GB/T 33647-2017 Determination of silicon content in motor gasoline — Inductively coupled plasma optical emission spectrometry

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Card type: Test method

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

• Standard number: GB/T 33647-2017
• Chinese title: Determination of silicon content in motor gasoline — Inductively coupled plasma optical emission spectrometry
• English title: Determination of silicon content in motor gasoline — Inductively coupled plasma optical emission spectrometry (ICP-OES)
• 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 2017-05-12, implemented on 2017-12-01
• Custodianship: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280)

2. Scope of application and non-applicability

• Applicable to the determination of motor gasoline with a silicon content of 1.0 mg/kg~50.0 mg/kg (volume fraction of oxygen-containing compounds not exceeding 15%), such as motor gasoline containing methyl tert-butyl ether, motor methanol gasoline (M15) and motor ethanol gasoline (E10).
• For motor gasoline samples with a silicon content higher than 50.0 mg/kg, they may be determined according to this standard method after dilution with a higher proportion of isooctane, but their precision has not yet been statistically evaluated.
• Certain elements in motor gasoline, such as sulfur, lead, iron, manganese, phosphorus and chlorine, will not cause interference effects on the silicon content determination results.
• Organosilicon compounds in motor gasoline can be determined; inorganic silicon compounds with a particle size of 15 μm or below can also be detected (Introduction).
• Not applicable: no explicit non-applicability clauses are provided in the available source.

3. Method principle

A portion of accurately weighed motor gasoline sample is diluted with isooctane as the dilution solvent at a mass ratio of 1:4. The sample solution is introduced into the ICP-OES instrument by a peristaltic pump for determination. The emission signal response value measured for the sample solution is compared with the standard working curve to calculate the silicon content in the sample.

4. Reagents and materials (purity / preparation)

• 6.1 Isooctane: analytical reagent grade.
• 6.2 Organosilicon reference material: prepare or purchase an organosilicon standard solution with a concentration of not less than 500 mg/kg, for example, hexamethyldisiloxane with a purity greater than 99% is diluted with isooctane to prepare a 1000 mg/kg organosilicon standard solution.
  • Note: For motor gasoline samples with a silicon content higher than 100 mg/kg, it is more appropriate to use hexamethyldisiloxane as the reference material; an organosilicon standard solution with a base oil matrix may cause high determination results.
• 6.3 Argon, oxygen: purity not less than 99.995% (volume fraction).
• 6.4 10% (mass fraction) nitric acid solution.
• 6.5 Quality control (QC) sample: select a motor gasoline sample with a silicon content similar to that of the motor gasoline to be tested as the QC sample; it may also be prepared by diluting an appropriate amount of organosilicon reference material with isooctane. The QC sample is recommended to be sealed and contained in a glass bottle with a screw cap, and stored away from light at below 10 ℃.

5. Instruments and equipment

• 5.1 Inductively coupled plasma optical emission spectrometer: an emission spectrometer equipped with a quartz torch, ICP instrument and high-frequency generator (RF-Generator) capable of forming plasma; an oxygen addition device and a spray chamber cooling device are recommended.
• 5.2 Nebulizer: a concentric nebulizer or a high-salt nebulizer may be used. Gasoline samples usually have no visible particles, and using a concentric nebulizer can achieve higher sensitivity. Note: Using different types of nebulizers may affect the silicon content determination results.
• 5.3 Peristaltic pump (recommended): to provide stable sample introduction operation, peristaltic pump introduction is recommended, with a pump speed range of 0.5 mL/min~3 mL/min.
• 5.4 Peristaltic pump sample introduction tubing: its performance should ensure contact with organic solvent (diluent) for at least 6 h without swelling, dissolving, hardening or other shape changes; synthetic rubber tubing is recommended.
• 5.5 Sample container: 30 mL~120 mL plastic bottle or glass bottle with a screw cap.
• 5.6 Balance: accurate to 0.000 1 g.

6. Recommended operating conditions

Table 1 Typical setting conditions for ICP-OES for silicon content determination:

• Emission power: 1 500 W
• Observation mode: vertical
• Spray chamber temperature: -10 ℃
• Silicon detection wavelength: 251.612 nm, 288.158 nm
• Cooling gas (argon) flow rate: 14 L/min~15 L/min
• Carrier gas (argon) flow rate: 0.5 L/min~0.8 L/min
• Auxiliary gas (argon) flow rate: 0.8 L/min~1.2 L/min
• Oxygen flow rate: 0.02 L/min~0.05 L/min

Note (9.1): Due to differences in equipment among various instruments and ICP excitation sources, unified fixed instrument operating conditions cannot be given; please refer to the operating conditions for organic solvent sample introduction in the operation manuals of each instrument. The typical setting conditions listed in Table 1 are with oxygen added to the auxiliary gas; if oxygen is added to the carrier gas, the oxygen flow rate and carrier gas flow rate should be appropriately reduced. After startup, preheat according to the time recommended in the instrument operation manual; after the plasma is ignited, first aspirate isooctane solvent into the sample introduction system and observe whether the plasma state is stable; if carbon deposits are found on the inner wall of the quartz torch, immediately stop sample introduction, replace the quartz torch and investigate the cause.

7. Sampling and sample preparation

• Sampling: sample according to the standard requirements of GB/T 4756 (Chapter 7).
• 8.1 Blank solution: use isooctane as the blank solution.
• 8.2 Preparation of standard solution: weigh 0.5 g (accurate to 0.000 1 g) of an organosilicon standard solution with a concentration of 1000 mg/kg into a 100 mL glass or plastic sample bottle, add about 49.5 g isooctane for dilution, then accurately weigh, and shake well to obtain a 10.0 mg/kg silicon standard solution. Then take this standard solution and dilute it with isooctane to separately prepare silicon series standard solutions of 0.1 mg/kg, 0.5 mg/kg, 2.0 mg/kg, 5.0 mg/kg, 10.0 mg/kg.
• 8.3 Preparation of sample solution: weigh 5 g (accurate to 0.000 1 g) of motor gasoline sample into a sample container, dilute at a sample:isooctane mass ratio of 1:4, then weigh again, shake thoroughly, cover and seal for storage until determination. When the silicon content of the sample is too high, a higher dilution ratio is permitted.
• 9.2 Sample container: before use, first clean with 10% (mass fraction) nitric acid solution, then rinse repeatedly several times with distilled water, and air dry. Do not directly use a sample container that has contained samples with excessively high silicon content.

8. Analysis procedure

• 10.1 Measure the blank solution (8.1) and the silicon series standard solutions (8.2) separately, with each solution measured three times repeatedly. Before determining the average response value of silicon in the standard solutions, subtract the average blank response value from the signal response value of each standard solution.
• 10.2 After each silicon standard solution measurement, flush the sample introduction system with isooctane solvent. If a high-concentration silicon standard solution has been measured, flush with isooctane and check the solvent signal response value to ensure that silicon in the sample introduction system has been flushed clean.
• 10.3 Establish a standard working curve with the silicon content of the standard solutions (mg/kg) as the X axis and the average response value as the Y axis. The linear correlation coefficient of the standard working curve should be at least not less than 0.99. The measured concentration of the sample solution should fall within the linear range of the standard working curve.
• 10.4 When measuring samples each day, the system performance must be checked with a standard solution at least once.
• 11.1 The blank solution (8.1) and the sample solution (8.3) are measured under the same measurement conditions as the standard solutions. Before each aspiration of the sample solution, first spray isooctane solvent for 60 s, then measure the emission signal response value of silicon in the sample solution.
• 11.2 The blank solution and the sample solution are measured three times repeatedly. Before determining the average response value of silicon in the sample solution, subtract the average blank response value from the signal response value of each sample solution.

9. Qualitative and quantitative determination and calculation formula

The silicon content X in motor gasoline samples [unit: milligrams per kilogram (mg/kg)] is calculated according to formula (1):

X = (I₀ − I_bk)/(S × K_E)

Where:

• I₀ — average response value of silicon in the sample solution;
• I_bk — average response value of the blank;
• S — slope of the standard curve (kg/mg);
• K_E — mass dilution coefficient, i.e. sample mass/total mass of sample plus dilution solvent (g/g).

(Note: In the original text, formula (1) source-text extraction is shown as "X=(1.-1ok)/(SXKB)"; the above symbols are organized according to the original symbol descriptions and require confirmation against the source standard (source-text extraction).)

10. Precision

• 14.1 Overview: According to the method of GB/T 6683, the precision of this standard was obtained from the test results of 12 cooperative laboratories on 5 motor gasoline samples with silicon content in the range of 1.0 mg/kg~50.0 mg/kg. The instruments used by the cooperative laboratories were all equipped with an oxygen addition device and a spray chamber cooling device. Judge the reliability of test results according to the following provisions (95% confidence level).
• 14.2 Repeatability r: For the same operator, using the same equipment, under stable operating conditions, the difference between two consecutive determination results for the same sample shall not exceed the calculated value of formula (2): r = 0.365 × x^0.505 Where: x — the average of the two test results, in milligrams per kilogram (mg/kg). (Note: In the original text, formula (2) source-text extraction is shown as "r=0.365z9.50s"; the exponent and symbol require confirmation against the source standard (source-text extraction).)
• 14.3 Reproducibility R: For different operators in different laboratories, the difference between two single, independent determination results obtained for the same sample shall not exceed the calculated value of formula (3): R = 0.623 × x^0.731 Where: x — the average of two test results, in milligrams per kilogram (mg/kg). (Note: In the original formula (3), source-text extraction is shown as “R =0.623z0.731”, requires confirmation against the source standard (source-text extraction).)
• 14.4 Bias: The bias of the method has not been determined.

11. Report

Report the silicon content result to the nearest 0.1 mg/kg (Chapter 15).

12. Referenced Documents

• GB/T 4756 Standard Practice for Manual Sampling of Petroleum Liquids
• GB/T 17476 Standard Test Method for Determination of Additive Elements, Wear Metals, and Contaminants in Used Lubricating Oils and Determination of Selected Elements in Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry
• Reference: GB/T 6683 Standard Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products

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