ASTM D6869-03(2011)
(Test Method)Standard Test Method for Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction (the Reaction of Iodine with Water)
Standard Test Method for Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction (the Reaction of Iodine with Water)
SIGNIFICANCE AND USE
Moisture will affect the processability of some plastics. High moisture content causes surface imperfections (that is, splay or bubbling) or degradation by hydrolysis. Low moisture (with high temperature) causes polymerization.
The physical properties of some plastics are affected by the moisture content.
SCOPE
1.1 This method uses the reaction of Iodine (I2) with water (Karl Fischer Reaction) to determine the amount of moisture in a polymer sample.
1.2 This test method is intended to be used for the determination of moisture in most plastics. Plastics containing volatile components such as residual monomers and plasticizers are capable of releasing components that will interfere with the I2/water reaction.
1.3 This method is suitable for measuring moisture over the range of 0.005 to 100 %. Sample size shall be adjusted to obtain an accurate moisture measurement.
1.4 The values stated in SI units are regarded as the standard.
Note 1—This standard is technically equivalent to ISO 15512 Method B.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6869 − 03 (Reapproved 2011)
Standard Test Method for
Coulometric and Volumetric Determination of Moisture in
Plastics Using the Karl Fischer Reaction (the Reaction of
Iodine with Water)
This standard is issued under the fixed designation D6869; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope collected in the solution within the titration cell is determined
using the reaction of water with I .
1.1 This method uses the reaction of Iodine (I ) with water
(Karl Fischer Reaction) to determine the amount of moisture in 3.2 Endpoint detection is made by instrumented methods.
a polymer sample. Determination of the moisture present is made using the
reaction of I with water.
1.2 This test method is intended to be used for the determi-
nation of moisture in most plastics. Plastics containing volatile 3.3 Coulometric instruments use Faraday’s law to measure
components such as residual monomers and plasticizers are the moisture present with 10.71 Coulombs (C) of generating
- -
capable of releasing components that will interfere with the current corresponding to 1 mg of water (2I → I +2e ).
I /water reaction. Volumetric instruments measure the volume of solution con-
taining I that is required to keep the current constant.
1.3 This method is suitable for measuring moisture over the
range of 0.005 to 100 %. Sample size shall be adjusted to
4. Significance and Use
obtain an accurate moisture measurement.
4.1 Moisture will affect the processability of some plastics.
1.4 The values stated in SI units are regarded as the
High moisture content causes surface imperfections (that is,
standard.
splay or bubbling) or degradation by hydrolysis. Low moisture
NOTE 1—This standard is technically equivalent to ISO 15512 Method
(with high temperature) causes polymerization.
B.
1.5 This standard does not purport to address all of the 4.2 The physical properties of some plastics are affected by
safety concerns, if any, associated with its use. It is the the moisture content.
responsibility of the user of this standard to establish appro-
5. Interferences
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5.1 Some compounds, such as aldehydes and ketones,
interfere in the determination of moisture content using this
2. Referenced Documents
method.
2.1 ISO Document:
6. Apparatus
ISO 15512 Plastics—Determination of Water Content
6.1 Heating Unit, consisting of an oven capable of heating
the sample to approximately 300°C, a furnace tube, a tempera-
3. Summary of Test Method
turecontrolunit,acarriergasflowmeter,anddesiccatingtubes
3.1 Samples are heated to vaporize water that is transported
for the carrier gas.
by a nitrogen carrier gas to the titration cell. The moisture
6.2 SamplePan(Boat),normallyaglasssampleboatorboat
manufactured of a suitable material to transfer the oven heat to
the sample. It is permitted to use aluminum foil as a disposable
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
liner for the sample pan.
and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.
Current edition approved Sept. 1, 2011. Published October 2011. Originally
6.3 Titration Unit, consisting of a control unit, titration cell
approved in 2003. Last previous edition approved in 2003 as D6869 - 03.
with a solution cathode, platinum electrode, and solution
DOI:10.1520/D6869-03R11.
See Appendix X1, History of Reagents Associated With the Karl Fischer
stirring capability.This apparatus has the capability to generate
Reaction, for an explanation of coulometric and volumetric techniques as well as an
or deliver iodine to react stoiciometrically with the moisture
explanation of the Karl Fischer Reaction and Karl Fischer Reagents.
present in the titration cell. The current or volume required to
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. generate the iodine converts to micrograms of water present.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6869 − 03 (2011)
The percent moisture in the sample is then calculated based on 10. Preparation of Apparatus
the sample weight used and is given as a direct digital readout.
10.1 Assemble the apparatus according to the manufactur-
er’s instructions. Molecular sieve or suitable desiccant must be
6.4 Analytical Balance, capable of weighing 0.1 mg (four
decimal place balance). used in the drying tubes for the nitrogen carrier gas.
10.2 Pourapproximately200mL(oranamountspecifiedby
6.5 Glass Capillary (Micropipette), used to measure a
the manufacturer) of generator (anode) solution into the
known amount of water, typically 2 mg (2000 µg).
titration cell.
7. Reagents and Materials
10.3 Add 10 mL of cathode solution to the cathode cell.
NOTE 3—The condition of both anode and cathode solutions are
7.1 Anode (Generator) Solution, per manufacturer’s recom-
determined by the appearance of the fluids. The solutions must be light
mendation.
amber in color.As solutions age, viscosity will increase and solution color
will turn dark. The instrument will indicate solution integrity by the
7.2 Cathode Solution, per manufacturer’s recommendation.
“background” value titration rate. Do not analyze samples containing low
NOTE 2—Hydranal or similar anode and cathode solutions are recom-
moisture content if the “background” value is greater than 0.10 µg/s.
mended. These reagents do not contain pyridine, are less toxic, and have
no offensive odor.
10.4 Turn the cell power switch on. If the cell potential
shows a negative value, indicating that the anode solution
7.3 Silica Gel, granules, approximately 2 mm, desiccant for
contains excess iodine, add approximately 50 to 200 µL of
drying tube of titration assembly (if applicable).
neutralization solution or check solution.
7.4 Special Grease, as supplied by manufacturer for ground
10.5 Disconnect the tube connecting the vaporizer unit to
glass joints.
the titration cell. Set nitrogen flow rate to achieve steady
7.5 Molecular Sieve, or suitable desiccant (for drying the
bubbling of nitrogen to the titration cell. (Aflow rate of 200 to
nitrogen carrier gas stream).
300 mL/min is recommended.)
7.6 Nitrogen Gas (N ), containing less than 5 µg/g of water.
2 10.6 Lift the titration cell and agitate the solution by gently
swirling the cell to remove any residual water from the walls.
7.7 Neutralization Solution, or check solution (per manu-
Stir the solution for a minute in the Titration Mode to dry and
facturer’s recommendation).
stabilize the inner atmosphere.
8. Hazards
10.7 Reconnect the tube from the vaporizer unit to the
titration cell. Keep the carrier gas flow on during the whole
8.1 Due to the low quantities of water measured, maximum
titration. The instrument is now ready for sample analysis.
care shall be exercised at all times to avoid contaminating the
sample with water from the sample container, the atmosphere 10.8 Set the oven and furnace tube temperature as required
or transfer equipment. Hygroscopic resin samples shall be
to obtain accurate results for the plastic to be tested. The
protected from the atmosphere. temperature is set so that the analysis is completed in a short
time period, yet eliminating the generation of water from
8.2 Due to the high temperatures and the chemicals in-
thermal degradation of the sample. Selection of Optimum
volved in this test method, safe lab practices must be followed
Heating Temperature is discussed below.
at all times.
10.9 Selection of Optimum Heating Temperature:
10.9.1 Select optimum heating temperature for material to
9. Sampling, Test Specimens, and Test Units
be tested by carrying out tests in several different temperatures
9.1 Unless otherwise agreed upon by interested parties or
to make a curve as shown in Fig. 1.
described in a specification, the material shall be sampled
statistically or the sample shall come from a process that is in
statistical control.
9.2 Samples that will determine the moisture of a larger lot
of material must be taken in such a manner that the moisture
content will not change from the original material. Sample
containers must be adequately dried and
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