ASTM D6869 Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction 

    What is ASTM D6869?

    ASTM D6869 is a standard test method that uses the Karl Fischer reaction (the reaction of iodine with water) to determine moisture content in a polymer sample. The laboratory heats the sample to vaporize the water, and a nitrogen carrier gas carries the vapor to a titration cell, where Karl Fischer titration measures it coulometrically or volumetrically. The method suits most plastics and measures moisture from 0.005 to 100 %. Moisture affects the processability of some plastics: high moisture causes surface imperfections such as splay or bubbling, or hydrolysis-induced degradation, and low moisture at high temperatures causes polymerization. The standard is equivalent to ISO 15512 Method B.

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    Get certified ASTM D6869 testing for accurate moisture control in plastics.

    ASTM D6869 testing gives manufacturers and buyers a documented moisture measurement before production starts. The laboratory verifies its apparatus with a known quantity of water or a hydrate sample, then reports the moisture as a percentage. Processors use the result to set drying conditions, especially for hygroscopic resins that absorb moisture during storage and handling; accurate moisture control helps reduce defects and material rejection. Our guide on moisture content in plastic pellets explains how Karl Fischer titration compares with loss-on-drying and infrared moisture balance methods.

    What is the scope of the ASTM D6869 test standard?

    ASTM D6869 is a standard test method that uses the Karl Fischer reaction (the reaction of iodine with water) to determine moisture content in a polymer sample. The method determines moisture in most plastics. SI units are standard.

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    The scope of ASTM D6869 includes

    • Purpose: the moisture content of a polymer sample, by the Karl Fischer reaction
    • Techniques: coulometric and volumetric Karl Fischer titration
    • Materials: most plastics; plastics with volatile components, such as residual monomers and plasticizers, can release components that interfere with the iodine-water reaction
    • Moisture range: 0.005 to 100 %, with the sample size adjusted for an accurate measurement
    • Sample handling: an oven heats the sample, and a nitrogen carrier gas carries the water vapor to the titration cell
    • Interferences: some compounds, such as aldehydes and ketones, interfere with the determination
    • Units: SI values are standard
    • Related standards: equivalent to ISO 15512 Method B

    What are the uses of ASTM D6869 testing?

    ASTM D6869 helps laboratories, processors, and manufacturers measure the moisture that affects how plastics process and perform. The result shows whether a material is dry enough for processing. This standard:

    • Determines the moisture content of most plastics from 0.005 to 100 %.
    • Helps processors avoid surface imperfections such as splay and bubbling.
    • Helps processors detect moisture levels that cause hydrolysis-related degradation.
    • Helps manufacturers judge how moisture affects the physical properties of some plastics.
    • Supports drying decisions and process optimization for moisture-sensitive polymers.
    • Gives laboratories a choice of coulometric or volumetric titration.

    What materials can be tested under ASTM D6869?

    ASTM D6869 applies to most plastics, including hygroscopic resins such as nylon, polycarbonate, PET, and ABS, which absorb moisture from the air during storage and handling.  Plastics containing volatile components, such as residual monomers and plasticizers, can release substances that interfere with the iodine-water reaction, so the laboratory handles those materials with extra care. Aldehydes and ketones also interfere with the determination.

    Why is ASTM D6869 important?

    Moisture affects the processability of some plastics. High moisture content causes surface imperfections, such as splay or bubbling, or degradation by hydrolysis, and low moisture at high temperature causes polymerization. Moisture also affects the physical properties of some plastics. ASTM D6869 gives laboratories a single, defined way to measure moisture across a wide range, so processors can compare results and set drying conditions. ASTM Committee D20 on Plastics, Subcommittee D20.70, maintains the test method.

    ASTM D6869 Equipment and sample preparation guide

    ASTM D6869 uses a heating unit with an oven, a sample pan, a titration unit, and a nitrogen carrier gas supply. The technician weighs the sample, heats it in the oven, and transfers the vaporized water to the titration cell.

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    Sample and specimen detailsThe specimen is a weighed plastic sample. The technician adjusts the sample size to the moisture level so the measurement stays accurate, and laboratories often use about 1 to 3 g.
    Specimen preparationThe technician handles and seals the sample to keep out moisture from the environment, then weighs it on an analytical balance. The technician places the sample in a pan made of a material that transfers oven heat to the sample, and can use disposable aluminum foil as a liner.
    Specimen dimensionsIt only requires the technician to adjust the sample size to obtain an accurate moisture measurement.
    InstrumentationThe laboratory uses a heating unit with an oven and furnace tube, a nitrogen carrier gas supply, a titration unit with a control unit and a titration cell, and an analytical balance. Coulometric instruments generate iodine and apply Faraday’s law, where 10.71 C of generating current corresponds to 1 mg of water. Volumetric instruments measure the volume of iodine-containing solution needed to maintain a constant current.

    Testing Procedures and Requirements for ASTM D6869

    The technician heats the sample to vaporize its water, and a nitrogen carrier gas carries the vapor to the titration cell, where iodine reacts with the water. The instrument detects the endpoint and calculates the moisture from the sample weight. The test procedure follows these steps:

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    Apparatus setupThe technician reconnects the tube from the vaporizer unit to the titration cell and keeps the carrier gas flowing during the whole titration.
    Calibration & standardizationThe technician verifies the apparatus by analyzing a known quantity of water or a hydrate sample that releases moisture on heating.
    Oven temperature selectionThe technician sets the oven and furnace tube temperature at the optimum heating temperature, which falls in the range where the measured water content stays nearly constant. At lower temperatures, the water does not vaporize fully, and the indicated water content rises with the temperature.
    Sample analysisThe technician weighs the sample, places it in the oven, and starts the titration. The instrument detects the endpoint and gives a direct digital readout based on the sample weight.
    ReportingThe analyst reports the moisture content in percent, and the laboratory repeats the measurement across samples to confirm repeatability.

    ASTM D6869 Testing Process and Data Collection

    The technician weighs the plastic sample and places it in the oven. The oven vaporizes the water, and the nitrogen carrier gas carries it into the titration cell. The instrument measures the iodine that reacts with the water, from the generated current in coulometric mode or from the solution volume in volumetric mode, and calculates the moisture content from the sample weight. The technician repeats the measurement on several samples to check repeatability.

    The image shows plastic samples being analyzed using a Karl Fischer moisture analyzer, with apparatus setup, calibration using a water standard, oven temperature selection, and controlled sample heating to determine moisture content. The instrument records moisture measurements to assess repeatability and report results under ASTM D6869.
    ASTM D6869 Testing Procedures for Determining Moisture Content in Plastics Using the Karl Fischer Reaction

    Common Challenges and Troubleshooting

    Plastics with volatile components, such as residual monomers and plasticizers, can release substances that interfere with the iodine-water reaction and give inaccurate results. Aldehydes and ketones also interfere. Outside moisture can enter during handling, so technicians seal samples and use closed systems. A heating temperature that is too low leaves water in the sample, and one that is too high can degrade the polymer, so the technician chooses a temperature from the range where the water content stays nearly constant. Sample size affects precision, so the technician adjusts it to the moisture level.

    ASTM D6869 Analysis Results and Interpretation

    ASTM D6869 reports moisture content as a percentage, with SI units as the standard. This report provides the plastic sample’s moisture content. Engineers compare the value with the material’s drying and processing requirements.

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    • The laboratory reports moisture content as a percentage of sample weight, ranging from 0.005 to 100%.
    • Analysts note whether the sample contains volatile components or interfering compounds that can affect the result.
    • Engineers read a high moisture value as a risk of splay, bubbling, or hydrolysis during processing.
    • Engineers interpret a low moisture value combined with high processing temperature as a polymerization risk.
    • The processor uses the value to adjust drying and processing conditions.
    • The laboratory repeats the measurement across samples to confirm repeatability.

    Link to ASTM D6869

    FAQ

    What does ASTM D6869 measure?
    ASTM D6869 measures the moisture content of most plastics by the Karl Fischer reaction, the reaction of iodine with water, in coulometric or volumetric mode.
    The method suits moisture over the range of 0.005 to 100 %, and the technician adjusts the sample size to get an accurate measurement.
    The oven vaporizes the water in the sample, and a nitrogen carrier gas carries the vapor to the titration cell, where the iodine reaction measures it.
    A loss-in-weight method such as ASTM D6980 measures the mass a sample loses on heating, so volatile substances other than water can raise the result. Karl Fischer titration measures the water itself through its reaction with iodine.
    ASTM D6869 states that it is equivalent to ISO 15512 Method B.

    Updated on October 29, 2026

    Malhar Khole
    About Author
    Malhar Khole
    Malhar Khole is a Material Testing Associate at Matestlab Inc. and holds a postgraduate degree in Material Science and Technology from IIT (BHU), Varanasi.
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