ASTM D5307 Determination of Boiling Range Distribution of Crude Petroleum by Gas Chromatography
6. Apparatus
6.1 Gas Chromatograph - Any gas chromatograph may be used that has the capabilities described below and meets the performance requirements in Section 10.
6.1.1 Detector - This test method is limited to the use of the flame ionization detector (FID). The detector must be capable of operating continuously at a temperature equal to or greater than the maximum column temperature employed, and it must be connected to the column so as to avoid cold spots.
6.1.2 Column Temperature Programmer - The chromatograph must be capable of reproducible, linear programmed temperature operation over a range sufficient to establish a retention time of at least 1 min for the IBP and to elute compounds with boiling points of 538°C (1000°F) before the end of the temperature ramp.
6.1.3 Cryogenic Column Oven - If the IBP of the crude oil is below 90°C (194°F), an initial column temperature below ambient will be required. This necessitates a cryogenic cooling option on the gas chromatograph. Typical initial column temperatures are listed in Table 1.
6.1.4 Sample Inlet System - Either of the following two types of sample inlet systems may be used.
6.1.4.1 Flash Vaporization - A vaporizing sample inlet system must be capable of operating continuously at a temperature equivalent to the maximum column temperature employed. The sample inlet system also must be connected to the chromatographic column so as to avoid any cold spots.
6.1.4.2 On-Column - Capable of introducing a liquid sample directly onto the head of the column. Means must be provided for programming the entire column, including the point of sample introduction, up to the maximum column temperature employed.
6.1.5 Flow Controller - The chromatograph must be equipped with a flow controller capable of maintaining carrier gas flow constant to +/-1 % over the full operating temperature range of the column. The inlet pressure of the carrier gas, supplied to the chromatograph, must be sufficiently high to compensate for the increase of backpressure in the column as the temperature is programmed upward. An inlet pressure of 550 kPa gage (80 psig) has been found satisfactory with the columns described in Table 1.
6.2 Data Retrieval System:
6.2.1 Recorder - A 0 - 1 mV range recording potentiometer or equivalent, with a full-scale response time of 2 s or less may be used for graphic presentation of the FID signal.
6.2.2 Integrator - Electronic integrator or computer-based chromatography data system must be used for detector signal integration and accumulation. The integrator/computer system must have normal chromatographic software for measuring retention time and areas of eluting peaks (peak detection mode). In addition, the system must be capable of converting the continuously integrated detector signal into area slices representing contiguous fixed duration time intervals (area slice mode). The recommended time interval is 1 s. No time interval shall be greater than 12 s. The system must be capable of subtracting the area slice of a blank run from the corresponding area slice of a sample run. Alternatively, the baseline chromatogram can be subtracted from the sample chromatogram and the net resulting chromatogram can be processed in the slice mode. A computer program that performs the slice calculation as a post-run calculation is also used.
6.3 Column - Any gas chromatographic column that provides separation in order of boiling points and meets the performance requirements of Section 10 can be used. Columns and conditions, which have been used successfully, are shown in Table 1.
6.4 Microsyringe - A 5 or 10 µL syringe is used for sample introduction. The use of an automated liquid sampling device is highly recommended.
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) for use with the FID. (Warning - Air is a compressed gas under high pressure and supports combustion.)
7.3 Calcium Chloride, Anhydrous (CaCl2).
7.4 Calibration Mixture - A mixture of n-paraffins dissolved in carbon disulfide (Warning - see 7.5) covering the boiling range of the sample through 538°C (1000°F). At least one compound in the mixture must have a boiling point equal to or lower than the IBP of the sample. Methane, ethane, propane, or butane can be added to the calibration mixture, if necessary, by injecting about 1 mL of the pure gaseous compound into a septum-capped, sealed vial containing the rest of the calibration mixture, using a gas syringe. If n-paraffin peaks can be unambiguously identified in the sample chromatogram, their retention times can be used for calibration.
7.5 Carbon Disulfide (CS2) - Carbon disulfide (99 % minimum purity) is used as a viscosity reducing solvent because it is miscible with crude oils and has only a slight response with the FID. (Warning - Carbon disulfide is extremely volatile, flammable, and toxic.)
7.6 Carrier Gas - Nitrogen or helium of high purity that has been dried over molecular sieves or similar suitable drying agents. (Warning - Helium and nitrogen are compressed gases under high pressure.)
7.7 Column Resolution Test Mixture - A mixture of 1 % each of n-C16 and n-C18 paraffin in a suitable solvent, such as n-octane, for use in testing the column resolution. (Warning - n-Octane is flammable and harmful if inhaled.)
7.8 Detector Response Test Mixture - An accurately weighed mixture of approximately equal masses of at least six n-paraffins covering the carbon number range from 10 to 44. Dissolve one part of this mixture with approximately five parts of CS2 (or sufficient CS2 to ensure a stable solution at room temperature).
7.9 Hydrogen - Hydrogen of high quality (hydrocarbon free) is used as fuel gas for the FID. (Warning - Hydrogen is an extremely flammable gas under high pressure.)
7.10 Internal Standard - A mixture of approximately equal amounts of four n-paraffins, n-C14 through n-C17. Concentrations of the individual components need not be known but must be within the linear range of the detector/electronics system used.
7.11 Liquid Phase - A nonreactive, nonpolar liquid or gum of low volatility. Silicone gum rubbers are typically used. In general, liquid phase loadings of 3 to 10 % have been found most satisfactory.
7.12 Solid Support - A diatomaceous earth or equivalent nonreactive particulate material. Typical particle size ranges are 60/80 or 80/100 mesh.
8. Sampling
8.1 Obtain samples for analysis by this test method in accordance with instructions given in Practice D4057.
8.1.1 Ensure that samples are received in sealed containers and show no evidence of leakage.
