GB/T 28768-2012 Determination of hydrocarbon types and oxygenates in motor gasoline—Multidimensional gas chromatography

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

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

• Standard number: GB/T 28768-2012
• Chinese full title: Determination of hydrocarbon types and oxygenates in motor gasoline—Multidimensional gas chromatography
• English title: Determination of hydrocarbon types and oxygenates in automotive-motor gasoline by multidimensional gas chromatography method
• Adoption relationship: Modified adoption by redrafting method of ISO 22854:2008 "Liquid petroleum products—Determination of hydrocarbon types and oxygenates in motor gasoline—Multidimensional gas chromatography" (MOD)
• Replacement relationship: not provided in the available source (no replacement of any standard is mentioned)
• Publication/implementation: published on 2012-11-05, implemented on 2013-03-01
• Custodianship: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280) Subcommittee on Petroleum Fuels and Lubricants (SAC/TC 280/SC 1)

2. Scope of application and non-applicability

This standard specifies a method for the determination of saturated hydrocarbons, olefins and aromatics in motor gasoline by gas chromatography. This standard can also determine benzene content, oxygenates and total oxygen content in motor gasoline.

Applicable determination ranges (volume fraction/mass fraction):

• Total aromatics content (volume fraction): not greater than 50%
• Total olefins content (volume fraction): 1.5%～30%
• Oxygenates content (volume fraction): 0.8%～15%
• Total oxygen content (mass fraction): 1.5%～3%
• Benzene content (volume fraction): not greater than 2%

Note 1: When this standard was developed, its final boiling point limit was 215°C. Note 2: For oxygenates, precision data were established for motor gasoline samples containing MTBE, ETBE, TAME, isopropanol, isobutanol, tert-butanol, methanol and ethanol; the precision data for methanol may also not follow the precision calculation formulas listed in this standard. Applicability has also been demonstrated for the determination of n-propanol, acetone and diisopropyl ether (DIPE), but precision data for these compounds have not been established. Although this standard can be used for gasoline samples with olefin content (volume fraction) up to 50%, precision data are given only for olefin content (volume fraction) from 1.5% to 30%. Although this standard can be used for the analysis of motor gasoline containing oxygenates, it can also be used for the analysis of other hydrocarbons with the same boiling point range, such as naphtha and reformate. Note 3: Although overlap of carbon 9 and carbon 10 aromatics may occur, the total amount is accurate; cumene is separated from carbon 8 aromatics and is included in carbon 9 aromatics.

Non-applicability: no explicit non-applicability clauses are listed in the available source.

3. Method principle

4.1 The sample is analyzed by gas chromatography, using a special column combination and column switching program, and separated into hydrocarbon groups. The sample is injected into the gas chromatography system and vaporized and separated into different groups, usually detected using a flame ionization detector (FID). The method flow diagram is shown in Figure 1 (original Figure 1: gasoline sample→sulfate column I→polar column→sulfate column II→olefin adsorption trap→13X molecular sieve column→hydrogenation catalyst→5A molecular sieve column→polystyrene column→nonpolar column→detection).

4.2 The mass concentration of each compound or hydrocarbon group to be determined is obtained by applying the relative response factor (see 9.1) to the detected peak area, then normalizing to 100%. For oxygenates contained in the sample that cannot be determined by this standard, the result shall be obtained by subtracting the content of oxygenates determined by other methods from 100%; the volume concentration of each compound or hydrocarbon group to be determined is obtained by calculating using the mass concentration of the measured peak and its density value (see 9.2) and normalizing to 100%.

4.3 After the above separation, the motor gasoline sample is separated into hydrocarbon groups, then separated by carbon number, and with the aid of the corresponding relative response factors, the content of each group can be calculated.

4. Reagents and materials (purity / preparation)

5.1 Gases

• 5.1.1 Hydrogen: purity 99.999%. Warning: an explosion can occur when the hydrogen concentration in air (volume fraction) reaches 4%~75%; refer to the instrument manufacturer's operation manual.
• 5.1.2 Helium: purity 99.999%.
• 5.1.3 Compressed air. Note: It is recommended to install suitable gas purifiers on the compressed air, hydrogen and helium lines.

5.2 Sample vials suitable for autosamplers: use sealed inert sample vials, such as small reagent bottles with rubber septa made of self-sealing polytetrafluoroethylene (PTFE) material.

5.3 (Various) reference samples: use gasoline with components and concentrations similar to the actual sample as the reference sample. Warning: flammable, harmful if inhaled. Note: Sulfur compounds in gasoline will be irreversibly adsorbed in the olefin adsorption trap and may reduce the capacity of the olefin adsorption trap to retain olefins; sulfur compounds may also be trapped in the alcohol and ether-alcohol-aromatic adsorption traps. Although low levels of sulfur compounds (for example, sulfur content less than 50 mg/kg) have little effect on the different adsorption traps or columns, attention should still be paid to gasoline samples with high sulfur content (for example, sulfur content greater than 1000 mg/kg).

5. Instruments and equipment

6.1 Gas chromatograph: a computer-controlled multidimensional gas chromatography apparatus, injection system, flame ionization detector (FID), suitable chromatographic columns, adsorption traps and hydrogenation catalyst, see the description in Annex B instrument specifications. 6.2 Switching valve: a suitable switching valve is used to transfer compounds within the gas chromatograph from one chromatographic column to another. The switching valve should have the characteristics of inert surface and small dead volume. 6.3 Adsorption trap: a suitably short chromatographic column (see Table B.1 in Annex B instrument specifications for recommended chromatographic column requirements) is used with temperature control to selectively retain certain components in motor gasoline; the adsorption of trapped compounds should be reversible. For an example of a typical elution order, see C.2 example in Annex C.

Annex B Table B.1 Recommended chromatographic column requirements (name | length/cm | internal diameter/mm | stationary phase | description):

• Sulfate column I | 30 | 2 | 150 μm~178 μm on Chromosorb 750, coated with 50% sulfate | traps alcohols and aromatics
• Polar column | 270 | 2 | 178 μm~250 μm on Chromosorb PAW, coated with 30% OV 275 | separates aliphatic hydrocarbons and low-boiling aromatics
• Nonpolar column | 1500 | 0.53 | 5 μm OV101 methylsiloxane | separates alcohols and high-boiling aromatics
• 13X molecular sieve column | 170 | 1.7 | 150 μm~178 μm on Chromosorb 750, coated with 3% 13X molecular sieve | separates alkanes and cycloalkanes
• Sulfate column II | 30 | 3 | 150 μm~178 μm on Chromosorb 750, coated with 50% sulfate | traps ethers
• Olefin adsorption trap | 30 | — | 8% silver salt coated on silica gel of 150 μm~178 μm | traps olefins
• Polystyrene column | 90 | 2 | 150 μm~178 μm of Porapak P | separates aromatics, alcohols and ethers
• Hydrogenation catalyst | 5.5 | 1.7 | 2% platinum coated on alumina | hydrogenates unsaturated hydrocarbons
• 5A molecular sieve column | 30 | 2 | 5A molecular sieve | separates normal hydrocarbons and isomeric hydrocarbons

Note: Chromosorb is a trade name of Johns-Manville company; Porapak is a trade name of Associates company (information is provided for user convenience; other products may also be used if they can be shown to give the same results).

6. Recommended operating conditions

8.4 The recommended suitable gas flow parameters are shown in Table 1 (unit: milliliters per minute):

The recommended temperature control condition parameters of the chromatographic system are shown in Annex C (normative annex) Table C.1～Table C.4.

Table C.1 Recommended temperature control condition parameters of the chromatographic system for motor gasoline (without oxygenates):

• Sulfate column I: 175 (isothermal)
• Polar column: 130 (isothermal)
• Nonpolar column: 130 (isothermal)
• Olefin adsorption trap: first-stage trapping temperature 95±5; olefin desorption temperature 280
• 13X molecular sieve column: 90~430, heating rate 10 °C/min
• Polystyrene column: 115 (isothermal)
• Sulfate column II: 110 (isothermal)
• Platinum column (hydrogenation catalyst): 180 (isothermal)
• 5A molecular sieve column: 120~450, heating rate 10 °C/min
• Chromatographic column switching valve: 130 (isothermal)
• Inlet: 130 (isothermal)
• Detector: 190 (isothermal)
• Column oven: 130 (isothermal)

Table C.2 Recommended temperature control condition parameters of the chromatographic system for motor gasoline (with oxygenates):

• Sulfate column I: initial temperature 163±3; oxygenate desorption temperature 280
• Polar column: 130 (isothermal)
• Nonpolar column: 130 (isothermal)
• Olefin adsorption trap: first-stage trapping temperature 95±5; second-stage trapping temperature 148±2; olefin desorption temperature 280
• 13X molecular sieve column: 90~430, heating rate 10 °C/min
• Polystyrene column: initial temperature 120±5, elution temperature 280
• Sulfate column II: initial temperature 170±5; oxygenate desorption temperature 280
• Platinum column (hydrogenation catalyst): 180 (isothermal)
• 5A molecular sieve column: 120~450, heating rate 10 °C/min
• Column switching valve: 130 (isothermal)
• Inlet: 130 (isothermal)
• Detector: 190 (isothermal)
• Column oven: 130 (isothermal)

Table C.3 Recommended temperature control condition parameters for the reforming gasoline chromatography system:

• Sulfate column I: 175 (isothermal)
• Polar column: 130 (isothermal)
• Nonpolar column: 130 (isothermal)
• Olefin adsorption trap: trapping temperature 165; olefin desorption temperature 280
• 13X molecular sieve column: 90~430, heating rate 10 °C/min
• Polystyrene column: 115 (isothermal)
• Sulfate column II: 110 (isothermal)
• Platinum column (hydrogenation catalyst): 180 (isothermal)
• 5A molecular sieve column: 120~450, heating rate 10 °C/min
• Column switching valve: 130 (isothermal)
• Inlet: 130 (isothermal)
• Detector: 190 (isothermal)
• Column oven: 130 (isothermal)

Table C.4 Recommended temperature control condition parameters for the reforming feedstock oil chromatography system:

• Sulfate column I: 175 (isothermal)
• Polar column: 130 (isothermal)
• Nonpolar column: 130 (isothermal)
• 13X molecular sieve column: 90~430, heating rate 10 °C/min
• Polystyrene column: 115 (isothermal)
• Sulfate column II: 110 (isothermal)
• Platinum column (hydrogenation catalyst): 180 (isothermal)
• 5A molecular sieve column: 150~450, heating rate 10 °C/min
• Column switching valve: 130 (isothermal)
• Inlet: 130 (isothermal)
• Detector: 190 (isothermal)
• Column oven: 130 (isothermal)

Note: In Tables C.1~C.4, some maximum heating time/maximum cooling time values source-text extraction appear incomplete, requires confirmation against the source standard (source-text extraction).

7. Sampling and Test Sample Preparation

7 Sampling: Unless otherwise specified, sampling shall be carried out in accordance with the provisions of GB/T 4756 or SY/T 5317.

8.2 Preparation of the analytical sample: Cool the sample to prevent volatilization loss, transfer the sample to be analyzed into a sample vial suitable for use with an autosampler (see 5.2) and quickly cap it tightly and seal it with a self-sealing polytetrafluoroethylene (see 5.2) lid. Note: It is recommended to cool the sample to between 0°C~5°C.

8.3 Injection volume: The injection volume shall be determined in such a way that it does not exceed the capacity of the chromatographic column and ensures that the detector is within its linear range. Note: The original text here source-text extraction is "the injection volume is. KL has been proven to be optimal", the specific value requires confirmation against the source standard (source-text extraction).

8. Analytical Procedure

8.1 Instrument preparation: Configure the instrument and equipment in accordance with the requirements of Appendix B Instrument Specification.

8.2 Preparation of the analytical sample: See Section 7.

8.3 Injection volume: See Section 7.

8.4 Verification of instrument and test conditions: Recommended appropriate gas flow parameters are given in Table 1, and recommended temperature control condition parameters for the chromatography system are given in Appendix C. Run (various) reference samples (see 5.3), and check the instrument parameters, cut times, and group separation times; if incorrect, adjust according to the parameters recommended by the instrument manufacturer and retest. Note that the group selectivity of chromatographic peaks should be close to the separation boundaries, such as benzene, olefins, and oxygenates; oxygenates should be carefully identified. It is recommended to use a gasoline reference sample spiked with pure components of the oxygenates of interest to identify complex oxygenates. The added pure oxygenate component content (volume fraction) is in the range of 0.8%~15%, and the purity of the pure component shall not be less than chromatographic grade. The sample chromatograms in Appendix D show several sample chromatograms and provide evidence for elution time division and possible interferences.

8.5 Check: Retest the reference sample and compare the obtained results with their standard values; the absolute difference from the standard value shall not exceed the repeatability requirements for each parameter listed in Chapter 11. It is advisable to check the reference sample once a week to check the normal function of the equipment. The reference sample for checking and the sample to be tested should preferably have similar components and concentrations. The standard values of the reference sample are values obtained through interlaboratory comparison tests by multiple (more than 16) qualified laboratories. Instrument verification should preferably be performed before testing samples containing new oxygenates.

8.6 Sample analysis: Prepare the analytical sample according to the preparation procedures specified in 8.2 and 8.3, introduce a representative gasoline test portion into the gas chromatograph established according to 8.1 using an autosampler, and the carrier gas brings the test portion into the gas chromatograph system to separate the components. An example of a typical sample elution separation order is shown in the C.2 example of Appendix C. Detect the components in the test portion with a flame ionization detector; the signal detected by the flame ionization detector is processed by a computer system to obtain the content of each component in the gasoline test portion.

Appendix C C.2.1 Example of typical elution order:

• First, alcohols and high-boiling aromatics are trapped on an adsorption trap (sulfate column I), and light aromatics are separated from other components through a polar chromatographic column (e.g., OV 275);
• Through another adsorption trap (sulfate column II), ethers are trapped and separated from other components;
• Olefins are separated from saturated hydrocarbons in two steps through an olefin adsorption trap (e.g., silver salt). Due to the limited trapping capacity of the olefin adsorption trap, for components with very high butene content or very high total olefin content, two-step trapping is necessary; as long as the capacity of the olefin adsorption trap permits, one-step separation may also be used;
• Next, the remaining saturated hydrocarbons are separated into alkanes and cycloalkanes by carbon number using a 13X molecular sieve chromatographic column;
• Ethers are desorbed from the adsorption trap (sulfate column II) and separated and detected according to their boiling points;
• After olefins are desorbed from the olefin adsorption trap, they are hydrogenated and saturated on a platinum column (hydrogenation catalyst) to convert into the corresponding saturated hydrocarbons, and separated and detected through a 13X molecular sieve chromatographic column;
• Alcohols and high-boiling aromatics are eluted from the polar chromatographic column and adsorption trap (sulfate column I), separated using a nonpolar chromatographic column (e.g., OV 101), and separated and detected according to their boiling points.

9. Qualitative and Quantitative Calculation Formulas

9.1 Calculation by mass fraction: Determined by integrating peak areas. Chromatographic peaks are classified according to the presence of the groups described in Chapter 3. Table 2 and Table 3 give the relative response factors for some group components and oxygenates. After correction with the relative response factors, the mass fractions of all partial group components can be calculated and normalized to 100%. Partial group components are classified according to hydrocarbon group type and carbon number. For oxygenates contained in the sample that cannot be determined by this standard, different methods such as SH/T 0720 or SH/T 0663 shall be used for determination; they will not be integrated, and the total area shall not be normalized to 100%. Instead, the content of oxygenates measured by other methods is subtracted from 100%, and its value shall be recorded in the report.

Table 2 Relative response factors of some group components under FID FRR.PG (carbon number | alkanes (n- + iso-) | cycloalkanes | olefins (n- + iso-) | cycloolefins | aromatics):

• 3 | 0.916 | 0.916 | — | — | —
• 4 | 0.906 | 0.906 | — | — | —
• 5 | 0.899 | 0.874 | 0.899 | — | —
• 6 | 0.895 | 0.874 | 0.895 | 0.874 | 0.811
• 7 | 0.892 | 0.874 | 0.892 | 0.874 | 0.820
• 8 | 0.890 | 0.874 | 0.890 | 0.874 | 0.827
• 9 | 0.888 | 0.874 | 0.888 | 0.874 | 0.832
• 10 | 0.887 | 0.874 | 0.887 | 0.874 | 0.837
• 11+ | 0.887 | 0.874 | 0.887 | 0.874 | 0.840

Note: In Table 2, some values source-text extraction are suspected of being misaligned, requires confirmation against the source standard (source-text extraction).

The calculation of the relative response factor FRR.PG for each partial group component (the response of methane is set to 1 units) is obtained from formula (1): FRR.PG = [(Mc×nc)+(MH×nH)] × 0.7487 /(Mc×nc) ⋯(1) Where: Mc— carbon atomic weight, 12.011; nc— number of carbon atoms in the group; MH— hydrogen atomic weight, 1.008; nH— number of hydrogen atoms in the group; 0.7487— correction factor that sets the methane response value to 1 units.

The mass fraction expression wPG for each partial group component is calculated by formula (2): wPG = 100 × APG × FRR.PG / Σ(APG,i × FRR.PG,i) ⋯(2) Where: APG— sum of the areas of each partial group component.

Table 3 Relative response factors of oxygenates under FID (oxygenate | FRR.PG):

• Methyl tert-butyl ether | 1.33
• Diisopropyl ether | 1.32
• Ethyl tert-butyl ether | 1.31
• tert-Amyl methyl ether | 1.24
• Methanol | 3.80
• Ethanol | 1.91
• n-Propanol | 1.87
• Isopropanol | 1.39
• n-Butanol | 1.39
• Isobutanol | 1.23
• sec-Butanol | 1.40
• tert-Butanol | not provided in the available source (no corresponding value is given in the source-text extraction table)
• 2-methyl-2-butanol | not provided in the available source (no corresponding value is given in the source-text extraction table) Note: The relative response factors of oxygenates have been determined experimentally.

9.2 Calculated by volume fraction: Using the density and mass fraction of the partial group components i, the volume fraction expressed as φPG can be converted, calculated by formula (3): φPG = 100 × wPG / ρPG / Σ (wPG,i / ρPG,i) ⋯ (3) Where: wPG— mass fraction of the partial group components, expressed as %; ρPG— density of the partial group components, in kilograms per cubic meter (kg/m³).

Table 4 Density of partial group components under 15°C (in kg/m³) (carbon number | alkanes (n-paraffins + isoparaffins) | naphthenes | olefins (n-olefins + isoolefins) | cycloolefins | aromatics):

• 3 | 506.5 | — | 502.4 | — | —
• 4 | 577.9 | — | 613.7 | — | —
• 5 | 626.9 | 750.3 | 656.5 | — | —
• 6 | 662.2 | 760.6 | 685.9 | — | 884.3
• 7 | 688.8 | 762.1 | 704.0 | 773.3 | 871.6
• 8 | 708.4 | 780.5 | 719.3 | 785.3 | 871.9
• 9 | 728.1 | 792.5 | 738.2 | 790.5 | 878.0
• 10 | 734.0 | 812.8 | 748.6 | 805.2 | 892.8
• 11+ | 759.0 | — | — | 812.5 | 894.4 Note: For isomeric mixtures, their density is calculated by weighting according to their proportion in motor gasoline. In Table 4, some numerical values source-text extraction arrangement has suspected misalignment, requires confirmation against the source standard (source-text extraction).

Table 5 Density of oxygenates under 15°C (in kg/m³) (oxygenate | ρPG):

• Methyl tert-butyl ether | 745.3
• Diisopropyl ether | 729.2
• Ethyl tert-butyl ether | 745.6
• tert-Amyl methyl ether | 775.2
• Methanol | 795.8
• Ethanol | 794.8
• n-Propanol | 813.3
• Isopropanol | 789.5
• n-Butanol | 813.3
• Isobutanol | 810.6
• sec-Butanol | 805.8
• tert-Butanol | 791.0
• 2-methyl-2-butanol | 813.5

9.3 Calculation of total oxygen content by mass fraction: Based on all known oxygenates i, the total oxygen content expressed as mass fraction wO is calculated by formula (4): wO = Σ (nO × MO / Mi × wi) ⋯ (4) Where: nO— number of oxygen atoms in the molecule (usually 1); MO— atomic weight of oxygen; Mi— molecular weight of the oxygenate; wi— mass fraction of component i in the sample, %. Example: Using MTBE (C5H12O) as the only oxygenate, using atomic weights C:12.011, H:1.008, O:16.000: wO = [1×16.000 / (5×12.011+12×1.008+1×16.000)] × wi = 0.1815 × wi Note: In the original example, the molecular formula source-text extraction appears as "C. H 2 O" and the denominator "6×12.011+39:008+1×16.000", there is source-text extraction noise, requires confirmation against the source standard (source-text extraction).

9.4 Report data according to gasoline specifications: To make the report consistent with current gasoline specifications, the results need to be rounded or summed:

• The determination of total saturated hydrocarbons is obtained by summing the volume fractions of alkanes, naphthenes, and high-boiling polycyclic naphthenes;
• The determination of total olefin content is obtained by summing the volume fractions of olefins and cycloolefins;
• The reporting of total aromatic content remains unchanged;
• Benzene content is reported as volume fraction;
• Oxygenate content is reported as volume fraction;
• Total oxygen content is calculated according to 9.3 and reported as mass fraction.

10 Expression of results: The results are reported as volume fraction or mass fraction according to the following requirements (see 9.4):

• Saturated hydrocarbon content is accurate to 0.1%;
• Aromatic content is accurate to 0.1%;
• Olefin content is accurate to 0.1%;
• Benzene content is accurate to 0.01%;
• Oxygenate content is accurate to 0.01%;
• Total oxygen content is accurate to 0.01%.

10. Precision

11.1 Overview: According to ISO 4259, precision is given by statistically analyzing test results from multiple laboratories. Table 6 lists the precision values calculated by the formula. The results are rounded to appropriate decimal places, which should be the same as specified in Chapter 10.

11.2 Repeatability (95% confidence level): For the same operator, using the same instrument, under the same test conditions, correctly following the standard operation, the difference between two test results on the same sample shall not exceed the repeatability value in Table 6 (r).

11.3 Reproducibility (95% confidence level): For two single and independent test results obtained by different operators in different laboratories, correctly following the standard operation, on the same sample, the difference shall not exceed the reproducibility value in Table 6 (R).

Note 1: The reproducibility data for isopropanol is higher than that for other components, especially when double peaks appear, the two peaks need to be properly identified (see Note in 4.2), formulated with reference to the EN/TR 15745 interlaboratory test study report. Note 2: The reproducibility data for methanol is much higher than the expected reproducibility data. Since methanol is an active component, care is needed during sampling and ensure it is introduced into the precolumn in a suitable manner, formulated with reference to the EN/TR 15745 interlaboratory test study report.

Table 6 Repeatability and reproducibility (volume fraction, %):

Note: X is the average of two results. In Table 6, some numerical values source-text extraction arrangement has suspected misalignment, requires confirmation against the source standard (source-text extraction).

11. Report

12 Report: The test report shall at least include the following information:

• Reference to this standard;
• Type and complete identification of the sample;
• Sampling method of the sample (see Chapter 7);
• Test results (see Chapter 10);
• If applicable, content of components determined quantitatively by other methods (see 9.1);
• Any differences from the procedure specified in this standard determined by agreement or other means;
• Date of testing.

12. Normative References

2 Normative references:

• GB/T 4756 Petroleum liquids—Manual sampling (GB/T 4756—1998, eqv ISO 3170:1988)
• SY/T 5317 Petroleum liquids—Automatic pipeline sampling (SY/T 5317—2006, ISO 3171:1988, IDT)

References:

• [1] SH/T 0663 Determination of certain alcohols and ethers in gasoline (gas chromatography)
• [2] SH/T 0720 Determination of oxygenates in gasoline (gas chromatography and oxygen-selective flame ionization detector method)
• [3] ISO 4259 Determination and application of precision data in relation to methods of test for petroleum products
• [4] EN/TR 15745 Liquid petroleum products—Determination of hydrocarbon types and oxygenates (multidimensional gas chromatography) interlaboratory test study report

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A