1、Designation: D3401 97 (Reapproved 2012)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 Department of Defense.1. Scope1.1 These test methods describe
3、 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-metri
4、c 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 requiresthe use
5、 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 moretraditional approach to KF water determinations. Althoughtitrators are specifically designed for KF volumetric determi-nations, ma
6、ny automatic titrators on the market can be adaptedto perform 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 titrators an
7、d 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 and health practices and determine the applica-bility of regulatory limitations prior to use. For
8、 specificprecautionary statements, see Sections 11 and 15.2. Referenced Documents2.1 ASTM Standards:2E203 Test Method for Water Using Volumetric Karl FischerTitration3. Summary of Test Methods3.1 In the Karl Fischer reaction, water will react with iodinein the presence of sulfur dioxide, alcohol, an
9、d an organic baseaccording to the following equation:H2O 1 I21 SO21 CH3OH 1 3RN RNH!SO4CH31 2RNH!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 consists of sulfur dioxide and an amin
10、edissolved 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 electrolytic cell where the iodine required
11、 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 resistance when the iodine has reacte
12、d 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 Extinguishing Agents and are the di
13、rectresponsibility of Subcommittee D26.04 on Test Methods.Current edition approved March 1, 2012. Published June 2012. Originallyapproved in 1975. Last previous edition approved in 2006 as D3401 97(2006).DOI: 10.1520/D3401-97R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, o
14、rcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.1 Water can c
15、ause 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 compounds or classes of compounds interferewith the accurate
16、 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 erroneously low water values.5.3 A more detailed discus
17、sion 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 control unit.6.2 Volumetric Titrator,5(for Test Method B
18、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, air circulating.6.7 Desiccator.6.8 Analytical Balance, c
19、apable 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 recommended by manufacturer oftitrator.7.3 Single Bath Re
20、agent, (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-hydroscopic solvent(s).Reagents with titers of 1.00, 2.00
21、, 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 was traditionally used inKarl Fisher reagents, however
22、, 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 halogenated solvents normally contain low con-centrat
23、ions 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 sampling techniques than in the titration process its
24、elf.8.3 Dry sample bottles and closures in an oven at 110C 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. of the top of thebottle. Immediately place the cap on
25、 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 fromthe bottle or if the sample is to be retained for f
26、urther 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 is beingremoved with a second syringe.TEST METHOD AWATER
27、 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 solutionconsisting of sulfur dioxide, iodide, and an amine in ame
28、thanol/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 from the iodide present. The iodine reactsstoichiometrical
29、ly 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 amount of water that was present in thesample.9.3 The
30、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 iodinefrom the iodide present in the single bath reagent. The io
31、dinereacts stoichiometrically with the water and the completion ofthe reaction is detected by a platinum sensing electrode. Thecoulombs 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 pre
32、sent in thesample.3Mitchell, J., Jr. and Smith, D. M., AquametryA Treatise on Methods for theDetermination of Water, Part IIIThe Karl Fischer Reagent, 2nd ed., J. Wiley andSons, Inc., New York, NY, 1977.4HydranalEugen Scholz Reagents for Karl Fischer Titration, 4th ed., byRiedel-deHaen Aktiengesells
33、chaft (US DistributorCresent Chemical Co., Inc.).5Automatic coulometric and volumetric titrators are manufactured by manydifferent companies.D3401 97 (2012)210. Verification of Instrument Accuracy10.1 Coulometric titrators do not have a titrant that needs tobe standardized since the iodine is being
34、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 Use a 5-L syringe to inject exactly 3.0 L of waterinto
35、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-turer to determine the cause.10.3 Alternatively, standa
36、rd 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 compared with thetheoretical amount stated by the supp
37、lier.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.11.2 Coulomatic reagents are hydroscopic and must bestored
38、 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 of excess atmo-spheric moisture that will decrease rea
39、gent 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 thereagents become too dilute, the stoichiometry and r
40、ate 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 titrator according to the manu-facturers instructions, and
41、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 by adding a small amount of an iodine/methanol solution
42、 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. Table1 lists recommended sample sizes for anticipated water
43、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 needle.12.6 Cover the syringe needle with a silicone rubber
44、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 silicone block and insert the needle intothe titration cell s
45、eptum. 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 the needle from the cell.12.9 Place the silicone block ba
46、ck 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 willdetermine the actual steps performed to carry out the titration
47、process. 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 digita
48、l 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:ppm H2O 5 g H2O found/grams of solvent injected (2)TEST METHOD BWATER DETERMINATIONUSIN
49、G A VOLUMETRIC KF TITRATOR14. Summary of Test Method14.1 The volumetric titration cell consists of a sealed glassvessel containing a dual platinum electrode. To the cell, asuitable solvent (usually methanol based) is added. The sampleis injected into the cell, the mixture is stirred thoroughly andtitrated with a Karl Fischer reagent. This reagent typicallycontains an organic amine, sulfur dioxide, and iodine dissolvedin a non-hydroscopic solvent such as xylene. The iodine reactsstoichiometrically with the water, and the completion of thereaction is detected wi
