NB/SH/T 0558-2016 Determination of boiling range distribution of petroleum fractions by gas chromatography

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: NB/SH/T 0558—2016
• Chinese title: Determination of boiling range distribution of petroleum fractions by gas chromatography
• English title: Standard test method for boiling range distribution of petroleum fractions by gas chromatography
• Replacement relationship: replaces SH/T 0558—1993 "Determination of boiling range distribution of petroleum fractions by gas chromatography"
• Adoption relationship: modified adoption of ASTM D2887-15
• Publication/implementation: published on 2016-12-05, implemented on 2017-05-01
• Issuing authority: National Energy Administration
• Drafting organizations: Sinopec Research Institute of Petroleum Processing, PetroChina Petrochemical Research Institute
• Main drafters: Jin Ke, Ma Chenfei, Wang Yamin, Xue Huifeng, Wang Chunyan, Lin Jun
• Administrative organization: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1)
• Proposing organization: China Petrochemical Corporation
• Main technical changes compared with SH/T 0558—1993:
  • Added a method for determining boiling range by wide-bore capillary column gas chromatography
  • Added method B (accelerated simulated distillation method)
  • The scope of application was broadened to biofuels; method B applies not only to petroleum products or distillate oils specified in SH/T 0558—1993, but also to the analysis of fuels containing biodiesel blends (B5, B10 and B20, etc.)
  • Added a simulated distillation algorithm to the calculations in Chapter 12
• Main technical differences compared with ASTM D2887-15:
  • The referenced standards adopt the current national standards and industry standards of our country; for standards referenced in ASTM D2887-15 for which our country has no corresponding national standard, their standards are directly cited
  • Added the determination results for domestic reference oil JB-2
  • Added chromatographic conditions using nitrogen as carrier gas, suitable for the carrier gas usage situation in our country

2. Scope of application and non-applicability

• This standard specifies a method for determining the boiling range distribution of petroleum products by gas chromatography.
• It applies to petroleum products and fractions with a final boiling point below 538 ℃ at atmospheric pressure and an initial boiling point above 55.5 ℃. These petroleum products and fractions have sufficiently low vapor pressure to allow sampling at room temperature.
• This standard includes method A and method B:
  • Method A (Chapter 6 to Chapter 14): allows the selection of more chromatographic columns (such as packed and wide-bore capillary columns) and analysis conditions, as well as thermal conductivity detectors and flame ionization detectors. The analysis time is 14 min to 60 min.
  • Method B (Chapter 15 to Chapter 23): limited to 3 types of wide-bore capillary columns, and the sample requires no dilution. In addition, method B is not only used for the sample types described in method A, but also applies to the analysis of fuels containing biodiesel blends B5, B10 and B20. When method B is used, the analysis time is reduced to about 8 min.
• Not applicable: This standard does not apply to the determination of gasoline or gasoline components. These types of samples should be determined using test method ASTM D3710.

3. Method principle

• Gas chromatographic simulated distillation technology is used to determine the boiling range distribution. When the sample passes through a non-polar packed column or open tubular capillary column, the hydrocarbon compounds in the sample can elute in order of increasing boiling point. The chromatographic column is heated at a reproducible linear rate, and the area on the chromatogram throughout the analysis is recorded. Under the same chromatographic conditions, a calibration curve is obtained by analyzing a known hydrocarbon mixture whose boiling range covers the boiling range of the sample to be tested, and boiling point values can be obtained from the time axis of the calibration curve. From these data, the boiling range distribution of the sample to be tested can be obtained.
• The results obtained by method A and method B are given in Chapter 14 and Chapter 23, as well as in the relevant research reports.

4. Reagents and materials (purity / preparation)

• 7.1 Reagent purity: analytical reagent grade or chromatographic grade reagents should be used. Other grades of reagents may also be used, but the reagent must first be determined to be of sufficiently high purity, and use is permitted when it is determined that accuracy is not reduced.
• 7.2 Chromatographic column stationary liquid: this test method uses methyl silicone rubber or methyl silicone liquid.
• 7.3 Packed column support: chromatographic grade diatomaceous earth, preferably with a particle size range of 0.15 mm to 0.18 mm.
• 7.4 Carrier gas: high-purity helium or nitrogen. It is recommended to use molecular sieves or other suitable reagents to remove water, oxygen and hydrocarbon compounds to further purify the carrier gas. The pressure used should be sufficient to ensure a constant carrier gas flow rate (see 6.1.5). Warning: helium and nitrogen are both high-pressure compressed gases.
• 7.5 Hydrogen: high-purity hydrogen (containing no hydrocarbon compounds) used as fuel gas for the flame ionization detector (FID). Warning: high-pressure gas, extremely flammable.
• 7.6 Air: high-purity compressed air (for example, containing no hydrocarbon compounds) used as combustion-supporting gas for the flame ionization detector (FID). Warning: high-pressure gas, combustion-supporting gas.
• 7.7 Chromatographic column resolution test mixture: for packed columns, standard mixture: dissolve n-C₁₀ with a mass fraction of 1% and n-C₁₈ with a mass fraction of 1% in a suitable solvent such as n-octane, to test the resolution of the chromatographic column. The calibration mixture described in 7.8.2 may also serve as a suitable alternative mixture, as long as the mass fractions of the n-C₁₀ and n-C₁₈ components are both 1% of the standard mixture. For open tubular columns, use the mixture specified in 7.8.4. Warning: n-octane is flammable and harmful if inhaled.
• 7.8 Calibration mixture: an accurately weighed mixture of approximately equal normal hydrocarbon compounds, dissolved in carbon disulfide (CS₂); the boiling points of this mixture should cover the boiling range from n-C₅ to n-C₄₄, but it is not required to include every carbon number (see Note in 7.8.2). Warning: carbon disulfide is extremely volatile, flammable and toxic.
  • 7.8.1 At least one compound in the mixture must have a boiling point lower than the initial boiling point of the sample (IBP), and at least one compound must have a boiling point higher than the final boiling point of the sample (FBP). The boiling points of normal alkanes are listed in Table 2.
  • 7.8.2 If necessary, to make the calibration mixture contain a compound with a boiling point lower than the initial boiling point of the sample, propane or butane may be added to the calibration mixture. Use a gas syringe to add the gaseous compound (non-quantitatively) to the mixture in a septum-sealed sample bottle. Note: It has been proven that a calibration mixture containing normal alkanes with carbon numbers 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20, 24, 28, 32, 36, 40 is sufficient to provide enough boiling point data points to construct a reliable calibration curve.
  • 7.8.3 Packed column: the final concentration should be close to 10 parts normal alkane mixture in 100 parts CS₂.
  • 7.8.4 Open tubular column: the final concentration should be close to 1 parts normal alkane mixture in 100 parts CS₂.
• Table 2 Boiling points of normal alkanes (unit: ℃):
  • Carbon number 1: -162; 2: -89; 3: -42; 4: 0; 5: 36; 6: 69; 7: 98; 8: 126; 9: 151; 10: 174; 11: 196; 12: 216; 13: 235; 14: 253; 15: 271; 16: 287; 17: 302; 18: 316; 19: 330; 20: 344; 21: 356; 22: 369; 23: 380; 24: 391; 25: 402; 26: 412; 27: 422; 28: 431; 29: 440; 30: 449; 31: 458; 32: 466; 33: 474; 34: 481; 35: 489; 36: 496; 37: 503; 38: 509; 39: 516; 40: 522; 42: 534; 43: 540; 44: 545
• 7.9 The cooperative laboratories participating in this test method analyzed ASTM reference gas oil 1 and gas oil 2, as well as reference oil JB-2. The statistical results of boiling range and the permissible differences are given in Table 3, Table 4 and Table 5, respectively.
• Method B Reagents and materials (Chapter 17):
  • 17.1 Calibration mixture: an accurately weighed mixture of normal hydrocarbon compounds, dissolved in carbon disulfide (CS₂), with a total mass of the hydrocarbon mixture of 1%. The boiling points of this mixture should cover the boiling range from n-C₅ to n-C₄₄, but it is not required to include every carbon number (see Note in 7.8.2). Warning: extremely volatile, flammable and toxic.
    • 17.1.1 The calibration mixture contains normal alkanes with carbon numbers 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20, 24, 28, 32, 36, 40 and 44.
    • 17.1.2 If the hydrocarbon peaks of the sample elute earlier than the C₅ peak, it is necessary for the calibration mixture to contain a compound with a boiling point lower than the initial boiling point IBP of the sample. Propane or butane may be added to the calibration mixture. Use a gas syringe to add the gaseous compound (non-quantitatively) to the mixture in a septum-sealed sample bottle.
    • 17.1.3 The total concentration limit of the hydrocarbon mixture in the mixture is 1%, in order to maintain the symmetry of the chromatographic peaks. CS₂ is usually used as the solvent. It can also be used as a solvent. Calibration mixtures can be purchased from many chromatography companies.
  • 17.2 The gases used for operation are given in method A, from 7.4 to 7.6.
  • 17.3 The temperature-programmed inlet requires air cooling. This air comes from the air used by the FID detector and is supplied through a separate line, with a purity requirement of being free of oil and moisture.
  • 17.4 Reference gas oil 1 number batch 2: used to check the entire system. Obtained from a chromatography supplier; users may also use batch 1.
  • 17.5 Filters and oxygen traps: these ensure a good chromatographic baseline signal and protect the column. The oxygen trap is equipped to indicate the presence of oxygen in the system. A failed oxygen trap should be replaced promptly.
  • 17.6 Carbon disulfide: may be used to clean the autosampler syringe between two injections. Carbon disulfide is toxic and flammable.

5. Instrumentation and Equipment

• 6.1 The gas chromatograph used in method A should have the following performance characteristics:
  • 6.1.1 Detector: A flame ionization detector or thermal conductivity detector may be used. The detector should have sufficiently high sensitivity to detect peaks with a height of at least 10% of the recorder full scale under the conditions described in this test method, without loss of the required resolution. At this sensitivity level, the detector stability should be such that baseline drift does not exceed 1% of full scale per hour. It should be capable of continuous operation at a temperature equal to the maximum operating temperature of the column. The connection between the column and the detector should be such that no part is below the column temperature. The thermal conductivity detector is operated above the maximum operating temperature of the column. Operating at higher temperatures generally produces higher noise levels and greater baseline drift, which shortens the service life of the detector.
  • 6.1.2 Temperature programming: The chromatograph should be capable of linear temperature programming over a sufficiently wide temperature range so that the initial boiling point (IBP) time is greater than 1 min. And before the temperature reaches the maximum temperature of the temperature program, compounds with boiling points as high as 538 ℃ can elute. It should be reproducible, so as to achieve a retention time reproducibility of 0.1 min (6 s) for each component in the calibration mixture as described in 7.8.
  • 6.1.3 Low-temperature cooling: If analyzing a sample with an initial boiling point (IBP) lower than 93 ℃, the initial temperature of the column must be below room temperature. This is usually achieved by adding dry ice or liquid nitrogen, controlled by the column oven circuit. An excessively low initial column temperature should be avoided to ensure that the stationary liquid remains liquid. The initial column temperature only needs to be low enough to obtain a calibration curve that meets the requirements of this method.
  • 6.1.4 Injection system: The injection system should be capable of continuous operation at a temperature equal to the maximum operating column temperature, or some method of temperature programming the entire column (including the sample introduction point) should be used to reach the required maximum temperature, thereby achieving on-column injection. The connection between the column and the injection system should be such that there is no part below the column temperature.
  • 6.1.5 Flow control: Equipped with a mass flow controller, so that the carrier gas flow rate can remain constant over the entire temperature operating range of the column (fluctuation range not provided in the available source). The carrier gas inlet pressure of the chromatograph should be high enough to compensate for the increased column head pressure due to the rise in column temperature. For the packed column described in Table 1, an inlet pressure of 550 kPa is sufficient. For open tubular columns, an inlet pressure of 10 kPa～70 kPa is more suitable.
  • 6.1.6 Microsyringe: A syringe is required for sample introduction. Note: An automatic sampling device or other injection methods, such as on-column injection, may also be used, provided that: the operating temperature of the system is high enough to completely vaporize hydrocarbon compounds with a boiling point of 538 ℃, and the connection between the system and the column should avoid any low-temperature zones.
• 6.2 Chromatographic column: Any column and conditions may be used as long as petroleum hydrocarbon compounds are separated in order of increasing boiling point and the column performance requirements of 9.3.1 and 9.3.3 are met. Table 1 gives columns and conditions that have been successfully applied.
• Table 1 Typical operating conditions:
  • Packed column 1: column length 1.2 m, column outer diameter 6.4 mm, stationary liquid OV-1, liquid phase percentage 3%, support Diatoport S (silanized), support particle size 0.25/0.18 mm, carrier gas flow rate 30 mL/min, initial column temperature -20 ℃, final column temperature 360 ℃, temperature program rate 10 ℃/min, carrier gas nitrogen, detector FID, detector temperature 350 ℃, injector temperature 340 ℃, injection volume 0.5 μL, sample concentration (mass fraction) 25%
  • Packed column 2: column length 1.5 m, column outer diameter 3.2 mm, stationary liquid SE-30, liquid phase percentage 5%, support Chromosorb G (AW-DMS), support particle size 0.25/0.18 mm, carrier gas flow rate 12 mL/min, initial column temperature -40 ℃, final column temperature 350 ℃, temperature program rate 6.5 ℃/min, carrier gas helium, detector FID, detector temperature 380 ℃, injector temperature cold on-column, injection volume 0.1～0.2 μL, sample concentration (mass fraction) 2%
  • Packed column 3: column length 0.5 m, column outer diameter 3.2 mm, stationary liquid UC-W98, liquid phase percentage 10%, support Chromosorb P (acid-washed), support particle size 0.18/0.15 mm, carrier gas flow rate 12 mL/min, initial column temperature -30 ℃, final column temperature 360 ℃, temperature program rate 10 ℃/min, carrier gas nitrogen, detector FID, detector temperature 370 ℃, injector temperature cold on-column, injection volume 0.3 μL, sample concentration (mass fraction) 1%
  • Packed column 4: column length 0.6 m, column outer diameter 6.4 mm, stationary liquid SE-30, liquid phase percentage 10%, support Chromosorb P, support particle size 0.25/0.18 mm, carrier gas flow rate 30 mL/min, initial column temperature -50 ℃, final column temperature 390 ℃, temperature program rate 7.5 ℃/min, carrier gas nitrogen, detector TCD, detector temperature 360 ℃, injector temperature 360 ℃, injection volume 4 μL, sample concentration (mass fraction) 5%
  • Open tubular column 5: column length 7.5 m, column inner diameter 0.53 mm, stationary phase DB-1, film thickness 1.5 μm, carrier gas flow rate 40 mL/min, initial column temperature 40 ℃, final column temperature 340 ℃, temperature program rate 10 ℃/min, carrier gas helium, detector FID, detector temperature 360 ℃, inlet temperature 360 ℃, injection volume 0.1～0.2 μL, sample concentration undiluted
  • Open tubular column 6: column length 5 m, column inner diameter 0.53 mm, stationary phase HP-1, film thickness 0.88 μm, carrier gas flow rate 30 mL/min, initial column temperature 35 ℃, final column temperature 350 ℃, temperature program rate 10 ℃/min, carrier gas helium, detector FID, detector temperature 370 ℃, inlet temperature 370 ℃, injection volume 0.1～0.2 μL, sample concentration undiluted
  • Open tubular column 7: column length 10 m, column inner diameter 0.53 mm, stationary phase HP-1, film thickness 2.65 μm, carrier gas flow rate 25 mL/min, initial column temperature 35 ℃, final column temperature 350 ℃, temperature program rate 20 ℃/min, carrier gas nitrogen, detector TCD, detector temperature 360 ℃, inlet temperature 350 ℃, injection volume 0.1～0.2 μL, sample concentration undiluted
• 6.3 Data acquisition system:
  • 6.3.1 Recorder: A recording potentiometer or equivalent instrument with a range of 0 mV～10 mV and a full-scale response time of 2 s or shorter may be used.
  • 6.3.2 Integrator: A method shall be provided for measuring the cumulative area on the chromatogram, which may be implemented by an electronic integrator or a computer-based chromatographic data system. The integrator/computer system shall be equipped with commonly used chromatography software for measuring the retention time and area of eluted peaks (peak detection mode). In addition, the system shall be capable of converting the continuous integrator detector signal into area slices of fixed time periods. The continuous area slices obtained throughout the analysis are stored for subsequent processing. The voltage range of the integrator/computer (e.g., 1 V, 10 V) shall be within the linear range of the detector/potentiometer system used. The system shall be capable of subtracting the area slices of a blank run from the area slices of the corresponding sample run. Note: Some gas chromatograph operating software has fixed algorithms that can store a mathematical model of the baseline profile in memory. This baseline profile can be automatically subtracted from the detector signal of subsequent sample analyses to compensate for baseline drift. Some integration systems also store and automatically subtract blank analyses from subsequent analytical runs.
• Method B Apparatus (Chapter 16):
  • 16.1 Chromatograph: The gas chromatograph used shall have the following performance parameters:
  • Table 10 Typical operating parameters for Method B:
    • Column 1: column length 10 m, column inner diameter ID 0.53 mm, stationary phase thickness 0.88 μm, carrier gas helium, carrier gas flow rate 26 mL/min, initial column temperature 60 ℃, final column temperature 360 ℃, oven temperature program rate 35 ℃/min, detector FID, detector temperature 360 ℃, inlet PTV, inlet initial temperature 100 ℃, inlet temperature program rate 35 ℃/min, inlet final temperature 360 ℃, injection volume 0.1 μL, dilution concentration undiluted, analysis time 8 min
    • Column 2: column length 5 m, column inner diameter ID 0.53 mm, stationary phase thickness 2.65 μm, carrier gas helium, carrier gas flow rate 35 mL/min, initial column temperature 40 ℃, final column temperature 350 ℃, oven temperature program rate 35 ℃/min, detector FID, detector temperature 360 ℃, inlet PTV, inlet initial temperature 100 ℃, inlet temperature program rate 35 ℃/min, inlet final temperature 350 ℃, injection volume 0.1 μL, dilution concentration undiluted, analysis time 7.8 min
    • Column 3: column length 7.5 m, column inner diameter ID 0.53 mm, stationary phase thickness 1.5 μm, carrier gas helium, carrier gas flow rate 37 mL/min, initial column temperature 40 ℃ (0.5 min), final column temperature 360 ℃, oven temperature program rate 35 ℃/min, detector FID, detector temperature 365 ℃, inlet cold on-column, inlet initial temperature 100 ℃ (0.5 min), inlet temperature program rate 35 ℃/min, inlet final temperature 350 ℃, injection volume 0.1 μL, dilution concentration undiluted, analysis time 8 min
    • Note: All columns contain a polydimethylsiloxane stationary phase.
  • 16.1.1 Detector: A flame ionization detector shall be used. The minimum carbon detectability of the detector for n-C₁₁ is 2.0 pgC/s or better. The detector carbon sensitivity reaches 0.005 μg～0.010 μg; when operated at this sensitivity level, the detector stability shall achieve a baseline drift not exceeding 10⁻¹² A/h～10⁻¹¹ A/h. This drift is used to measure the change in detector current per unit time. The detector shall be capable of continuous operation at a temperature equivalent to the maximum column temperature used (see Table 10). The connection between the column and the detector shall be such that a temperature lower than the column temperature never occurs. Accumulation of column bleed deposits can cause premature reduction of the detector nozzle tip; to avoid this, it is recommended that the flame nozzle have an orifice of 0.5 mm±0.08 mm.
  • 16.1.2 Temperature programming: The gas chromatograph shall be capable of linear temperature programming at a rate of 35 ℃/min over the entire range of conditions listed in Table 9 (sic, suspected to be Table 10, requires confirmation against the source standard (source-text extraction)). Note: For rapid temperature increases, some instrument manufacturers may require different voltages.
  • 16.1.3 Injection system: This method preferably uses a temperature-programmed inlet or a cold on-column inlet. The temperature-programmed inlet (PTV) directly injects the sample onto the column without split venting of the sample and is usually equipped with a liner. The cold on-column inlet does not contain any liner. This method does not recommend a constant-temperature inlet.
  • 16.1.4 Injection septum: The choice of septum is very important; the septum shall maintain maximum stability at the maximum operating temperature of the inlet. The septum shall be replaced periodically after 50 instrument runs. Septum particles from the inlet can cause ghost peaks in the blank baseline.
  • 16.1.5 Electronic pneumatic control: The gas chromatograph shall be equipped with an electronic flow controller so that the carrier gas flow rate can remain constant over the entire column temperature operating range (fluctuation range ±1% or better). Flow control shall be achieved by a flow sensor, i.e., using a program that calculates pressure to maintain constant flow. At 350 ℃, there shall be a pressure difference of not less than 135 kPa between the gas source pressure and the column head pressure.
  • 16.1.6 Autosampler: Using an automatic sampling device equipped with a 0.1 μL graduated microsyringe can ensure retention time reproducibility.
  • 16.2 Column: Any one of the 3 columns in Table 10 may be used. These columns all use polydimethylsiloxane (PDMS) as the stationary phase. They elute n-alkanes in order of increasing boiling point.
  • 16.3 Data acquisition system:
    • 16.3.1 Computer: A computer equipped with data acquisition software is necessary; it can control the chromatograph to perform the injection process, including syringe washing, sample aspiration, and sample injection, and can digitize and acquire signals. The data acquisition software operates in peak detection mode and/or slice mode.
    • 16.3.2 Simulated distillation calculations are implemented in software, and the software complies with the algorithm described in Chapter 12.

6. Recommended operating conditions

• Typical operating conditions for Method A are given in Table 1 (see Section 5 Apparatus).
• Typical operating parameters for Method B are given in Table 10 (see Section 5 Apparatus).
• Appendix E gives the operating conditions for Method A and Method B with hydrogen and nitrogen carrier gases:
  • Table E.1 Chromatographic conditions for hydrogen carrier gas:
    • D2887A Hydrogen carrier gas: column 10 m, 0.53 mm inner diameter, 0.88 μm, polydimethylsiloxane; carrier gas flow rate 10 mL/min; oven temperature program 40 ℃ raised at 15 ℃/min to 350 ℃, held for 17 min; inlet cold on-column, 100 ℃ raised at 15 ℃/min to 350 ℃; FID temperature 360 ℃; sample 0.1 μL, diluted with CS₂ to 10%～20%
    • D2887B Hydrogen carrier gas: column 10 m, 0.53 mm inner diameter, 0.88 μm, polydimethylsiloxane; carrier gas flow rate 35 mL/min; oven temperature program 40 ℃ raised at 35 ℃/min to 350 ℃, held for 0 min; inlet PTV, 100 ℃ raised at 30 ℃/min to 350 ℃; FID temperature 355 ℃; sample 0.1 μL, undiluted
  • Table E.4 gives the operating conditions for Method A and Method B with nitrogen carrier gas (specific values not provided in the available source)
• Note: Because the precision and bias information for the methods using alternative carrier gases in this appendix and the operating conditions are not listed according to the ASTM IIS process as a research basis, this appendix is for informational purposes only. Results obtained under the conditions described in this appendix shall not be regarded as valid results, nor as representative data. Warning: Use caution when using hydrogen as a carrier gas.

7. Sampling and sample preparation

• 8.1 Samples analyzed by Method A shall follow the sampling procedure of GB/T 4756.
• 8.2 The sample to be analyzed shall be homogeneous and free of dust and insoluble matter.
• 11.1 The sample amount shall neither overload the column stationary phase nor exceed the linear range of the detector. Samples with a narrow boiling range require a smaller injection volume than samples with a wide boiling range.
• 11.1.1 To determine the linear range of the detector, please refer to ASTM E594 for the requirements for flame ionization detectors, or refer to ASTM E516 for the requirements for thermal conductivity detectors.
• 11.1.2 The chromatogram of the calibration mixture can be used to estimate the maximum amount of a specific sample component relative to a particular column stationary phase that can be tolerated without overloading (see 10.3.1). Note that the corresponding sample signal intensity for this sample injection volume should not exceed this peak height.
• 11.1.3 Samples with sufficiently low vapor pressure may be injected directly at room temperature using a syringe. Such samples may also be dissolved in CS₂ to control the sample amount to meet the requirements of 11.1.1.
• 11.1.4 For samples that are too viscous or waxy for direct injection with a syringe, they may be dissolved with CS₂. Typical sample injection volumes are listed in Table 6.
• Table 6 Typical sample injection volumes:
  • Stationary phase loading 10%: net sample volume 1.0 μL
  • Stationary phase loading 5%: net sample volume 0.5 μL
  • Open tubular column 1.5 μm: net sample volume 0.1～0.2 μL
  • Open tubular column 0.88 μm: net sample volume 0.1～0.5 μL
  • Open tubular column 2.65 μm: net sample volume 0.2～1.0 μL
• Method B Sample preparation (20.1):
  • 20.1.1 Fill the autosampler vial to a certain volume, leaving a small space above. For very viscous samples, there are usually two options: 1) adjust the autosampler aspiration speed, i.e., slow down the needle aspiration speed, to avoid creating a vacuum that results in non-reproducible volumes, or 2) add 2 drops of CS₂ to the autosampler vial.
  • 20.1.2 When injecting reference oil, use reduced-volume autosampler vials as much as possible, or use vial inserts to reduce the volume. Reference oils are usually expensive and limited in supply, and should be used sparingly.
  • 20.1.3 If the autosampler does not have a CS₂ wash bottle, adjust the autosampler to use a sufficient number of sample washes to clean the injection needle.
  • 20.1.4 If the gas chromatograph has been idle for more than 2 h, it is best to run a blank to remove accumulated trace impurities from the septum, carrier gas impurities, and other retained substances at the lower standby temperature of the inlet, as well as accumulations at the column inlet. This run is not to be used as a blank run for verifying instrument calibration.

8. Analysis procedure

• 9.1 Instrument preparation:
  • 9.1.1 Install the chromatograph according to the manufacturer's instructions; typical operating conditions are shown in Table 1.
  • 9.1.2 When using FID, periodically remove deposits formed in the detector. These are formed by combustion of silicone liquid phase degradation products. These deposits may alter the response characteristics of the detector.
  • 9.1.3 Heat the injection system to above 300 ℃. After installing a new septum, a blank run analysis should be performed to ensure that no additional detector response from septum bleed occurs. At the sensitivity levels typically used in this test method, aging the septum at the operating temperature of the injection system for several hours can minimize this problem. The recommended practice is to replace the septum at the end of a series of analyses rather than at the beginning.
• 9.2 Prepare the chromatographic column as follows:
  • 9.2.1 Packed column: Any suitable method capable of preparing a column that meets the requirements of 9.3.1 and 9.3.3 may be used. Generally, a stationary liquid loading of 3%～10% is used. Age the column at the maximum operating temperature to reduce baseline drift caused by column packing bleed. The following procedure can be used to age the column quickly and effectively:
    • 9.2.1.1 Connect the column to the inlet, but do not connect the column outlet to the detector.
    • 9.2.1.2 Purge the column thoroughly with carrier gas at room temperature.
    • 9.2.1.3 Turn off the carrier gas and allow the column to fully depressurize.
    • 9.2.1.4 Seal the open end (detector end) of the column with a suitable septum.
    • 9.2.1.5 Raise the column temperature to the maximum operating temperature.
    • 9.2.1.6 Hold the column at this temperature for at least 1 h with no carrier gas flowing through the column.
    • 9.2.1.7 Cool the column to room temperature.
    • 9.2.1.8 Remove the sealing cap from the detector end of the column and turn on the carrier gas.
    • 9.2.1.9 At normal carrier gas flow rate, repeat several times programming the column temperature to the maximum temperature. After aging, connect the free end of the column to the detector.
    • 9.2.1.10 An effective aging method for a column with an initial stationary liquid loading of 10% is to purge the column at normal carrier gas flow rate while maintaining the column at the maximum operating temperature for 12 h～16 h, with the column outlet not connected to the detector during this process.
  • 9.2.2 Open tubular column: Many manufacturers provide open tubular columns with cross-linked and bonded stationary phases, which are usually pre-aged. These columns have much lower column bleed than packed columns. Aging of these columns is not as important as for packed columns, but aging under some conditions is necessary. The following procedure can be used to age these columns quickly and effectively:
    • 9.2.2.1 Once the open tubular column is properly installed on the gas chromatograph and checked for leaks, set the column and detector gas flows. Before heating the column, purge the system with carrier gas at room temperature for at least 30 min.
    • 9.2.2.2 Raise the column temperature at a rate of 5 ℃～10 ℃ per minute until the final operating temperature, and hold for about 30 min.
    • 9.2.2.3 Repeat aging the column under temperature-programmed conditions until the baseline is stable.
• 9.3 Verify system performance indicators as follows:
  • 9.3.1 Column resolution: The resolution of the column is affected by the physical parameters of the column and the operating conditions, and resolution affects the determination of the entire boiling range distribution. Therefore, different systems (laboratories) using this test method should maintain comparable resolution. For column resolution, the normal alkanes C₁₀ and C₁₈ in a test mixture can be analyzed, and the resolution calculated using equation (1) (see 7.7 and Chapter 10), as shown in Figure 1. Using the same conditions as for sample analysis, the resolution should be at least 3:
    • R = [2(t₁₈ - t₁₀)] / [1.699(W₁₀ + W₁₈)] (1)
    • Where: R— resolution; t₁₀—time at the maximum of the n-C₁₀ peak, in seconds (s); t₁₈—time at the maximum of the n-C₁₈ peak, in seconds (s); W₁₀—half-peak width of the n-C₁₀ peak, in seconds (s); W₁₈—half-peak width of the n-C₁₈ peak, in seconds (s).
  • 9.3.2 Detector response calibration: This test method assumes that the detector response for petroleum hydrocarbon compounds is proportional to the mass of the individual components. This should be verified when applying the instrument system and whenever the system or operating parameters are changed. Analyze the calibration mixture using the same procedure as for sample analysis (see Chapter 10). Calculate the relative response factor for each normal alkane (relative to n-decane) according to ASTM D4626 and equation (2):
    • Fₙ = (Mₙ/Aₙ) / (M₁₀/A₁₀) (2)
    • Where: Fₙ—relative response factor; Mₙ—mass of the normal alkane in the mixture; Aₙ—peak area of the normal alkane in the mixture; M₁₀—mass of n-decane in the mixture; A₁₀—peak area of n-decane in the mixture.
    • The deviation of the relative response factor (Fₙ) for each normal alkane from the integer (1) should not be greater than ±10%.
  • 9.3.3 Column elution characteristics: The column material, stationary phase, or other parameters can affect the elution order of the normal alkane sample components, leading to deviations in the relationship between TBP and retention time. If the stationary phase used is not listed in 7.3, the retention times of several alkylbenzenes spanning the sample boiling range (such as m-xylene, n-butylbenzene, 1,3,5- triisopropylbenzene, n-decylbenzene, and tetradecylbenzene) should be analyzed to ensure that the column separates in order of boiling point (see Appendix A).
• 10 Calibration and standardization:
  • 10.1 Analysis procedure: Determine and use a predetermined analysis procedure designed to achieve the best reproducibility for these determinations. The procedure includes cooling the column temperature to the initial temperature, equilibration time, sample injection, system start, analysis, and final high-temperature duration.
    • 10.1.1 After setting the chromatographic conditions to meet the performance requirements, program the column temperature to the maximum temperature to be used and hold at that temperature for the selected time. According to the analysis procedure, cool the column temperature to the initial temperature.
    • 10.1.2 During cooling and equilibration, prepare the integrator/computer system. If retention time or detector response calibration is to be performed, use peak detection mode. For sample and baseline compensation measurements, use integrated area slice mode. The recommended integration slice rate for this test method is given in 12.1.2. Other integration slice rates may also be used, provided that the integration slice rate falls within the limits of 0.02% to 0.2% of the retention time of the final calibration component (C₄₄). If, when determining the boiling range distribution, the accumulated (aggregated) slice data can be within the above limits, a larger integration slice may also be used