ASTM D3710 for Boiling Range Distribution of Gasoline and Gasoline Fractions
ASTM D3710 Standard Test Method for Boiling Range Distribution of Gasoline and Gasoline Fractions by Gas Chromatography
6. Apparatus
6.1 Chromatograph - Any gas chromatograph may be used that meets the performance requirements in Section 8. Place in service in accordance with manufacturer's instructions. Typical operating conditions are shown in Table 1.
6.1.1 Detector - Either a thermal conductivity or a flame ionization detector may be used. Detector stability must be such that the sensitivity and baseline drift requirements as defined in Section 8 are met. The detector also must be capable of operating continuously at a temperature equivalent to the maximum column temperature employed, and it must be connected to the column so as to avoid any cold spots.

NOTE 1 - Care must be taken that the sample size chosen does not allow some peaks to exceed the linear range of the detector. This is especially critical with the flame ionization detector. With thermal conductivity detectors, sample sizes of the order of 1 to 5 µL generally are satisfactory. With flame ionization detectors, the sample size should not exceed 1 µL.

NOTE 2 - It is not desirable to operate the detector at temperatures much higher than the maximum column temperature employed. Operation at higher temperatures only serves to shorten the useful life of the detector, and generally contributes to higher noise levels and greater drift.

6.1.2 Column Temperature Programmer - The chromatograph must be capable of program temperature operation over a range sufficient to establish a retention time of at least 15 s for propane and of allowing elution of the entire sample within a reasonable time period. Subambient capability may be required. The programming rate must be sufficiently reproducible to meet the requirements of 8.7.

NOTE 3 - If the column is operated at subambient temperature, excessively low initial column temperature must be avoided, to ensure that the stationary phase remains liquid. The initial temperature of the column should be only low enough to obtain a calibration curve meeting the specifications of this test method.

6.1.3 Sample Inlet System - The sample inlet system must be capable of operating continuously at a temperature equivalent to the maximum column temperature employed, or provide on-column injection with some means of programming the entire column, including point of sample introduction up to the maximum temperature required. The sample inlet system must be connected to the chromatographic column so as to avoid any cold spots.

6.1.4 Flow Controllers - Chromatographs must be equipped with constant-flow controllers capable of holding carrier gas flow constant to ±1 % over the full operating temperature range.

6.2 Sample Introduction - Sample introduction may be either by means of a constant-volume liquid sample valve or by injection with a microsyringe through a septum. If the sample is injected manually, cool the syringe to 0 to 4°C (32 to 40°F) before taking the sample from the sample vial.

NOTE 4 - Automatic liquid-sampling devices or other sampling means, such as sealed septum-capped vials, may be used, provided no loss of light ends occurs. The system must be operated at a temperature sufficiently high to vaporize completely hydrocarbons with an atmospheric boiling point of 500°F (260°C), and the sampling system must be connected to the chromatographic column so as to avoid any cold spots.

6.3 Recorder - A recording potentiometer or equivalent with a full-scale response time of 2 s or less may be used.

6.4 Column - Any column and conditions may be used, provided, under the conditions of the test method, separations are in order of boiling points and the column meets the performance requirements in Section 8. See Table 1 for columns and conditions that have been used successfully. Since a stable baseline is an essential requirement of this test method, provisions must be made to compensate for column bleed. Traditionally this is done by using matching dual columns and detectors. At best, this procedure is only marginally successful. An even more satisfactory procedure is to record the area profile of the column bleed during a blank run, and subtract this profile from subsequent sample runs, as outlined in 11.1.
6.4.1 Column Preparation - Any satisfactory method, used in the practice of the art, that will produce a column meeting the requirements of Section 8, may be used. The column must be conditioned at the maximum operating temperature to reduce baseline shifts due to bleeding of column substrate.

NOTE 5 - The column can be conditioned very rapidly and effectively by the following procedure:
(1) Disconnect column from detector.
(2) Purge the column thoroughly at ambient temperature with carrier gas.
(3) Turn off the carrier gas and allow the column to depressurize completely.
(4) Raise the column temperature to the maximum operating temperature and hold at this temperature for at least 1 h with no flow through the column.
(5) Cool the column to at least 100°C before turning on carrier gas again.
(6) Program the column temperature up to the maximum several times with normal carrier gas flow. The column then should be ready for use.

NOTE 6 - An alternative method of column conditioning, which has been found effective for columns with an initial loading of 10 % liquid phase, consists of purging the column with carrier gas at the normal flow rate while holding the column at maximum operating temperature for 12 to 16 h.

6.5 Integrator - Means must be provided for determining the accumulated area under the chromatogram. This can be done by means of a computer, or automatic operation can be achieved with electronic integration. A timing device is used to record the accumulated area at set time intervals. The same basis for measuring time must be used to determine retention times in the calibration, the blank, and the sample. If an electronic integrator is used, the maximum area measurement must be within the linear range of the integrator.

6.6 Sample Containers - Pressure cylinders or vials with septums should be provided for the calibration mixture and samples to avoid loss of light ends.

6.7 System - Any satisfactory combination of the above components that will meet the performance requirements of Section 8.

7. Reagents and Materials
7.1 Calibration Mixture - A synthetic mixture of pure liquid hydrocarbons of known boiling point covering the boiling range of the sample. At least one compound in the mixture must have a boiling point equal to or lower than the initial boiling point of the sample, and one compound must have a retention time greater than any component in the sample. The concentration of all compounds heavier than n-butane must be known within 0.1 %. The synthetic composition shown in Table 1 should be used for gasoline analysis. Compounds necessary for evaluation of system performance are noted in Table 2.

NOTE 7 - If the sample contains significant quantities of compounds that can be identified on the chromatogram, these peaks may be used as internal boiling point calibrations.

NOTE 8 - Two calibration mixtures can be used for convenience. One that contains known concentrations of isopentane and heavier compounds can be used for determining response factors, sensitivity, and concentration repeatability. The other would contain a complete boiling range of compounds including propane, butane, and isobutane, whose concentrations are known only approximately. It would be used for measuring resolution, skewness, retention time repeatability, polarity, and retention time-boiling point relationship.

NOTE 9 - If the sample is known to contain more than 5 % benzene, 2,4 dimethylpentane should be replaced with benzene in the calibration mixture. (Warning - Benzene is poisonous and carcinogenic, harmful or fatal if swallowed.)

7.2 Carrier Gas - Helium or hydrogen for use with thermal conductivity detectors. Nitrogen, argon, or helium for use with flame ionization detectors. (Warning - Helium, nitrogen, and argon are compressed gases under high pressure.) (Warning - Hydrogen is an extremely flammable gas under high pressure.)

7.3 Liquid Phase for Columns:
NOTE 10 - The following materials have been used successfully as liquid phases:
Silicone gum rubber GE-SE-30
Silicone gum rubber OV-1
Silicone gum rubber OV-101
Silicone gum rubber Supelco 2100
Silicone gum rubber UC-W98

7.4 Solid Support - Usually crushed fire brick or inert diatomaceous earth such as Chromosorb P, G, or W, acid-washed, dimethyl silanized. Sieve size and support loading should be such that it will give optimum resolution and analysis time. In general, support loadings of 3 to 10 % have been found most satisfactory but higher ones have been used as shown in Table 1.