GB/T 8021-2003 Determination of saponification value of petroleum products

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Card type: Test method

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

• Standard number: GB/T 8021-2003
• Chinese title: Determination of saponification value of petroleum products
• English title: Petroleum products--Determination of saponification number
• Replacement relationship: Replaces GB/T 8021-1987 "Determination of saponification value of petroleum products". GB/T 8021-1987 is not equivalent to ISO 6293:1983.
• Adoption relationship: Modified adoption of ASTM D94-2000 "Determination of saponification value of petroleum products", redrafted according to ASTM D94-2000.
• Contains two methods: Method A—— color indicator method (Chapter 6 to Chapter 11); Method B—— potentiometric titration method (Chapter 12 to Chapter 19).
• Publication/implementation: Published on 2003-03-28, implemented on 2003-09-01.
• Drafting organization: Lanzhou Lubricating Oil Research and Development Center of PetroChina Company Limited; main drafters: Gao Jun, Xue Yonghong, Zhou Yabin.
• Secretariat: Petrochemical Research Institute of China Petroleum & Chemical Corporation; proposed by: former Bureau of Petroleum and Chemical Industry.

2. Scope of application and non-applicability

• 1.1 applies to the determination of the content of saponifiable components in petroleum products (such as lubricating oils, additives, transmission fluids, etc.) under the test conditions.
• 1.2 Because some sulfur, phosphorus, halogen compounds and compounds of other elements added to petroleum products can also consume acid or alkali, the determination results depend not only on the existing saponifiable components in the oil but are also affected by the above external factors. For petroleum products containing such compounds, as well as used internal combustion engine oils, crankcase oils and turbine oils, the external influencing factors shall be described in detail for the saponification value determination results.
• 1.2 Note: The substances mentioned above that affect the determination of saponification value include inorganic acids and certain organic acids, as well as most non-alkaline soaps, etc. These substances are generally considered to be non-saponifiable substances, and their presence can cause the saponification value determination results of fatty saponifiable substances to be high. If there is a hydrogen sulfide odor near the end point of the back titration, it indicates the presence of certain active sulfides in the sample. When there are other compounds containing active sulfur, nitrogen, phosphorus elements and other interfering substances in the sample, there is no obvious test phenomenon during the determination process that can identify the presence of these substances; the gravimetric determination of the actual content of fatty acids may be the most reliable method for determining these compounds.
• 1.3 This standard only describes certain special hazards related to the test process and does not mention all safety issues. Users should establish appropriate safety and protective measures and formulate corresponding management systems before using this standard.
• Non-applicability: The source text does not explicitly list "non-applicability" clauses.

3. Method principle

• 4.1 A certain amount of sample is dissolved in a suitable solvent, such as butanone (methyl ethyl ketone), xylene, solvent naphtha, or their mixed solvents, and heated together with a quantitative potassium hydroxide ethanol solution. The excess alkali is titrated with a standard acid solution, and finally the saponification value is calculated.
• 4.2 The titration end point can be determined by the color indicator method (Method A) or the potentiometric titration method (Method B).
• Terms: Saponification (saponify) — the process of hydrolyzing fats into fatty acid salts and alcohols under alkaline conditions; Saponification value (saponification number) — the number of milligrams of potassium hydroxide consumed per 1 g of sample under the test conditions (Note: The saponification value measured by this standard is affected by the presence of other substances that readily react with alkali, see the note in 1.2).

4. Reagents and materials (purity / preparation)

Method A (Chapter 7):

• 7.1 Unless otherwise specified, all chemical reagents used in the test are analytical grade reagents. Water shall meet the specifications for grade three water in GB/T 6682.
• 7.1.1 Ethanol: 95% ethanol, or anhydrous ethanol, or a mixture of 95% ethanol and methanol (volume ratio 9:1). Note 1: Flammable. Note 2: It has been found that using 99% isopropanol instead of ethanol can give very satisfactory results, but isopropanol cannot be used instead of ethanol in arbitration tests.
• 7.1.2 0.5 mol/L Hydrochloric acid standard solution: Standardized with potassium hydroxide ethanol standard solution (see 7.1.6), accurate to 0.000 5 mol/L during standardization. Note: When determining samples with a saponification value less than 1 mgKOH/g, to ensure determination precision, the 0.5 mol/L potassium hydroxide ethanol standard solution and the 0.5 mol/L hydrochloric acid standard solution used in the determination process shall be replaced with the corresponding 0.1 mol/L standard solutions.
• 7.1.3 Butanone: Chemically pure, stored in dark or brown bottles. Note: Flammable.
• 7.1.4 Petroleum ether: 60℃～90℃. Note: Flammable, harmful when inhaled.
• 7.1.5 Neutral phenolphthalein indicator solution: Dissolve 1.0 g±0.1 g phenolphthalein in 100 mL ethanol (see 7.1.1). Adjust to a pale red color with 0.1 mol/L potassium hydroxide ethanol solution to make it neutral.
• 7.1.6 0.5 mol/L Potassium hydroxide ethanol standard solution: Prepare a 0.5 mol/L potassium hydroxide ethanol solution with ethanol. Place this solution in the dark, let it stand for 24 h before use, and filter or siphon before use. The potassium hydroxide ethanol solution is standardized with potassium hydrogen phthalate standard solution (see Notes 2 and 7.1.7 of this clause). Note 1: Alternatively, a commercially available potassium hydroxide ampoule (carbonate-free) and 95% ethanol can be mixed to prepare a 0.5 mol/L or 0.1 mol/L potassium hydroxide ethanol standard solution; using this solution can give continuously stable blank values. Note 2: Because the volume expansion coefficient of organic liquids such as alcohols is relatively large, the temperature during standardization of the above standard solution should be close to the temperature during titration of the sample.
• 7.1.7 0.1 mol/L Potassium hydrogen phthalate standard solution: Dry potassium hydrogen phthalate at 110℃±5℃ to constant weight, then accurately weigh 2.042 2 g±0.000 2 g and place in a 100 mL volumetric flask, dissolve with water. Slight heating may be used to promote dissolution; after cooling, dilute with water to 100 mL.
• 7.1.8 Xylene. Note: Extremely flammable, harmful when inhaled.
• 7.1.9 Solvent naphtha: Meets the requirements in SH 0005.
• 7.2 Materials: Nitrogen: ordinary nitrogen, purity greater than 99%.

Method B (Chapter 13):

• Unless otherwise specified, all reagents used in the test are analytical grade reagents. Water shall meet the specifications for grade three water in GB/T 6682.
• 13.1 Ethanol: 95% ethanol, or anhydrous ethanol, or a mixture of 95% ethanol and methanol (volume ratio 9:1).
• 13.2 0.5 mol/L Hydrochloric acid standard solution: Standardized with potassium hydroxide ethanol standard solution (see the note in 7.1.2 and clause 13.6). Accurate to 0.000 5 mol/L during standardization.
• 13.3 Butanone: Chemically pure, stored in dark or brown bottles.
• 13.4 Petroleum ether: 60℃～90℃.
• 13.5 0.5 mol/L Potassium hydroxide ethanol standard solution: Prepare a 0.5 mol/L potassium hydroxide ethanol solution with ethanol. Place this solution in the dark, let it stand for 24 h before use, and filter or siphon before use. Note: A commercially available potassium hydroxide ampoule (carbonate-free) and 95% ethanol can be mixed to prepare a 0.5 mol/L or 0.1 mol/L potassium hydroxide ethanol standard solution; using this solution can give continuously stable blank values (see Note 2 in 7.1.6). The potassium hydroxide ethanol solution is standardized with potassium hydrogen phthalate standard solution (see Notes 2 and clause 13.6 of 7.1.6).
• 13.6 0.1 mol/L Potassium hydrogen phthalate standard solution: Dry potassium hydrogen phthalate at 110℃±5℃ to constant weight, then accurately weigh 2.042 2 g±0.000 2 g and place in a 100 mL volumetric flask, dissolve with water. If necessary, slight heating may be used to promote dissolution; after cooling, dilute with water to 100 mL.
• 13.7 3.0 mol/L Potassium chloride aqueous solution: Prepare a 1.0 L solution with water and 225.2 g potassium chloride.
• 13.8 Xylene.
• 13.9 Chlorobenzene.
• 13.10 Solvent naphtha: Meets the requirements in SH 0005.

5. Apparatus and equipment

Method A (Chapter 6):

• 6.1 Conical flask and condenser: An alkali-resistant conical flask of capacity 250 mL or 300 mL, which can be connected to a straight or spherical reflux condenser. The straight condenser is tightly connected to the conical flask through a ground joint; the spherical condenser is loosely connected to the conical flask to allow air passage. The water-cooled reflux condenser may also be replaced by an air condenser. Note: Do not use scratched or etched conical flasks, because potassium hydroxide will react at the scratches or etched areas. Glassware shall be chemically cleaned; chromic acid cleaning solution is recommended (Warning — chromic acid cleaning solution can cause severe burns, is a confirmed carcinogen; and is a strong oxidant that can cause fire upon contact with other substances; it is also hygroscopic). Chromium-free cleaning solutions or other similar cleaning solutions may also be used.
• 6.2 Water bath: A suitable water bath heated by electricity or steam.
• 6.3 Burette: 25 mL, or 50 mL, with graduations of 0.1 mL.
• 6.4 Pipette: 25 mL.
• 6.5 Volumetric flask: 100 mL.

Method B (Chapter 12):

• 12.1 Conical flask and condenser: An alkali-resistant conical flask of capacity 250 mL or 300 mL, which can be connected to a straight or spherical reflux condenser. The straight condenser is tightly connected to the conical flask through a ground joint, and the spherical condenser is loosely connected to the conical flask to allow air passage. The water-cooled reflux condenser may be replaced by an air condenser.
• 12.2 Water bath: A suitable water bath heated by electricity or steam.
• 12.3 A potentiometric titrator capable of manual or automatic recording.
• 12.4 Electrodes: High-quality electrodes must be used. A composite electrode or suitable glass electrode and reference electrode may be used, or a silver chloride/saturated potassium chloride alcohol solution or a glass sleeve-type calomel electrode filled with saturated potassium chloride solution. Daily cleaning and maintenance of the electrodes are very important.
• 12.5 Beaker: 250 mL or 300 mL. Note: Unless a combination electrode is used, potentiometric titration cannot be performed in the conical flask after heating under reflux, because the small mouth of the conical flask cannot accommodate the electrode pair.
• 12.6 Stirrer, titration vessel, titration stand: a typical potentiometric titration cell assembly is shown in Figure 2.
• 12.6.1 Adjustable-speed stirrer: magnetic stirrer or electric stirrer, both must be chemically inert. When an electric stirrer is used, it must be grounded to eliminate the influence on readings during titration from parts connected or not connected to the motor. When such a situation is encountered, it is best to use a magnetic stirrer.
• 12.6.2 Burette: 10 mL or 20 mL, with graduations of 0.05 mL, accuracy of ±0.02 mL, or an automatic burette of similar accuracy.
• 12.6.3 Titration stand: can hold the beaker, electrodes, stirrer, and burette, and when the beaker is moved it will not touch the electrodes, burette, or stirrer. Note: Some instruments are very sensitive and susceptible to interference from electrostatic fields. When the operator approaches the titration apparatus (beaker and electrodes), the pointer of the potentiometer can be seen swinging back and forth unstably. To prevent this, a grounded cylindrical copper mesh can be placed over the beaker to form an electrical shield.
• 12.7 Magnetic stirring bar: because during titration immiscible two phases appear and potassium chloride precipitates, the stirring conditions are critical, so vigorous stirring is very necessary. Note: If a large magnetic stirring bar is used, a lower speed is sufficient; if too small a stirring bar is used, even at the highest speed most of the solution cannot be stirred sufficiently. The most suitable magnetic stirring bar is a cylindrical stirring bar of length 2.5 cm, wrapped with 0.5 cm thick polytetrafluoroethylene. Spiral or paddle-shaped stirring can also be used.

6. Recommended operating conditions

• Reflux heating time: 30 min (8.1.1 Note 5: Although the standard reflux time requires 30 min, some esters can be completely saponified within 10 min; in addition, some difficult-to-saponify substances require more than two hours to be completely saponified. Unless coordinated and agreed with the relevant department, shortening or extending the saponification time is not allowed).
• Heating temperature: must be higher than the boiling point of methyl ethyl ketone 10℃～15℃ (methyl ethyl ketone boiling point is 78℃), shake frequently during reflux, and swirl the conical flask (8.1.1 Note 8).
• After saponification is completed, add 50 mL petroleum ether: it not only cleans the condenser tube but also cools the reaction mixture (8.1.1 Note 6).
• For insulating oil, it is not necessary to add 50 mL petroleum ether (8.1.1 Note 7).
• Sample amount selection: make the amount of titrant consumed by the sample during titration account for 40%～80% of the amount of titrant consumed in the blank titration, but the sample amount should not exceed 20 g (8.2.2, 15.2).
• Recommended sample amount (8.2.2): saponification value 181～400 mgKOH/g→1 g; 111～180→2 g; 71～110→3 g; 31～70→5 g; 16～30→10 g; 0～15→20 g.
• Method B titration speed: on the potentiometric titrator, titrate the blank with 0.5 mol/L hydrochloric acid standard solution at a speed of 2 mL/min (15.1.4).
• Method B potential reading: before adding titrant, the potential is approximately −520 mV; the first inflection point is relatively sharp, appearing near −300 mV; the second inflection point is very sharp, appearing near 50 mV (15.3.4.1).
• Method B stirring: adjust the rotation speed so that it is as high as possible without generating bubbles and splashing of the solution (15.1.3).

7. Sampling and sample preparation

• 8.2.1 Sampling: sample according to the GB/T 4756 standard.
• 8.2.2 The sample must be in a homogeneous state before determination. Appropriately select the sample amount so that the amount of titrant consumed by the sample during titration accounts for 40%～80% of the amount of titrant consumed in the blank titration, but the sample amount should not exceed 20 g. For recommended sample amounts see Section 6.
• 8.3.1 Weigh the sample from a small beaker into a conical flask, and weigh accurately to 0.01 g, add 25 mL±1 mL methyl ethyl ketone or other optional solvent, then accurately measure 25 mL±0.03 mL potassium hydroxide ethanol standard solution with a burette or pipette and inject it into the flask.
• 8.3.2 For samples that are difficult to dissolve, such as lubricating oils or additives, before adding methyl ethyl ketone, first add 15 mL～25 mL of solvent naphtha or xylene.
• 15.2 The sample must be in a homogeneous state before determination. Appropriately select the sample amount so that the amount of titrant consumed by the sample accounts for 40%～80% of the amount of titrant consumed in the blank titration, but the sample amount should not exceed 20 g (see 8.2.2).
• 15.3.1 Weigh the sample from a small beaker into a conical flask, and weigh accurately to 0.01 g. Add 25 mL±1 mL methyl ethyl ketone or other optional solvent, then accurately measure 25 mL±0.03 mL potassium hydroxide ethanol standard solution with a burette or pipette (see Note 3 in 8.1.1) and inject it into the flask.
• 15.3.2 For samples that are difficult to dissolve, such as lubricating oils or additives, before adding methyl ethyl ketone, first add 15 mL～25 mL of solvent naphtha or xylene.

8. Analytical procedure

Method A (Chapter 8):

• 8.1 Blank test
  • 8.1.1 For each batch of samples (one or more), the blank value must be determined simultaneously during the determination. Accurately measure 25 mL±0.03 mL of potassium hydroxide ethanol standard solution with a burette or pipette, add it to a conical flask, and add 25 mL±1 mL of methyl ethyl ketone or other optional solvent. Connect the condenser tube and the conical flask and heat, heating under reflux for the same length of time as when determining the sample. Immediately after reflux ends, carefully add 50 mL of petroleum ether along the condenser tube (when using a spherical condenser tube, slightly loosen the connection between the condenser tube and the conical flask), and during titration add 3 drops of neutral phenolphthalein indicator solution. To increase the shaking intensity, at this time place a suitably sized stirring bar into the solution, and titrate while hot with 0.5 mol/L hydrochloric acid standard solution under nitrogen protection. No further heating is required during the blank titration.
    • Note 1: The following titration conditions may also be used: the titrant is 0.5 mol/L (or 0.1 mol/L) hydrochloric acid ethanol standard solution, and no nitrogen protection is added during titration. However, in case of dispute, hydrochloric acid standard solution must be used, and nitrogen protection must be added during titration.
    • Note 2: For samples with very high precision requirements, two blank tests should be performed and the average value taken. For routine tests, only one blank value needs to be determined.
    • Note 3: When using a pipette to transfer the potassium hydroxide ethanol standard solution, the tip of the pipette must be rested against the wall of the conical flask for 30 s to ensure complete drainage.
    • Note 4: The reflux condenser tube must be clamped tightly to prevent it from falling onto the hot bath and breaking the glassware.
    • Note 5: Standard reflux time 30 min (see Section 6 for details).
    • Note 6: After saponification is completed, adding 50 mL petroleum ether not only cleans the condenser tube but also cools the reaction mixture.
    • Note 7: For insulating oil, it is not necessary to add 50 mL petroleum ether.
    • Note 8: The heating temperature must be higher than the boiling point of methyl ethyl ketone 10℃～15℃ (methyl ethyl ketone boiling point is 78℃), shake frequently during reflux, and swirl the conical flask.
  • 8.1.2 After the color of the indicator disappears, add a few more drops of indicator solution. If the titration solution develops color again after adding the indicator, continue titrating until the color disappears, then add a few more drops of indicator, and if necessary, continue titrating until the endpoint. When the color of the indicator completely disappears and the titration solution no longer develops color after adding the indicator, it indicates that the titration endpoint has been reached; record the blank value V₁. Note: When approaching the titration endpoint, to prevent emulsification of the titration mixture, the conical flask should be swirled vigorously to ensure sufficient contact between the two phases.
• 8.2 Sample preparation (see Section 7)
• 8.3 Sample determination
  • 8.3.1 See Section 7.
  • 8.3.2 See Section 7.
  • 8.3.3 Connect the condenser tube and the conical flask and heat; after reflux begins, continue heating for 30 min (see Note 5 in 8.1.1). Then immediately carefully pour 50 mL of petroleum ether along the inner wall of the condenser tube into the conical flask (see Note 7 in 8.1.1) (Warning—do not pour petroleum ether onto the water bath). If a spherical condenser tube is used, slightly loosen the connection between the condenser tube and the conical flask before adding the petroleum ether.
  • 8.3.4 Add 3 drops of neutral phenolphthalein indicator to the sample solution in the conical flask. To increase the shaking intensity, place a suitably sized stirring bar into this solution, and titrate while hot with 0.5 mol/L hydrochloric acid standard solution under nitrogen protection (no further heating). After the color of the indicator disappears, add a few more drops of indicator solution. If the titration solution develops color again after adding the indicator, continue titrating until the color disappears, then add a few more drops of indicator. If necessary, continue titrating until the endpoint. When the color of the indicator completely disappears and the solution does not develop color after adding the indicator, it indicates that the titration endpoint has been reached; record the titrant consumption at this time as V₂. When determining wax-containing samples, to prevent the sample from solidifying during titration, the solution may be reheated if necessary.

Method B (Chapter 15):

• 15.1 Blank test
  • 15.1.1 For each batch of samples (one or more) (see Note 2 in 8.1.1), a blank value shall be determined simultaneously during the measurement. Using a burette or pipette (see Note 3 in 8.1.1), accurately measure 25 mL±0.03 mL of potassium hydroxide ethanol standard solution and add it to the conical flask, and add 25 mL±1 mL of butanone or other optional solvent. Connect the condenser and the conical flask and heat (see Note 8 in 8.1.1), after continuing heating for 30 min from the start of reflux (see Note 5 in 8.1.1), immediately carefully pour 50 mL of petroleum ether (see Note 7 in 8.1.1) along the inner wall of the condenser into the conical flask, this process must be very careful to prevent the petroleum ether from rushing out of the condenser (when using a spherical condenser, slightly loosen the joint between the condenser and the conical flask), then while hot (without further heating) perform potentiometric titration with 0.5 mol/L of hydrochloric acid standard solution.
  • 15.1.2 Transfer the solution in the conical flask to a 200 mL beaker, then carefully rinse the conical flask twice with 10 mL petroleum ether respectively, and pour the washings into the beaker.
  • 15.1.3 Place a magnetic stirring bar into the beaker containing the titration solution, then place this solution on a magnetic stirrer. Insert the electrodes into the solution and as far away from the stirring bar as possible. Adjust the speed so that it is as high as possible without generating bubbles and splashing of the solution.
  • 15.1.4 On the potentiometric titrator, titrate the blank with 0.5 mol/L of hydrochloric acid standard solution at a rate of 2 mL/min. There are two inflection points corresponding to the equivalence points. One is the inflection point of free potassium hydroxide (counted as V_B in 17.1), the other is the inflection point of the small amount of potassium carbonate contained in commercial potassium hydroxide and the potassium carbonate generated by the solution absorbing carbon dioxide from the air during titration (see Figure 3).
  • 15.1.5 In the early stage of the blank titration, a certain amount of titrant may be added first to speed up the titration process.
• 15.2 Sample preparation (see Section 7)
• 15.3 Sample determination
  • 15.3.1 See Section 7.
  • 15.3.2 See Section 7.
  • 15.3.3 Connect the condenser and the conical flask and heat, after reflux begins continue heating for 30 min (see Note 4 and Note 5 in 8.1.1). Then immediately carefully pour 50 mL of petroleum ether along the inner wall of the condenser into the conical flask (Warning—do not pour the petroleum ether onto the water bath). If a spherical condenser is used, slightly loosen the joint between the condenser and the conical flask before adding the petroleum ether.
  • 15.3.4 While hot, titrate the above solution with 0.5 mol/L hydrochloric acid standard solution (without further heating). The titration procedure is the same as the blank titration steps (see clause 15.1). Figure 3 gives a complete sample titration curve. The difference between sample titration and blank titration is that the blank titration does not pre-add titrant, and in addition, the titration conditions are not too stringent.
  • 15.3.4.1 The potential reading is relatively stable. Before adding titrant, the potential is approximately −520 mV. The first inflection point is relatively sharp, appearing near −300 mV, and the second inflection point is very sharp, appearing near 50 mV.

Chapter 14 Preparation, inspection and maintenance of the electrode system:

• 14.1 Preparation of electrodes
  • 14.1.1 If the internal liquid of the calomel electrode is to be changed from a non-aqueous salt bridge to an aqueous salt bridge, first empty the non-aqueous solution, rinse several times with water and methanol (or anhydrous ethanol), then rinse the outer sleeve (salt bridge) several times with 3.0 mol/L of potassium chloride electrolyte. Finally, fill the electrode from the injection port with 3.0 mol/L of potassium chloride aqueous solution.
  • 14.1.2 If a sleeve-type electrode is used, first carefully loosen the glass sleeve, thoroughly wipe the ground surface of the sleeve, then loosely reposition the sleeve, and drop a few drops of electrolyte on it to completely wet the ground surface of the sleeve. Tighten the sleeve, fill the electrode from the injection port with 3.0 mol/L of potassium chloride aqueous solution, and clean the electrode with chlorobenzene.
  • 14.1.3 During use, the liquid level of the electrolyte in the calomel electrode must be higher than the liquid level in the titration cup to prevent components in the titration cup from entering the calomel electrode and contaminating the salt bridge. When not in use, fill the calomel electrode with 3.0 mol/L of potassium chloride aqueous solution, plug the injection port with a stopper, then insert both the calomel electrode and the glass electrode into a beaker containing water, and always keep the liquid level of the electrolyte in the calomel electrode higher than the water level.
• 14.2 Inspection of electrodes: New electrodes or electrodes used once a month shall be inspected by the method of calibrating 10 mL of 0.5 mol/L of potassium hydroxide ethanol standard solution with 0.5 mol/L of hydrochloric acid standard solution.
• 14.3 Maintenance of electrodes
  • 14.3.1 When the glass electrode is in continuous use, it shall be cleaned at least once a week with cold chromic acid cleaning solution or non-chromium cleaning solution.
  • 14.3.2 The 3.0 mol/L of potassium chloride aqueous solution in the calomel electrode shall be replaced at least once a week, filling to the injection port each time, and ensuring that potassium chloride crystals are present in the solution. At all times, the liquid level of the electrolyte in the calomel electrode shall be kept higher than the liquid level of the solution in the titration cup.
  • 14.3.3 When not in use, insert the lower half of the electrode pair into a beaker containing water. When there is a long interval between two adjacent titrations, the electrode pair must not be left in the titration solution. The electrodes should be handled gently during operation. Note: Thoroughly cleaning the electrodes, removing foreign matter at the sleeve joint, and performing daily inspections are very important for obtaining good repeatability results. Because external contaminants can cause unpredictable, unstable and not easily detected liquid junction potentials, leading to poor repeatability of measurement results.
  • 14.3.4 At the end of the blank titration and between two consecutive titration processes, a thin layer of potassium chloride crystals will coat the electrodes and the tip of the burette. At this time, a plastic wash bottle with a nozzle containing water can be used to rinse to remove the potassium chloride crystals, and the electrodes are inserted into a beaker containing water to rinse for a few minutes, then the water on the electrode surface is blotted dry with filter paper, but the electrodes must not be wiped.
  • 14.3.5 After continuous determination of a batch of samples, a mixture of potassium chloride crystals and sample particles will cover the electrodes and the tip of the burette. At this time, the electrodes and the tip of the burette can be inserted into a beaker containing the following solutions for rinsing: 50 mL of solvent naphtha; 38 mL of isopropanol; 38 mL of water. Stir for a sufficiently long time (less than 5 min) to completely dissolve the covering, and rinse away the residual washing liquid with water. Then insert the electrodes into a beaker containing water and rinse for a few more seconds. Then blot the water on the electrode surface dry with filter paper, but do not wipe the electrodes.
  • 14.3.6 The electrodes must be firmly fixed on the support to prevent the electrodes from vibrating during vigorous stirring. Electrode vibration can cause electronic noise, which in turn interferes with the detection of the titration endpoint and reduces the repeatability of measurement results.

Chapter 16 Quality control checks:

• 16.1 Ensure the accuracy of the measurement method by measuring quality control samples, and representative samples should be selected for testing as much as possible.
• 16.2 Before using this standard, the user shall determine the average value and upper and lower limits of the saponification value of the quality control sample through actual measurement.
• 16.3 Use quality control charts and other statistical comparison methods to record and analyze quality control data, and obtain quality control information for the entire testing process. Any abnormal quality control data should be investigated and the root cause found, and these investigation results prompt the standard user to correct the entire testing process.
• 16.4 The frequency of quality control evaluation depends on the strictness of the test, the stability of the test process, and the actual needs of the customer. Generally speaking, quality control samples must be analyzed on each measurement working day. If a large number of samples need routine analysis, the frequency of quality control evaluation must be increased. However, when the test results are within the control range, the quality control tests can be reduced accordingly. Periodically check the precision of the quality control tests according to the precision data of this method to ensure the quality of the test data.
• 16.5 It is recommended to select those samples that can represent daily testing as quality control test samples as much as possible. During the planned testing period, sufficient quality control samples must be provided, and these samples must be uniform and stable under the predetermined storage conditions.

9. Qualitative and quantitative and calculation formulas

• Method A (9.1) Sample saponification value A (mgKOH/g) is calculated according to formula (1): A = 56.1c(V₁ − V₂)/m Where: c—— concentration of hydrochloric acid standard solution, mol/L; 56.1—— molar mass of potassium hydroxide, g/mol; V₁——volume of hydrochloric acid standard solution consumed for titrating the blank, mL; V₂——volume of hydrochloric acid standard solution consumed for titrating the sample, mL; m—— sample amount, g.
• Method B (17.1) Sample saponification value A (mgKOH/g) is calculated according to formula (2): A = 56.1c(V_B − V_S)/m Where: 56.1—— molar mass of potassium hydroxide, g/mol; c—— concentration of hydrochloric acid standard solution, mol/L; V_B—— volume of hydrochloric acid standard solution consumed for titrating the blank, mL; V_S—— volume of hydrochloric acid standard solution consumed for titrating the sample, mL; m—— sample amount, g.
• 17.2 The first inflection point is the equivalence point of hydroxide, and is therefore confirmed as the titration endpoint. If the added potassium hydroxide contains carbonate contaminants or the solution absorbs carbon dioxide from the air during titration to form carbonate, a second inflection point will appear (see Figure 3). If this situation is found, the first inflection point is used as the V_B of the blank titration endpoint and the V_S of the sample titration endpoint.

10. Precision

Method A (11.1):

• Judge the reliability of the measurement results according to Figure 1 (95% confidence level). Note: Figure 1 does not provide precision data for dark-colored new oils, used oils, or oils whose solution color darkens during saponification. Because dark-colored oils interfere with the judgment of the titration endpoint. For such oil samples, the potentiometric titration method (Method B) can be used for determination.
• 11.1.1 Repeatability——The difference between two results obtained by the same operator using the same instrument under the same test conditions for repeated determination of the same sample shall not exceed the data shown in Figure 1.
• 11.1.2 Reproducibility——The difference between two independent results obtained by different operators in different laboratories for the determination of the same sample shall not exceed the data shown in Figure 1.
• 11.2 Bias: Since this method is a test method and there is no reference material for comparison, no bias data has been established for this method.

Method B (19.1):

• Judge the reliability of the results according to the following provisions (95% confidence level).
• 19.1.1 Repeatability—the difference between two results obtained by the same operator using the same instrument under the same test conditions on the same test sample for repeated determinations shall not exceed 2.76 mgKOH/g.
• 19.1.2 Reproducibility—the difference between two independent results obtained by different operators in different laboratories on the same test sample shall not exceed 10.4 mgKOH/g.
• 19.2 Bias: Because this method is a test method and there is no reference material available for comparison, no bias data for this method have been established.

11. Report

Method A (Chapter 10):

• For test samples with saponification value lower than 50 mgKOH/g, report the result to the nearest 0.5 mgKOH/g.
• For test samples with saponification value greater than or equal to 50 mgKOH/g, report the result to the nearest integer.
• For electrical insulating oil, report the result to the nearest 0.1 mgKOH/g.
• When reporting the saponification value result, indicate the referenced method, such as: method A of GB/T 8021.

Method B (Chapter 18):

• For test samples with saponification value lower than 50 mgKOH/g, report the result to the nearest 0.5 mgKOH/g.
• For test samples with saponification value greater than or equal to 50 mgKOH/g, report the result to the nearest integer.
• For electrical insulating oil, report the result to the nearest 0.1 mgKOH/g.
• When reporting the saponification value result, indicate the referenced method: such as method B of GB/T 8021.

12. Referenced Documents

• GB/T 4756 Petroleum liquids—Manual sampling (GB/T 4756-1998, eqv ISO 3170:1988)
• GB/T 6682 Specifications and test methods for water used in analytical laboratories (GB/T 6682-1992, neq ISO 3696:1987)
• SH 0005 Solvent naphtha for the paint industry
• Reference adopted: ASTM D94-2000 "Determination of saponification value of 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 Q&A Reference