1、Designation: D 1533 00 (Reapproved 2005)Standard Test Method forWater in Insulating Liquids by Coulometric Karl FischerTitration1This standard is issued under the fixed designation D 1533; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 This test method c
3、overs the measurement of waterpresent in insulating liquids by coulometric Karl Fischertitration. This test method is used commonly for test specimensbelow 100 % relative saturation of water in oil. The coulom-etric test method is known for its high degree of sensitivity(typically 10 g H2O). This te
4、st method requires the use ofequipment specifically designed for coulometric titration.1.2 This test method recommends the use of commerciallyavailable coulometric Karl Fischer titrators and reagents.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are i
5、ncluded in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practice and determine the applica-bility of regulatory limitations prior
6、 to use. For specificprecautionary statements see 8.1 and A2.1.2. Referenced Documents2.1 ASTM Standards:2D 923 Practices for Sampling Electrical Insulating LiquidsD 3613 Practice for Sampling Insulating Liquids for GasAnalysis and Determination of Water Content2.2 IEC Standard:IEC 60814: Insulating
7、 LiquidsOil-Impregnated Paper andPressboardDetermination of Water by Automatic Cou-lometric Karl Fischer Titration33. Summary of Test Method3.1 This test method is based on the reduction of iodinecontaining reagent according to the traditional Karl Fischerreaction. The proposed reaction mechanism is
8、 as follows:4SO21 CH3OH 1 RN 5 RNHSO3CH3(1)H2O 1 I21 RNHSO3CH31 2RN 5 RNHSO4CH31 2RNHIRN 5 Base!The endpoint is determined amperometrically with a plati-num electrode that senses a sharp change in cell resistancewhen the iodine has reacted with all of the water in the testspecimen.3.2 The coulometri
9、c Karl Fischer test method requires theuse of an automatic titrator with commercially availablereagents. Karl Fischer instruments regenerate iodine coulo-metrically from the iodide in the Karl Fischer reagent. The testspecimen is injected into a titration cell where the iodineconsumed by the reactio
10、n with water is electrolytically regen-erated by anodic oxidation of iodide. The completion of thereaction is detected with a platinum sensing electrode. Thecoulombs of electricity required to generate the necessaryamount of iodine then is converted into the amount of waterpresent in the test specim
11、en by use of the Faraday equation.3.3 Titration CellThe coulometric titration cell consists ofeither a sealed vessel containing both an anode and cathodewhich are separated by a diaphragm or a sealed vesselcontaining an anode and cathode which are not separated by adiaphragm. In both cells the anode
12、 compartment contains asolution consisting of sulfur dioxide, iodide, and an amine in asolvent containing methanol/chloroform or methanol/longerchain alcohol. In the cell with a diaphragm the cathodecompartment contains similar reagents optimized for cathodicreduction.4. Significance and Use4.1 Elec
13、trical characteristics of an insulating liquid may beaffected deleteriously by excessive water content. A high water1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D27.06 on Chemical Test.Cu
14、rrent edition approved Oct. 1, 2005. Published November 2005. Originallyapproved in 1958. Last previous edition approved in 2000 as D 1533 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vol
15、ume information, refer to the standards Document Summary page onthe ASTM website.3American National Standards Institute, 11 West 42nd Street, New York, NY100368002.4Scholz, E., “Karl-Fischer Titration,” Springer-Verlag, Berlin, Heidelberg, NewYork, Tokyo, 1984, 140 pp.1Copyright ASTM International,
16、100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.content may make a dielectric liquid unsuitable for someelectrical applications due to deterioration of properties such asthe dielectric breakdown voltage.4.2 These tests are suitable for use in acceptance specifica-
17、tions, in control of processing, and in evaluating the conditionof dielectric liquids in service.5. Interferences5.1 Compounds such as aldehydes, ketones, free halogens,most acids, and oxidizing or reducing agents may interferewith coulometric Karl Fischer titrators. If a drifting end pointis noted,
18、 an alternative solvent system or another titrationmethod is warranted. If this drifting end point cannot becorrected, the water values should be regarded as suspect. Adetailed discussion of interfering substances can be found inthe treatise on aquametry.55.2 Studies have shown that the water conten
19、t of an insu-lating liquid sample may be influenced significantly by thesample container.6A sample may either gain or lose water onstorage in a glass container depending upon the initial watercontent of the sample, the manner in which the container iscleaned and dried, and the length of storage time
20、 beforeanalysis. In addition, sample bottles should not be dried attemperature in excess of 110C and should be rinsed with theliquid being tested prior to taking the test specimen.5.3 Erroneous low readings may be obtained if previousspent oil test specimens are not removed from the solventsystem on
21、 a routine basis. Excess oil may not mix thoroughlywith the solvent system thus preventing the total water contentof that test specimen from being measured properly. Stirringshould be at such a rate that an oil layer will not form on topof the reagent. If such an oil layer does form while at theinst
22、ruments maximum stirrer speed, stop testing and removethe oil layer. If accurate results can not be obtained, thesolution should be discarded.5.4 Upon setting up of the titration vessel and solventsystem, the walls of the titration vessel should be wetted byswirling the solvent system solution aroun
23、d in the vessel.6. Apparatus6.1 Coulometric Titrator, consisting of a detector electrode,generator electrode, titration vessel, magnetic stirrer, andcontrol unit.6.1.1 Detector ElectrodesThis electrode pair ampero-metrically determines the end point of titration by measuring asharp change in cell re
24、sistance.6.1.2 Generator ElectrodesThis electrode pair performsthe cathodic reduction of iodide, which allows the Karl Fischerreaction to take place. It may consist of two platinum meshesor wires separated by a diaphragm within a glass assembly ortwo platinum meshes or wires not separated by a diaph
25、ragm.6.2 Titration FlaskThe titration flask will be of suitablecapacity and will be protected against atmospheric moisture. Abottom drain cock is desirable but not necessary for removingreagents.6.3 StirrersMeans for agitation during titration will con-sist of a magnetic stirrer with a glass or TFE-
26、fluorocarbon-covered stirring bar about 2 to 5 cm long or appropriate to thetitration vessel. The bar should be cleaned thoroughly, rinsedwith methanol, dried in an oven for1hat100C, and stored ina desiccator until used. In a sealed system, recleaning andredrying are not necessary for routine use.6.
27、4 Transfer SyringesSyringes shall be used of a suitablesize to accommodate instrument manufacturers recommenda-tion of sample size. Syringes may be glass or plastic. Glasssyringes shall be cleaned and dried for1hat100C prior touse. Plastic syringes shall be disposed of following eachsample use.6.5 N
28、eedlesNeedles that are to be fitted to the transfersyringes shall be long enough to inject samples directly belowthe surface of the Karl Fischer reagent. They should be of alarge enough gauge to allow for easy transfer of the sample.6.6 Septums, used to seal sample port, allowing the intro-duction o
29、f test specimens with a minimum amount of contami-nation from atmospheric moisture.6.7 Sealing GreaseIf the apparatus does not have a gasketseal, use a sealing grease to seal the titration chamber againstatmospheric moisture.6.8 Drying Oven, vacuum or air circulating.6.9 Desiccator, standard laborat
30、ory type with color changeindicator.6.10 Analytical Balance, capable of weighing to 6 0.001 g.7. Reagents7.1 Purity of ReagentsUnless otherwise indicated, allreagents shall conform to the specifications of the Committeeon Analytical Reagents of the American Chemical Society,where such specifications
31、 are available.77.2 Coulometric Karl Fischer Reagent, can be obtainedcommercially. Refer to Annex A1 for information on alterna-tive solvent systems.7.2.1 Anode Reagent, frequently referred to as vessel solu-tion.7.2.2 Cathode Reagent, frequently referred to as generatorsolution.7.3 Verification Sol
32、utionsVerification solutions are avail-able commercially.8Verification solutions may be formulatedin-house from long chain alcohols.5Mitchell, J., Jr. and Smith, D. M., “AquametryATreatise on Methods for theDetermination of Water, Part IIIthe Karl Fischer Reagent,” 2nd ed., J. Wiley andSons, Inc., N
33、ew York, NY 1977.6Gedemer, T., “Determination of Water in Oil by Karl Fischer Method, Part II,Changes in Moisture Content During Storage,” American Laboratory 7 (10), pp.4350 (1975).7Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestion
34、s on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.8The sole source of supply of verif
35、ication solutions, RM 8506 and RM 8507,known to the committee at this time is the National Institute of Standards andTechnology (NIST), Gaithersburg, MD 20899. If you are aware of alternativesuppliers, please provide this information to ASTM International Headquarters.Your comments will receive care
36、ful consideration at a meeting of the responsibletechnical committee,1which you may attend.D 1533 00 (2005)27.3.1 The moisture content of water-saturated octanol is:Water-saturated 1-Octanol 39.2 6 0.85 mg/mL of solution97.3.2 The water-saturated alcohol can be prepared by addingdeionized water to t
37、he alcohol (ACS reagent grade) at 25Csuch that the final mixture consists of a two-phase system inwhich the lower water phase is at least 2 cm high. Initially, thissolution should be mixed thoroughly and allowed to stand atroom temperature for at least three days to achieve completeequilibration.NOT
38、E 1For the best accuracy the solution should not be mixed orshaken after standing. Remove the sample aliquot from the top phase andinject it immediately into the titration cell. The degree of saturation of thewater-saturated 1-Octanol varies 1 % between 10 and 30C.7.3.3 The response of the instrumen
39、t shall be verified with 1to 2 L of water; this can give a response value of 1000 to 2000g within the specified precision of the instrument.8. Safety Precautions8.1 Pyridine was the organic amine that was traditionallyused in Karl Fischer reagents; however, pyridine-free formu-lations are now availa
40、ble commercially. Pyridine-free reagentstitrate faster and are less toxic, less odorous, and more stablethan pyridine types. The reagents may contain potentiallyhazardous chemicals, such as iodine, pyridine, sulfur dioxide,methanol, chloroform, chlorinated hydrocarbons, or other or-ganic materials.
41、Wear chemical resistant gloves when mixingthe reagents and removing solution from the titration chamber.Care must be exercised to avoid unnecessary inhalation ofreagent vapors or direct contact of the reagents with the skin oreyes. Following accidental spillage, flush the affected area withcopious a
42、mounts of water.NOTE 2Carefully read and follow manufacturers instructions andMaterial Safety Data Sheet when using commercially available reagentsystems.9. Sampling9.1 The preferred method for sampling insulating liquids isPractice D 3613; however, Practices D 923 also are suitable. Ifthe test spec
43、imen is cloudy or contains free water, it may bedifficult to obtain a representative specimen.10. Preparation of Apparatus10.1 Thoroughly clean and dry the titration vessel and thenreassemble according to the manufacturers recommendations.Follow the instructions provided in Annex A2 for detailedinst
44、ructions on cleaning.10.2 Fill reagent reservoirs with appropriate reagents ac-cording to the manufacturers instructions.10.3 Turn the instrument on and allow to stabilize.11. Verification of System Operation11.1 The accuracy of titration of the instrument and reagentsshall be verified prior to begi
45、nning of testing by use of asuitable verification solution (see 7.3) containing a knownquantity of moisture. It is desirable to verify the systemoperation using a solution that approximates the same range ofwater expected to be in the samples. Verification solutions shallbe run with new reagents pri
46、or to testing. If verificationsolution results lie outside parameters established by themanufacturer for acceptable moisture content of the solution,reagents shall be changed and reverified.12. Procedure12.1 After verifying the system is operating properly, allowthe instrument to restabilize prior t
47、o use.12.2 Follow the manufacturers instructions for suggestedspecimen size for an expected range of moisture content.12.3 Using an appropriate syringe and needle (see 6.4 and6.5) sample the insulating fluid to be tested. Prior to sampling,rinse the syringe and needle with the liquid to be tested on
48、etime.12.4 Determine the sample mass by difference to threesignificant figures by weighing the test specimen before andafter injection. Alternately, inject a known volume of a samplewhose density is known at the test temperature to determinesample size.12.5 Reagent solutions can be used until verifi
49、cation solu-tions no longer test accurately. See Section 11 for instructionson the use of verification solutions.13. Calculation13.1 Most commercially available coulometric Karl Fischerinstruments automatically calculate the water content in ppm orpercent. If not, calculate the amount of water in the sample asfollows:Water Content, mg/kg ppm!5A/B (2)where:A = mass of water, (g) (instrument readout), andB = mass of test specimen, g.14. Report14.1 Report the following information:14.1.1 Water content of the test specimen in mg/kg (ppm)rounded to
