ASTM D1533-00(2005)
(Test Method)Standard Test Method for Water in Insulating Liquids by Coulometric Karl Fischer Titration
Standard Test Method for Water in Insulating Liquids by Coulometric Karl Fischer Titration
SIGNIFICANCE AND USE
Electrical characteristics of an insulating liquid may be affected deleteriously by excessive water content. A high water content may make a dielectric liquid unsuitable for some electrical applications due to deterioration of properties such as the dielectric breakdown voltage.
These tests are suitable for use in acceptance specifications, in control of processing, and in evaluating the condition of dielectric liquids in service.
SCOPE
1.1 This test method covers the measurement of water present in insulating liquids by coulometric Karl Fischer titration. This test method is used commonly for test specimens below 100 % relative saturation of water in oil. The coulometric test method is known for its high degree of sensitivity (typically 10 g H2O). This test method requires the use of equipment specifically designed for coulometric titration.
1.2 This test method recommends the use of commercially available coulometric Karl Fischer titrators and reagents.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
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 practice and determine the applicability of regulatory limitations prior to use. For specific precautionary statements see and .
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: D1533 − 00(Reapproved 2005)
Standard Test Method for
Water in Insulating Liquids by Coulometric Karl Fischer
Titration
This standard is issued under the fixed designation D1533; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope lometric Karl Fischer Titration
1.1 This test method covers the measurement of water
3. Summary of Test Method
present in insulating liquids by coulometric Karl Fischer
3.1 This test method is based on the reduction of iodine
titration.Thistestmethodisusedcommonlyfortestspecimens
containing reagent according to the traditional Karl Fischer
below 100 % relative saturation of water in oil. The coulomet-
reaction. The proposed reaction mechanism is as follows:
ric test method is known for its high degree of sensitivity
(typically 10 µg H O). This test method requires the use of SO 1CH OH1RN 5 @RNH#SO CH (1)
2 2 3 3 3
equipment specifically designed for coulometric titration.
H O1I 1@RNH#SO CH 12RN 5 @RNH#SO CH 12@RNH#I
2 2 3 3 4 3
1.2 This test method recommends the use of commercially
available coulometric Karl Fischer titrators and reagents.
RN 5 Base
~ !
1.3 The values stated in SI units are to be regarded as
The endpoint is determined amperometrically with a plati-
standard. No other units of measurement are included in this
num electrode that senses a sharp change in cell resistance
standard.
when the iodine has reacted with all of the water in the test
1.4 This standard does not purport to address all of the specimen.
safety concerns, if any, associated with its use. It is the
3.2 The coulometric Karl Fischer test method requires the
responsibility of the user of this standard to establish appro-
use of an automatic titrator with commercially available
priate safety and health practice and determine the applica-
reagents. Karl Fischer instruments regenerate iodine coulo-
bility of regulatory limitations prior to use. For specific
metrically from the iodide in the Karl Fischer reagent. The test
precautionary statements see 8.1 and A2.1.
specimen is injected into a titration cell where the iodine
consumed by the reaction with water is electrolytically regen-
2. Referenced Documents
erated by anodic oxidation of iodide. The completion of the
2.1 ASTM Standards:
reaction is detected with a platinum sensing electrode. The
D923 Practices for Sampling Electrical Insulating Liquids
coulombs of electricity required to generate the necessary
D3613 Practice for Sampling Insulating Liquids for Gas
amount of iodine then is converted into the amount of water
AnalysisandDeterminationofWaterContent(Withdrawn
present in the test specimen by use of the Faraday equation.
2007)
3.3 Titration Cell—The coulometric titration cell consists of
2.2 IEC Standard:
either a sealed vessel containing both an anode and cathode
IEC 60814: Insulating Liquids—Oil-Impregnated Paper and
which are separated by a diaphragm or a sealed vessel
Pressboard—Determination of Water by Automatic Cou-
containing an anode and cathode which are not separated by a
diaphragm. In both cells the anode compartment contains a
This test method is under the jurisdiction of ASTM Committee D27 on solution consisting of sulfur dioxide, iodide, and an amine in a
Electrical Insulating Liquids and Gasesand is the direct responsibility of Subcom-
solvent containing methanol/chloroform or methanol/longer
mittee D27.06 on Chemical Test.
chain alcohol. In the cell with a diaphragm the cathode
Current edition approved Oct. 1, 2005. Published November 2005. Originally
compartment contains similar reagents optimized for cathodic
approved in 1958. Last previous edition approved in 2000 as D1533 – 00. DOI:
10.1520/D1533-00R05.
reduction.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on American National Standards Institute, 11 West 42nd Street, New York, NY
the ASTM website. 10036–8002.
The last approved version of this historical standard is referenced on Scholz, E., “Karl-Fischer Titration,” Springer-Verlag, Berlin, Heidelberg, New
www.astm.org. York, Tokyo, 1984, 140 pp.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1533 − 00 (2005)
4. Significance and Use reaction to take place. It may consist of two platinum meshes
or wires separated by a diaphragm within a glass assembly or
4.1 Electrical characteristics of an insulating liquid may be
two platinum meshes or wires not separated by a diaphragm.
affected deleteriously by excessive water content.Ahigh water
content may make a dielectric liquid unsuitable for some 6.2 Titration Flask—The titration flask will be of suitable
electricalapplicationsduetodeteriorationofpropertiessuchas
capacity and will be protected against atmospheric moisture.A
the dielectric breakdown voltage. bottom drain cock is desirable but not necessary for removing
reagents.
4.2 These tests are suitable for use in acceptance specifica-
tions, in control of processing, and in evaluating the condition
6.3 Stirrers—Means for agitation during titration will con-
of dielectric liquids in service.
sist of a magnetic stirrer with a glass or TFE-fluorocarbon-
covered stirring bar about 2 to 5 cm long or appropriate to the
5. Interferences
titration vessel. The bar should be cleaned thoroughly, rinsed
5.1 Compounds such as aldehydes, ketones, free halogens,
with methanol, dried in an oven for1hat 100°C, and stored in
most acids, and oxidizing or reducing agents may interfere
a desiccator until used. In a sealed system, recleaning and
with coulometric Karl Fischer titrators. If a drifting end point
redrying are not necessary for routine use.
is noted, an alternative solvent system or another titration
6.4 Transfer Syringes—Syringes shall be used of a suitable
method is warranted. If this drifting end point cannot be
size to accommodate instrument manufacturers’ recommenda-
corrected, the water values should be regarded as suspect. A
tion of sample size. Syringes may be glass or plastic. Glass
detailed discussion of interfering substances can be found in
syringes shall be cleaned and dried for1hat 100°C prior to
the treatise on aquametry.
use. Plastic syringes shall be disposed of following each
5.2 Studies have shown that the water content of an insu-
sample use.
lating liquid sample may be influenced significantly by the
6.5 Needles—Needles that are to be fitted to the transfer
sample container. A sample may either gain or lose water on
syringes shall be long enough to inject samples directly below
storage in a glass container depending upon the initial water
the surface of the Karl Fischer reagent. They should be of a
content of the sample, the manner in which the container is
large enough gauge to allow for easy transfer of the sample.
cleaned and dried, and the length of storage time before
analysis. In addition, sample bottles should not be dried at 6.6 Septums, used to seal sample port, allowing the intro-
duction of test specimens with a minimum amount of contami-
temperature in excess of 110°C and should be rinsed with the
liquid being tested prior to taking the test specimen. nation from atmospheric moisture.
5.3 Erroneous low readings may be obtained if previous
6.7 Sealing Grease—If the apparatus does not have a gasket
spent oil test specimens are not removed from the solvent seal, use a sealing grease to seal the titration chamber against
system on a routine basis. Excess oil may not mix thoroughly
atmospheric moisture.
with the solvent system thus preventing the total water content
6.8 Drying Oven, vacuum or air circulating.
of that test specimen from being measured properly. Stirring
6.9 Desiccator, standard laboratory type with color change
should be at such a rate that an oil layer will not form on top
indicator.
of the reagent. If such an oil layer does form while at the
instruments maximum stirrer speed, stop testing and remove
6.10 Analytical Balance, capable of weighing to 6 0.001 g.
the oil layer. If accurate results can not be obtained, the
solution should be discarded.
7. Reagents
5.4 Upon setting up of the titration vessel and solvent
7.1 Purity of Reagents—Unless otherwise indicated, all
system, the walls of the titration vessel should be wetted by
reagents shall conform to the specifications of the Committee
swirling the solvent system solution around in the vessel.
on Analytical Reagents of the American Chemical Society,
where such specifications are available.
6. Apparatus
7.2 Coulometric Karl Fischer Reagent, can be obtained
6.1 Coulometric Titrator, consisting of a detector electrode,
commercially. Refer to Annex A1 for information on alterna-
generator electrode, titration vessel, magnetic stirrer, and
tive solvent systems.
control unit.
7.2.1 Anode Reagent, frequently referred to as vessel solu-
6.1.1 Detector Electrodes—This electrode pair ampero-
tion.
metrically determines the end point of titration by measuring a
7.2.2 Cathode Reagent, frequently referred to as generator
sharp change in cell resistance.
solution.
6.1.2 Generator Electrodes—This electrode pair performs
the cathodic reduction of iodide, which allows the Karl Fischer
Mitchell, J., Jr. and Smith, D. M., “Aquametry—ATreatise on Methods for the Reagent Chemicals, American Chemical Society Specifications, American
Determination of Water, Part III—the Karl Fischer Reagent,” 2nd ed., J. Wiley and Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Sons, Inc., New York, NY 1977. listed by the American Chemical Society, see Analar Standards for Laboratory
Gedemer, T., “Determination of Water in Oil by Karl Fischer Method, Part II, Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Changes in Moisture Content During Storage,” American Laboratory 7 (10), pp. and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
43–50 (1975). MD.
D1533 − 00 (2005)
7.3 Verification Solutions—Verification solutions are avail- 10.2 Fill reagent reservoirs with appropriate reagents ac-
able commercially. Verification solutions may be formulated cording to the manufacturer’s instructions.
in-house from long chain alcohols.
10.3 Turn the instrument on and allow to stabilize.
7.3.1 The moisture content of water-saturated octanol is:
Water-saturated 1-Octanol 39.2 ± 0.85 mg/mL of solution
11. Verification of System Operation
7.3.2 Thewater-saturatedalcoholcanbepreparedbyadding
11.1 Theaccuracyoftitrationoftheinstrumentandreagents
deionized water to the alcohol (ACS reagent grade) at 25°C
shall be verified prior to beginning of testing by use of a
such that the final mixture consists of a two-phase system in
suitable verification solution (see 7.3) containing a known
which the lower water phase is at least 2 cm high. Initially, this
quantity of moisture. It is desirable to verify the system
solution should be mixed thoroughly and allowed to stand at
operation using a solution that approximates the same range of
room temperature for at least three days to achieve complete
waterexpectedtobeinthesamples.Verificationsolutionsshall
equilibration.
be run with new reagents prior to testing. If verification
solution results lie outside parameters established by the
NOTE 1—For the best accuracy the solution should not be mixed or
manufacturer for acceptable moisture content of the solution,
shaken after standing. Remove the sample aliquot from the top phase and
inject it immediately into the titration cell. The degree of saturation of the
reagents shall be changed and reverified.
water-saturated 1-Octanol varies <1 % between 10 and 30°C.
12. Procedure
7.3.3 The response of the instrument shall be verified with 1
to2µLofwater;thiscangivearesponsevalueof1000to2000
12.1 After verifying the system is operating properly, allow
µg within the specified precision of the instrument.
the instrument to restabilize prior to use.
12.2 Follow the manufacturer’s instructions for suggested
8. Safety Precautions
specimen size for an expected range of moisture content.
8.1 Pyridine was the organic amine that was traditionally
12.3 Using an appropriate syringe and needle (see 6.4 and
used in Karl Fischer reagents; however, pyridine-free formu-
6.5) sample the insulating fluid to be tested. Prior to sampling,
lations are now available commercially. Pyridine-free reagents
rinse the syringe and needle with the liquid to be tested one
titrate faster and are less toxic, less odorous, and more stable
time.
than pyridine types. The reagents may contain potentially
hazardous chemicals, such as iodine, pyridine, sulfur dioxide,
12.4 Determine the sample mass by difference to three
methanol, chloroform, chlorinated hydrocarbons, or other or- significant figures by weighing the test specimen before and
ganic materials. Wear chemical resistant gloves when mixing after injection.Alternately, inject a known volume of a sample
the reagents and removing solution from the titration chamber. whose density is known at the test temperature to determine
Care must be exercised to avoid unnecessary inhalation of sample size.
reagent vapors or direct contact of the reagents with the skin or
12.5 Reagent solutions can be used until verification solu-
eyes.Followingaccidentalspillage,flushtheaffectedareawith
tions no longer test accurately. See Section 11 for instructions
copious amounts of water.
on the use of verification solutions.
NOTE 2—Carefully read and follow manufacturers instructions and
13. Calculation
Material Safety Data Sheet when using commercially available reagent
systems.
13.1 Most commercially available coulometric Karl Fischer
instrumentsautomaticallycalculatethewatercontentinppmor
9. Sampling
percent. If not, calculate the amount of water in the sample as
9.1 The preferred method for sampling insulating liquids is
follows:
Practice D3613; however, Practices D923 also are suitable. If
Water Content, mg/kg ~ppm! 5A/B (2)
the test specimen is cloudy or contains free water, it may be
difficult to obtain a representative specimen.
where:
A = mass of water, (µg) (instrument readout), and
10. Preparation of Apparatus
B = mass of test specimen, g.
10.1 Thoroughly clean and dry the titration vessel and then
14. Report
reassemble according to the manufacturer’s recomme
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