GB/T 12582-1990 Determination of electrical conductivity of liquid hydrocarbons (precision electrometer method)

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Card type: Test method

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

• Standard number: GB/T 12582-90
• Chinese name: Determination of electrical conductivity of liquid hydrocarbons (precision electrometer method)
• English name (original): Liquld hydrocarbons-Determ Inatlon of electrical conductlvity—Precision meter (requires confirmation against the source standard (source-text extraction), the original English spelling contains obvious noise)
• Replacement relationship: not provided in the available source
• Reference adoption: ASTM D4308-83 "Precision standard test method for electrical conductivity of liquid hydrocarbons" (see additional notes)
• Approval/implementation: approved by the State Bureau of Technical Supervision on 1990-12-14, implemented on 1991-10-01

2. Scope of application and non-applicability

• Applicable to the determination of the "static" electrical conductivity of aviation fuels and other similar low-conductivity liquid hydrocarbons.
• Applicable to a precision test method for measuring the "static" electrical conductivity of liquid hydrocarbons in the laboratory or in the field.
• Measurement range: 0.1 to 2 000 pS/m.
• Not applicable: not provided in the available source.

3. Method principle

Place the sample in a clean conductivity measuring cell and connect it in series with a direct-current power supply and a sensitive direct-current ammeter. The electrical conductivity is automatically calculated based on Ohm's law from the conductivity measuring cell constant, the voltage applied to the measuring cell, and the nearly instantaneous peak current reading.

4. Reagents and materials (purity / preparation)

• 5.1 Toluene: analytical reagent grade.
• 5.2 n-Heptane: analytical reagent grade, its electrical conductivity must be lower than 1 pS/m.
• 5.3 Isopropanol: analytical reagent grade.
• 5.4 Cyclohexane: analytical reagent grade; at the calibration temperature, its dielectric constant must fluctuate within the range of the literature value (2.023) ±5%.
• 5.5 Acetone: analytical reagent grade.
• 5.6 Silica gel: 100 to 200 mesh.
• 4.2 Material Nitrogen: ordinary nitrogen (purity above 95%).
• Toluene-isopropanol mixed liquid: mix toluene and isopropanol in a volume ratio of 2:3 (see 6.2).

5. Instruments and equipment

• 4.1.1 Conductivity measuring cell: composed of inner and outer electrodes and a cover. The inner and outer electrodes are insulated with polytetrafluoroethylene. The outer electrode and the cover form a grounding path and can also serve as electrostatic shielding (see Figure 1).
• 4.1.2 Electrometer: four-and-a-half-digit digital display, with zero calibration and 20, 200, 2000, 20 000, a total of six selection buttons; range: 0 to 20 000 pS/m; accuracy: ±0.5%±1 digits (see Figure 1). (requires confirmation against the source standard (source-text extraction): the original text "a total of six selection buttons" appears inconsistent with the number of buttons listed)
• 4.1.3 Triaxial cable: used to connect the electrometer and the conductivity measuring cell (see Figure 1).
• 4.1.4 Thermometer: scale division value 0.5°C, test range 0 to 50°C.
• 4.1.5 Glass tube: inner diameter 60 to 70 mm, length 1 500 mm, the lower end of the tube is tapered and has a glass stopcock.
• 4.1.6 Porcelain dish: a perforated porcelain dish with a diameter of 25 mm.
• Figure 1 Precision measuring instrument for electrical conductivity of liquid hydrocarbons: 1— conductivity measuring cell, 2— electrometer, 3— triaxial cable.

6. Recommended operating conditions

• Sample temperature measurement: use a clean thermometer, read accurately to 1°C (9.9).
• If the sample electrical conductivity is expected to be less than 1 pS/m, the sample must stand for 15 min before testing (9.8).
• Filtration rate of n-heptane: 2 to 3 L/h (7.1.4).
• Silica gel activation: activate for 24 h under the condition of 180°C (7.1.1).
• Other operating conditions: not provided in the available source.

7. Sampling and sample preparation

• 6.1 The sample should be at least 0.7 L, and should be clean and transparent.
• 6.2 A glass bottle may be selected for sampling. Before sampling, it should be thoroughly cleaned in sequence with hot water, distilled water, acetone, and a toluene-isopropanol mixed liquid (toluene and isopropanol mixed in a volume ratio of 2:3), and dried with nitrogen. The container cap must avoid any contamination.
• 6.3 Rinse the glass bottle three times with the sample to be tested. Then fill the sample bottle and let it stand upright, then empty the sample and refill the sample bottle.
• 7.1 Pretreat n-heptane:
  • 7.1.1 Place 2000 g 100 to 200 mesh silica gel under the condition of 180°C and activate for 24 h. Then place the activated silica gel in a desiccator to cool (the desiccator must be evacuated or filled with nitrogen).
  • 7.1.2 Place 0.58 glass fiber in n-heptane and soak for 24 h. (requires confirmation against the source standard (source-text extraction): the original text "0.58" appears to be missing a unit)
  • 7.1.3 Place a perforated porcelain dish at the lower end of the glass tube, place the soaked glass fiber on the porcelain dish, then load the activated silica gel into the glass tube; the filling should be uniform, and the height of the silica gel layer should be about 1250 mm. To avoid the influence of light, the glass tube should be wrapped with black paper.
  • 7.1.4 Add n-heptane to the glass tube and filter slowly; the filtration rate is 2 to 3 L/h. Discard the first 3 L. During filtration, be careful not to let the n-heptane in the glass column run dry. The silica gel load should be sufficient to filter 1000 L n-heptane.

8. Analytical procedure

8.1 Calibrate the electrometer

• 8.1.1 Remove the measuring cell and cable from the electrometer.
• 8.1.2 Press the selection button "20"; after 3 s, the display should show the number 0.000±0.01 pS/m. If the reading exceeds ±0.01 pS/m, either adjust it to zero, or record the difference from zero so as to calibrate the final test value. (requires confirmation against the source standard (source-text extraction): the original text "0.000.01pS/m" is suspected to be "0.000±0.01 pS/m")
• 8.1.3 Press the selection button "Calibration"; the display should show the reading 1 000±3 pS/m. (requires confirmation against the source standard (source-text extraction): the original text "1 0003 pS/m" is suspected to be "1 000±3 pS/m")
• 8.1.4 If a low voltage appears on the display during measurement or calibration, the battery pack should be replaced immediately.

8.2 Verify the measuring cell constant

• 8.2.1 The measuring cell constant must be verified only when the measuring cell is damaged; the procedure for verifying the measuring cell constant is as follows.
• 8.2.1.1 Use a precision alternating-current bridge to measure the total capacitance CE of the empty measuring cell; without changing the equipment, add 100 mL cyclohexane and measure the new total capacitance Cs.
• 8.2.1.2 Use a clean thermometer to measure the temperature of the cyclohexane, reading accurately to 1°C.
• 8.2.2 The effective capacitance CA of the empty measuring cell (F) is calculated according to formula (1): CA = (Cs-CE) / (εs-1) ……………… (1) Where: Cs— is the total capacitance after adding 100 mL cyclohexane to the measuring cell, F; CE— is the total capacitance of the empty measuring cell, F; εs— is the dielectric constant of cyclohexane at the measurement temperature.
• 8.2.3 The measuring cell constant K is calculated according to formula (2): K = 8.854/CA ……………… (2)
• 8.2.4 The new measuring cell constant is 1.0. Usually, the measuring cell constant will not change greatly unless the measuring cell suffers accidental severe damage.

8.3 Clean the conductivity measuring cell

• 7.2.1 The cleaning procedure depends on the electrical conductivity of the sample.
• 7.2.2 For samples whose electrical conductivity is expected to be less than 1 pS/m, the conductivity measuring cell should be disassembled and thoroughly cleaned, then, wearing clean protective gloves, the measuring cell should be reassembled.
  • 7.2.2.1 The procedure for disassembling the measuring cell is as follows: first remove the measuring cell cover and the outer electrode connector, remove the base and loosen the screws, press the inner electrode toward the bottom of the outer electrode, and remove the fluoroplastic insulating part of the inner electrode.
  • 7.2.2.2 Each part of the measuring cell should be thoroughly cleaned five times with clean toluene-isopropanol mixed liquid. Then rinse with treated n-heptane, and finally dry with clean nitrogen.
  • 7.2.2.3 While wearing clean protective gloves, reassemble the measuring cell, then rinse with treated n-heptane.
  • 7.2.2.4 According to the requirements of Chapters 9 to 10, measure the electrical conductivity of the treated n-heptane. If the electrical conductivity is lower than 0.05 pS/m, it indicates that the measuring cell has been cleaned. Otherwise, the measuring cell should be cleaned again.
• 7.2.3 For samples whose electrical conductivity is expected to be greater than 1 pS/m, the measuring cell may first be rinsed with clean toluene-isopropanol mixed liquid; after rinsing five times, rinse with treated n-heptane, and finally dry with nitrogen.
  • 7.2.3.1 According to the requirements of Chapters 9 to 10, measure the electrical conductivity of the treated n-heptane. If the electrical conductivity is less than 0.1 pS/m, it indicates that the measuring cell has been cleaned.
• 7.2.4 If the measuring cell is used to test samples of high electrical conductivity (1000 pS/m and above), the measuring cell should be disassembled and placed in equipment containing toluene-isopropanol (water bath 70°C) for several hours.
• 7.2.5 If the measuring cell is to test both low-conductivity samples (less than 1 pS/m) and high-conductivity samples (greater than 1 000 pS/m), it is recommended to use separate measuring cells (two measuring cells), respectively for high- and low-conductivity samples.

8.4 Clean auxiliary equipment

• 7.3.1 Rinse the pipette used for sampling with clean toluene-isopropanol mixed liquid, then dry it with clean nitrogen and keep it dry.
• 7.3.2 Rinse the thermometer with clean toluene-isopropanol mixed liquid, then dry it with clean nitrogen and keep it dry.

8.5 Test procedure

• 9.1 Connect the clean measuring cell to the electrometer.
• 9.2 Press the selection button "Zero"; the display should indicate the same value given by 8.1.2.
• 9.3 Press the selection key "Calibration"; the display should show the reading of 1000±5 pS/m. (requires confirmation against the source standard (source-text extraction): the original text "1000 5 pS/m" is suspected to be "1000±5 pS/m")
• 9.4 Rinse the measuring cell three times with the sample. Drain the sample completely, then inject the sample into the outer chamber of the measuring cell until the sample just overflows into the inner chamber.
• 9.5 Turn the selector switch to the automatic position and select the appropriate key. If the conductivity of the sample is known, the corresponding key can be selected directly; if the conductivity of the sample is unknown, first select the 2000 pS/m key, and then select the corresponding key according to the measured conductivity value.
• 9.6 Release the selected key, and the reading will be displayed on the display; after 3 s the reading stabilizes and continues to display 9 s; record the conductivity value. (requires confirmation against the source standard (source-text extraction): the original text "release" is suspected to be "press")
• 9.7 After an interval of 1 min, repeat the conductivity test as required in clause 9.6.
• 9.8 If the conductivity of the sample is expected to be less than 1 pS/m, then before testing, the sample must stand for 15 min.
• 9.9 Using a clean thermometer, measure the temperature of the sample, reading accurately to 1°C.
• 9.10 Generally, the conductivity of a sample varies with temperature, and the relationship between the conductivity and temperature of the sample also differs among samples. If the conductivity needs to be corrected to a specified temperature, each laboratory must establish the relationship between conductivity and the sample within the required temperature range.

9. Qualitative and Quantitative and Calculation Formulas

• Calculation of the measuring cell constant:
  • Formula (1): CA = (Cs-CE)/(εs-1)
  • Formula (2): K = 8.854/CA
• Result correction (Chapter 10): If in 8.1.2 the zero error is greater than ±0.01 and the zero point has not been adjusted, then the reading should be reduced by the positive zero error or increased by the negative zero error.
  • Example: sample reading (clause 9.6) 1.67; uncorrected zero error (8.1.2) +0.03; result 1.64.
• Report: The conductivity of the sample is expressed in pS/m, and the sample temperature is reported (Chapter 12).

10. Precision

Judge the reliability of the test results according to the following provisions (95% confidence level).

• 11.1 Repeatability: The difference between two results obtained by the same operator in repeated determinations shall not exceed the value in Figure 2.
• 11.2 Reproducibility: The difference between two results submitted by different laboratories shall not exceed the value in Figure 2.
• Figure 2 Precision: The abscissa is the average of two conductivity readings (pS/m), and the ordinate is precision (repeatability r, reproducibility R), pS/m; the scale markings in the figure include 0.1, 10, 100, 1000, etc. (requires confirmation against the source standard (source-text extraction): the specific numerical curves of Figure 2 could not be completely extracted from the original text).

11. Report

The conductivity of the sample is expressed in pS/m, and the sample temperature is reported.

12. Referenced Documents

• ASTM D4308-83 "Standard Test Method for Precision Conductivity of Liquid Hydrocarbons" (referenced and adopted, see additional notes).
• Other referenced documents: not provided in the available source.

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 for Questions and Answers