GB/T 25963-2022 Determination of aromatic hydrocarbon content in middle distillates containing fatty acid methyl esters — High performance liquid chromatography with differential refractive index detector

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

• Standard number: GB/T 25963—2022
• Chinese full title: Determination of aromatic hydrocarbon content in middle distillates containing fatty acid methyl esters — High performance liquid chromatography with differential refractive index detector
• English title: Determination of aromatic hydrocarbon types in middle distillates containing fatty acid methyl esters—High performance liquid chromatography method with refractive index detection
• Replacement relationship: replaces GB/T 25963—2010 (this is the first revision; first published in 2010)
• Publication/implementation: published on 2022-10-12, implemented on 2022-10-12
• Responsible committee: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280)
• Drafting organizations: Luoyang Technology R&D Center of Sinopec Engineering (Group) Co., Ltd., Research Institute of Petroleum Processing, China Petroleum & Chemical Corporation, Luoyang Branch of China Petroleum & Chemical Corporation, Sinopec (Luoyang) Technology Co., Ltd.
• Main drafters: Wang Qian, Jia Ran, Song Chunxia, Bai Zhengwei, Li Yi, Li Xiang, Cui Lingyan, Liu Zelong, Wang Juan
• Main technical changes compared with 2010 edition (the original lists a~o): in a) scope, the original determination procedure is defined as procedure A, and high-wax diesel procedure B is added; in b) FAME the limit is changed from “volume fraction less than 5%” to “volume fraction not greater than 30%”; in c) the method summary is changed and a backflush description is added; in d) a “Interferences” chapter is added; in e) inertness requirements and recommendations for the liquid chromatograph with respect to FAME are added; in f) recommended sample filter material is added; in g) column system requirements are changed; in h) volumetric flask requirements are changed; in i) sample storage conditions and method requirements before and after testing are added; in j) the test procedure is changed to procedure A, procedure B and common parts; in k) a typical high-wax diesel sample chromatogram is added (Figure 5); in l) the general description of the precision chapter is changed; in m) precision for procedure B is added (Table 3); in n) backflush content is added (Appendix A); in o) a practical guide for high-wax diesel determination is added (Appendix B)

2. Scope of application and non-applicability

• This document describes a test method for determining aromatic hydrocarbon content in middle distillates by high performance liquid chromatography with a differential refractive index detector.
• It is applicable to determining the content of monocyclic aromatic hydrocarbons, dicyclic aromatic hydrocarbons and tricyclic and higher aromatic hydrocarbons in diesel with a fatty acid methyl ester (FAME) volume fraction not greater than 30%, high-wax diesel with a FAME volume fraction not greater than 7%, and petroleum fractions with a distillation range of 150 °C~400 °C.
• The polycyclic aromatic hydrocarbon content is obtained by summing the dicyclic aromatic hydrocarbon and tricyclic and higher aromatic hydrocarbon contents; the total aromatic hydrocarbon content is obtained by summing the monocyclic aromatic hydrocarbon, dicyclic aromatic hydrocarbon and tricyclic and higher aromatic hydrocarbon contents.
• Procedure A: applicable to diesel containing FAME volume fraction not greater than 30% and petroleum fractions with a distillation range of 150 °C~400 °C; monocyclic aromatic hydrocarbon content (mass fraction) 6%~30%, dicyclic aromatic hydrocarbons 1%~10%, tricyclic and higher aromatic hydrocarbons 0%~2%, polycyclic aromatic hydrocarbons 1%~12%, total aromatic hydrocarbons 7%~42%.
• Procedure B: applicable to high-wax diesel with FAME volume fraction not greater than 7%; total aromatic hydrocarbon content (mass fraction) 0.2%~2%.
• Not applicable: no explicit “not applicable” clause is provided in the available source.
• Note (original note): aromatic hydrocarbon types are defined by comparison with model compounds according to elution behavior on a specific liquid chromatography column; a single aromatic compound is used as an external standard for each of monocyclic/dicyclic/tricyclic and higher aromatic hydrocarbons, which may represent (or may not represent) the aromatic hydrocarbons present in the sample; other methods may define and quantify each aromatic hydrocarbon type differently from this method (for example: tetralin has a higher refractive index than o-xylene, and n-hexylbenzene has a lower refractive index than o-xylene, which may cause the quantitative results for monocyclic aromatic hydrocarbons to be inconsistent with the actual situation).

3. Method principle

• For diesel and petroleum fractions, select procedure A; for high-wax diesel, select procedure B.
• Procedure A: after a known amount of sample is diluted with n-heptane, a certain amount of the sample solution is injected into a high performance liquid chromatography system equipped with a polar column.
• Procedure B: a certain amount of sample is injected into a high performance liquid chromatography system equipped with a polar column.
• The polar column has almost no affinity for non-aromatic hydrocarbons but has good selectivity for aromatic hydrocarbons; aromatic hydrocarbons and non-aromatic hydrocarbons are separated, and according to ring structure are separated into monocyclic aromatic hydrocarbon, dicyclic aromatic hydrocarbon and tricyclic and higher aromatic hydrocarbon bands.
• Subsequent steps of procedure A and procedure B: the chromatographic column is connected to a differential refractive index detector, and the components are detected after elution; the detector electrical signal is continuously monitored by a data processor; the signal magnitude produced by the aromatic hydrocarbons in the sample solution is compared with the signal of a pre-measured standard solution to calculate the monocyclic aromatic hydrocarbon, dicyclic aromatic hydrocarbon and tricyclic and higher aromatic hydrocarbon contents; polycyclic aromatic hydrocarbons are obtained by summing dicyclic + tricyclic and higher, and total aromatic hydrocarbons are obtained by summing monocyclic + dicyclic + tricyclic and higher.
• Backflush: after all aromatic hydrocarbons have flowed out of the chromatographic column, backflushing may be performed to backflush residual compounds in the chromatographic column (such as fatty acid methyl esters) out as a backflush peak; this can better clean the chromatographic column but may reduce column life. Note: backflushing is part of internal laboratory maintenance.

4. Reagents and materials (purity / preparation)

Warning (original): aromatic compounds are highly volatile and flammable, and their vapors can form explosive mixtures with air; inhalation or skin contact may cause acute or chronic harm; may cause water pollution.

• 6.1 Cyclohexane: mass fraction not less than 99%. Note: may contain benzene impurity.
• 6.2 n-Heptane: high performance liquid chromatography (HPLC) grade, used as the liquid chromatography mobile phase. Note 1: batch-to-batch changes in water content, viscosity, refractive index and purity of the mobile phase may lead to unpredictable column behavior; dehydrating the mobile phase (for example, through activated 5A molecular sieves) and filtering help reduce the effects of trace impurities. Note 2: poor degassing may cause negative peaks; helium purging, vacuum degassing or ultrasonic agitation degassing may be used.
• 6.3 Dodecylbenzene: mass fraction not less than 98%.
• 6.4 o-Xylene: mass fraction not less than 98%.
• 6.5 Hexamethylbenzene: mass fraction not less than 98%.
• 6.6 Naphthalene: mass fraction not less than 98%.
• 6.7 Fluorene: mass fraction not less than 98%.
• 6.8 Phenanthrene: mass fraction not less than 98%.
• 6.9 Dibenzothiophene: mass fraction not less than 95%.
• 6.10 9-Methylanthracene: mass fraction not less than 95%.
• 6.11 Anthracene (the extracted chemical name is garbled, requires confirmation against the source standard (source-text extraction)): mass fraction not less than 95%.
• 6.12 Fatty acid methyl esters: meet the requirements of GB 25199.
• 6.13 Quality control sample: a stable, representative sample.
• System performance verification solution SCS1 preparation (9.4): weigh 1.0 g±0.1 g cyclohexane, 0.1 g±0.01 g dodecylbenzene, 0.5 g±0.05 g o-xylene, 0.1 g±0.01 g hexamethylbenzene, 0.1 g±0.01 g naphthalene, 0.05 g±0.005 g dibenzothiophene, 0.05 g±0.005 g 9-methylanthracene, to the nearest 0.000 1 g, place in a 100 mL volumetric flask, use ultrasound to dissolve all components in cyclohexane and o-xylene, and dilute to the mark with n-heptane. Note: if the volumetric flask is well sealed and stored under cold and dark conditions (such as in a refrigerator), SCS1 may be used for one year.
• System performance verification solution SCS2 preparation (9.5): weigh 0.4 g±0.1 g fatty acid methyl esters, 0.04 g±0.01 g anthracene (the extracted chemical name is garbled, requires confirmation against the source standard (source-text extraction)), to the nearest 0.000 1 g, place in a 100 mL volumetric flask, add an appropriate amount of n-heptane, use ultrasound at 35 °C to dissolve all components, ensure complete dissolution with no residue, then add n-heptane to the mark. Note 1: placing in an ultrasonic bath for 25 min can ensure complete dissolution. Note 2: if the volumetric flask is well sealed and stored under cold and dark conditions (such as in a refrigerator), SCS2 may be used for one year.
• Standard solutions A, B, C, D preparation (10.1): prepare according to the concentrations in Table 1, weigh the standard substances to the nearest 0.000 1 g, place in a 100 mL volumetric flask, and dilute to the mark with n-heptane. Note: if the volumetric flask is well sealed and stored under cold and dark conditions (such as in a refrigerator), the standard solutions may be used for six months.
• Table 1 Concentrations of standard solutions (unit: grams per hundred milliliters):

(Note: the phenanthrene D value in Table 1 is originally “0.91”, suspected to be source-text extraction noise, requires confirmation against the source standard (source-text extraction).)

5. Instruments and equipment

• 7.1 Liquid chromatograph: any high-performance liquid chromatograph that can make the mobile phase enter the system at a flow rate of 0.5 mL/min~1.5 mL/min, with precision better than 0.5% under the conditions specified in Chapter 9, and fluctuation less than 1% of full scale, may be used. Equipment used to treat or determine samples should be insensitive to fatty acid methyl esters; recommended materials: polytetrafluoroethylene, fluororubber, and polyamide.
• 7.2 Injection system: any injection system capable of injecting 10 µL of sample solution with repeatability better than 1% may be used. Note 1: Manual and automatic injection systems that meet the repeatability requirement (partially filled injection loop or completely filled injection loop) may both be used; with the partial-fill injection mode, good results can be obtained when the injection volume is less than half the loop volume; with the complete-fill injection mode, good results can be obtained only after filling the injection loop with the sample to be tested at least 6 times. Note 2: The repeatability of the injection system can be determined by injecting at least 4 times SCS1 (see 9.4) and comparing the peak areas. Note 3: The injection volume may be other than 10 µL, for example 3 µL~20 µL, and may be used as long as the injection volume repeatability requirement, the differential refractive index detector sensitivity and linearity requirements (see 10.4), and the column resolution requirement (see 9.10) are met.
• 7.3 Sample filter: if necessary (see 11.1 and 11.2), it is recommended to use a microfilter with a pore size not greater than 0.45 µm to remove particles from the sample solution, and it is required to be inert to hydrocarbon solvents. Note: Polytetrafluoroethylene filters are suitable.
• 7.4 Column system: as long as the resolution requirements specified in 9.7, 9.8, 9.10, and 9.12 are met, any high-performance liquid chromatography stainless steel column packed with an amino-bonded (or polar amino/cyano-bonded) silica stationary phase, with a particle size of 3 µm, 5 µm, or 10 µm, may be used. Refer to Annex A to select a suitable column.
• 7.5 Temperature control system: the high-performance liquid chromatography column oven is required to be able to maintain a constant temperature within the range of 20 °C~40 °C (±1 °C); a heating block, air circulation, or other constant-temperature methods (such as a constant-temperature laboratory) may be used. Note: A differential refractive index detector is sensitive to both sudden and gradual changes in mobile phase temperature; take measures as appropriate to keep the system temperature constant; optimize according to the temperature dependence of the stationary phase.
• 7.6 Differential refractive index detector: any differential refractive index detector with a refractive index detection range within 1.3~1.6, a linear response within the measurement range, and the ability to output a suitable signal to the data system may be used. Note: If the differential refractive index detector has a separate temperature control device, set it to the same temperature as the column oven.
• 7.7 Computer or integrator: any data system that matches the differential refractive index detector, has a minimum acquisition rate of 1 Hz, and can measure peak areas and retention times may be used; it should be capable of basic post-processing functions such as baseline correction and reintegration.
• 7.8 Volumetric flask: capacities of 10 mL and 100 mL, with accuracy meeting the A class requirements specified in GB/T 12806—2011.
• 7.9 Analytical balance: readability 0.1 mg.
• Figure 1 Key to the liquid chromatography schematic: 1—— pump; 2—— injection system; 3—— column oven; 4—— chromatographic column; 5—— differential refractive index detector; 6—— data processing system.

6. Recommended operating conditions

• Mobile phase flow rate (9.3): adjust to 0.8 mL/min~1.2 mL/min and keep constant, ensuring that the reference cell of the differential refractive index detector is filled with mobile phase; if there is a temperature control device, ensure that the column temperature and the differential refractive index detector temperature are stable and consistent. Note: Keeping the reference cell filled with mobile phase minimizes baseline drift; two suitable methods: 1) before analysis, pass the mobile phase through the reference cell, then seal it to prevent volatilization; 2) continuously replenish the reference cell with mobile phase at a constant flow rate to compensate for solvent volatilization; optimize the replenishment flow rate in advance to minimize mismatch between the reference cell and the analytical cell; for some detectors, the replenishment flow rate can be set to one tenth of the analytical flow rate.
• Column temperature: 20 °C~40 °C constant temperature (±1 °C) (see 7.5).
• Injection volume: 10 µL (see 7.2, 9.6, 9.12, 10.2, 11.3.2); alternatively 3 µL~20 µL (see Note 3 to 7.2).
• Chromatographic column: amino-bonded (or polar amino/cyano-bonded) silica stationary phase, particle size 3 µm, 5 µm, or 10 µm (see 7.4); Annex A recommends a column length of 150 mm–300 mm and an inner diameter of 4 mm–5 mm; it is best to use a guard column (e.g., specifications 4.6 mm×30 mm, packed with amino-bonded silica) and replace it regularly.
• System performance verification (9.6): after the operating conditions are stable (after the baseline is level), inject 10 µL SCS1, record the chromatogram, and ensure that the baseline drift during the analysis period does not exceed 0.5% of the cyclohexane peak height. Note: Exceeding this value may indicate problems with the temperature control of the chromatographic column and the differential refractive index detector, and/or loss of polar material from the chromatographic column.
• Elution order (9.7): the SCS1 components elute in the following order: cyclohexane, dodecylbenzene, o-xylene, hexamethylbenzene, naphthalene, dibenzothiophene, 9- methylanthracene.
• Separation requirement (9.8): all SCS1 components achieve baseline separation (see Figure 2).
• Resolution requirement (9.10): the resolution between cyclohexane and o-xylene is between 5.7~10 (see 12.2).
• SCS2 Check (9.12): ensure that the SCS2 sample is uniform, inject 10 µL SCS2 standard solution so that anthracene (the extracted chemical name is garbled, requires confirmation against the source standard (source-text extraction)) elutes just before the first peak of the fatty acid methyl esters or together with it; ensure that the retention time of anthracene is longer than that of 9- methylanthracene. Note: When starting to use a new chromatographic column, when the activity of the chromatographic column decreases after a period of use, or when analyzing samples containing FAME, first use SCS2 to check the performance of the chromatographic column.
• Figure 2 Key to the chromatogram of the system performance verification solution (SCS1): 1—— cyclohexane; 2—— dodecylbenzene; 3—— o-xylene; 4—— hexamethylbenzene; 5—— naphthalene; 6—— dibenzothiophene; 7——9- methylanthracene.
• Figure 3 Key to the chromatogram of standard solution A: 1—— o-xylene; 2—— fluorene; 3—— phenanthrene.

7. Sampling and sample preparation

• Sampling (Chapter 8): the sample used for laboratory analysis shall be representative; unless otherwise specified in the product standard, the sample shall be obtained in accordance with GB/T 4756 or GB/T 27867 or an equivalent method. Before testing, the sample shall be allowed to stand until it reaches room temperature. If the sample has been exposed to above 25 °C for a long time during storage or custody, this shall be stated in the report.
• Procedure A Sample preparation (11.1): weigh 0.9 g~1.1 g (accurate to 0.001 g) of sample, place it in a 10 mL volumetric flask; add an appropriate amount of n-heptane, shake vigorously to mix the sample solution uniformly, then dilute to the mark with n-heptane, mix well, and let stand for 10 min; if necessary, filter to remove particulate matter from the sample solution (see 7.3). For some samples, the aromatic concentration exceeds the range of the working curve; prepare a more concentrated (e.g., 2 g/10 mL) or more dilute (e.g., 0.5 g/10 mL) sample as appropriate. Note: If a dilution factor different from the above is used, the retention time and the calculated content may change.
• Procedure B Sample preparation (11.2): using a 10 mL volumetric flask, weigh to obtain the mass of 10 mL high-wax diesel sample (accurate to 0.001 g), let stand for 10 min, and if necessary, filter to remove particulate matter from the sample solution (see 7.3).
• Instrument preparation (9.1): the instrument equipment and sample distribution system shall be ensured to be clean and dry before use.
• Instrument connection (9.2): connect the liquid chromatograph (see 7.1), column system (see 7.4), differential refractive index detector (see 7.6), and computer or integrator (see 7.7) according to the corresponding manual and Figure 1; if there is a column oven (see 7.5), the chromatographic column should be installed in the column oven; the injection valve should be at the same temperature as the sample solution, usually room temperature. Note: To keep the system stable, perform regular maintenance on the liquid chromatograph and its components; leaks or partial blockages in filters, filter plates, syringe needles, and injection valves can cause unstable mobile phase flow rate or poor injection volume repeatability of the injection system.

8. Analytical procedure

• 9.6 After the operating conditions are stable (after the baseline is level), inject 10 µL SCS1 into the chromatographic injection system (see 9.4), record the chromatogram, and ensure that the baseline drift during the analysis period does not exceed 0.5% of the cyclohexane peak height.
• 9.9 Measure the retention times of cyclohexane, dodecylbenzene, o-xylene, hexamethylbenzene, naphthalene, dibenzothiophene, and 9- methylanthracene.
• 9.11 Determine the cutting time by the method described in 12.3.
• 10.2 After the operating conditions are stable (see 9.6), inject 10 µL of standard solution A, record the chromatogram, and measure the peak area of each standard substance (see Figure 3).
• 10.3 Repeat step 10.2 with standard solutions B, C, and D; if the phenanthrene area in standard solution D is too small to be measured accurately, prepare a new standard solution D* containing a higher concentration of phenanthrene (e.g., 0.02 g/100 mL).
• 10.4 Plot the peak areas against the concentrations (g/100 mL) of the aromatic reference materials (o-xylene, fluorene, phenanthrene); the working curve should be a straight line, the correlation coefficient should be greater than 0.999, and the intercept should be less than ±0.01 g/100 mL. Note: A computer or data processing system may be used to construct the working curve.
• 11.3.1 It is recommended to measure a quality control sample or standard solution A at least once per batch; if the laboratory has established a quality control and quality assurance program, the reliability of the measurement results may be confirmed according to it; if not established, the measurement results may be evaluated according to NB/SH/T 0843.
• 11.3.2 When the operating conditions are stable (see 9.6) and are the same as those when the working curve was constructed (Chapter 10), inject the sample solution 10 µL into the chromatographic injection system (see 11.1 or 11.2), and acquire data (see Figure 4). Note: Figure 4 is a typical chromatogram of diesel; the chromatogram of high-wax diesel (see Figure 5) is fundamentally different from that of diesel.
• 11.3.3 Correctly distinguish monocyclic aromatics, dicyclic aromatics, and tricyclic+ aromatics: the retention time of monocyclic aromatics is between point t_b and point t_c (see 12.3); the retention time of dicyclic aromatics is between point t_c and point t_d (see 12.3); the retention time of tricyclic+ aromatics is between point t_d and point t_e (see 12.3).
• 11.3.4 When using step A and step B, after all aromatics have eluted from the chromatographic column, the column may be backflushed, eluting residual compounds such as fatty acid methyl esters as a backflush peak; although backflushing can better clean the column, it affects column life.
• 11.3.5 Draw a baseline from the beginning of the non-aromatic peak (A, t_a in Figure 4) to the point just after the end of the tricyclic+ aromatic peak (E, t_e in Figure 4); at E the signal returns to the baseline value (equal to the value at point A after compensating for baseline drift, see 9.6). If the sample solution does not contain dicyclic aromatics and/or tricyclic+ aromatics, point E should be moved forward to the point where the signal just returns to the baseline value (equal to the value at point A after compensating for baseline drift, see 9.6). Note: High-wax diesel generally contains no or only very small amounts of aromatic compounds, and its compound composition differs from that of petroleum-refined diesel; the liquid chromatograms of the two diesels are not the same; the recommended operating guide for high-wax diesel determination is given in Annex B.
• 11.3.6 Draw a perpendicular to the baseline from the valley between the non-aromatic peak and the monocyclic aromatic peak (B, t_b in Figure 4) (see 11.3.5); if there are many valleys, choose the one closest to t_b (see 12.3).
• 11.3.7 Draw a perpendicular to the baseline from the valley between the monocyclic aromatic peak and the dicyclic aromatic peak (C, t_c in Figure 4) (see 11.3.5); if there are many valleys, choose the one closest to t_c (see 12.3).
• 11.3.8 Draw a perpendicular to the baseline from the valley between the dicyclic aromatic peak and the tricyclic+ aromatic peak (D, t_d in Figure 4) (see 11.3.5); if there are many valleys, choose the one closest to t_d (see 12.3).
• 11.3.9 Integrate from point B to point C; this is monocyclic aromatics.
• 11.3.10 Integrate from point C to point D; this is dicyclic aromatics.
• 11.3.11 Integrate from point D to point E; this is tricyclic+ aromatics.
• 11.3.12 If chromatographic data processing is performed automatically, check whether peak identification and peak area integration are correct.
• Figure 4 Typical chromatogram of diesel sample with labeled reference numbers: 1—— monocyclic aromatics (MAH); 2—— dicyclic aromatics (DAH); 3—— tricyclic+ aromatics (T+AH); A—— beginning of the non-aromatic peak, t_a; B—— beginning of monocyclic aromatics, t_b; C—— valley between monocyclic and dicyclic aromatics, t_c; D—— valley between dicyclic and tricyclic+ aromatics, t_d; E—— end of integration area, t_e.
• Figure 5 Typical chromatogram of high-wax diesel sample (including integration and chromatographic peak identification) with labeled reference numbers: 1—— non-aromatics; 2—— monocyclic aromatics (MAH); 3—— dicyclic aromatics (DAH); 4—— tricyclic+ aromatics (T+AH).

9. Qualitative and Quantitative Calculation Formulas

• 12.1 Retention times of reference materials (measured from the chromatogram of SCS1, see 9.9): cyclohexane retention time t_1 (s); dodecylbenzene t_2 (s); o-xylene t_3 (s); hexamethylbenzene t_4 (s); naphthalene t_5 (s); dibenzothiophene t_6 (s); 9- methylanthracene t_7 (s).
• 12.2 Column resolution: the resolution R of cyclohexane and o-xylene is calculated by formula (1): R = 1.699(t_3 − t_1) / (Y_1 + Y_3) (the source source-text extraction shows "R=1.699 (21+33)", formula form requires confirmation (source-text extraction)) Where: t_1—— cyclohexane retention time (s); t_3—— o-xylene retention time (s); Y_1—— cyclohexane half-peak width (s); Y_3—— o-xylene half-peak width (s); 2—— reciprocal of the average peak width coefficient 1/2; 1.699—— coefficient of peak width/half-peak width.
• 12.3 Cut time:
  • t_a is the point on the baseline just before the non-aromatic peak;
  • t_b = 0.5(t_1 + t_2);
  • t_d = t_6 + 0.4(t_7 − t_5) (the source source-text extraction has "ta=t6+0.4 (t-ts)", requires confirmation (source-text extraction));
  • t_e is the point on the baseline after all tricyclic+ aromatic peaks.
  • Note: For samples containing fatty acid methyl esters, t_a is the point on the baseline before the first fatty acid methyl ester peak.
  • (The source does not give the calculation formula for t_c, requires confirmation (source-text extraction)/not provided in the available source)
• 12.4 Contents of various aromatic types: the contents (mass fractions) w of monocyclic aromatics, dicyclic aromatics, and tricyclic+ aromatics are obtained directly by the data system or calculated by formula (2): w = (A × S + I × V) / m (the source source-text extraction shows "EAXS) + IJXV", formula form requires confirmation (source-text extraction)) Where: A—— peak area of monocyclic aromatics or dicyclic aromatics or tricyclic+ aromatics; S—— slope of the corresponding working curve (g/100 mL versus peak area); I—— intercept of the corresponding working curve; V—— total volume of sample solution (mL) (see 11.1 or 11.2); m—— sample amount (g) (see 11.1 or 11.2).
• 12.5 The content of polycyclic aromatics is obtained by summing the content of dicyclic aromatics and the content of tricyclic+ aromatics (DAH + T+AH); the total aromatic content is obtained by summing the contents of monocyclic aromatics, dicyclic aromatics, and tricyclic+ aromatics (MAH + DAH + T+AH); the contents of all aromatic types are expressed as mass fractions.
• 13 Expression of results: report the contents of monocyclic aromatics, dicyclic aromatics, tricyclic+ aromatics, polycyclic aromatics, and total aromatics, all expressed as mass fractions, to the nearest 0.1%.

10. Precision

• 14.1 Overview: When determining the method precision in step A, the sample monocyclic aromatic content (mass fraction) is 6%~30%, dicyclic aromatics 1%~10%, tricyclic+ aromatics 0%~2%, polycyclic aromatics 1%~12%, total aromatics 7%~42%; when determining the method precision in step B, the sample total aromatic content (mass fraction) is 0.2%~2%. Judge the reliability of test results according to the following provisions (95% confidence level).
• 14.2 Repeatability (r): the difference between two repeat test results obtained by the same operator, in the same laboratory, using the same instrument, according to the same method, on the same sample, with correct operating procedures in continuous determinations, shall not exceed the values in Table 2 (step A) and Table 3 (step B).
• 14.3 Reproducibility (R): the difference between two single, independent test results obtained by different operators, in different laboratories, using different instruments, according to the same method, on the same sample, shall not exceed the values in Table 2 (step A) and Table 3 (step B).
• Table 2 Precision (step A):

(Note: In Table 2, the values for tricyclic + aromatics reproducibility and total aromatics repeatability/reproducibility are doubtful due to source-text extraction line misalignment, requires confirmation against the source standard (source-text extraction).)

• Table 2 Note 1: X_1 is the average of two repeat test results obtained; X_2 is the average of two single, independent test results obtained. Note 2: When determining method precision, the fatty acid methyl ester content (volume fraction) of the sample is 0%~30%.
• Table 3 Precision (Procedure B):

• Table 3 Note 1: X_1 is the average of two repeat test results obtained; X_2 is the average of two single, independent test results obtained. Note 2: When determining method precision, the fatty acid methyl ester content (volume fraction) of the sample is 0%~7%.

11. Report

• Chapter 15 The test report shall include at least the following:
  • Sample name;
  • Standard used (number of this document);
  • Test results (see Chapter 13);
  • Deviations from the specified procedure;
  • Test date.
• Chapter 8: If the sample is exposed to above 25 °C for a long time during storage or custody, it shall be stated in the report.

12. Normative references

• GB/T 4756 Petroleum liquids — Manual sampling
• GB/T 12806—2011 Laboratory glassware — One-mark volumetric flasks
• GB 25199 B5 Diesel fuel
• GB/T 27867 Petroleum liquids — Automatic pipeline sampling
• NB/SH/T 0843 Statistical techniques for the evaluation of analytical testing systems in the petrochemical industry
• Reference document (basis for drafting this document): GB/T 1.1—2020 "Guidelines for standardization work — Part 1: Structure and drafting rules for standardization documents"

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