GB/T 32693-2016 Determination of aniline compounds in gasoline by gas chromatography-mass spectrometry

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Card type: Test method

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

• Standard number: GB/T 32693—2016
• Chinese name: Determination of aniline compounds in gasoline by gas chromatography-mass spectrometry
• English name: Determination of the aniline compounds in gasoline—By gas chromatography-mass spectrometry
• Replacement relationship: not provided in the available source (the foreword only states that it was drafted in accordance with GB/T 1.1—2009, and does not mention any replaced standard)
• Publication/implementation: published on 2016-06-14, implemented on 2017-01-01
• Custodian: Subcommittee on Petroleum Fuels and Lubricants of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC280/SC1)
• Drafting organizations: Shenzhen Institute of Metrology and Quality Inspection, Petrochemical Research Institute of PetroChina Company Limited, CNOOC Refining and Chemical Co., Ltd.

2. Scope of application and non-applicability

• Applicable to the determination of aniline substances in gasoline.
• Aniline compounds include: aniline, o-methylaniline, m-methylaniline, p-methylaniline, N--methylaniline, N,N--dimethylaniline (6 types in total).
• Determination range for each aniline compound: 10 mg/L～1000 mg/L; samples outside this range may also be determined by this method, but the precision has not been investigated.
• Interference note: alcohols, ethers, acetone, ethyl acetate, sec-butyl acetate and dimethyl carbonate in gasoline do not interfere with the determination of aniline compounds by this method.
• Non-applicability: no explicit non-applicability clause is provided in the available source.

3. Method principle

A certain concentration of hydrochloric acid solution is reacted with aniline compounds in gasoline to form amine salts soluble in the acidic aqueous solution, and n-pentane is used to remove residual oily substances in the acidic aqueous solution after the reaction. Sodium hydroxide solution is added to neutralize the acidic aqueous solution to weakly alkaline, so that the aniline compounds in the acidic aqueous solution are liberated, and then dichloromethane is used to extract the aniline compounds from the neutralized aqueous solution; dilute to volume and mix well. Determination is carried out using a gas chromatograph-mass spectrometer, with quantification by the external standard method.

4. Reagents and materials (purity / preparation)

Unless otherwise specified, only reagents confirmed to be not lower than analytical grade are used in the analysis.

• 6.1 Water: grade two water conforming to GB/T 6682—2008, or higher requirements.
• 6.2 Hydrochloric acid: ρ=1.19 g/mL, 37% (mass fraction).
• 6.3 Dichloromethane. (Warning: volatile and toxic compound; if ingested, inhaled or absorbed through the skin, it will cause harm or death to the human body)
• 6.4 n-Pentane.
• 6.5 n-Heptane.
• 6.6 Sodium hydroxide.
• 6.7 1.2 mol/L hydrochloric acid solution: take hydrochloric acid (6.2) 100 mL and dissolve it in 500 mL water, mix, and dilute to volume to 1 L.
• 6.8 1 mol/L sodium hydroxide solution: weigh 40.27 g sodium hydroxide (6.6) and dissolve it in 1.0 L water, dissolve and mix well, prepare immediately before use.
• 6.9 Aniline compound standards: aniline (CAS No. 62-53-3), o-methylaniline (CAS No. 95-53-4), m-methylaniline (CAS No. 108-44-1), p-methylaniline (CAS No. 106-49-0), N--methylaniline (CAS No. 100-61-8), N,N--dimethylaniline (CAS No. 121-69-7), all requiring a purity of mass fraction above 98.5%.
• 6.10 Mixed aniline compound standard stock solution: accurately weigh appropriate amounts of each aniline compound standard (6.9), and use dichloromethane (6.3) or another high-boiling solvent capable of dissolving aniline compounds (for example: toluene) to prepare a mixed standard stock solution with concentrations of aniline, o-methylaniline, m-methylaniline, p-methylaniline, N--methylaniline, N,N--dimethylaniline of 1000 mg/L. Note: the standard stock solution should preferably be stored protected from light and sealed in a refrigerator at 0 ℃～4 ℃, with a validity period of 3 months.
• 6.11 Aniline compound standard working solutions: pipette an appropriate amount of the mixed aniline compound standard stock solution (6.10), and use dichloromethane (6.3) or another high-boiling solvent capable of dissolving aniline compounds (for example: toluene) to prepare a series of standard working solutions. The concentrations of the low-content series standard working solutions are respectively 10.0 mg/L, 25.0 mg/L, 50.0 mg/L, 100 mg/L, 150 mg/L and 200 mg/L; the concentrations of the high-content series standard working solutions are respectively 200 mg/L, 400 mg/L, 600 mg/L, 750 mg/L, 800 mg/L and 1000 mg/L. The standard working solutions shall contain at least six concentration levels and cover the concentration range of the test sample.
• 6.12 Precision pH test paper (6.0～8.0).
• 6.13 Helium: carrier gas purity ≥99.999%. (Warning: high-pressure gas, pay attention to safety)
• 6.14 Quality control (QC) samples: used to monitor the reliability of the method; through analysis of quality control samples, verify whether the precision of the results is within the range of the method. For quality control samples, a stable sample representative of the characteristics of the sample to be tested may be selected as the QC sample, and the QC sample shall be checked for the effectiveness of the test process according to the method described in Chapter 12. The QC sample shall be sealed and packaged in a brown glass bottle, stored at low temperature, and remain unchanged during storage.

5. Instruments and equipment

Install and use the instruments according to the manufacturer's instructions; all instrument parts that come into contact with the experimental sample shall be made of materials inert to the sample and not themselves undergoing chemical reaction (for example, glass).

• 7.1 Gas chromatograph-mass spectrometer (GC-MS): the instrument shall at least include a vaporization chamber, a temperature-controlled column oven, a mass spectrometric detector equipped with an electron impact ionization source (EI source) and a chromatography workstation; either a microsyringe or an autosampler can inject samples well.
• 7.2 Analytical balance: accurate to 0.0001 g.
• 7.3 Separatory funnels: 250 mL, several.
• 7.4 Brown volumetric flasks: capacity 100 mL, class A.
• 7.5 Brown chromatographic vials: 2.0 mL.
• 7.6 Single-mark pipettes: capacity 100 mL, class GB/T 12808 A.

6. Recommended operating conditions

10.1 Gas chromatography reference conditions

• Column: highly cross-linked polymeric polar capillary chromatographic column; other types of columns may also be used for this standard if verified to achieve good separation.
• Column temperature: initial temperature 80 ℃, hold for 4 min, then raise to 150 ℃ at 20 ℃/min, hold for 14 min, then raise to 230 ℃ at 30 ℃/min, hold for 2 min.
• Inlet temperature: 250 ℃.
• Transfer line temperature: 250 ℃.
• Ion source temperature: 230 ℃.
• Carrier gas: helium, purity ≥99.999%; flow rate 1.2 mL/min.
• Injection volume: 1.0 μL.
• Split ratio: 10∶1.

10.2 Mass spectrometry reference conditions

• Ionization mode: EI.
• Mass scanning mode: use full scan or simultaneous selected ion scan. Full scan mass range: 40 u～200 u; the scanned ions for selected ion scan are the qualitative ions in Table 1.
• Ionization energy: 70 eV.
• Solvent delay: an appropriate solvent delay time may be determined according to the test conditions, such as 11.0 min.

7. Sampling and sample preparation

8 Sampling

• 8.1 Sampling shall be carried out in accordance with GB/T 4756 or another equivalent method.
• 8.2 From the time the laboratory receives the sample, before completing any subsampling, the original container shall be cooled to 0 ℃～5 ℃ and stored.
• 8.3 If necessary, transfer the cooled sample to a pressure-sealed container and store at 0 ℃～5 ℃ until analysis is required.

9 Sample preparation

• 9.1 Use a single-mark pipette (7.6) to accurately measure 100 mL of the gasoline test sample into a 250 mL separatory funnel, add 10 mL hydrochloric acid solution (6.7), shake thoroughly (frequency 60 times/min; laboratories with the conditions may carry out this in a shaking extractor, with a shaking frequency not lower than 60 times/min), and extract for 20 min. Allow to stand for 5 min until layers separate, then transfer the lower acidic liquid to another 250 mL separatory funnel; for the remaining sample, add 10 mL hydrochloric acid solution (6.7) and repeat the extraction once, combining the acidic extracts; then extract the remaining sample three times with 10 mL water (about 2 min each time), combine the aqueous phases into the funnel containing the acidic extract, and discard the oil phase.
• 9.2 Take about 25 mL n-pentane (6.4) or n-heptane (6.5), add it to the acidic extract, extract for 2 min, allow to stand for layer separation, and discard the n-pentane layer; repeat extraction once with n-pentane (6.4) or n-heptane (6.5) to remove substances dissolved in n-pentane from the acidic liquid, and place the acidic liquid after extraction with n-pentane (6.4) or n-heptane (6.5) into a beaker.
• 9.3 In a beaker, add about 24.5 mL sodium hydroxide solution (6.8) to neutralize the extract to weakly alkaline [the pH value is about 8.0, measured with precision pH test paper (6.12)]. Transfer the neutralized extraction solution to a separatory funnel, and repeatedly extract twice with dichloromethane (6.3) 25 mL, each extraction time about 5 min. Combine the dichloromethane solutions from the two extractions, then wash the extracted dichloromethane solution once with 10 mL distilled water, extraction time about 2 min. After layering, combine the washed dichloromethane extraction solutions and transfer to a 100 mL brown volumetric flask (7.4), dilute to volume with dichloromethane (6.3), mix well, for GC-MS (7.1) determination.
• Note 1: If the concentration of aniline compounds in the sample exceeds the range of the standard working solution (6.11) curve, the sample may be appropriately diluted with an appropriate amount of isooctane/xylene (volume ratio 5:1) before sampling for testing.
• Note 2: The extraction process should be operated in a standardized manner, vented in a timely manner, and care should be taken that the vent of the separatory funnel is not pointed at people, to avoid danger during operation.
• Note 3: During the precision investigation of this standard, the pretreatment degreasing solvent was n-pentane.

8. Analysis Steps

• For instrument preparation, see Chapter 10 (gas chromatography reference conditions, mass spectrometry reference conditions).
• Qualitative analysis: Under the same instrument analysis conditions, determine the standard solution and sample solution, and perform qualitative analysis based on the characteristic ion pairs of aniline compounds and the retention times of the chromatographic peaks (qualitative and quantitative ions are shown in Table 1, retention times refer to Appendix A). If the retention time of a chromatographic peak detected in the sample solution overlaps with that of the standard solution chromatographic peak, and after background subtraction, all selected ions appear in the sample mass spectrum, and the deviation between the relative abundance ratio of the selected monitored ion pairs and the relative abundance ratio of the standard ion pairs is within the specified allowable range (see Table 2), then the presence of the corresponding analyte in the sample can be determined. For the total ion chromatogram, see Figure A.1 in Appendix A; for the mass spectra of each aniline compound, see Figures A.2 to A.7 in Appendix A.
• Quantitative analysis: Inject the working solution and sample solution separately into the instrument for determination. Inject the standard working solutions sequentially from low to high concentration, record the quantitative selected ion integrated peak areas, plot with the concentration of the standard working solution as the abscissa and the peak area as the ordinate to obtain the standard curve regression equation, with a linear correlation coefficient of γ≥0.999. Substitute the peak areas of the aniline compounds in the sample solution into the standard curve to calculate the concentrations of the various aniline compounds.
• Quality control (Chapter 12): By analyzing QC samples to ensure the instrument status is normal or the detection process is error-free, the standard curve may be verified once after every 5 samples run per batch, or QC samples may be analyzed. The difference between the measurement result and the reference value of the QC sample should be less than the reproducibility requirement; otherwise, the source of error should be determined, and necessary checks should be made on the method operation and instrument status. If the laboratory has already established QC or quality assurance (QA) protocols, they may be used when confirming the reliability of test results.

9. Qualitative and Quantitative Determination and Calculation Formulas

Table 1 Qualitative and Quantitative Ions of Aniline Compounds

Table 2 Maximum Allowable Deviation of Relative Ion Abundance for Qualitative Confirmation

13 Result Calculation

• 13.1 Calculate the concentrations of the various aniline compounds from the standard curve ci (mg/L), and substitute into formula (1) to obtain the concentration of aniline compounds in the test sample c (mg/L): c = ci × K ……………………(1) Where: c—— concentration of the various aniline compounds in the test sample, mg/L; ci—— concentration of the various aniline compounds read from the standard curve, mg/L; K—— dilution factor of the test sample; usually K=1 (see 9.1), if the test sample has been diluted (see Chapter 9 Note 1), then K is the volume dilution factor.
• 13.2 If the concentration result is expressed in units of mass fraction, convert according to formula (2): w = c / (10 × ρ) ……………………(2) Where: w—— mass fraction of the various aniline compounds in the test sample, %; c—— concentration of the various aniline compounds in the test sample, mg/L; ρ—— density of the test sample measured according to GB/T 1884 and GB/T 1885, kg/m³.
• 13.3 Report the concentration of aniline compounds c (mg/L), with the result accurate to 1 mg/L; report the mass fraction of aniline compounds w (%), with the result accurate to 0.0001%.

10. Precision

• 14.1 Overview: According to the GB/T 6683 statistical method, the precision of this standard is given based on test results from 5 collaborative laboratories, using 10 different gasoline samples, with aniline compound concentrations in the range of 10 mg/L～1000 mg/L; Table 3 lists the precision values calculated by the formula.
• 14.2 Repeatability (95% confidence level): For the same operator, using the same instrument, under the same test conditions, correctly operating according to the standard, the difference between two determination results for the same test sample shall not exceed the repeatability value in Table 3 (r).
• 14.3 Reproducibility (95% confidence level): For different operators, using different instruments, in different laboratories, correctly operating according to the standard, the difference between two single and independent determination results obtained for the same test sample shall not exceed the reproducibility value in Table 3 (R).

Table 3 Repeatability and Reproducibility

Note: X is the arithmetic mean of two results (mg/L). (Note: In the original text of source-text extraction, exponents are presented in line-break form, such as “0.363X” “0.713”; here they are organized in power form; the exponent symbols and values require confirmation against the source standard (source-text extraction).)

11. Report

The test report shall at least give the following contents:

• a) Description of the test sample;
• b) Standard used;
• c) Test results (13.3);
• d) Differences from the specified analysis steps;
• e) Abnormal phenomena observed during the test;
• f) Test date.

12. Normative References

• GB/T 1884 Standard Test Method for Density of Crude Oil and Liquid Petroleum Products by Laboratory Determination (Hydrometer Method)
• GB/T 1885 Petroleum Measurement Tables
• GB/T 4756 Standard Practice for Manual Sampling of Petroleum Liquids
• GB/T 6682—2008 Specifications and Test Methods for Water Used in Analytical Laboratories
• GB/T 6683 Standard Practice for Determining Precision Data for Test Methods of Petroleum Products
• GB/T 12808 Laboratory Glassware — Single-Volume Pipettes
• Appendix A (Informative Appendix) Total Ion Chromatogram and Mass Spectra of Aniline Compounds

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 Reference Q&A