GB/T 34102-2017 in English

Interpretation of GB/T 34102—2017 National Standard of the People's Republic of China

Determination of 2,6-di-tert-butyl-p-cresol in jet fuel - Differential Pulse Voltammetry

Background and significance: Jet fuel produced by hydrocracking and hydrorefining processes needs to be added with a certain concentration of 2,6-di-tert-butyl-p-cresol antioxidant to improve its storage and oxidation stability. Rapid and accurate determination of the antioxidant content is crucial to the quality control and safe use of jet fuel.

Scope and applicability of standard

Instrument and technical requirements

Electrochemical workstation: High stability, sensitivity better than $10^{-9}~\mathrm{A}/\mathrm{V}$. Specific requirements include wide potential range ($\pm2.4~\mathrm{V}$), high current resolution (better than $10~\mathrm{pA}$) and input impedance (higher than $1\times10^{12}~\Omega$). Support three/four-electrode settings.

Combined electrode: Diameter $8~\mathrm{mm}$, length $55~\mathrm{mm}$. The working electrode is a glassy carbon electrode (diameter $3~\mathrm{mm}$), and the auxiliary and reference electrodes are platinum wire electrodes (diameter $0.5~\mathrm{mm}$).

Reagents and Materials

• Absolute ethanol: Analytical grade.
• n-heptane: Analytical grade.
• 2,6-di-tert-butyl-p-cresol standard: Analytical grade.
• Potassium hydroxide: Analytical grade, saturated anhydrous ethanol solution must be prepared.

Determination steps and data analysis

Standard addition method: Prepare a series of standard solutions of different concentrations ($0.0~\mathrm{mg/L}$, $5.0~\mathrm{mg/L}$, $15.0~\mathrm{mg/L}$, $25.0~\mathrm{mg/L}$), and record the oxidation peak height by differential pulse voltammetry.

Data Analysis: According to the standard addition method, a calibration curve ($i_{\mathrm{~p}} = kc + b$) was established to calculate the content of 2,6-di-tert-butyl-p-cresol in the sample to be tested. The correlation coefficient $R$ should be greater than 0.95.

Precision and Bias Analysis

Repeatability: The difference between two independent measurements by the same operator using the same instrument should not be greater than $0.58x^{0.5}~\mathrm{mg/L}$.

Reproducibility: The difference between two independent measurements by different operators in different laboratories should not be greater than $1.08x^{0.5}~\mathrm{mg/L}$.

Bias Analysis: At a 95% confidence level, the limit error is $3.2~\mathrm{mg/L}$. This method is suitable for the determination of samples within the concentration range of $8~\mathrm{mg/L{\sim}31~mg/L}$.

Implementation suggestions

1. Laboratory conditions: Ensure that the instrument meets the technical requirements. The operator must have relevant experience and receive professional training.
2. Sample processing: Sampling should be carried out in accordance with GB/T4756. Ensure that the samples are stored in a sealed container to avoid oxidation or contamination.
3. Data analysis: Use the least squares formula in Appendix A to calculate the calibration curve parameters, and strictly calculate the content of the sample to be tested according to formula (2).
4. Quality control: Regularly verify the accuracy of the standard solution and the performance of the instrument to ensure the reliability of the measurement results.