1、Designation: E 203 08Standard Test Method forWater Using Volumetric Karl Fischer Titration1This standard is issued under the fixed designation E 203; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numb
2、er 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. Scope*1.1 This test method is intended as a general guide for theap
3、plication of the volumetric Karl Fischer (KF) titration fordetermining free water and water of hydration in most solid orliquid organic and inorganic compounds. This test method isdesigned for use with automatic titration systems capable ofdetermining the KF titration end point potentiometrically;ho
4、wever, a manual titration method for determining the endpoint visually is included as Appendix X1. Samples that aregaseous at room temperature are not covered (see AppendixX4). This test method covers the use of both pyridine andpyridine-free KF reagents for determining water by the volu-metric titr
5、ation. Determination of water using KF coulometrictitration is not discussed. By proper choice of the sample size,KF reagent concentration and apparatus, this test method issuitable for measurement of water over a wide concentrationrange, that is, parts per million to pure water.1.2 The values state
6、d in SI units are to be regarded asstandard.1.3 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 regulat
7、ory limitations prior to use. Specific warningsare given in 3.1 and 7.3.3.1.4 Review the current Material Safety Data Sheets (MSDS)for detailed information concerning toxicity, first aid proce-dures, and safety precautions for chemicals used in this testprocedure.2. Referenced Documents2.1 A list of
8、 existing ASTM Karl Fischer methods, theirapplications to various products, and the sponsoring commit-tees is given in Appendix X3.2.2 ASTM Standards:2D 789 Test Methods for Determination of Solution Viscosi-ties of Polyamide (PA)D 803 Test Methods for Testing Tall OilD 890 Test Method for Water in
9、Liquid Naval StoresD 1123 Test Methods for Water in Engine Coolant Concen-trate by the Karl Fischer Reagent MethodD 1152 Specification for Methanol (Methyl Alcohol)D 1193 Specification for Reagent WaterD 1348 Test Methods for Moisture in CelluloseD 1364 Test Method for Water in Volatile Solvents (Ka
10、rlFischer Reagent Titration Method)D 1533 Test Method for Water in Insulating Liquids byCoulometric Karl Fischer TitrationD 1568 Test Methods for Sampling and Chemical Analysisof Alkylbenzene SulfonatesD 1631 Test Method for Water in Phenol and RelatedMaterials by the Iodine Reagent MethodD 2072 Tes
11、t Method for Water in Fatty Nitrogen Com-pounds3D 2575 Methods of Testing Polymerized Fatty Acids3D 3277 Test Methods for Moisture Content of Oil-Impregnated Cellulosic InsulationD 3401 Test Methods for Water in Halogenated OrganicSolvents and Their AdmixturesD 4017 Test Method for Water in Paints a
12、nd Paint Materialsby Karl Fischer MethodD 4377 Test Method for Water in Crude Oils by Potentio-metric Karl Fischer TitrationD 4672 Test Methods for Polyurethane Raw Materials:Determination of Water Content of PolyolsD 4928 Test Methods for Water in Crude Oils by Coulom-etric Karl Fischer TitrationD
13、5460 Test Method for Rubber Compounding Materials1This test method is under the jurisdiction of ASTM Committee E15 onIndustrial and Specialty Chemicals and is the direct responsibility of SubcommitteeE15.01 on General Standards.Current edition approved Oct. 1, 2008. Published November 2008. Original
14、lyapproved in 1962 as E 203 62 T. Last previous edition approved in 2001 asE 203 01.2For referenced ASTM standards, visit 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 p
15、age onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.W
16、ater in Rubber AdditivesD 5530 Test Method for Total Moisture of Hazardous WasteFuel by Karl Fischer TitrimetryD 6304 Test Method for Determination of Water in Petro-leum Products, Lubricating Oils, and Additives by Coulo-metric Karl Fischer TitrationE 180 Practice for Determining the Precision of A
17、STMMethods for Analysis and Testing of Industrial and Spe-cialty ChemicalsE 1064 Test Method for Water in Organic Liquids byCoulometric Karl Fischer Titration3. Summary of Test Method3.1 The sample, containing a maximum of 100 mg of water,is dissolved or dispersed in a suitable liquid and titrated w
18、ithKF reagent, which consists of iodine, sulfur dioxide, organicbase, and a solvent (typically an alcohol, such as methanol,ethylene glycol, or 2-methoxyethanol). The titration end pointis determined potentiometrically with a platinum electrodewhich senses a sharp change in cell resistance when the
19、iodineis reduced by sulfur dioxide in the presence of water.(WarningKF reagent contains four toxic compounds,namely, iodine, sulfur dioxide, pyridine or other organic bases,and methanol or glycol ether. The reagent should be dispensedin a well-ventilated area. Care must be exercised to avoidinhalati
20、on of the reagent or direct contact of the reagent withthe skin.)3.2 The general equation to this reaction is as follows:H2O 1 I21 SO21 R8OH 1 3 RN . RNH!SO4R8 1 2RNH!I (1)where:RN = an organic base such as pyridine, andR8OH = alcohol.4. Significance and Use4.1 Titration techniques using KF reagent
21、are one of themost widely used for the determination of water.4.2 Although the volumetric KF titration can determine lowlevels of water, it is generally accepted that coulometric KFtitrations (see Test Method E 1064) are more accurate forroutine determination of very low levels of water. As a genera
22、lrule, if samples routinely contain water concentrations of 500mg/kg or less, the coulometric technique should be considered.4.3 Applications can be subdivided into two sections: (1)organic and inorganic compounds, in which water may bedetermined directly, and (2) compounds, in which water cannotbe
23、determined directly, but in which interferences may beeliminated by suitable chemical reactions or modifications ofthe procedure. Further discussion of interferences is includedin Section 5 and Appendix X2.4.4 Water can be determined directly in the presence of thefollowing types of compounds:Organi
24、c CompoundsAcetals EthersAcids (Note 1) HalidesAcyl halides Hydrocarbons (saturated and unsaturated)Alcohols Ketones, stable (Note 4)Aldehydes, stable (Note 2) NitrilesAmides OrthoestersAmines, weak (Note 3) Peroxides (hydro, dialkyl)Anhydrides SulfidesDisulfides ThiocyanatesEsters ThioestersInorgan
25、ic CompoundsAcids (Note 5) Cupric oxideAcid oxides (Note 6) DesiccantsAluminum oxides Hydrazine sulfateAnhydrides Salts of organic and inorganic acids (Note 6)Barium dioxideCalcium carbonateNOTE 1Some acids, such as formic, acetic, and adipic acid, are slowlyesterified. For high accuracy with pyridi
26、ne-based reagents, use 30 to 50 %pyridine in methanol as the solvent. When using pyridine-free reagents,commercially available buffer solutions4can be added to the sample priorto titration. With formic acid, it may be necessary to use methanol-freesolvents and titrants (1).5NOTE 2Examples of stable
27、aldehydes are formaldehyde, sugars,chloral, etc. Formaldehyde polymers contain water as methylol groups.This combined water is not titrated. Addition of an excess of NaOCH3inmethanol permits release and titration of this combined water, afterapproximate neutralization of excess base with acetic acid
28、 (see Note 9).NOTE 3Weak amines are considered to be those with Kbvalue2.4 3 105. Use salicylic acid-methanol solution (Section 7). Glacialacetic acid is applicable in certain cases.NOTE 9Addition of acetic acid eliminates the interference.4Cresent Chemicals, 1324 Motor Parkway, Hauppauge, NY, 11788
29、, Hydranaltbuffer has been found satisfactory.5The boldface numbers in parentheses refer to the list of references at the end ofthis test method.E203082NOTE 10Ferric fluoride does not interfere. Reaction with8-hydroxyquinoline is reported to eliminate this interference (3).NOTE 11With pyridine-based
30、 reagent, add 1 mol/L SO2in 1+1pyridine-methanol or spent KF reagent. With pyridine-free reagents, thetwo component reagent methods should be used and 1 mL of sulfuric acidis added to the solvent prior to titration (Note 15).NOTE 12Olefin addition reaction eliminates interferences (2). Oxida-tion wi
31、th neutral iodine solution eliminates the interference of mercaptans(4).NOTE 13Sulfuric acid, above 92 %. Add the sample (10 g) to a largeexcess of pyridine (35 mL), swirl to dissolve precipitate, and titrate.Addition of 8 mL of 1 + 1 pyridine-dioxane/1 g of sample also issatisfactory, maintaining a
32、 homogeneous solution throughout the titration.5.3 If there is a question of compounds listed in 5.2 causingan interference, the recovery of spiked additions of water to thesample matrix should be checked.5.4 Many materials react stoichiometrically with KF re-agent. When their concentration is known
33、, suitable correctionscan be applied. A list of such materials is given in AppendixX2.6. Apparatus6.1 Karl Fischer Volumetric Titrator,6consisting of a titra-tion cell, dual platinum electrode, magnetic stirrer, dispensingburet and control unit. Many manufacturers of general purposelaboratory titrat
34、ors offer optional accessories that allow theirinstrument to perform KF titrations.7. Reagents7.1 Purity of ReagentsUse reagent grade chemicals in alltests. Unless otherwise indicated, all reagents shall conform tothe specifications of the Committee on Analytical Reagents ofthe American Chemical Soc
35、iety7where such specifications areavailable. Other grades may be used, provided it is firstascertained that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the determi-nation.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall mean re
36、agent water as defined by Type II and IIIof Specification D 1193.7.3 Karl Fischer ReagentsTraditionally, pyridine was theorganic base used in KF reagents. Pyridine-free formulations,however, are available now and are preferred by most KFinstrument manufacturers for use with their equipment. Theserea
37、gents are less toxic, less odorous, and more stable than thosecontaining pyridine. The use of pyridine-free reagents isrecommended whenever possible.7.3.1 Pyridine-Free Karl Fischer TitrantTypically con-sists of a mixture of an organic base, sulfur dioxide and iodinedissolved in a solvent such as me
38、thanol or 2-methoxyethanol.Reagents with titers of 1.00, 2.00, and 5.00 mg H2O/mLcan becommercially obtained.7.3.2 Pyridine-Free Karl Fischer Solvent8Anhydrousmethanol is the most frequently used solvent, however, otheralcohols including glycols and glycol ethers are used. Somecommercially available
39、 solvents also contain an organic baseand sulfur dioxide.7.3.3 Karl Fischer Reagent Containing PyridineThe KFreagent may be either prepared in the laboratory or purchased.Two types of reagent are commonly used. Directions forpreparing these and diluting if necessary, along with commer-cial sources o
40、f supply, are as follows: (WarningFollowstandard precautions for handling toxic gases in preparing thereagents (1)or(2) as described in 7.3.3.1 and 7.3.3.2. Carry outall operations in a hood. Wear rubber gloves and a face shieldwhen handling pyridine and sulfur dioxide and when mixingchemicals. Spec
41、ial precautions must be observed when dis-pensing sulfur dioxide to prevent drawback of the solution intothe gas cylinder, which might cause an explosion. This is bestaccomplished by placing a trap in the line between the gascylinder and absorption vessel.)7.3.3.1 Karl Fischer Reagent (Ethylene Glyc
42、ol MonomethylEther Solution, 1 mL = 6 mg H2O) (2)For each litre ofsolution, dissolve 133 6 1 g iodine in 425 6 5 mL of pyridinein a dry glass-stoppered bottle. Add 425 6 5 mL of ethyleneglycol monomethyl ether. Cool to below 4C in an ice bath.Bubble 102 to 105 g of gaseous sulfur dioxide (SO2) into
43、thecooled mixture. Determine the amount of SO2added by thechange in weight of the SO2cylinder or the increase in volume(about 70 mL) of the reagent mixture. Alternatively, add about70 mL of freshly drawn liquid SO2in small increments. Mixwell and set aside for at least 12 h before using. (Warningsee
44、 7.3.3.)7.3.3.2 Karl Fischer Reagent (Methanol Solution, 1 mL = 6mg H2O)For each litre of solution, dissolve 133 6 1gofiodine in 4256 5 mL of pyridine in a dry, glass-stopperedbottle. Add 425 6 5 mL of methanol. Cool the mixture in anice bath to below 4C. Bubble 102 to 105 g of gaseous sulfurdioxide
45、 (SO2) into the cooled mixture. Determine the amountof SO2added by the change in weight of the SO2cylinder orthe increase in volume (about 70 mL) of the reagent mixture.Alternatively, add about 70 mL of freshly drawn liquid SO2insmall increments. Mix well and set aside for at least 12 hbefore using.
46、 (Warningsee 7.3.3.)7.3.3.3 Karl Fischer Reagent (Ethylene Glycol MonomethylSolution, Stabilized,1mL=6mgH2O).9,107.3.3.4 Karl Fischer Reagent, DilutePrepare more dilutesolutions of the KF reagent by diluting with the proper solventas follows:Desired Strength, mg H2O/mL Litres of Diluent to Add/litre
47、 of 6 mg/mL KF reagent3 0.8521.6Automatic volumetric titrators specifically designed for KF determinations aremanufactured by many different companies. Models are available from EM Science,Metrohm, Mettler, Photovolt, Mitsubishi, and others.7Reagent Chemicals, American Chemical Society Specification
48、s , AmericanChemical Society, Washington, DC. For suggestions 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, I
49、nc. (USPC), Rockville,MD.8Pyridine-free KF reagents can be purchased from Cresent Chemical, JT Baker,EM Science, GFS Chemicals, and others.9Fisher Scientific Co., Catalog No. SK 3-500 has been found satisfactory for thispurpose.10Mallinckrodt Catalog No. 5651 has been found satisfactory for this purpose.E20308313.20.5 5.7These dilute solutions cannot be prepared by simple propor-tion, since water added with the diluent must be accounted for.The volumes to add, indicated above, are calculated assumingthe diluent contains 0.05 % water.7.4 Methanol, Standar
