GB/T 17474-1998 Determination of benzene in hydrocarbon solvents (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 name / replacement relationship

• Standard number: GB/T 17474—1998
• Chinese full title: Determination of benzene in hydrocarbon solvents (gas chromatography)
• English name: Standard test method for benzene in hydrocarbon solvents by gas chromatography
• Replacement relationship: not provided in the available source (the foreword only states equivalent adoption of ASTM D4367-94, and does not mention replacement of an old standard)
• Adoption relationship: equivalent adoption of ASTM D4367-94 "Determination of benzene in hydrocarbon solvents by gas chromatography"
• Main differences from ASTM D4367-94 (foreword):
  1. The referenced standards are changed to the corresponding national standards of our country; ASTM D4367-94 the cited ASTM D3606 is no longer referenced in this standard because the method principle is the same and the text does not mention specific referenced content.
  2. In addition to the chromatographic system and conditions provided by ASTM D4367-94, an alternative chromatographic system and conditions are added; for the non-polar pre-cut column, an optional support type is added; the polar analytical column uses a domestic stationary phase of the same type and lowers the stationary phase ratio to improve resolution; according to the performance of the domestic stationary phase, the column aging conditions and analytical conditions are slightly changed.
  3. A conversion formula is added for converting volume percentage to mass percentage using the densities of benzene and the sample when 20℃ is used.
• Publication/implementation: issued by 1998-08-20, implemented by 1999-01-01; issued by the State Bureau of Quality and Technical Supervision
• Proposal/administration: proposed by China Petrochemical Corporation; administration by the Petrochemical Research Institute of China Petrochemical Corporation
• Drafting organization: Petrochemical Research Institute of China Petrochemical Corporation; main drafters: Li Changxiu, Yang Haiying, Chen Yinai

2. Scope of application and non-applicability

• 1.1 is applicable to the determination of benzene content in hydrocarbon solvents by gas chromatography in the concentration range of 0.01% (V/V) to 1% (V/V).
• 1.2 involves certain hazardous materials, operations, and equipment, but it is not intended to address all safety issues related to them; users should establish appropriate safety and protective measures and determine applicable management systems before use.
• For information related to hazardous materials in 1.3, refer to the relevant hazardous materials data sheets; for special hazard descriptions, refer to Chapter 7.
• Non-applicable scope: not explicitly listed in the available source.

3. Method principle

• Chapter 3 Method summary: The test sample containing the internal standard substance butanone is injected into a dual-column system. The sample first passes through a packed column filled with the non-polar stationary phase methyl silicone, and the components are separated in order of boiling point. After octane is eluted, components with boiling points higher than octane are backflushed out. Components with boiling points lower than octane then enter a chromatographic column packed with the strongly polar stationary phase 1,2,3- tri-(2- cyanoethoxy) propane (TCEP), so that aromatic and non-aromatic hydrocarbons are separated. The eluted components are detected by a conventional detector and the chromatogram is recorded, and quantification is performed based on the peak areas of each component and the internal standard.
• Chapter 4 Significance and application: Benzene is considered a type of toxic and carcinogenic substance; understanding the benzene content in solvents is helpful for estimating the risk of harm to health that the solvent may pose to users, but the purpose of this standard is not to evaluate such risk.

4. Reagents and materials (purity / preparation)

• 6.1 Reagent purity: not lower than analytical grade. Other grades of reagents may also be used when it has been previously determined that the reagent has sufficient purity not to affect the accuracy of the determination.
• 6.2 Acetone
• 6.3 Chloroform
• 6.4 Red diatomaceous earth support: acid-washed, 80 to 100 mesh; white diatomaceous earth support: acid-washed, 60 to 80 mesh (adoption note 1]: white silanized support may also be used)
• 6.5 Hydrogen: purity not lower than 99.99%
• 6.6 Nitrogen: purity not lower than 99.99% (the extracted gas name is garbled; requires confirmation against the source standard (source-text extraction))
• 6.7 Helium: purity not lower than 99.99%
• 6.8 Methanol
• 6.9 Dichloromethane
• 6.10 Butanone: purity greater than 99.9% (m/m)
• 6.11 Methyl silicone
• 6.12 1,2,3- tri-(2- cyanoethoxy) propane (TCEP)
• 6.13 Calibration standard samples:
  • 6.13.1 Benzene: purity greater than 99% (m/m)
  • 6.13.2 Isooctane: purity greater than 99% (m/m)
  • 6.13.3 n-Nonane: purity greater than 99% (m/m)
• Preparation of standard solution (11.1): measure a certain volume of benzene according to Table 3, place it in a 100 mL volumetric flask, dilute to the mark with isooctane at room temperature, and mix uniformly.
• Table 3 Volume of benzene required for preparing standard solutions:

  Standard sample concentration %(V/V)	1	0.5	0.25	0.10	0.05	0.01	0.005
  Benzene, mL	1	0.5	0.25	0.10	0.05	0.01	0.005

• Calibration standard solution (11.2): accurately measure 0.5 mL butanone, place it in a 100 mL volumetric flask, dilute to the mark with the first standard solution in Table 3, and mix uniformly; repeat this process with each of the other standard solutions.
• Sample solution (12.1): accurately measure 0.5 mL butanone into a 100 mL volumetric flask, dilute to the mark with the sample, and mix uniformly.
• Preparation of column packing (9.1):
  • 9.1.1 Weigh 45 g white diatomaceous earth support (the source source-text extraction writes "458", requires confirmation against the source standard (source-text extraction)), place it in a 500 mL flask, dissolve 5 g methyl silicone in about 50 mL chloroform, pour into the flask, connect to a rotary evaporator and vacuum pump, turn on the infrared lamp until uniformly mixed and completely dry.
  • 9.1.2 Weigh 85 g (or 75 g) red diatomaceous earth support, place it in a 500 mL flask, dissolve 15 g (or 25 g) TCEP in 200 mL acetone, pour into the flask, connect to a rotary evaporator and vacuum pump, mix uniformly and completely dry at less than 100℃.

5. Instruments and equipment

• 5.1 Chromatograph: any gas chromatograph equipped with a backflush system and a flame ionization detector and capable of operating under the conditions in Table 1. The detection and recording system at maximum sensitivity must produce a response of 4 mm for a sample with a benzene content of 1 μL of 0.05% (V/V).
• 5.2 Chromatographic column: one stainless steel chromatographic column of length 0.8 m, outer diameter 3.2 mm, or length 1.0 m, outer diameter 3.0 mm, inner diameter 2.0 mm; one stainless steel chromatographic column of length 4.6 m, outer diameter 3.2 mm, or length 4.6 m, outer diameter 3.0 mm, inner diameter 2.0 mm.
• 5.3 Recorder: full scale 1 mV, response time not greater than 2 s, maximum noise level not greater than ±0.3% of full scale.
• 5.4 Microsyringe: 5 μL (the source source-text extraction writes "5 l", requires confirmation against the source standard (source-text extraction))
• 5.5 Pipettes: 1 mL and 2 mL, minimum scale 0.01 mL; 5 mL, 10 mL and 20 mL
• 5.6 Volumetric flask: 100 mL
• 5.7 Electronic oscillator
• 5.8 Vacuum pump
• 5.9 Vacuum rotary evaporator
• 5.10 Round-bottom flask: 500 mL, suitable for connection to a rotary evaporator
• 5.11 Infrared lamp

6. Recommended operating conditions

• Table 1 Instrument conditions suitable for the determination of low-concentration benzene content in hydrocarbon solvents (System 1 is equivalent to the conditions in ASTM D4367-94, and System 2 is an added optional system):

• Note 1): When a dual-gas-path flame ionization detector is used, a reference column shall be used.
• Column aging (10.1):
  • 10.1.1 According to the stationary phase TCEP maximum operating temperature limit, use aging conditions 1 or 2.
  • 10.1.2 Aging condition 1: Connect column A and column B as shown in Figure 1, connect the inlet of column A to the vaporization chamber, adjust the helium or nitrogen flow rate to approximately 40 mL/min, and age according to the timetable in Table 2.
  • 10.1.3 Aging condition 2: 10.1.3.1 Connect the inlet of column A to the vaporization chamber as shown in Figure 1, adjust the helium or nitrogen flow rate to approximately 40 mL/min, and age column A according to the timetable in Table 2; 10.1.3.2 Connect column A and column B as shown in Figure 1, adjust the helium or nitrogen flow rate to approximately 40 mL/min, and age column B according to the timetable in Table 2.
• Table 2 Column aging timetable:

(Note: Table 2 contains unrecognized characters in the source extraction; requires confirmation against the source standard (source-text extraction))

• 10.2 Connect the outlet of column B to the detector, set the operating conditions according to Table 1, first shut down the detection system, and check the system for gas tightness.
• 10.3 Adjustment of column flow rate:
  • 10.3.1 Use helium or hydrogen as carrier gas.
  • 10.3.2 Place the valve in the normal state (Figure 2(a)), adjust valve A to obtain the required flow rate (see Table 1). The column flow rate is measured from the detector outlet.
  • 10.3.3 Place the valve in the backflush state (Figure 2(b)), and measure the column flow rate through the detector outlet. If the column flow rate changes, adjust valve B so that the column flow rate differs from the required flow rate by no more than ±1 mL/min.
  • 10.3.4 Turn on the detection system, switch the valve repeatedly several times from the normal state to the backflush state, and observe the baseline at the same time. The baseline must not change significantly or drift before and after valve switching. If the baseline changes, gently adjust valve B to obtain a stable baseline (a unidirectional baseline drift indicates that there is a leak in the system).
• 10.4 Determination of backflush time:
  • 10.4.1 Prepare an isooctane-n-nonane mixture containing 5% (V/V). Place the system in the normal state, use the 11.3 injection technique to inject 1 μL of the isooctane-n-nonane mixture, and record the chromatogram until all n-nonane has eluted and the recorder pen returns to the baseline. Use a stopwatch to record the time from injection until the recorder pen returns to the baseline after the isooctane peak. At this time all isooctane has eluted from the column while no n-nonane has eluted. The backflush time is close to half of this time, in the range of 30~150 s.
  • 10.4.2 Repeat the injection, and at the selected backflush time place the system in the backflush state. The resulting chromatogram should show the isooctane peak while the n-nonane peak is very small or the n-nonane peak is not visible.
  • 10.4.3 Repeat the above operations as actually required until in the chromatogram all isooctane elutes while n-nonane does not elute or elutes very little. In subsequent calibration and analysis processes, the operation must be carried out according to the backflush time determined in this way.

7. Sampling and sample preparation

• Chapter 8 Sampling: Sample according to GB/T 6680 or GB/T 4756.
• Sample solution preparation (12.1): Accurately measure 0.5 mL of methyl ethyl ketone into a 100 mL volumetric flask, dilute to the mark with the sample, and mix uniformly.

8. Analysis procedure

• 11.3 Chromatographic analysis: Using the conditions established in 10.3 and 10.4, inject each calibration standard solution and record the chromatogram as follows: Rinse a 5 μL microsyringe three times with the calibration standard solution, draw 3 μL of the calibration standard solution, expel air bubbles, slowly push out the solution until 1 μL of solution remains in the syringe, wipe the syringe needle clean, then pull back the syringe to draw in 1 μL of air. Insert the syringe into the vaporization chamber, and quickly inject the calibration standard solution into the vaporization chamber. Note: This injection technique helps to obtain sharp and symmetrical chromatographic peaks.
• 11.4 Standard curve: Measure the chromatographic peak areas of benzene and methyl ethyl ketone by a conventional method (see Note 1), and calculate the ratio of the chromatographic peak area of benzene to that of methyl ethyl ketone. Plot this ratio against the benzene content as shown in Figure 3 to obtain the standard curve. This calibration process must be carried out to ensure that the entire chromatographic system operates normally and that samples at any concentration do not exceed the linear range of response of any part, including the chromatographic column, detector, integrator, and other parts. The calibration curve should be linear (see Note 2). At the same time, determine the retention time of each component for future qualitative use.
  • Note 1: The statements about precision in Chapter 15 are calculated from the results of an integrator or an online computer. This precision does not apply to other integration methods or peak area calculation methods.
  • Note 2: If the standard curve is linear, the least squares method may be used to establish a linear equation and calculate the correlation coefficient. The precision data in Chapter 15 are derived from the standard curve and do not apply to the case where a linear equation and correlation coefficient are used.
• 12.2 Under the chromatographic conditions described in 10.3, 10.4, inject using the injection technique of 11.3 and record the chromatogram. Note: At the determined backflush time, place the valve in the backflush state to prevent unnecessary components from entering the chromatographic column.
• 12.3 Determine the benzene and methyl ethyl ketone peaks in the chromatogram according to retention time. A typical chromatogram is shown in Figure 4. Note: When the aforementioned chromatographic column is used, the elution order of the chromatographic peaks is non-aromatics, benzene, methyl ethyl ketone, and toluene.
• 12.4 Measure the chromatographic peak areas of benzene and methyl ethyl ketone by a conventional method.
• Column preparation (9.2):
  • 9.2.1 Clean the stainless steel tube: Connect one end of the column tube to a glass funnel and hold it upright, place a beaker at the lower outlet, add 50 mL of dichloromethane to the funnel and let it flow through the column tube into the beaker; then add 50 mL of acetone and repeat the cleaning. Remove the funnel, connect the column tube to the air line, and blow the solvent in the column tube dry with purified air.
  • 9.2.2 Pack the 0.8 m (or 1.0 m) chromatographic column (column A) with methyl silicone stationary phase (see 9.1.1), and pack the 4.6 m chromatographic column (column B) with TCEP stationary phase (see 9.1.2): Pre-shape column A and column B to fit the instrument installation, plug one end of the column with copper mesh and connect it to a vacuum pump, connect the other end to a small funnel, turn on the vacuum pump, and fill an appropriate amount of stationary phase packing through the funnel into the column until the column tube is full. During filling, gently tap the chromatographic column or use an electronic vibrator to vibrate so that the packing is uniform. Remove the funnel and turn off the vacuum pump. Pour out the stationary phase at the top 6 mm and plug with copper mesh.
  • 9.3 Commercial chromatographic columns meeting the requirements of Tables 1, 5.2, 9.1, and 9.2 may also be used.

9. Qualitative and quantitative determination and calculation formulas

• Qualitative: Determine the benzene and methyl ethyl ketone peaks in the chromatogram according to retention time (12.3). The elution order of the chromatographic peaks is non-aromatics, benzene, methyl ethyl ketone, and toluene.
• Quantitative: 13.1 Calculate the ratio of the benzene peak area to the methyl ethyl ketone peak area in the sample, and read from the standard curve the volume percentage of benzene in the sample corresponding to this ratio.
• 13.2 If the benzene content in the sample is expressed as mass percentage [Y% (m/m)], convert according to formula (1) or formula (2):
  • Y = (X/D) × 0.8789 ... (1)
  • Y = (X/D₁) × 0.8844 ... (2)
  • Where: X—— benzene content, % (V/V); D——20℃ density of the sample at that time, g/cm³; D₁——density of the sample at 15.6℃, g/cm³; density of benzene at 0.8789——20℃, g/cm³; density of benzene at 0.8844——15.6℃, g/cm³.
  • Explanation of adoption 1]: This standard adds formulas for conversion using the densities of the sample and benzene at 20℃.
• 14 Report: The volume percentage or mass percentage of benzene, accurate to 0.005%.

10. Precision

• 15.1 Precision: derived from statistical analysis of results from 6 laboratories on 7 types of samples including n-heptane, naphtha, several solvent oils, toluene, etc., measured on two different dates. To each solvent initially containing no benzene, benzene was added at 0.1% (V/V) to 0.5% (V/V). When the degrees of freedom are 42, the within-laboratory standard deviation is 0.0094%; when the degrees of freedom are 49, the between-laboratory standard deviation is 0.022%. Based on these standard deviations, at the 95% confidence level, the reliability of measurement results is judged according to the following criteria:
  • 15.1.1 Repeatability: two results, each the average of two replicate measurements, obtained by the same operator on different dates, the difference between the two results shall not exceed 0.027%.
  • 15.1.2 Reproducibility: two results, each the average of two replicate measurements, obtained by operators in different laboratories, the difference between the two results shall not exceed 0.063%.
• 15.2 Bias: because no substance with a standard value was available for testing, the bias of this standard has not been determined.

11. Report

• Clause 14 Report: volume percentage or mass percentage of benzene, accurate to 0.005%.

12. Referenced Documents

• GB/T 4756 Manual sampling of petroleum liquids
• GB/T 6680 General rules for sampling of liquid chemical products
• GB/T 9722 Chemical reagents - General rules for gas chromatography
• Note: Clause 2 specifies that the provisions of the following standards, through reference, constitute a part of this standard. Unless otherwise explicitly specified in the standard, the following referenced standards shall be the currently effective versions.

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