1、Designation: D7923 16Standard Test Method forWater in Ethanol and Hydrocarbon Blends by Karl FischerTitration1This standard is issued under the fixed designation D7923; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st 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 covers the determination of water from0.05 % to 5.0 % by mass in blends of ethanol, hydrocarbon,and cor
3、responding blends. It is intended for measuring watercontent of gasoline or other hydrocarbon blendstock, denaturedfuel ethanol as cited in Specification D4806, and ethanol fuelblends such as those cited in Specification D5798 and PracticeD7794. This test method is not applicable to samples that are
4、phase separated.1.1.1 Procedure AFor measurement of water up to 2 % bymass in ethanol and hydrocarbon blends using coulometricKarl Fischer titration. This is the referee method for samplescontaining up to 2 % ethanol.1.1.2 Procedure BFor measurement of water up to 5.4 %by mass in ethanol and hydroca
5、rbon blends using volumetricKarl Fischer titration.1.2 This method measures mass percent water and allowsfor the alternative reporting of volume percent. This testmethod recommends the use of pyridine-free reagents.1.3 The values stated in SI units are to be regarded asstandard. No other units of me
6、asurement are included 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 practices and determine the applica-bility of regulatory l
7、imitations prior to use. Specific precau-tionary statements are given in Section 8.2. Referenced Documents2.1 ASTM Standards:2D1152 Specification for Methanol (Methyl Alcohol)D1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4175 Terminology R
8、elating to Petroleum Products, LiquidFuels, and LubricantsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD4806 Specification for Denatured Fuel Ethanol for Blend-ing with Gasolines for Use as Automotive Spark-IgnitionEngine FuelD5798 Specification for Ethanol Fuel Blends for
9、 Flexible-Fuel Automotive Spark-Ignition EnginesD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System PerformanceD6708 Practice for Statistical Assessment and Improvementof Expected Agreement Between Two Test Methods thatPur
10、port to Measure the Same Property of a MaterialD7794 Practice for Blending Mid-Level Ethanol FuelBlends for Flexible-Fuel Vehicles withAutomotive Spark-Ignition EnginesE203 Test Method for Water Using Volumetric Karl FischerTitrationE1064 Test Method for Water in Organic Liquids by Coulo-metric Karl
11、 Fischer Titration3. Terminology3.1 For general terminology, refer to Terminology D4175.3.2 Definitions:3.2.1 denatured fuel ethanol, nfuel ethanol made unfit forbeverage use by the addition of denaturants under formula(s)approved by the applicable regulatory agency to prevent theimposition of bever
12、age alcohol tax. D48063.2.2 hydrocarbon, na compound composed solely ofhydrogen and carbon. D57983.2.2.1 DiscussionThe hydrocarbon mixtures used inethanol fuel blends will be unleaded gasoline, gasoline blend-stock for oxygenate blending (BOB), natural gasoline, or otherhydrocarbons in the gasoline
13、boiling range. The hydrocarbonblend components will also contain trace quantities of otherelements.3.3 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility
14、ofSubcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.Current edition approved July 1, 2016. Published August 2016. DOI: 10.1520/D7923-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStanda
15、rds 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 19428-2959. United States13.3.1 coulometric titration, nin reference to Karl Fischertitration methods, a process of measurin
16、g the water content ofa sample using an electrolytic process to generate iodine insitu.3.3.2 pre-titration, nthe process of adding titrant to reactwith any water in the Karl Fischer system so the system istotally dry prior to addition of a test sample.3.3.3 volumetric titration, nin reference to Kar
17、l Fischertitration methods, a process of measuring the water content ofa sample by the physical delivery of a titration reagentcontaining iodine.4. Summary of Test Method4.1 This test method is based on the Karl Fischer (KF)reaction for determining water. Iodine is consumed by water ina one to one m
18、olar ratio in the presence of sulfur dioxide,organic base, and methanol or other alcohols. The coulometricmethod generates iodine from iodide by anodic oxidation whilethe iodine is already present in the volumetric KF reagents.5. Significance and Use5.1 Blends of fuel ethanol and hydrocarbon have a
19、limitedsolvency for water that is dependent upon temperature and theratio of ethanol to hydrocarbon. Good handling practices areimportant during the blending, storage, and transportation offuel to avoid water contamination. High concentrations ofwater can cause haze or phase separation in ethanol an
20、dhydrocarbon blends and lead to freezing problems at lowtemperatures. Water has also been associated with corrosionand filter plugging.6. Interferences6.1 A number of functional groups are known to interferewith Karl Fischer titrations. In hydrocarbons, the most com-mon interferences are mercaptans
21、and sulfides. In ethanol,aldehydes and ketones are known to interfere with the KarlFischer reagent. Some interferences can be mitigated with theuse of applicable reagents. For fuel grade ethanol and gasolinein areas with stringent environmental regulations, the magni-tude of the interference should
22、be negligible under mostcircumstances. A list of several additional functional groupsthat can interfere with Karl Fischer titrations is included in theAppendix (X1.1.1).7. Apparatus7.1 Automatic Titrator:7.1.1 Coulometric Automatic Titrator, consisting of a con-trol unit, titration vessel, dual plat
23、inum sensing electrode,generator electrode assembly, and magnetic stirrer. The instru-ment is designed to coulometrically generate iodine that reactsstoichiometrically with the water present in the sample solu-tion. The coulombs of electricity required to generate thereagent are converted to microgr
24、ams of water, which isobtained as a direct digital readout.7.1.2 Volumetric Automatic Titrator, consisting of a controlunit, titration vessel, dual platinum sensing electrode, dispens-ing buret, and magnetic stirrer. The instrument is designed toaccurately dose an iodine containing titrant into the
25、titrationvessel that reacts stoichiometrically with the water present inthe sample solution. The titrant solution is standardized todetermine milligrams of water per milliliter of Karl Fischerreagent it will neutralize in the sample.7.2 Gas-tight Syringe, fitted with a cannula needle ofappropriate l
26、ength and gauge for introducing sample into thetitration chamber or removing excess solution from titrationchamber (see Note 1). The syringe shall be made of glass orother suitably inert material. The volume of the syringe willdepend on the sample size. When injecting by volume, thesample should occ
27、upy at least 25 % of the syringe volume.7.2.1 Rinse all glass syringes and needles with dry methanolor ethanol after cleaning, then dry in an oven at 100 C for atleast 1 h and store in a desiccator.7.3 Sample Bottle, suitable for collecting sample and main-taining an air-tight enclosure to prevent i
28、ntrusion of atmo-spheric moisture.7.4 Oven, temperature 100 C 6 5 C.7.5 Desiccator, standard laboratory type with desiccantcontaining color change indicator.7.6 Analytical Balance, capable of weighing to 60.0001 g.8. Safety Precautions8.1 The reagents contain one or more of the following:iodine, org
29、anic base, sulfur dioxide, and methanol or otheralcohol. Wear chemically resistant gloves when mixing thereagents and removing solution from the titration chamber.Exercise care to avoid inhalation of reagent vapors, or directcontact of the reagent with the skin.9. Sampling9.1 Sampling is defined as
30、all of the steps required to obtainan aliquot representative of the contents of any pipe, tank orother system and to place the sample into a container foranalysis by a laboratory or test facility. Sampling practices arecovered in Practices D4057 and D4177.9.2 Due to the low concentration of water to
31、 be measured,and the hygroscopic nature of ethanol, exercise care at all timesto avoid contaminating the sample with moisture from thesample container, the atmosphere, or transfer equipment.9.3 Samples shall be at room temperature at time of analy-sis.9.4 Verify that samples are single phase before
32、taking analiquot to test. Water or water/ethanol blend will separate fromhydrocarbon if the solubility limit is exceeded. The solubilitylimit depends on the gasoline makeup, concentration of ethanolor other emulsifiers, and sample temperature. Water is infi-nitely soluble in ethanol.9.4.1 For a tran
33、sparent container, this observation can bedetermined by visual inspection. If the material has two phases,shake the sample vigorously to combine. If the separate layerre-forms, the sample is not suitable for testing.9.4.2 If the sample is contained in a non-transparentcontainer, mix the sample and i
34、mmediately pour a portion ofthe remaining sample into a clear glass container and observeD7923 162for evidence of phase separation. If the separate layer forms,the sample is not suitable for testing.9.4.3 Because of the volatile and hygroscopic nature of thesamples, mixing with a mechanical or elect
35、ronic mixer is notrecommended.9.5 Remove the test specimens for analysis from the samplebottle with a dry, inert gas-tight syringe.PROCEDURE A (COULOMETRIC)10. Reagents10.1 Purity of ReagentsUnless otherwise indicated, it isintended that all reagents shall conform to the specifications ofthe Committ
36、ee onAnalytical Reagents of theAmerican Chemi-cal Society, where such specifications are available.3Othergrades may be used, provided it is first ascertained that thereagent is of sufficiently high purity to permit its use withoutlessening the accuracy of the determination.10.2 Purity of WaterUnless
37、 otherwise indicated, referenceto water shall be understood to mean Type II or Type IIIreagent water, conforming to Specification D1193, or better.10.3 Karl Fischer ReagentsCommercial coulometric KFreagents and reagent systems of various types are available foruse with autotitrators for water determ
38、ination. Traditionally,pyridine was the organic base used in KF reagents. Pyridine-free formulations are available and are preferred by most KFinstrument manufacturers for use with their equipment. Thepyridine-free reagents are less toxic, less odorous, and morestable than those containing pyridine.
39、 The use of pyridine-freereagents is recommended whenever possible. Coulometrictitrations normally require two reagent solutions: an anolyteand a catholyte or generator solution. However, with the use ofan integrated or diaphragm-less cell, a single solution thatcontains all of the reagents needed f
40、or a KF titration may beused.10.3.1 Catholyte solution, contains ammonium salts andmethanol.10.3.2 Anolyte solution, contains iodide, sulfur dioxide andimidazole buffer in a suitable solvent.10.3.3 One component solution, iodide, sulfur dioxide, imi-dazole buffer, and bases in a suitable solvent. Th
41、is solution maybe used as the only solution in a coulometric system with adiaphragm-less generator cell or as the anolyte solution in adiaphragm cell if specified by the manufacturer.10.3.4 Water Standards, 0.1 % by mass and 1 % by mass,commercially prepared in organic solvent recommended forthis me
42、thod.11. Preparation of Apparatus11.1 Clean, dry, and assemble the titration chamber asdirected in the manufacturers instructions. Care should betaken to ensure the vessel is sealed from atmospheric moisture.Replace the desiccant if saturated. Connect the leads from thesensing and generator electrod
43、es to the titrator.11.2 Add catholyte solution (10.3.1) to the generator elec-trode assembly and reseal the vessel according to manufacturerinstructions.11.3 Fill the anode reservoir with anolyte solution (10.3.2)as directed by the manufacturer. The level of the catholytesolution in the inner chambe
44、r shall be below the level of theanolyte solution to prevent backflow contamination of thetitration (anolyte) solution. The anolyte solution may have tobe removed periodically to maintain the lower level. (Note 1)NOTE 1A coulometric system with a diaphragm-less generator elec-trode should be filled
45、with the appropriate one component solution.11.4 Agitate the titration solution by gently swirling thetitration chamber to remove any residual moisture from thewalls. Allow the solution to stir until inner atmosphere mois-ture is removed and the baseline has been established.12. Verification of Cali
46、bration and Quality Control12.1 Autotitrators vary in calibration procedures by manu-facturer. Consult the operating manual for the autotitrator inuse. Stable, prepackaged quality control (QC) water standardsare commercially available with 0.1 % by mass and 1 % bymass water content for this purpose.
47、 It is desirable to verifycalibration with a standard solution that approximates the samerange of water expected to be in the samples.12.2 It is recommended that a control chart measuring a QCstandard sample be established and maintained according togenerally accepted guidelines. Practice D6299 may
48、be used forthis purpose. Measure the control sample each day a sample(s)is tested. If the measured value exceeds 65 % of the knownamount, take appropriate action before proceeding with thesample test (see Note 2).NOTE 2This may require replacing the reagent solutions.13. Procedure13.1 Assemble a dry
49、 syringe and needle. Withdraw 1 mL to2 mL of the sample into the syringe and discard the contentsinto a waste container. Repeat rinsing the syringe with sampletwo additional times to assure a representative sample andremove any residual moisture from the syringe. Duringsampling, minimize sample exposure to atmospheric moisture.Using the following table as a guide, withdraw the properamount of test sample into the syringe. Invert the syringe andeject to remove any air. Wipe any excess liquid from theneedle. Obtain a mass to 60.1 mg (W1). See Table 1.3Reagent Chemicals,
