1、Designation: D7375 08Standard Test Method forTrace Quantities of Water in Aromatic Hydrocarbons andTheir Mixtures by Coulometric Karl Fischer Titration1This standard is issued under the fixed designation D7375; the number immediately following the designation indicates the year oforiginal adoption o
2、r, in the case of revision, the 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.1. Scope1.1 This test method describes the use of the CoulometricKarl Fischer (KF) titrati
3、on for the determination of water inaromatic hydrocarbons and their mixtures, derivatives andrelated chemicals.1.2 This test method is applicable to samples with waterconcentrations from 10 to 400 mg/kg.1.3 In determining the conformance of the test results usingthis method to applicable specificati
4、ons, results shall berounded off in accordance with the rounding-off method ofPractice E29.1.4 Values stated in SI units are to be regarded as thestandard. The preferred units are milligrams per kilogram(mg/kg).1.5 This standard does not purport to address all of thesafety concerns, if any, associat
5、ed 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 a specifichazard statement see Section 8.2. Referenced Documents2.1 ASTM Standards:2D1193 Specifica
6、tion for Reagent WaterD3437 Practice for Sampling and Handling Liquid CyclicProductsD6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and Related Ma-terialsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE203 T
7、est Method for Water Using Volumetric Karl FischerTitration2.2 Other Standard:OSHARegulations, 29 CFR paragraphs 1910 and 1910.120033. Summary of Test Method3.1 In the Karl Fischer reaction, water will react with iodinein the presence of sulfur dioxide, alcohol and an organic baseaccording to the fo
8、llowing equation:H2O1I21SO21CH3OH13RNRNH!SO4CH312RNH!I (1)where:RN = organic base.3.2 In the coulometric titration test method, the sample isinjected into an electrolytic cell where the iodine required forthe reaction with water is produced by an anodic oxidation ofiodide. With this technique, no st
9、andardization of reagents isrequired.4. Significance and Use4.1 High water concentrations can have a detrimental effecton many uses of aromatic hydrocarbons, their mixtures andrelated compounds.4.2 Water can inhibit desired reactions when aromatichydrocarbons, their mixtures and related compounds ar
10、e usedin formulations and chemical processes.4.3 Water can cause corrosion problems and detrimentaleffects during the manufacture and processing of aromatichydrocarbons, their mixtures and related compounds.5. Interferences5.1 Certain compounds or classes of compounds interferewith the accurate dete
11、rmination 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.1This test method is under the j
12、urisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.04 on Instrumental Analysis.Current edition approved Jan. 1, 2008. Published February 2008. DOI: 10.1520/D7375-08.2For referenced ASTM standards, visit the ASTM website
13、, 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.3Available from U.S. Government Printing Office Superintendent of Documents,732 N. Capitol St., NW, Mail Stop: SDE,
14、 Washington, DC 20401, http:/www.access.gpo.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesNOTICE: This standard has either been superseded and replaced by a new version or withdrawn.Contact ASTM International (www.astm.org) for t
15、he latest information15.3 A more detailed discussion of KF interferences can befound in Test Method E203 and other sources.46. Apparatus6.1 Coulometric TitratorConsisting of a single or dualbath electrolytic cell, dual platinum electrode, magnetic stirrerand control unit.6.1.1 Dual Bath Electrolytic
16、 CellThe dual bath coulom-etic titration cell consists of a sealed vessel containing both ananode and cathode compartment (a Fritted Cathode Cell). Theanodic compartment usually contains a solution consisting ofsulfur dioxide, iodide and an amine in an alcoholic basedsolvent. The cathodic compartmen
17、t contains similar reagentsoptimized for the cathodic reduction. When a sample contain-ing water is injected into the anode compartment, the electro-lytic cell generates its own supply of iodine from the iodidepresent. The iodine reacts stoichiometrically with the water andthe completion of the reac
18、tion is detected with a dual platinum-sensing electrode. The coulombs of electricity required togenerate the necessary amount of iodine is then translated bythe microprocessor in the control unit into the amount of waterthat was present in the sample.6.1.2 Single Bath Electrolytic Cell The single ba
19、th elec-trolytic cell consist of a sealed vessel with an anode andcathode electrode (a Frittless Cathode Cell), a dual platinumsensing electrode and is filled with a single bath reagent. Whena sample containing water is injected into the vessel, theelectrolytic cell generates its own supply of iodin
20、e from theiodide present. The iodine reacts stoichiometrically with thewater and the completion of the reaction is detected with a dualplatinum-sensing electrode. The coulombs of electricity re-quired to generate the necessary amount of iodine is thentranslated by the microprocessor in the control u
21、nit into theamount of water that was present in the sample.6.2 Sampling Syringes5 and 10-mL gastight syringes.6.3 Standard Gastight Syringe10-L size.6.4 Silicone Rubber Blocks Silicone Rubber Septa, orequivalent.6.5 Drying OvenAir circulating capable of maintaining adrying temperature of 110C.6.6 De
22、siccator with desiccant.6.7 Analytical BalanceCapable of weighing to the nearest0.0001 g accurately.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the
23、AmericanChemical Society where such specifications are available.5Other grades may be used, providing it is first ascertained thatthe reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated referencesto
24、 water shall be understood to mean reagent water conformingto Type II of Specification D1193.7.3 Anode ReagentFor dual bath titration use reagentrecommended by manufacturer of titrator.7.4 Cathode ReagentFor dual bath titration use reagentrecommended by manufacturer of titrator.7.5 Single Bath Reage
25、ntFor single bath titration usereagent recommended by manufacturer of titrator.7.6 TolueneReagent grade.7.7 Dry Molecular Sieve Type 4A4-8 mesh.7.8 Dried Toluene SolutionFill a narrow top 1 L glassbottle with approximately 2 in. of Molecular Sieve Type 4A,4-8 Mesh and fill the bottle with reagent gr
26、ade toluene takingcare to minimize or eliminate the headspace. Agitate/mix thetoluene and molecular sieve in the bottle and let the solutionstand for 2 days in a flammable storage cabinet or fume hoodbefore using.7.9 Quality Assurance (QA) Samples Samples that arearomatic hydrocarbons or standards o
27、f known water content.These (QA) samples are to be used to check the validity of thetesting process as described in Section 11. An ample supply ofQAsample material should be available for the intended periodof use and must also be homogenous and stable under theanticipated storage time and condition
28、s.8. Hazards8.1 Consult current OSHA regulations and suppliers Mate-rial Safety Data Sheets (MSDS) for materials used in this testmethod.9. Sampling9.1 Obtain a test sample in accordance with Practice D3437.Since aromatic hydrocarbons normally contain low concentra-tions of water, care must be taken
29、 to eliminate the introductionof water from sampling equipment and atmospheric moisture.9.2 Without taking the proper sampling precautions, moreerror is typically introduced into the determination of waterthrough sampling techniques than in the titration process itself.9.3 Dry sample bottles and clo
30、sures in an oven at 110C for1 to 2 h. Place caps on the bottles immediately after removingfrom the oven.9.4 Transfer the sample to the bottles as quickly as possible.Adjust the liquid level to achieve as close to zero headspace as4Mitchell, J. Jr. and Smith, D. M., AquametryA treatise on Methods for
31、 theDetermination of Water, Part IIIThe Karl Fischer Reagent, 2nded., J. Wiley andSons, Inc., New York, NY, 1977.5Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Soci
32、ety, 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.D7375 082possible, taking into account the type of sample. Immediatelyplace the cap on the bottle and t
33、ighten.9.5 When removing a portion of sample from the bottle forKF analysis use syringes that have been thoroughly dried asoutlined in 12.5. Replace the cap on the bottle immediately.9.6 If more that one portion of sample is to be taken fromthe bottle or if the sample is to be retained for further w
34、ateranalysis, 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.10. Verification of Instru
35、ment Accuracy10.1 Coulometric titrators do not have a titrant 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 byanalyzing either:(a) A standard solution available f
36、rom reagent supplier foraccuracy verification containing a known amount of waterdissolved in an appropriate solvent or(b) A known amount of distilled reagent water.10.2 Standard SolutionA known volume or weight of astandard solution is analyzed and amount of water determinedis compared with the cert
37、ified (theoretical) amount of waterstated by the manufacturer. The deviation from the certified(theoretical) value should not be larger than 65%.10.3 Distilled Reagent WaterUse a 10-L syringe toaccurately inject 3.0 Lof water into the titration cell. Once thetitration is complete, the analyzer shoul
38、d report a value of 3000g (3.0 mg) H2O. The deviation from the theoretical valueshould not be larger than 65%.11. Preparation of Apparatus11.1 Amounts of coulometric reagents recommended foraddition to the electrolytic titration cell usually have thecapacity to react with approximately 200 to 500 mg
39、 of water.These reagents must be replaced when they are depleted.11.2 Coulometric reagents are hygroscopic 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
40、state, it is important tokeep the cell sealed to prevent introduction of excess atmo-spheric moisture that will decrease reagent life.11.4 The total amount of solution plus sample in the anodesection of the electrolytic titration cell can affect the KFreaction. Typically, the total liquid volume of
41、sample added tothe anode section of the electrolytic titration cell should notexceed 50 % of the original reagent volume. If the reagentsbecome too dilute, the stochiometry and rate of the KarlFischer reaction can be adversely affected. This fact should beconsidered and taken into account when using
42、 large samplesizes.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 add the proper amount of reagents.12.2 The cell solutions must be anhydrous prior to introduc-tion of
43、 sample. Follow the manufacturers instructions fordrying down the titration cell.12.3 The amount of aromatic sample that is injected into thetitration cell is dependent upon the quantity of water in thesample. Table 1 lists recommended sample size for the antici-pated water concentration. Other samp
44、les sizes may be used aslong as the analysis meets the performance criteria of themethod.12.4 When more than one replicate of a sample will beanalyzed, determine the syringe size that will contain thedesired sample injection volume multiplied by the number ofreplicates desired plus 0.5 mL. Follow th
45、e same calculation forother replicates and sample sizes. Table 2 is an example ofsyringe size determination for different injection volumes whenthe number of replicates equals three.12.5 Prepare the syringe for injection by one of the follow-ing methods as outlined in section 12.5.1, 12.5.2,or12.5.3
46、.12.5.1 Rinse the gastight syringe with the Dried TolueneSolution (see 7.8) a minimum of 5 times.12.5.2 Thoroughly clean and dry the sampling syringe.Drying the syringe in an oven at 110C and storing in adesiccator before use has proven to be an effective method.12.5.3 Other approaches may be used a
47、s long as the theymeet the performance criteria of the method.12.6 Fill the syringe to the desired volume for the totalnumber of replicates to be analyzed as determined in 12.4 andTable 2. Take care when filling the syringe to slowly withdrawthe plunger thereby not agitating or mixing inside the syr
48、ingebody the sample with air. Displace enough sample from thesyringe to eliminate any air bubble that remains inside theneedle of the syringe.12.7 Cover the syringe needle with a silicone rubber blockor piece of silicone rubber septa to prevent evaporation orspillage during the weighing process.12.8
49、 Transfer the filled syringe to an analytical balance andweigh the syringe and contents to the nearest 0.0010 g.12.9 Follow the manufacturers directions to prepare theanalyzer for sample analysis and injection.12.10 Remove the syringe from the balance. Remove thesilicone block and insert the needle into the titration cellthrough the septum taking care the tip of the needle isTABLE 1 Recommended Injection Volume vs. Expected MoistureConcentrationSample VolumemLExpected Concentrationmg/kg1.50 mL 0 20 mg/kg1.00 mL 24 400 mg/kgD7375 083nt
