ASTM D5186 Determination of Aromatic Content and Polynuclear Aromatic Content
ASTM D5186 Standard Test Method for Determination of the Aromatic Content and Polynuclear Aromatic Content of Diesel Fuels and Aviation Turbine Fuels By Supercritical Fluid Chromatography
6. Apparatus
6.1 Supercritical Fluid Chromatograph (SFC) - Any SFC instrumentation can be used that has the following capabilities and meets the performance requirements in Section 8.
6.1.1 Pump - The SFC instrumentation must include a pump capable of delivering supercritical carbon dioxide to the column without pressure fluctuations and at constant flow. The pump is typically a single-stroke-type (syringe) pump or a highly dampened reciprocating pump with pressure fluctuations not exceeding ±0.3 % of the operating pressure.
6.1.2 Detector - This test method is limited to the use of the flame ionization detector (FID). The detector must have sufficient sensitivity to detect 0.1 mass % toluene in hexadecane under instrument conditions employed in this test method.
6.1.3 Column Temperature Control - The chromatograph must be capable of column temperature control of at least ±0.5°C (1°F) at the operating temperature.
6.1.4 Sample Inlet System - A liquid sample injection valve is required, capable of reproducibly introducing samples in the 0.05 to 0.50-µL liquid volume range. The inlet system should be operated at between 25 and 30°C. The sample inlet system must be connected to the chromatographic column so that loss of chromatographic efficiency is avoided.
6.1.5 Post-column Restrictor - A device capable of maintaining mobile phase supercritical conditions within the column and up to the detector inlet must be connected to the end of the column.
6.1.6 Column - Any liquid or supercritical fluid chromatographic column may be used that provides separation of nonaromatic, monoaromatic, and polynuclear aromatic hydrocarbons and meets the performance requirements of Section 8. Some columns and conditions that have been used successfully are shown in Table 1.
6.1.7 Integrator - Means must be provided for the determination of both discrete chromatographic peak areas and the accumulated area under the chromatogram. This can be done by means of a computer or electronic integrator. The computer or integrator must have the capability of correcting for baseline shifts during the run.
7. Reagents and Materials
7.1 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.
7.2 Air - Zero grade (hydrocarbon-free) is used as the FID oxidant. (Warning - Air is usually supplied as a compressed gas under high pressure and supports combustion.)
7.3 Carbon Dioxide (CO2) - Supercritical fluid chromatographic grade, 99.99 % minimum purity, supplied pressurized in a cylinder equipped with a dip tube for removal of liquid CO2. (Warning - Liquid at high pressure. Release of pressure results in production of extremely cold solid CO2 and gas, which can dilute available atmospheric oxygen.)
7.4 Check Standard - A commercial standard reference material, which has accepted reference values, in accordance with in Section 6 on Reference Materials in Practice D6299. Alternatively, samples subjected to round robin may be used as check standards. It is important that the standard deviation of the values of the laboratory exchange program not be statistically greater than the reproducibility for the test method.
7.5 Hydrogen - Hydrogen of high quality (hydrocarbon-free) is used as the fuel for the flame ionization detector. (Warning - Hydrogen is usually supplied under high pressure and is extremely flammable.)
7.6 Performance Mixture - A quantitative mixture of approximately 75 mass % hexadecane (n-C16), 20 mass % toluene, 3 mass % tetralin (1,2,3,4-tetrahydronaphthalene), and 2 mass % naphthalene is used for performance checks.
7.7 Quality Control Sample - A homogeneous material having similar physical and chemical properties to the samples to be analyzed. The choice of such material should be guided by Section 6 on Reference Materials in Practice D6299. Examples of such material can be motor diesel fuel, aviation turbine fuel or other typical samples containing aromatics and polynuclear aromatics similar to the samples to be analyzed.
