ASTM D7213 Test Method for Boiling Range Distribution of Petroleum Distillates
ASTM D7213 Standard Test Method for Boiling Range Distribution of Petroleum Distillates in the Boiling Range from 100 to 615°C by Gas Chromatography
6. Apparatus
6.1 Chromatograph - The gas chromatographic system used shall have the following performance characteristics:
6.1.1 Column Oven - Capable of sustained and linear programmed temperature operation from near ambient (for example, 35 to 50°C) up to 400°C.

6.1.2 Column Temperature Programmer - The chromatograph shall be capable of linear programmed temperature operation up to 400°C at selectable linear rates up to 20°C/min. The programming rate shall be sufficiently reproducible to obtain the retention time repeatability of 0.1 min (6 s) for each component in the calibration mixture described in 7.5.

6.1.3 Detector - This test method requires a flame ionization detector (FID). The detector shall meet or exceed the following specifications as detailed in Practice E 594. The flame jet should have an orifice of approximately 0.05 to 0.07 mm.
6.1.3.1 Operating Temperature, , 400°C.

6.1.3.2 Sensitivity, >0.005 coulombs/g carbon.

6.1.3.3 Minimum Detectability, 1 x 10(-11) g carbon/s.

6.1.3.4 Linear Range, >10(6).

6.1.3.5 Connection of the column to the detector shall be such that no temperature below the column temperature exists. Refer to Practice E 1510 for proper installation and conditioning of the capillary column.

6.1.4 Sample Inlet System - Any sample inlet system capable of meeting the performance specification in 7.6 may be used. Programmed temperature vaporization (PTV) and programmable cool on-column injection systems have been used successfully.

6.1.5 Carrier Gas Flow Control - The chromatograph shall be equipped with carrier gas pressure or flow control capable of maintaining constant carrier gas flow control through the column throughout the column temperature program cycle.

6.2 Microsyringe - A microsyringe with a 23 gauge or smaller stainless steel needle is used for on-column sample introduction. Syringes of 0.1 to 10 µL capacity are available.
6.2.1 Automatic syringe injection is recommended to achieve best precision.

6.3 Column - This test method is limited to the use of non-polar wall coated open tubular (WCOT) columns of high thermal stability. Glass, fused silica, and stainless steel columns, with a 0.53 mm diameter have been successfully used. Cross-linked or bonded 100 % dimethyl-polysiloxane stationary phases with film thickness of 0.5 to 1.0 mm have been used. The column length and liquid phase film thickness shall allow the elution of at least C60n-paraffin (BP = 615°C). The column and conditions shall provide separation of typical petroleum hydrocarbons in order of increasing boiling point and meet the column resolution requirements of 8.2.1. The column shall provide a resolution between one and ten using this test method's operating conditions.

6.4 Data Acquisition System:
6.4.1 Recorder - A 0 to 1 mV range recording potentiometer or equivalent, with a full-scale response time of 2 s or less may be used to provide a graphical display.

6.4.2 Integrator - Means shall be provided for determining the accumulated area under the chromatogram. This can be done by means of an electronic integrator or computer-based chromatography data system. The integrator/computer system shall have normal chromatographic software for measuring the retention time and areas of eluting peaks (peak detection mode). In addition, the system shall be capable of converting the continuously integrated detector signal into area slices of fixed duration (area slice mode). These contiguous area slices, collected for the entire analysis, are stored for later processing. The electronic range of the integrator/computer (for example, 1 V, 10 V) shall be operated within the linear range of the detector/electrometer system used.

NOTE 1 - Some gas chromatographs have an algorithm built into their operating software that allows a mathematical model of the baseline profile to be stored in memory. This profile is automatically subtracted from the detector signal on subsequent sample runs to compensate for the column bleed. Some integration systems also store and automatically subtract a blank analysis from subsequent analytical determinations.

7. Reagents and Materials
7.1 Carrier Gas - Helium, nitrogen or hydrogen of high purity. (Warning - Helium and nitrogen are compressed gases under high pressure; hydrogen is an extremely flammable gas under high pressure.) These gases may be used as the carrier gas and should not contain more than 5 mL/m3 of oxygen. The total amount of impurities should not exceed 10 mL/m3. Additional purification is recommended by the use of molecular sieves or other suitable agents to remove water, oxygen, and hydrocarbons. Available pressure shall be sufficient to ensure a constant carrier gas flow rate.

7.2 Hydrogen - Hydrogen of high purity (for example, hydrocarbon-free) is used as fuel for the flame ionization detector (FID). (Warning - Hydrogen is an extremely flammable gas under high pressure.)

7.3 Air - High purity (for example, hydrocarbon-free) compressed air is used as the oxidant for the flame ionization detector (FID). (Warning - Compressed air is a gas under high pressure and supports combustion.)

7.4 Solvents - Unless otherwise indicated, it is intended that all solvents 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 solvent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
7.4.1 Carbon Disulfide (CS2) - (99+ % pure) may be used as a viscosity reducing solvent and as a means of reducing mass of sample introduced onto the column to ensure linear detector response and reduced peak skewness. It is miscible with asphaltic hydrocarbons and provides a relatively small response with the FID. The quality (hydrocarbon content) should be determined by this test method prior to use as a sample diluent. (Warning - Carbon disulfide is extremely flammable and toxic.)

7.5 Cyclohexane (C6H12) - (99+ % pure) may be used as a viscosity reducing solvent. It is miscible with asphaltic hydrocarbons, however, it responds well to the FID. The quality (hydrocarbon content) should be determined by this test method prior to use as a sample diluent. (Warning - Cyclohexane is flammable.)

7.6 Calibration Mixture - A qualitative mixture of n-paraffins (nominally C5 to C60) dissolved in a suitable solvent. The final concentration should be approximately one part of n-paraffin mixture to one hundred parts of solvent. At least one compound in the mixture shall have a boiling point lower than the initial boiling point of the sample being analyzed, as defined in the scope of this test method (1.1). The calibration mixture shall contain at least 13 known n-paraffins (for example, C6, C7, C8, C9, C10, C12, C16, C20, C30, C40, C50, C52, C60). Boiling points of n-paraffins are listed in Table 1.

NOTE 2 - A suitable calibration mixture can be obtained by dissolving a polyolefin wax (for example, Polywax 5004) in a volatile solvent (for example, carbon disulfide or cyclohexane). Solutions of one part Polywax to one hundred parts solvent can be prepared. Lower boiling point paraffins will have to be added to insure conformance with 7.6. Fig. 1 illustrates a typical calibration mixture chromatogram.

7.7 Response Linearity Mixture - Prepare a quantitatively weighed mixture of at least ten individual paraffins (>99 % purity), covering the boiling range of the test method. The highest boiling point component should be at least n-C60. The mixture shall contain n-C40. Use a suitable solvent to provide a solution of each component at approximately 0.5 to 2.0 % by mass.

7.8 Reference Material - A reference sample that has been analyzed by laboratories participating in the test method cooperative study. Consensus values for the boiling range distribution of this sample are being determined.