GB/T 11133-2015 Determination of Water Content in Petroleum Products, Lubricating Oils and Additives - Karl Fischer Coulometric Titration Method

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Card type: Test method

1. Method number / Full name / English name / Replacement relationship

• Standard number: GB/T 11133-2015
• Chinese name: Determination of Water Content in Petroleum Products, Lubricating Oils and Additives - Karl Fischer Coulometric Titration Method
• English name: Standard test method for determination of water in petroleum products, lubricating oils, and additives—Coulometric Karl Fischer titration method
• Replacement relationship: Replaces GB/T 11133—1989 "Determination of Water Content in Liquid Petroleum Products (Karl Fischer Method)"
• Adoption relationship: Modified adoption using redrafting method of ASTM D6304-07
• Publication/Implementation: Published on 2015-12-31, implemented on 2016-06-01
• Custodianship: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC 280/SC 1)
• Drafting organization: Lubricant Branch of China Petroleum & Chemical Corporation
• Main drafters: Zhou Bo, Tian Deying
• First publication: First published in 1989, this is the first revision

2. Scope of application and non-applicability

• This standard specifies a method for direct determination of water content in petroleum products and hydrocarbon compounds using an automatic titrator.
• The direct titration method determines water content in the range of 10 mg/kg~25 000 mg/kg.
• This standard also specifies an indirect method for determining water content of samples: water in the sample is separated by heating, carried by dry inert gas into a Karl Fischer titrator for analysis.
• Applicable to the determination of water content in additives, lubricating oils, base oils, automatic transmission fluids, hydrocarbon solvents and other petroleum products using commercially available Karl Fischer coulometric reagents.
• By selecting an appropriate sample injection amount, the determination range is from milligram/kilogram level to mass percentage level.
• Interferences: Interferences of mercaptans, sulfides, sulfur and other compounds on the test method are described in Chapter 4.
• Note: For the method of determining water content in liquid petroleum products using Karl Fischer volumetric method, see Appendix A.
• Non-applicability: No explicit "non-applicability" clause is listed in the source text.

3. Method principle

• 3.1 A certain amount of sample is added to the titration cell of a Karl Fischer coulometer. The iodine generated at the anode of the titration cell undergoes the Karl Fischer reaction with water in the sample in a ratio of 1:1. When all the water in the titration cell has been consumed by the reaction, the titrator determines the titration endpoint by detecting the electrical signal generated by excess iodine and terminates the titration. According to Faraday's law, the amount of water titrated is proportional to the total integrated current.
• 3.2 The measurement unit for sample injection amount can be either mass unit or volume unit.
• 3.3 For samples with high viscosity or interfering reactions, a water evaporator can be used for measurement: the sample is added to the water evaporator and heated, and the evaporated water is carried by dry carrier gas into the Karl Fischer titration cell for titration analysis.

4. Reagents and materials (purity / preparation)

• 6.1 Distilled water: Meets the requirements for Grade 2 water in GB/T 6682.
• 6.2 Xylene: Analytical reagent grade, water content less than 300 mg/kg, dried with molecular sieve before use. Warning—Flammable, vapor toxic.
• 6.3 Karl Fischer reagent: Commercially available standard reagent for Karl Fischer coulometric titration.
  • 6.3.1 Anolyte: Prepared by mixing commercially available Karl Fischer anodic reagent with xylene in a volume ratio of 6:4. It is recommended to use freshly prepared electrolyte. Different ratios can be prepared according to specific reagent, instrument and sample requirements. For some samples, xylene may not need to be added; for other samples, xylene may need to be added to improve solubility. Warning—Flammable, toxic by inhalation, ingestion or skin absorption. Note: Toluene can be used instead of xylene; however, the precision data in Chapter 15 were obtained using xylene.
  • 6.3.2 Catholyte: It is recommended to use commercially available freshly prepared standard catholyte. Warning—Flammable, can be fatal if inhaled, swallowed or absorbed through skin, may have carcinogenic risk.
  • 6.3.3 One-component Karl Fischer electrolyte: Can replace anolyte in titration units with a diaphragm or replace two-component electrolyte in titration units without a diaphragm. It is recommended to use commercially available freshly prepared electrolyte. It can be prepared with xylene in different ratios according to specific reagent, instrument and sample requirements. For some samples, xylene may not need to be added; for other samples, xylene may need to be added to improve solubility. Warning—Flammable, can be fatal if inhaled, swallowed or absorbed through skin, may have carcinogenic risk.
  • 6.3.4 If the sample contains ketones, commercially available Karl Fischer reagents specifically for water content determination of such substances can be used. Note: Since some laboratories often do not know whether the samples being tested contain ketones, adding ketone-suppressing reagent is included as part of the standard analysis procedure.
• 6.4 n-Hexane: Analytical reagent grade, water content less than 200 mg/kg, dried with molecular sieve before use. Warning—Flammable, vapor toxic.
• 6.5 White oil: Analytical reagent grade.
• 6.6 5A Molecular sieve: Particle size 1.70 mm~2.36 mm.

5. Instruments and equipment

• 5.1 Karl Fischer coulometric titrator: Commercially available automatic Karl Fischer coulometric titrators of various models, consisting of a titration cell, platinum electrode, magnetic stirrer and control unit. For specific operating methods, refer to the manufacturer's operating instructions.
• 5.2 Water evaporator: Commercially available automatic water evaporators of various models. For specific operating methods, refer to the manufacturer's operating instructions.
• 5.3 Syringe: Suitable for injecting samples into the titration cell using a glass syringe with precise graduations or a disposable syringe. The syringe needle (hypodermic needle with Luer taper fitting) should be long enough to penetrate the injection port septum and immerse below the surface of the anolyte. The needle bore should be as small as possible, but should ensure that no back pressure or blockage occurs during sample aspiration.
  • 5.3.1 Syringe of capacity 10 μL: Capable of accuracy to 0.1 μL, with a needle conforming to 5.3. This type of syringe can accurately inject trace amounts of water to check reagent performance, see Chapter 10.
  • 5.3.2 Select the following syringe capacities according to Table 1: 250 μL, accurate to 10 μL; 500 μL, accurate to 10 μL; 1 mL, accurate to 0.01 mL; 2 mL, accurate to 0.01 mL; 3 mL, accurate to 0.01 mL. It is recommended to use glass syringes with good airtightness equipped with plungers made of tetrafluoroethylene-type resin material and Luer taper fittings.
• 5.4 Balance: Sensitivity of 0.1 mg.

6. Recommended operating conditions

• 8.1 Prepare and operate the titration equipment according to the titrator manufacturer's equipment instructions.
• 8.2 Seal all ports and connections to prevent moisture from air entering the instrument.
• 8.3 If using two-component Karl Fischer electrolyte:
  • 8.3.1 According to the Karl Fischer titrator manufacturer's recommendation, add an appropriate amount of Karl Fischer anolyte to the anode (outer) compartment of the titration cell.
  • 8.3.2 Add Karl Fischer catholyte to the cathode (inner) compartment of the titration cell. The catholyte level should be lower than the anolyte level by 2 mm~3 mm.
• 8.4 If using one-component Karl Fischer electrolyte, according to the Karl Fischer titrator manufacturer's recommendation, add an appropriate amount of electrolyte directly into the titration cell.
• 8.5 Turn on the instrument, turn on the magnetic stirring device, and adjust the stirring speed to be uniform and stable. Pre-titrate the residual trace water in the titration cell until the titration endpoint is reached. Before proceeding to the next step, ensure that the background current (or background titration rate) is stable and below the manufacturer's recommended maximum value. Note: If the instrument shows high background current for a long time, it may be due to trace water on the inner wall of the titration cell. Gently swirl the titration cell (or increase the stirring rate) to allow the electrolyte to rinse the inner wall of the container. Keeping the titrator turned on can stabilize the background current at a lower level.
• 12.1 Water evaporator indirect titration method: Before the test, add 10 mL white oil to the evaporator accessory, and purge with 300 mL/min dry nitrogen. Heat the white oil to the heating temperature recommended by the instrument manufacturer for the specific instrument type.

7. Sampling and sample preparation

• 7.1 Sampling refers to all steps of obtaining a certain amount of representative sample from pipelines, storage tanks or other systems and placing it in a sample container for analysis in a laboratory or testing institution.
• 7.2 Laboratory sample: A petroleum product sample analyzed by this standard in a laboratory or testing institution. The laboratory sample of this standard should be a representative sample taken according to the procedures specified in GB/T 4756, and handled and mixed according to the requirements of ASTM D5854. Note: Examples of laboratory samples include: bottled samples obtained by manual sampling, samples sealed in containers obtained by automatic samplers, and stored samples retained from previous analyses.
• 7.3 Test sample: A certain amount of sample taken from the laboratory sample for analysis by this test method.
• 7.4 According to the expected water content of the test sample, select the sample injection amount according to Table 1.

Table 1 Sample injection amount based on expected water content of the sample

• 12.2 Accurately weigh 5 g±0.01 g of the viscous sample and add it to a 10 mL volumetric flask, then add anhydrous n-hexane to the mark. Shake the volumetric flask until the sample is completely dissolved. Note 1: All glassware must be thoroughly dried before use. The presence of trace moisture will lead to inaccurate results. For the first few analyses, a standard substance with known water content must be tested to determine whether the system is working properly. For water-ethanol standard substances, sealing with a rubber septum is more effective than with a rubber stopper. Note 2: If the water content of the sample is very low, the sample injection amount may be appropriately increased.

8. Analytical Procedure

• 9 Calibration and standardization: Theoretically, this method does not require standardization, because according to metrology and the principle of the Karl Fischer reaction, the amount of water titrated is directly proportional to the amount of coulombic charge consumed. However, in actual operation, as the number of tests increases, the performance of the reagent will decrease. By injecting a known amount (a typical value within the water content range of the test sample) of pure water (see 6.1), such as 10 000 μg or 10 μL, the reagent performance can be monitored periodically. The monitoring interval may be when a new reagent is first used for the initial determination, and thereafter after every ten determinations (see 10.3).
• 10 Test Procedure A (direct mass titration method):
  • 10.1 According to 8.3 or 8.4, add freshly prepared electrolyte to the titration unit, turn on the instrument, and pre-titrate the reagent until the endpoint conditions described in Chapter 8 are reached.
  • 10.2 Add the sample to the titration cell according to the following steps:
    • 10.2.1 Select a clean, dry syringe of suitable capacity (see Table 1 and the note), draw in and discard at least 3 portions of sample. Then immediately draw in one portion of sample, wipe the needle with a clean filter paper, and weigh to the nearest 0.1 mg. Insert the syringe needle through the instrument injection port septum, immerse it below the surface of the anolyte, start the titration, and inject the sample. Withdraw the syringe, wipe the needle with a filter paper, and weigh to the nearest 0.1 mg. After reaching the titration endpoint, record the micrograms of water titrated. Note: If the water content in the sample is unknown, to avoid excessively long titration time and reagent consumption, a small amount of sample may be added for a trial. Adjust the sample injection amount according to the titration result.
    • 10.2.2 After the titration is completed, when the background current or titration rate returns to a stable reading as described in 8.5, the test may be continued according to the procedure in 10.2.1.
  • 10.3 Replace the electrolyte and re-prepare the instrument according to the procedure in Chapter 8 when the following situations occur:
    • 10.3.1 The value of the background current remains continuously high and unstable.
    • 10.3.2 Stratification appears in the anode region or the oil sample covers the electrode surface.
    • 10.3.3 The amount of sample injected into the titration vessel exceeds one quarter of the total volume of the solution in the anode compartment.
    • 10.3.4 The electrolyte in the titration cell has not been replaced for more than one week.
    • 10.3.5 When the instrument displays an error message: directly or indirectly suggesting replacement of the electrolyte (please consult the instrument operation manual).
    • 10.3.6 The measurement result of injecting a 10 μL pure water sample exceeds the range of 10 000 μg±200 μg.
  • 10.4 If the titration cell is contaminated by the sample, the anode and cathode parts must be thoroughly cleaned with xylene. Acetone or other ketones should not be used for cleaning. Blockage of the electrode diaphragm will cause instrument malfunction.
  • 10.5 If the sample is too viscous to be easily drawn with a syringe, the sample may first be placed in a dry, clean bottle, and the mass of the bottle, dropper, and sample weighed. Then, by an appropriate method such as using a dropper, rapidly transfer a suitable amount of sample into the titration cell. Weigh the bottle, dropper, and sample again, and perform the titration according to the procedure in 10.2.
• 11 Test Procedure B (direct volumetric titration method): Use a syringe to draw an appropriate volume of sample, and perform the test according to the procedure from 10.2.1 to 10.5 in Procedure A. Note 1: Use a Karl Fischer coulometric analyzer to titrate a certain volume of sample to the electrochemical endpoint. Unless otherwise specified, the other test procedures are the same as Procedure A. However, it should be ensured that the accuracy of the sample volume measurement is not affected by the vapor pressure and viscosity of the sample. Note 2: The arbitration method for the determination of water content in liquid petroleum products by the Karl Fischer coulometric method is Procedure A, that is, a certain mass of sample is taken for analysis. Note 3: The presence of bubbles in the syringe will affect the precision of the test. The tendency of each sample to generate bubbles is affected by the combined effect of two factors: the sample type and the corresponding vapor pressure. High-precision syringes have been shown to be difficult for accurately measuring the volume of viscous samples. Note 4: Appendix A provides helpful information for obtaining reliable results.
• 12 Test Procedure C (indirect titration method with water evaporator):
  • 12.1 The indirect titration method with a water evaporator is suitable for samples that cannot be directly titrated according to Procedure A or B due to high viscosity, the presence of interfering reactions, or very low water content (for example, less than 100 mg/kg). Before the test, add 10 mL white oil to the evaporator accessory, and purge with 300 mL/min dry nitrogen. Heat the white oil to the heating temperature recommended by the instrument manufacturer for the specific instrument type.
  • 12.2 Accurately weigh 5 g±0.01 g of the viscous sample and add it to a 10 mL volumetric flask, then add anhydrous n-hexane to the mark. Shake the volumetric flask until the sample is completely dissolved.
  • 12.3 Inject 1 mL of the dissolved sample into the evaporator. Start the operation according to the process from 10.1 to 10.5 in Procedure A. After reaching the titration endpoint, record the micrograms of water displayed on the digital display.
• 13 Quality control check: The performance of the equipment in use or the test process can be confirmed by analyzing a quality control sample (QC sample) daily. The selected QC sample should be representative of typical samples analyzed routinely. If a large number of samples need to be analyzed in daily work, the frequency of quality control checks should be increased. The data of the quality control sample may be analyzed using control charts or other statistical techniques. If the analytical results are within the statistical control limits, the frequency of checks may be reduced. However, if the measured data indicate that the laboratory is out of control, for example, the analytical data exceed the laboratory control limits, then the cause should be investigated and corrective measures taken before continuing the test to bring the analytical process back into a controlled state. For future use, it should be ensured that the quantity of the quality control sample is sufficient and that it can remain homogeneous and stable under the expected storage conditions. Before monitoring the measurement process, the method operator needs to determine the average water content of the QC sample and establish control limits. To ensure the quality of the data, the precision of the water content data of the quality control sample should be checked according to the precision of the method.

9. Qualitative and Quantitative Determination and Calculation Formulas

• 14.1 Calculate the water content in the sample according to formula (1) or formula (2):
  • X₁ = W₁ / W₂ ………………(1)
  • X₂ = V₁ / V₂ ………………(2)
  • Where: X₁ — water content in the sample, in milligrams per kilogram (mg/kg); X₂ — water content in the sample, in microliters per milliliter (μL/mL); W₁ — mass of water titrated, in micrograms (μg); W₂ — sample injection amount, in grams (g); V₁ — volume of water titrated, in microliters (μL); V₂ — sample injection amount, in milliliters (mL).
• 14.2 Calculate the mass fraction (%) or volume fraction (%) of water content in the sample according to formula (3) or formula (4):
  • X₃ = W₁ / 10000 × W₂ ………………(3)
  • X₄ = V₁ / 10 × V₂ ………………(4)
  • Where: X₃ — mass fraction of water content in the sample, %; X₄ — volume fraction of water content in the sample, %. Among them, the meanings of W₁, W₂, V₁, and V₂ are the same as described in 14.1.
  • Requires confirmation against the source standard (source-text extraction): the denominator form in formulas (3) and (4) is suspected to be source-text extraction noise; no explicit parentheses are provided in the available source.
• 14.3 Formulas (5) and (6) may be used to calculate the water content in the sample expressed in different units, to obtain volume fraction from mass fraction, or vice versa.
  • X₄ = X₃ × ρ₁ / ρ₂ ………………(5)
  • X₃ = X₄ × ρ₂ / ρ₁ ………………(6)
  • The density may be measured using GB/T 1884 or SH/T 0604. If the unit of the sample density is g/mL, and the density of water measured at the test temperature can be approximated as 1 g/mL, formulas (5) and (6) can be simplified to formulas (7) and (8):
  • X₄ = X₃ × ρ₁ ………………(7)
  • X₃ = X₄ / ρ₁ ………………(8)
  • Where: ρ₁ — density of the sample at the test temperature, in grams per milliliter (g/mL); ρ₂ — density of water at the same temperature as the test temperature of the sample, in grams per milliliter (g/mL). Among them, the meanings of X₃ and X₄ are the same as described in 14.2.
  • Requires confirmation against the source standard (source-text extraction): the correspondence between the variable subscripts in formulas (5) to (8) and 14.2 is suspected to have source-text extraction confusion.

10. Precision

• 15.1 Precision: Judge the reliability of the test results according to the following provisions (95% confidence level).
  • 15.1.1 Repeatability: For the same operator, in the same laboratory, using the same instrument, according to the same method, the difference between two test results obtained consecutively on the same sample shall not exceed the corresponding value in Table 2.
  • 15.1.2 Reproducibility: the difference between two single, independent test results obtained by different operators, in different laboratories, using different instruments, following the same method, on the same test sample shall not exceed the corresponding value in Table 2.

Table 2 Precision

• Where X is the average of two test results, volume fraction (%) or mass fraction (%).
• Requires confirmation against the source standard (source-text extraction): the exponent superscript in Table 2 is suspected to contain source-text extraction noise; the clear exponent is not provided in the available source.
• 15.2 Bias: because the determination of water content by the coulometric method is defined only by this test method, there is no bias in determining water content by this test method.

11. Report

• 16.1 Report the water content in the test sample, to the nearest 1 mg/kg or 0.01% (mass fraction); or to the nearest 1 μL/mL or 0.01% (volume fraction).
• The report shall indicate which of the test procedures A, B, C in this standard was used to obtain the result.

12. Normative references

• GB/T 1884 Standard test method for density of crude petroleum and liquid petroleum products by laboratory determination (hydrometer method) (GB/T 1884—2000, eqv ISO 3675:1998)
• GB/T 1885 Petroleum measurement tables (GB/T 1885—1998, eqv ISO 91-2:1991)
• GB/T 4756 Standard practice for manual sampling of petroleum liquids (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 6682 Specifications and test methods for water for analytical laboratory use (GB/T 6682—2008, ISO 3696:1987, MOD)
• SH/T 0604 Standard test method for density of crude petroleum and petroleum products (U-type vibrating tube method) (SH/T 0604—2000, eqv ISO 12185:1996)
• ASTM D5854 Standard practice for mixing and handling samples of petroleum and liquid petroleum products (Practice for Mixing and Handling of Liquid Samples of Petroleum and Petroleum Products)
• ASTM E203 Standard test method for water content by Karl Fischer volumetric method (Test Method for Water Using Volumetric Karl Fischer Titration)

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