SH/T 0251-1993 Determination of base number of petroleum products (perchloric acid potentiometric titration method)

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Card type: Test method

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

• Standard number: SH/T 0251-93
• Chinese name: Determination of base number of petroleum products (perchloric acid potentiometric titration method)
• English name: not provided in the available source
• Replacement relationship: replaces SH/T 0251-92
• Approval/implementation: approved by China Petrochemical Corporation 1993-06-11, implemented on 1994-05-01
• Reference adoption: ASTM D2896-88 "Determination of base number of petroleum products (perchloric acid potentiometric titration method)"
• First release: 1978 year 5 month
• Technical administration: technical administration by the Research Institute of Petroleum Processing; drafting: Lanzhou Refining and Chemical General Plant; main drafters: Guo Yunhua, Zhou Yabin

2. Scope of application and non-applicability

• This standard specifies a method for determining the base number of samples by perchloric acid potentiometric titration.
• The method includes two types, direct titration and back titration, and each type is further divided into method A and method B.
• Note: Tests show that for additives, new and used oils, the results determined by these two methods are consistent from a statistical point of view. For arbitration tests, method A shall prevail.
• Applicable to the determination of basic components in petroleum products, used oils and additives; these components include organic bases, inorganic bases, amino compounds, weak acid salts (soaps), polybasic acid salts and heavy metal salts.
• Not applicable: not provided in the available source (the main text does not list non-applicable clauses; Appendix A indicator method explicitly does not apply to dark petroleum products and used petroleum products, but this limitation belongs to Appendix A).

3. Method principle

• Method A and method B have basically the same operation; the difference lies in the different amounts of sample and titration solvent.
• 4.1 Direct titration method: The sample is dissolved in the titration solvent, with perchloric acid glacial acetic acid standard titration solution as the titrant, a glass electrode as the indicator electrode, and a calomel electrode as the reference electrode for potentiometric titration; the end point is judged by the potential jump of the potentiometric titration curve.
• 4.2 Back titration method: The sample is dissolved in the titration solvent, an excess of perchloric acid glacial acetic acid standard titration solution is added, and after the reaction is complete, titration is carried out with sodium acetate glacial acetic acid standard titration solution; the end point is judged by the potential jump of the potentiometric titration curve.
• 4.3 When the potential jump of the direct titration curve of the sample is not obvious, the back titration method is then used.
• Significance (Chapter 5): When additives are added to petroleum products, the petroleum products may contain basic components, and the relative content of these components can be determined by acid titration. It is used to measure the degradation of additives during the use of lubricating oil, so as to determine the necessary practical discard limit.

4. Reagents and materials (purity / preparation)

• 7.1 Glacial acetic acid: analytical reagent.
• 7.2 Acetic anhydride: analytical reagent.
• 7.3 Chlorobenzene: analytical reagent.
  • Caution: Glacial acetic acid, acetic anhydride and chlorobenzene are toxic and irritating and should be used in a fume hood.
• 7.4 Petroleum ether: analytical reagent, 60~90°C.
• 7.5 Perchloric acid: analytical reagent, concentration 70%~72% (m/m).
• 7.6 Sodium perchlorate: analytical reagent.
  • Caution: Perchloric acid and sodium perchlorate are toxic, irritating, and strong oxidants; contact with organic matter when dry or heated may cause explosion. If splashed on the skin, immediately rinse thoroughly with water.
• 7.7 Anhydrous sodium carbonate: analytical reagent.
• 7.8 Potassium hydrogen phthalate: primary standard reagent.

Preparation and standardization:

• 8.1 Preparation of sodium perchlorate electrolyte: prepare a saturated solution of sodium perchlorate in glacial acetic acid; it is necessary to keep excess undissolved sodium perchlorate present in the sodium perchlorate solution.
• 8.2 Titration solvent: add 1 volumes of glacial acetic acid to 2 volumes of chlorobenzene and mix uniformly.
  • Note: When petroleum ether can dissolve the sample, petroleum ether may be used instead of chlorobenzene, but for arbitration tests and standardization, chlorobenzene must be used.
• 8.3 c(HClO₄)=0.1mol/L Preparation and standardization of perchloric acid glacial acetic acid standard titration solution
  • 8.3.1 Preparation: Add 8.5mL perchloric acid to a mixture of 500mL glacial acetic acid and 30mL acetic anhydride, mix uniformly, then dilute to 1L with glacial acetic acid. Allow this solution to stand for 24h, then standardize. Standardize once a week to detect changes in 0.0005mol/L.
    • Caution: see the caution in clause 7.6.
    • Note: When preparing the solution, avoid adding excess acetic anhydride to prevent acetylation of small amounts of primary and secondary amines in the solution.
  • 8.3.2 Standardization: Take an appropriate amount of potassium hydrogen phthalate, heat it in an oven at 120°C for 2h, then cool to room temperature, weigh 0.1~0.2g of potassium hydrogen phthalate (accurate to 0.0002g), place it in a dry 150mL beaker, dissolve it with warm 40mL glacial acetic acid, then add 80mL chlorobenzene, and after cooling, perform potentiometric titration with perchloric acid glacial acetic acid solution (8.3.1); the operation and end point judgment are the same as in direct titration method A. At the same time, carry out a blank test with 40mL glacial acetic acid and 80mL chlorobenzene mixed solvent.
  • 8.3.3 Calculation formula (1): c(HClO₄) = m₁ / [0.2042 × (V₁ − V₀)] Where: m₁——mass of potassium hydrogen phthalate weighed, g; V₁——volume of perchloric acid glacial acetic acid solution (8.3.1) used in titration, mL; V₀——volume of perchloric acid glacial acetic acid solution (8.3.1) used in the blank test, mL; 0.2042—— and 1.00mL mass of potassium hydrogen phthalate, expressed in grams, equivalent to perchloric acid glacial acetic acid standard titration solution [c(HClO₄)=1.000mol/L].
    • Note: The perchloric acid glacial acetic acid standard titration solution should be standardized before use. Because the volume expansion coefficient of organic liquids is relatively large, the use temperature of the perchloric acid glacial acetic acid standard titration solution should be within ±5°C of its standardization temperature. If used at a temperature higher than the standardization temperature by 5°C, the volume used in titration shall be multiplied by the coefficient [1 − (t×0.001)]; if used at a temperature lower than the standardization temperature by 5°C, the volume used in titration shall be multiplied by the coefficient [1 + (t×0.001)]. Here t is the difference between the standardization temperature and the use temperature, in degrees Celsius (°C), and its value is taken as positive.
• 8.4 c(CH₃COONa)=0.1mol/L Preparation and standardization of sodium acetate glacial acetic acid standard titration solution
  • 8.4.1 Preparation: Weigh 5.3g anhydrous sodium carbonate, dissolve it in 300mL glacial acetic acid, and after complete dissolution dilute to 1L with glacial acetic acid. Standardize once a week to detect changes in 0.0005mol/L.
  • 8.4.2 Standardization: There are the following two methods.
    • 8.4.2.1 Method A: Add 8.00mL perchloric acid glacial acetic acid standard titration solution (8.3) to 120mL titration solvent, and titrate with sodium acetate glacial acetic acid solution (8.4.1); the operation and end point judgment are the same as in direct titration method A. Formula (2): c(CH₃COONa) = [(8.00 − V₀) × c(HClO₄)] / V₂ Where: V₀——volume of perchloric acid glacial acetic acid standard titration solution (8.3) used in the blank test, same as V₀ in formula (1), mL; V₂——volume of sodium acetate glacial acetic acid solution (8.4.1) used in titration, mL; c(HClO₄)——actual concentration of perchloric acid glacial acetic acid standard titration solution (8.3), mol/L.
    • 8.4.2.2 Method B: The operating steps are the same as method A, except that the amounts of reagents and titration solvent used in method A are correspondingly halved. Formula (3): c(CH₃COONa) = [(4.00 − V₀) × c(HClO₄)] / V₂ Where: V₀——volume of perchloric acid glacial acetic acid standard titration solution (8.3) used in the blank test (60mL titration solvent), mL; V₂——volume of sodium acetate glacial acetic acid solution (8.4.1) used in titration, mL; c(HClO₄)——same as formula (2).
• Appendix A Reagents (indicator method, reference item):
  • A5.1 Toluene: analytical reagent.
  • A5.2 p-naphtholbenzein indicator.
  • A5.3 Crystal violet indicator.
  • A6.1 Titration solvent: petroleum ether (or toluene) and glacial acetic acid mixed uniformly in the ratio 2:1 (V/V).
  • A6.2 2g/L Crystal violet glacial acetic acid indicator solution: weigh 0.20g crystal violet and dissolve it in 100mL glacial acetic acid.
  • A6.3 5g/L p-naphtholbenzein glacial acetic acid indicator solution: weigh 0.5g p-naphtholbenzein and dissolve it in 100mL glacial acetic acid.
  • A6.4 c(HClO₄)=0.1mol/L Preparation and standardization of perchloric acid glacial acetic acid standard titration solution: A6.4.1 preparation is the same as 8.3.1 of this standard; A6.4.2 standardization: take an appropriate amount of potassium hydrogen phthalate, heat it in an oven at 120°C for 2h, then cool to room temperature, weigh 0.1–0.2g potassium hydrogen phthalate (accurate to 0.0002g), place it in a dry 250mL conical flask, add warm 50mL glacial acetic acid to dissolve, then add 4–5 drops of crystal violet glacial acetic acid indicator solution (A6.2), titrate with perchloric acid glacial acetic acid solution (8.3), until the solution changes from purple to blue; A6.4.3 the actual concentration is calculated according to 8.3.3 of this standard.

5. Instruments and equipment

• 6.1 Potentiometric titrator (or acidity meter): automatic or manual titration is acceptable.
• 6.2 Glass electrode: type 231.
• 6.3 Calomel electrode: type 232 or type 271, or silver-silver chloride electrode. The internal electrolyte of the electrode must be changed to a non-aqueous solution as a salt bridge (see 8.6.2).
• 6.4 Magnetic stirrer: adjustable speed and well grounded.
• 6.5 Burette: 10 or 20mL, graduation 0.05mL, allowable scale error after calibration ±0.02mL, or an automatic burette with the same precision.
• 6.6 Beaker: 100, 150mL. Method A uses 150mL beaker, method B uses 100mL beaker.
• 6.7 Titration stand: used to support the burette, beaker, electrode pair, and stirrer. The arrangement on the titration stand is best such that there is no interference with the electrodes when the beaker is moved.
  • Note: Some instruments are very sensitive to electrostatic interference, manifesting as abnormal drift of the potentiometric titrator's pointer or recorded value when the operator approaches the titration apparatus; in this case, a good grounding method should be used.
• Appendix A Apparatus: A4.1 conical flask 250mL; A4.2 graduated cylinder 50mL; A4.3 microburette 5mL, with graduations of 0.02mL; A4.4 burette 25mL.

6. Recommended operating conditions

• 8.6.3 Adjustment of the potentiometric titrator: either an automatic potentiometric titrator or other type of titrator may be used, adjusted according to the instructions. When using a ZD-2 type instrument, it is necessary to use 100mL glacial acetic acid to adjust the instrument to the potential range of glacial acetic acid, such as 650～700mV (equivalent to 5～6 pH units).
• 8.6.4 Detection of electrode potential: New electrodes, electrodes that have been left standing for a long time, and potentiometric titration apparatuses when first used must all undergo the following detection: add 0.2g (accurate to 0.0001g) potassium hydrogen phthalate to 100mL glacial acetic acid, stir to dissolve, then insert the electrode pair into this solution and read the potential value on the potentiometric titrator. Remove the electrodes and wash them with chlorobenzene. Then immerse the electrodes in a 100mL glacial acetic acid solution to which 1.50mL perchloric acid glacial acetic acid standard titration solution (8.3) has been added, and read the potential value on the potentiometric titrator. The difference between the above two readings must be at least 300mV; otherwise, they must not be used, and the electrodes should be reprocessed.
• 9.1.4 The electrodes should be immersed as low as possible, at least below the sample solution by 10mm. Start stirring; the stirring speed should be controlled to be as high as possible without splashing the solution or generating bubbles.
• 9.1.5.1 Manual titration: The titration speed is generally controlled at 0.1mL/min; during the titration, the titration speed may be changed according to the magnitude of change in the solution's potential value. When adding 0.1mL/min titrant, if the change in the solution's potential value is greater than 30mV or equivalent to 0.5 pH, an inflection point may appear in the titration curve. At this time, the titration speed may be reduced to 0.05mL/min. In the final stage of titration, when adding 0.1mL titrant, if the change in the sample solution's potential is less than 5mV or equivalent to 0.1 pH, the titration may be ended.
• 9.1.5.2 Automatic titration: Adjust the instrument according to the instructions for the instrument used, adjust the titration speed; the maximum titration speed is 1.0mL/min. After the titration is completed, the titration curve is automatically recorded and the result is calculated.
• 9.1.8 During manual titration, plot the potentiometric titration curve according to the recorded titrant volume and the corresponding potential value of the potentiometric titrator, and determine the endpoint from the inflection point of the titration curve. Record the titration volume at the endpoint. A practical method is to determine the endpoint according to the criterion that 0.1mL titrant causes at least a change of 50mV in the potential value of the sample solution.
• 9.4.5 / 9.5.5 Back titration stir the solution in the beaker for 2min.
• Appendix A Indicator method: A7.1 Viscous samples should be heated to 40–50°C; A7.3 Add 40mL petroleum ether to dissolve the sample; after the sample is completely dissolved, then add 20mL glacial acetic acid and 4–5 drops of p-naphtholbenzein glacial acetic acid indicator solution (A6.3), and titrate with constant shaking; the endpoint is when the yellow color of the solution disappears and green just appears.

7. Sampling and sample preparation

• 8.5 Preparation of the sample: Since precipitates in the sample may be acidic or basic substances, or may have adsorbed acidic or basic substances from the sample, it is very important to ensure that the sample is representative. If necessary, the sample may be heated (generally not exceeding 60°C) to help better mixing. For used oil samples, before sampling, they should be shaken vigorously to ensure sample homogeneity.
• 8.6.1 Glass electrode: A new glass electrode must be soaked in distilled water for at least 24h before use. After the test, the electrode should be washed successively with titration solvent and distilled water, and soaked in distilled water for later use. When the glass electrode has been used continuously for one week, if the bulb surface is contaminated, the electrode may be soaked in cold chromic acid cleaning solution or other strongly oxidizing acid cleaning solution for no more than 5min; after removal, wash with water, then soak in distilled water for later use.
  • Caution: Chromic acid cleaning solution is a strong oxidant, hygroscopic agent, and toxic substance. If splashed on the skin during use, it can easily cause severe burns.
• 8.6.2 Reference electrode: Either a calomel electrode or a silver-silver chloride electrode may be used. The salt bridges of commercially available reference electrodes are all aqueous solutions and should be changed to non-aqueous salt bridges. First drain the aqueous solution, rinse out all potassium chloride crystals with water, then rinse the salt bridge sleeve multiple times with sodium perchlorate electrolyte, and finally carefully add sodium perchlorate electrolyte to the sleeve until the liquid level reaches the injection hole. When using a sleeve-type calomel electrode, inject sodium perchlorate electrolyte into the clean outer sleeve, wet the two ground-glass surfaces of the connector with sodium perchlorate electrolyte, secure the outer sleeve, and rinse the electrode with chlorobenzene. When the electrode is in use, the liquid level of the internal electrolyte should be kept higher than the liquid level of the solution in the titration beaker. When the electrode is not in use, the small hole should be plugged with a stopper.
• Appendix A: A7.1 Shake the sample thoroughly; viscous samples should be heated to 40~50°C.

8. Analytical procedure

9.1 Direct titration method A

• 9.1.1 Sample amount X₁ (g) is calculated according to formula (4): X₁ = 28 / BN₁, where BN₁——estimated base number, mgKOH/g.
  • Note: If the estimated base number is unknown, a simple test can be used to quickly and roughly estimate it. Weigh 0.2~0.3g of sample, titrate to 570mV as the endpoint, calculate the sample's base number, and use this value as the sample's estimated base number.
• 9.1.2 According to the provisions of Table 1, weigh the sample in a beaker.

Table 1 (g)

(Note: In source-text extraction, there is a suspected misalignment between the row order and the corresponding numerical values in Table 1, requires confirmation against the source standard (source-text extraction).)

• 9.1.3 Add 120mL titration solvent to the beaker containing the weighed sample, place the beaker on the titration stand, and stir until the sample is completely dissolved.
  • Note: When some samples are difficult to dissolve, 80mL chlorobenzene may first be added to the beaker to dissolve the sample, and then 40mL glacial acetic acid may be added. Some used oil samples contain insoluble solid substances; this is normal.
• 9.1.4 Insert the prepared glass-calomel electrode pair into the sample solution, with the immersion position as low as possible, at least below the sample solution by 10mm. Start stirring; the stirring speed should be controlled to be as high as possible without splashing the solution or generating bubbles.
• 9.1.5 Titration (for manual/automatic, see Section 6).
• 9.1.6 After titration is completed, remove the beaker, rinse the electrodes and burette tip with titration solvent (8.2), then wash with distilled water, then wash with titration solvent. After the test is finished, when the electrodes are no longer used, they should be soaked in distilled water.
  • Note: Use titration solvent to wash off oily substances on the electrodes, and use distilled water to wash off sodium perchlorate around the calomel electrode sleeve; at the same time, this can restore the hydrogel layer of the glass electrode.
• 9.1.7 A blank test of 120mL titration solvent must be performed for each batch of tests. During manual titration, the titrant increment for the blank test is 0.05mL per portion. After each portion of titrant is added, wait for the solution potential to stabilize, then read the burette reading and the potential value of the potentiometric titrator. For automatic titration, proceed as described in 9.1.5.2.
• 9.1.8 During manual titration, plot the potentiometric titration curve according to the recorded titrant volume and the corresponding potential value of the potentiometric titrator, and determine the endpoint from the inflection point of the titration curve. Record the titration volume at the endpoint. A practical method is to determine the endpoint according to the criterion that 0.1mL titrant causes at least a change of 50mV in the potential value of the sample solution.

9.2 Direct titration method B

• 9.2.1 Sample amount X₂ (g) is calculated according to formula (5): X₂ = 10 / BN₂, where BN₂——estimated base number, mgKOH/g.
  • Note: If the estimated base number is unknown, a simple test can be done, namely weigh 0.1~0.15g of sample, titrate to 570mV as the endpoint; in this way, the sample's base number can be quickly estimated.
• 9.2.2 According to the provisions of Table 2, weigh the sample in a beaker.

Table 2 (g)

(Note: In source-text extraction, there is a suspected misalignment between the row order and the corresponding numerical values in Table 2, requires confirmation against the source standard (source-text extraction).)

• Note: For Method B, when determining samples with high base number, the sample amount must be small, so accurate weighing is very important.
• 9.2.3 In the beaker containing the weighed sample, add 60mL titration solvent, place the beaker on the titration stand, and stir the solution until the sample is completely dissolved.
  • Note: When some samples are difficult to dissolve, 40mL chlorobenzene may first be added to the beaker to dissolve, then 20mL glacial acetic acid may be added.
• 9.2.4 Same as 9.1.4.
• 9.2.5 Same as 9.1.5.
• 9.2.6 Same as 9.1.6.
• 9.2.7 A blank test of 60mL titration solvent must be performed for each batch of tests. Its operation is the same as 9.1.7.
• 9.2.8 Same as 9.1.8.

9.4 Back titration method A

When titrating according to the direct titration method A in clause 9.1, for certain samples (especially used oil samples) where there is no inflection point or the inflection point is not obvious, this method may be used.

• 9.4.1 The sample amount should be less than the amount specified in Table 1 of clause 9.1; usually the maximum sample amount is 5g. If the sample amount is 5g and there is no inflection point during titration, the sample amount should be further reduced and the test repeated.
• 9.4.2 Same as 9.1.3.
• 9.4.3 Use a pipette or burette to accurately add 8.00mL perchloric acid glacial acetic acid standard titration solution (8.3) to the beaker.
  • Note: It must be ensured that the added perchloric acid glacial acetic acid standard titration solution is in excess.
• 9.4.4 same as 9.1.4.
• 9.4.5 stir the solution in the beaker 2min.
• 9.4.6 titrate the excess perchloric acid in glacial acetic acid standard titration solution (8.4) with sodium acetate in glacial acetic acid standard titration solution (8.3). The titration procedure is the same as 9.1.5.
• 9.4.7 Another method is that if, for a sample subjected to direct titration according to 9.1.5, when the sample amount does not exceed 5g and a satisfactory inflection point cannot be obtained in the titration, then the sample already titrated in 9.1.5 may be directly subjected to back titration (that is, it is not necessary to weigh a new sample), but the volume of perchloric acid in glacial acetic acid standard titration solution (8.3) used must be accurately recorded, and then back titration is carried out according to 9.4.6. It is worth noting that when standardizing the sodium acetate in glacial acetic acid standard titration solution (8.4), the volume of 8.00mL perchloric acid in glacial acetic acid standard titration solution used should also be correspondingly corrected and should be consistent with the volume used in the test.

9.5 Back titration method B

When performing titration according to the direct titration method B in clause 9.2, this method may be used for certain samples (especially used oil samples) for which there is no inflection point or the inflection point is not obvious.

• 9.5.1 Accurately weigh the sample according to Table 2 in clause 9.2; the maximum sample amount shall not exceed 2.5g. If the sample amount is 2.5g and there is no inflection point in the titration, the sample amount should be reduced and the test performed again.
• 9.5.2 First dissolve the sample with 40mL chlorobenzene, then add 20mL glacial acetic acid.
• 9.5.3 Using a pipette or burette, accurately add 4.00mL perchloric acid in glacial acetic acid standard titration solution (8.3) to the beaker; the perchloric acid in glacial acetic acid standard titration solution must be in excess, and if necessary, the amount used may be increased.
• 9.5.4 same as 9.1.4.
• 9.5.5 stir the solution in the beaker 2min.
• 9.5.6 same as 9.4.6.
• 9.5.7 Another method is that if, for a sample subjected to direct titration according to 9.2.5, when the sample amount does not exceed 2.5g and a satisfactory inflection point cannot be obtained in the titration, then the sample already titrated in 9.2.5 may be subjected to back titration (that is, it is not necessary to weigh a new sample), but the volume of perchloric acid in glacial acetic acid standard titration solution (8.3) used must be accurately recorded, and then back titration is carried out according to 9.4.6. However, when standardizing the sodium acetate in glacial acetic acid standard titration solution (8.4), the volume of 4.00mL perchloric acid in glacial acetic acid standard titration solution (8.3) used should also be correspondingly corrected and should be consistent with the volume used in the test.

Appendix A Indicator method (reference item)

• A1 Subject content and scope of application: This method specifies a method for determining the base number of samples by the color indicator method using perchloric acid in glacial acetic acid standard titration solution as the titrant. This method is applicable to petroleum products and additives, and is not applicable to dark petroleum products or used petroleum products.
• A2 Terms: base number is the same as in Chapter 3 of this standard.
• A3 Method summary: The sample is dissolved in the titration solvent and titrated with perchloric acid in glacial acetic acid standard titration solution, using p-naphtholbenzein as indicator; the titration endpoint is when the color of the sample solution changes from orange-yellow to green.
• A7 Test procedure:
  • A7.1 Shake the sample thoroughly; viscous samples should be heated to 40~50°C, weigh the sample X₃ (g) and calculate according to formula (A1): X₃ = 28 / BN₃, where BN₃——estimated base number, mgKOH/g.
  • A7.2 According to Table A1, weigh the sample in a conical flask; the maximum sample amount shall not exceed 20g.

Table A1 (g)

(Note: In source-text extraction, there is a suspected misalignment between the row order of Table A1 and the corresponding numerical values; requires confirmation against the source standard (source-text extraction).)

• A7.3 Add 40mL petroleum ether to the conical flask containing the weighed sample to dissolve the sample; after the sample is completely dissolved, add 20mL glacial acetic acid and 4~5 drops of p-naphtholbenzein in glacial acetic acid indicator solution (A6.3); while shaking continuously, titrate with perchloric acid in glacial acetic acid standard titration solution (A6.4); the endpoint is when the yellow color of the solution disappears and green just appears. Record the volume of perchloric acid in glacial acetic acid standard titration solution (A6.4) used in the titration.
  • Note: For additive samples and poorly soluble samples, chlorobenzene or toluene may be used instead of petroleum ether.
• A7.4 Blank test: no sample is weighed into the conical flask; all other steps are the same as A7.3.

9. Qualitative and quantitative determination and calculation formulas

• Terms (Chapter 3): base number——under the specified test conditions, the amount of perchloric acid used to titrate 1g sample with standard titration solution, expressed in units of mgKOH/g.
• 9.3 Calculation: Method A and Method B use the same calculation method for base number determination results.
  • 9.3.1 The base number of the sample BN₁ (mgKOH/g) is calculated according to formula (6): BN₁ = (V₁ − V₀) × c(HClO₄) × 0.0561 × 1000 / m₂ Where: V₁——the volume of perchloric acid in glacial acetic acid standard titration solution (8.3) used when titrating the sample, mL; V₀——when using Method A, the same as V₀ in formula (1); when using Method B, the same as V₀ in formula (3), mL; c(HClO₄)——the actual concentration of perchloric acid in glacial acetic acid standard titration solution, mol/L; the mass of potassium hydroxide expressed in grams equivalent to 0.0561—— and 1.00mL perchloric acid in glacial acetic acid standard titration solution [c(HClO₄)=1.000mol/L]; m₂——the mass of the sample, g.
• 9.6 Calculation: Method A and Method B use the same calculation for base number determination results.
  • 9.6.1 The base number of the sample BN₂ (mgKOH/g) is calculated according to formula (7): BN₂ = (V₃ − V₀) × c(CH₃COONa) × 0.0561 × 1000 / m₃ Where: V₃——the volume of sodium acetate in glacial acetic acid standard titration solution (8.4) used when standardizing with perchloric acid in glacial acetic acid standard titration solution (8.3) [when using Method A, the same as V₂ in formula (2), or when using Method B, the same as V₂ in formula (3)], mL; c(CH₃COONa)—— the actual concentration of sodium acetate in glacial acetic acid standard titration solution (8.4), mol/L; V₀——the volume of sodium acetate in glacial acetic acid standard titration solution (8.4) used when titrating the sample, mL; m₃——the mass of the sample, g; 0.0561—— is the same as in formula (6). (Note: In formula (7), the symbol definitions of V₃ and V₀ are misaligned and repeated in the text of source-text extraction; requires confirmation against the source standard (source-text extraction).)
• Appendix A: A8 Calculation——the base number of the sample BN₄ (mgKOH/g) is calculated according to formula (6) in 9.3.1 of this standard. In the formula, V₀ is the measured value of A7.4.

10. Precision

• 10.1 Method A: Judge the reliability of test results according to the following provisions (95% confidence level).
  • 10.1.1 Repeatability: The difference between two results obtained by repeated determination by the same operator shall not exceed the following value.
  • 10.1.2 Reproducibility: The difference between two determination results submitted by different laboratories shall not exceed the following value.

• 10.2 Method B: Judge the reliability of test results according to the following provisions (95% confidence level).
  • 10.2.1 Repeatability: The difference between two results obtained by repeated determination by the same operator shall not exceed the following value.
  • 10.2.2 Reproducibility: The difference between two determination results submitted by different laboratories shall not exceed the following value.

• Note: This precision was obtained from statistical tests using samples with base numbers of new oil from 6～70; base numbers of additives from 5～300; and base numbers of used oil from 5～27.
• Appendix A Indicator method precision: Judge the reliability of test results according to the following provisions (5% confidence level).
  • A9.1 Repeatability: The difference between two results obtained by repeated determination by the same operator shall not exceed the following value.

(Note: In source-text extraction, there is a suspected issue in the correspondence between the table values of A9.1 and the base number ranges; requires confirmation against the source standard (source-text extraction).)

• A9.2 Reproducibility: The difference between two determination results submitted by different laboratories shall not exceed the following value.

(Note: In source-text extraction, there is a suspected issue in the correspondence between the table values of A9.2 and the base number ranges; requires confirmation against the source standard (source-text extraction).)

11. Report

• 11.1 Take the arithmetic mean of two determination results as the base number of the sample. The base number is taken to three significant figures.
• 11.2 Report format: determination result of base number (SH/T 0251— Method A or Method B, direct titration or back titration).
• Appendix A: A10.1 Take the arithmetic mean of two determination results as the base number of the test sample. The base number is taken to three significant figures. A10.2 Report format: determination result of base number (SH/T 0251— indicator method).

12. Referenced documents

• GB 663 (the extracted entry begins with GB 663 but its title is garbled; verify the referenced document against the original standard)
• ASTM D2896-88 "Determination of base number of petroleum products (perchloric acid potentiometric titration method)" (referenced and adopted)

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