculate sample concentrations from peak area measurements is recommended but not essential.
6.8 Volumetric Flasks, Grade B, or better, of 10 mL and 100 mL capacity.
6.9 Analytical Balance, accurate to more or less 0.0001 g.
7. Reagents
7.1 Cyclohexane, >99 % pure.
NOTE 5 - Cyclohexane may contain benzene as an impurity.
7.2 Heptane, HPLC Grade. For use as HPLC mobile phase. (Warning - Hydrocarbon solvents are highly flammable and may cause irritation by inhalation, ingestion, or skin contact.)
NOTE 6 - It is recommended practice to degas the HPLC mobile phase before use.
7.3 1-Methylnaphthalene, not less than 98 % pure. (Warning - Gloves should be worn when handling aromatic compounds (for example, disposable vinyl gloves).)
NOTE 7 - Purity is determined by gas chromatography with flame ionization detection. The highest purity standards available should be used. Standards of $ 98 % purity are commercially available from all major suppliers.
7.4 o-Xylene (1,2-Dimethylbenzene), not less than 98 % pure.
8. Sampling
8.1 The laboratory fuel sample from which an aliquot is being drawn for the purposes of this test method shall be representative of the lot of fuel. The laboratory sample should be obtained by following Practice D4057 or D4177, or a similar standard.
