ASTM D1533-00
(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
SCOPE
1.1 These test methods cover the determination of water present in insulating liquids, in concentrations most commonly below 200 ppm.
1.2 Annex A2 lists modified solvent systems which allow the use of these methods for the titration of some high viscosity oils, as well as silicones.
1.3 The values stated in acceptable metric units are to be regarded as the standard.
1.4 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. Specific precautionary statements are given in A3.1.1 and A3.4.1.
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Designation:D1533–00
Standard Test Method for
Water in Insulating Liquids by Coulometric Karl Fischer
Titration
This standard is issued under the fixed designation D 1533; 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 (e) 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 3. Summary of Test Method
1.1 This test method covers the measurement of water 3.1 This test method is based on the reduction of iodine
present in insulating liquids by coulometric Karl Fischer containing reagent according to the traditional Karl Fischer
titration.Thistestmethodisusedcommonlyfortestspecimens reaction. The proposed reaction mechanism is as follows:
below 100 % relative saturation of water in oil. The coulom-
SO 1 CH OH 1 RN5@RNH#SO CH (1)
2 3 3 3
etric test method is known for its high degree of sensitivity
H O 1 I 1@RNH#SO CH 1 2RN5@RNH#SO CH 1 2@RNH#I
2 2 3 3 4 3
(typically 10 µg H O). This test method requires the use of
~RN 5 Base!
equipment specifically designed for coulometric titration.
1.2 This test method recommends the use of commercially The endpoint is determined amperometrically with a plati-
available coulometric Karl Fischer titrators and reagents. num electrode that senses a sharp change in cell resistance
1.3 The values stated in SI units are to be regarded as the when the iodine has reacted with all of the water in the test
standard. specimen.
1.4 This standard does not purport to address all of the 3.2 The coulometric Karl Fischer test method requires the
safety concerns, if any, associated with its use. It is the use of an automatic titrator with commercially available
responsibility of the user of this standard to establish appro- reagents. Karl Fischer instruments regenerate iodine coulo-
priate safety and health practice and determine the applica- metrically from the iodide in the Karl Fischer reagent. The test
bility of regulatory limitations prior to use. For specific specimen is injected into a titration cell where the iodine
precautionary statements see 8.1 and Note A2.1. consumed by the reaction with water is electrolytically regen-
erated by anodic oxidation of iodide. The completion of the
2. Referenced Documents
reaction is detected with a platinum sensing electrode. The
2.1 ASTM Standards: coulombs of electricity required to generate the necessary
D 923 Test Method for Sampling Electrical Insulating Liq-
amount of iodine then is converted into the amount of water
uids present in the test specimen by use of the Faraday equation.
D 3613 TestMethodsofSamplingElectricalInsulatingOils
3.3 Titration Cell—Thecoulometrictitrationcellconsistsof
for Gas Analysis and Determination of Water Content either a sealed vessel containing both an anode and cathode
2.2 IEC Standard:
which are separated by a diaphragm or a sealed vessel
IEC60814: InsulatingLiquids—Oil-ImpregnatedPaperand containing an anode and cathode which are not separated by a
Pressboard—Determination of Water by Automatic Cou-
diaphragm. In both cells the anode compartment contains a
lometric Karl Fischer Titration solution consisting of sulfur dioxide, iodide, and an amine in a
solvent containing methanol/chloroform or methanol/longer
chain alcohol. In the cell with a diaphragm the cathode
This test method is under the jurisdiction of ASTM Committee D-27 on
compartment contains similar reagents optimized for cathodic
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom-
reduction.
mittee D27.06 on Chemical Test.
Current edition approved April 10, 2000. Published June 2000. Originally
published as D 1533 – 58T. Last previous edition D 1533–99.
Annual Book of ASTM Standards, Vol 10.03.
3 4
American National Standards Institute, 11 West 42nd Street, New York, NY Scholz, E., “Karl-Fischer Titration,” Springer-Verlag, Berlin, Heidelberg, New
10036–8002. York, Tokyo, 1984, 140 pp.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D1533–00
4. Significance and Use or wires separated by a diaphragm within a glass assembly or
two platinum meshes or wires not separated by a diaphragm.
4.1 Electrical characteristics of an insulating liquid may be
6.2 Titration Flask—The titration flask will be of suitable
affected deleteriously by excessive water content.Ahigh water
capacity and will be protected against atmospheric moisture.A
content may make a dielectric liquid unsuitable for some
bottom drain cock is desirable but not necessary for removing
electricalapplicationsduetodeteriorationofpropertiessuchas
reagents.
the dielectric breakdown voltage.
6.3 Stirrers—Means for agitation during titration will con-
4.2 These tests are suitable for use in acceptance specifica-
sist of a magnetic stirrer with a glass or TFE-fluorocarbon-
tions, in control of processing and in evaluating the condition
covered stirring bar about 2 to 5 cm long or appropriate to the
of dielectric liquids in service.
titration vessel. The bar should be cleaned thoroughly, rinsed
5. Interferences with methanol, dried in an oven for1hat 100°C, and stored in
a desiccator until used. In a sealed system, recleaning and
5.1 Compounds such as aldehydes, ketones, free halogens,
redrying are not necessary for routine use.
most acids and oxidizing or reducing agents may interfere with
6.4 Transfer Syringes—Syringes shall be used of a suitable
coulometric Karl Fischer titrators. If a drifting end point is
size to accommodate instrument manufacturers’ recommenda-
noted,analternativesolventsystemoranothertitrationmethod
tion of sample size. Syringes may be glass or plastic. Glass
is warranted. If this drifting end point cannot be corrected, the
syringes shall be cleaned and dried for1hat 100°C prior to
water values should be regarded as suspect. A detailed discus-
use. Plastic syringes shall be disposed of following each
sion of interfering substances can be found in the treatise on
sample use.
aquametry.
6.5 Needles—Needles that are to be fitted to the transfer
5.2 Studies have shown that the water content of an insu-
syringes shall be long enough to inject samples directly below
lating liquid sample may be influenced significantly by the
the surface of the Karl Fischer reagent. They should be of a
sample container. A sample may either gain or lose water on
large enough gage to allow for easy transfer of the sample.
storage in a glass container depending upon the initial water
6.6 Septums, used to seal sample port, allowing the intro-
content of the sample, the manner in which the container is
duction of test specimens with a minimum amount of contami-
cleaned and dried, and the length of storage time before
nation from atmospheric moisture.
analysis. In addition, sample bottles should not be dried at
6.7 Sealing Grease—If the apparatus does not have a gasket
temperature in excess of 110°C and should be rinsed with the
seal, use a sealing grease to seal the titration chamber against
liquid being tested prior to taking the test specimen.
atmospheric moisture.
5.3 Erroneous low readings may be obtained if previous
6.8 Drying Oven, vacuum or air circulating.
spent oil test specimens are not removed from the solvent
6.9 Desiccator, standard laboratory type with color change
system on a routine basis. Excess oil may not mix thoroughly
indicator.
with the solvent system thus preventing the total water content
6.10 Analytical Balance, capable of weighing to 6 0.001 g.
of that test specimen from being measured properly. Stirring
should be at such a rate that an oil layer will not form on top
7. Reagents
of the reagent. If such an oil layer does form while at the
7.1 Purity of Reagents—Unless otherwise indicated, all
instruments maximum stirrer speed, stop testing and remove
the oil layer. If accurate results can not be obtained, the reagents shall conform to the specifications of the Committee
solution should be discarded. on Analytical Reagents of the American Chemical Society,
5.4 Upon setting up of the titration vessel and solvent where such specifications are available.
system, the walls of the titration vessel should be wetted by 7.2 Coulometric Karl Fischer Reagent, can be obtained
swirling the solvent system solution around in the vessel. commercially. Refer to Annex A1 for information on alterna-
tive solvent systems.
6. Apparatus
7.2.1 Anode Reagent, frequently referred to as vessel solu-
6.1 Coulometric Titrator, consisting of a detector electrode, tion.
generator electrode, titration vessel, magnetic stirrer, and 7.2.2 Cathode Reagent, frequently referred to as generator
control unit. solution.
6.1.1 Detector Electrodes—This electrode pair ampero- 7.3 Verification Solutions—Verification solutions are avail-
metrically determines the end point of titration by measuring a able commercially. Verification solutions may be formulated
sharp change in cell resistance. in house from long chain alcohols.
6.1.2 Generator Electrodes—This electrode pair performs
the cathodic reduction of iodide, which allows the Karl Fischer
reaction to take place. It may consist of two platinum meshes
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory
Mitchell, J., Jr. and Smith, D. M., “Aquametry—ATreatise on Methods for the Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Determination of Water, Part III—the Karl Fischer Reagent,” 2nd ed., J. Wiley and and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
Sons, Inc., New York, NY 1977. MD.
6 8
Gedemer, T., “Determination of Water in Oil by Karl Fischer Method, Part II, Water in transformer oil verification solutions, RM 8506 and RM 8507, are
Changes in Moisture Content During Storage,” American Laboratory 7 (10), pp. available from the National Institute of Standards and Technology (NIST), Gaith-
43–50 (1975). ersburg, MD 20899.
D1533–00
7.3.1 The moisture content of water saturated octanol is: suitable verification solution (see 7.3) containing a known
quantity of moisture. It is desirable to verify the system
Water saturated 1-Octanol 39.2 6 0.85 mg/mL of solution
operation using a solution that approximates the same range of
7.3.2 Thewater-saturatedalcoholcanbepreparedbyadding
waterexpectedtobeinthesamples.Verificationsolutionsshall
deionized water to the alcohol (ACS reagent grade) at 25°C
be run with new reagents prior to testing. If verification
such that the final mixture consists of a two-phase system in
solution results lie outside parameters established by the
which the lower water phase is at least 2 cm high. Initially, this
manufacturer for acceptable moisture content of the solution,
solution should be mixed thoroughly and allowed to stand at
reagents shall be changed and reverified.
room temperature for at least three days to achieve complete
equilibration.
12. Procedure
NOTE 1—Caution: For the best accuracy the solution should not be
12.1 After verifying the system is operating properly, allow
mixed or shaken after standing. Remove the sample aliquot from the top
the instrument to restabilize prior to use.
phase and inject it immediately into the titration cell. The degree of
12.2 Follow the manufacturer’s instructions for suggested
saturation of the water-saturated 1-Octanol varies <1 % between 10 and
specimen size for an expected range of moisture content.
30°C.
12.3 Using an appropriate syringe and needle (see 6.4 and
7.3.3 The response of the instrument shall be verified with 1
6.5) sample the insulating fluid to be tested. Prior to sampling,
to2µLofwater,thiscangivearesponsevalueof1000to2000
rinse the syringe and needle with the liquid to be tested one
µg within the specified precision of the instrument.
time.
12.4 Determine the sample mass by difference to three
8. Safety Precautions
significant figures by weighing the test specimen before and
8.1 Pyridine was the organic amine that was traditionally
after injection.Alternately, inject a known volume of a sample
used in Karl Fischer reagents; however, pyridine-free formu-
whose density is known at the test temperature to determine
lations are now available commercially. Pyridine-free reagents
sample size.
titrate faster and are less toxic, less odorous, and more stable
12.5 Reagent solutions can be used until verification solu-
than pyridine types. The reagents may contain potentially
tions no longer test accurately. See Section 11 for instructions
hazardous chemicals, such as iodine, pyridine, sulfur dioxide,
on the use of verification solutions.
methanol, chloroform, chlorinated hydrocarbons, or other or-
ganic materials. Wear chemical resistant gloves when mixing
13. Calculation
the reagents and removing solution from the titration chamber.
13.1 Most commercially available coulometric Karl Fischer
Care must be exercised to avoid unnecessary inhalation of
instrumentsautomaticallycalculatethewatercontentinppmor
reagent vapors or direct contact of the reagents with the skin or
percent. If not, calculate the amount of water in the sample as
eyes.Followingaccidentalspillage,flushtheaffectedareawith
follows:
copious amounts of water.
Water Content, mg/kg ~ppm!5 A/B (2)
NOTE 2—Carefully read and follow manufacturers instructions and
Material Safety Data Sheet when using commercially available reagent
where:
systems.
A = mass of water, (µg) (instrument readout), and
B = mass of test specimen, g.
9. Sampling
9.1 The preferred method for sampling insulating liquids is
14. Report
Test Methods D 3613, however Test Method D 923 also is
14.1 Report the following information:
suitable. If the test specimen is cloudy or contains free water,
14.1.1 Water content of the test specimen in mg/kg (ppm)
it may be difficult to obtain a representative specimen.
rounded to the nearest integer.
14.1.2 Sample identification.
10. Preparation of Apparatus
14.1.3 Sample temperature when collected, if available.
10.1 Thoroughly clean and dry the titration vessel and then
reassemble according to the manufacturer’s recommendations.
15. Precision and Bias
Follow the instructions provided in Annex A2 for detailed
15.1 Precision:
instructions on cleaning.
15.1.1 The following criteria may be used for judging
10.2 Fill reagent reservoirs with appropriate reagents ac-
precision of test results on new and used oils at the 95 %
cording to the manufacturer’s
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