1、Designation: D3401 97 (Reapproved 2017)Standard Test Methods forWater in Halogenated Organic Solvents and TheirAdmixtures1This standard is issued under the fixed designation D3401; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 These test methods des
3、cribe the use of the Karl Fischer(KF) titration for determination of water in halogenated or-ganic solvents and mixtures thereof. Water concentrations from2 to 1000 ppm can be determined in these solvents. Two testmethods are covered as follows:1.1.1 Test Method A, Water Determination Using a Coulo-
4、metric KF TitratorThe coulometric test method is known forits high degree of sensitivity (typically 10 g H2O) andshould be the test method of choice if water concentrations aretypically below 50 ppm or if only small amounts of sample areavailable for water determinations. This test method requiresth
5、e use of equipment specifically designed for coulometrictitrations.1.1.2 Test Method B, Water Determination Using a Volumet-ric KF TitratorThe volumetric test method is a more tradi-tional approach to KF water determinations. Although titratorsare specifically designed for KF volumetric determinatio
6、ns,many automatic titrators on the market can be adapted toperform KF titrations.1.2 Either of these test methods can be used to determinetypical water concentrations (15 to 500 ppm) found in haloge-nated solvents.1.3 These test methods recommend the use of commerciallyavailable Karl Fischer titrato
7、rs and reagents.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, health, and environmental practices and deter-mine the applicability of regulatory limitati
8、ons prior to use.For specific precautionary statements, see Sections 11 and 15.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides a
9、nd Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standard:2E203 Test Method for Water Using Volumetric Karl FischerTitration3. Summary of Test Method3.1 In the Karl Fischer reaction, water will react with iodinein t
10、he presence of sulfur dioxide, alcohol, and an organic baseaccording to the following equation:H2O1I21SO21CH3OH13RNRNH!SO4CH312RNH!I (1)where RN = organic base.3.2 When the volumetric titration test method is used forthis determination, the halogenated sample is added to a KFsolvent that usually con
11、sists of sulfur dioxide and an aminedissolved in anhydrous methanol. This solution is titrated withan anhydrous solvent containing iodine. The iodine titrant isfirst standardized by titrating a known amount of water.3.3 In the coulometric titration test method, the sample isinjected into an electrol
12、ytic cell where the iodine required forthe reaction with water is produced by anodic oxidation ofiodide. With this technique, no standardization of reagents isrequired.3.4 In both test methods, the end point is determinedamperometrically with a platinum electrode that senses a sharpchange in cell re
13、sistance when the iodine has reacted with allof the water in the sample.4. Significance and Use4.1 High water concentrations can have a detrimental effecton many uses of halogenated solvents.1These test methods are under the jurisdiction of ASTM Committee D26 onHalogenated Organic Solvents and Fire
14、Extinguishing Agents and are the directresponsibility of Subcommittee D26.04 on Test Methods.Current edition approved Nov. 1, 2017. Published December 2017. Originallyapproved in 1975. Last previous edition approved in 2012 as D3401 97(2012).DOI: 10.1520/D3401-97R17.2For referenced ASTM standards, v
15、isit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-
16、2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technica
17、l Barriers to Trade (TBT) Committee.14.1.1 Water can cause corrosion and spotting when solventsare used for metal cleaning.4.1.2 Water can reduce the shelf life of aerosol formula-tions.4.1.3 Water can inhibit desired reactions when solvents areused in formulations.5. Interferences5.1 Certain compou
18、nds or classes of compounds interferewith the accurate determination of water by the Karl Fischertest method. They include aldehydes, ketones, free halogens,ferric salts, and strong oxidizing and reducing agents.5.2 Free halogens can oxidize the iodate in the KF reagentsto form iodine; this causes e
19、rroneously low water values.5.3 A more detailed discussion of KF interferences can befound in Test Method E203 and other sources.3,46. Apparatus6.1 Coulometric Titrator,5(for Test Method A only) con-sisting of a single or dual bath electrolytic cell, dual platinumelectrode, magnetic stirrer, and con
20、trol unit.6.2 Volumetric Titrator,5(for Test Method B only) consist-ing of a titration cell, dual platinum electrode, magnetic stirrer,dispensing buret, and control unit.6.3 Syringes, 2, 5, 10, or 20-mL sizes.6.4 Syringe, 5-L size.6.5 Silicon Rubber Blocks or Silicon Rubber Septa.6.6 Drying Oven, ai
21、r circulating.6.7 Desiccator.6.8 Analytical Balance, capable of weighing to 60.01 g.7. Reagents7.1 Anode Reagent, for dual bath titration (for Test MethodA only), use reagent recommended by manufacturer of titrator.7.2 Cathode Reagent, for dual bath titration (for TestMethod A only), use reagent rec
22、ommended by manufacturer oftitrator.7.3 Single Bath Reagent, (for Test Method A only), usereagent recommended by manufacturer of titrator.7.4 Karl Fischer Volumetric Titrant,4(for Test Method Bonly) typically consists of a mixture of an organic amine, sulfurdioxide, and iodine dissolved in a non-hyd
23、roscopic solvent(s).Reagents with titers of 1.00, 2.00, and 5.00 mg of H2O/mL canbe commercially obtained.7.5 Karl Fischer Solvent,4(for Test Method B only)typically consists of a mixture of an organic amine and sulfurdioxide dissolved in anhydrous methanol.NOTE 1Pyridine was the organic amine that
24、was traditionally used inKarl Fisher reagents, however, pyridine-free formulations are now avail-able and preferred by most KF instrument manufacturers for use with theirequipment. Pyridine-free reagents are said to be less toxic, less odorous,and more stable than pyridine types.8. Sampling8.1 Since
25、 halogenated solvents normally contain low con-centrations of water, care must be taken to eliminate theintroduction of water from sampling equipment and atmo-spheric moisture.8.2 Without taking the proper sampling precautions, moreerror is typically introduced into the determination of waterthrough
26、 sampling techniques than in the titration process itself.8.3 Dry sample bottles and closures in an oven at 110 C forseveral hours. Place caps on the bottles immediately afterremoving from the oven.8.4 Transfer solvent to the bottles as quickly as possible.Adjust the liquid level to come within 1 in
27、. of the top of thebottle. Immediately place the cap on the bottle and tighten.8.5 When removing a portion of sample from the bottle forKF analysis, use pipets or syringes that have been thoroughlydried. Replace the cap on the bottle immediately.8.6 If more than one portion of sample is to be taken
28、fromthe bottle or if the sample is to be retained for further wateranalysis, it is a good practice to blanket the top of the bottlewith dry nitrogen when removing the sample. If septum capclosures are being used, dry nitrogen can be introduced with asyringe at the same time a portion of the sample i
29、s beingremoved with a second syringe.TEST METHOD AWATER DETERMINATIONUSING A COULOMETRIC KF TITRATOR9. Summary of Test Method9.1 The dual bath coulometric titration cell consists of asealed vessel containing both an anode and cathode compart-ment. The anodic compartment usually contains a solutionco
30、nsisting of sulfur dioxide, iodide, and an amine in amethanol/chloroform solvent. The cathodic compartment con-tains similar reagents optimized for cathodic reduction.9.2 When a sample containing water is injected into theanode compartment, the electrolytic cell generates its ownsupply of iodine fro
31、m the iodide present. The iodine reactsstoichiometrically with the water and the completion of thereaction is detected with a platinum sensing electrode. Thecoulombs of electricity required to generate the necessaryamount of iodine is then translated by the microprocessor in thecontrol unit into the
32、 amount of water that was present in thesample.9.3 The single bath coulometric titration cell consists of asealed vessel filled with single bath reagent and dual platinumelectrodes. When a sample containing water is injected into thevessel, the electrolytic cell generates its own supply of iodinefro
33、m the iodide present in the single bath reagent. The iodinereacts stoichiometrically with the water and the completion ofthe reaction is detected by a platinum sensing electrode. The3Mitchell, J., Jr. and Smith, D. M., AquametryA Treatise on Methods for theDetermination of Water, Part IIIThe Karl Fi
34、scher Reagent, 2nd ed., J. Wiley andSons, Inc., New York, NY, 1977.4HydranalEugen Scholz Reagents for Karl Fischer Titration, 4th ed., byRiedel-deHaen Aktiengesellschaft (US DistributorCresent Chemical Co., Inc.).5Automatic coulometric and volumetric titrators are manufactured by manydifferent compa
35、nies.D3401 97 (2017)2coulombs of electricity required to generate the necessaryamounts of iodine is then translated by the microprocessor inthe control unit into the amount of water that was present in thesample.10. Verification of Instrument Accuracy10.1 Coulometric titrators do not have a titrant
36、that needs tobe standardized since the iodine is being generated on demandby the titration cell. However, occasional checks of theinstrument accuracy are recommended. This can be done bytitrating a known amount of water and comparing this amountwith the amount of water reported by the titrator.10.2
37、Use a 5-L syringe to inject exactly 3.0 L of waterinto the titration cell. Once the titration is complete, the titratorshould report a value of 3000 g (3.0 mg) H2O. The deviationfrom this value should not be larger than 10 %. If the value islarger than 10 %, consult the instrument manual or manufac-
38、turer to determine the cause.10.3 Alternatively, standard solutions containing knownamounts of water dissolved in either methanol or a non-hydroscopic solvent are available from reagent suppliers foraccuracy verification. A known volume of this solution istitrated and the reported amount of water is
39、 compared with thetheoretical amount stated by the supplier.11. Precautions11.1 Amounts of coulomatic reagents usually recommendedfor addition to the reaction cell typically have the capacity toreact with approximately 100 to 200 mg of water. Thesereagents must be replaced when they are depleted.11.
40、2 Coulomatic reagents are hydroscopic and must bestored in tightly capped containers to reduce the absorption ofatmospheric moisture.11.3 Since the titrator automatically generates iodine tokeep the reaction vessel in a dehydrated state, it is important tokeep the cell sealed to prevent introduction
41、 of excess atmo-spheric moisture that will decrease reagent life.11.4 The total amount of solution in the anode compartmentcan affect the KF reaction. Typically, the total volume ofsample liquids that are added to the reaction cell should notexceed 50 % of the original reagent in the compartment. If
42、 thereagents become too dilute, the stoichiometry and rate of theKarl Fischer reaction can be adversely affected. This factshould be considered when using large sample sizes.11.5 Follow the recommended maintenance procedures ofthe instrument manufacturer.12. Procedure12.1 Set up the coulometric titr
43、ator according to the manu-facturers instructions, and add the proper amount of coulomatreagents to the anode and cathode compartments of the titrationcell.12.2 The cell solutions must be anhydrous prior to introduc-tion of the sample. This is accomplished by either pretitratingthe cell contents or
44、by adding a small amount of an iodine/methanol solution until a faint brownish coloration appears.Following the procedure recommended by the instrumentmanufacturer is suggested.12.3 The amount of halogenated solvent that is injected intothe cell depends on the quantity of water in the solvent. Table
45、1 lists recommended sample sizes for anticipated water con-centrations.12.4 Thoroughly clean and dry the sampling syringe. Onemethod is to dry it in an oven and desiccate before use.12.5 Fill the syringe to the desired level with sample anddraw back the plunger so that no sample remains in the needl
46、e.12.6 Cover the syringe needle with a silicone rubber blockor piece of silicone rubber septa to further prevent evaporationor spillage during the weighing process.12.7 Transfer the filled syringe to an analytical balance andweigh the syringe and contents to the nearest 0.01 g.12.8 Remove the silico
47、ne block and insert the needle intothe titration cell septum. Inject the sample slowly, taking carenot to touch the needle to the surface of the anode solution.While the syringe is still inside the cell, draw any remainingsample that may remain in the syringe needle back into thebarrel and remove th
48、e needle from the cell.12.9 Place the silicone block back onto the tip of the needleand reweigh the empty syringe. The weight difference betweenthe first and second weighings will be the amount of sampleinjected into the titration cell.12.10 The make and model of the titrator being used willdetermin
49、e the actual steps performed to carry out the titrationprocess. In most cases, all that is required is pressing a starttitration or run key on the instrument keyboard either just priorto or just after the sample injection.12.11 Once the titration is complete, the amount of water(g or mg) that was found in the solvent will appear on theinstruments digital display. Most instruments will also calcu-late concentrations (ppm or %) if the sample weight is keyedinto the instruments control panel.13. Calculation13.1 Calculate the water content of the solvent as follows:
