1、Designation: D7923 16D7923 17Standard 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 ye
2、ar 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. Scope Scope*1.1 This test method covers the determination of water from 0.05 % to 5.0 % by mass in blends of ethanol, hyd
3、rocarbon, andcorresponding blends. It is intended for measuring water content of gasoline or other hydrocarbon blendstock, denatured fuelethanol as cited in Specification D4806, and ethanol fuel blends such as those cited in Specification D5798 and Practice D7794.This test method is not applicable t
4、o samples that are phase separated.1.1.1 Procedure AFor measurement of water up to 2 % by mass in ethanol and hydrocarbon blends using coulometric KarlFischer titration. This is the referee method for samples containing up to 2 % ethanol.1.1.2 Procedure BFor measurement of water up to 5.4 % by mass
5、in ethanol and hydrocarbon blends using volumetric KarlFischer titration.1.2 This method measures mass percent water and allows for the alternative reporting of volume percent. This test methodrecommends the use of pyridine-free reagents.1.3 The values stated in SI units are to be regarded as standa
6、rd. No other units of measurement are included in this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the appli
7、cability of regulatorylimitations prior to use. Specific precautionary statements are given in Section 8.1.5 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of Internati
8、onal Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1152 Specification for Methanol (Methyl Alcohol)D1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleu
9、m and Petroleum ProductsD4175 Terminology Relating to Petroleum Products, Liquid Fuels, and LubricantsD4177 Practice for Automatic Sampling of Petroleum and Petroleum ProductsD4806 Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use asAutomotive Spark-Ignition Engine FuelD57
10、98 Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition EnginesD6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-ment System PerformanceD6708 Practice for Statistical Assessment and Improvement of Exp
11、ected Agreement Between Two Test Methods that Purportto Measure the Same Property of a MaterialD7794 Practice for Blending Mid-Level Ethanol Fuel Blends for Flexible-Fuel Vehicles with Automotive Spark-IgnitionEnginesE203 Test Method for Water Using Volumetric Karl Fischer TitrationE1064 Test Method
12、 for Water in Organic Liquids by Coulometric Karl Fischer Titration1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of SubcommitteeD02.06 on Analysis of Liquid Fuels and Lubricants.Current edition a
13、pproved July 1, 2016May 1, 2017. Published August 2016May 2017. Originally approved in 2016. Last previous edition approved in 2016 as D7923 16.DOI: 10.1520/D7923-16.10.1520/D7923-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.o
14、rg. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit
15、 may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at
16、 the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 For general terminology, refer to Terminology D4175.3.2 Definitions:3.2.1 denatured fuel ethanol, nfuel ethanol made unfit for beverage use by
17、the addition of denaturants under formula(s)approved by the applicable regulatory agency to prevent the imposition of beverage alcohol tax. D48063.2.2 hydrocarbon, na compound composed solely of hydrogen and carbon. D57983.2.2.1 DiscussionThe hydrocarbon mixtures used in ethanol fuel blends will be
18、unleaded gasoline, gasoline blendstock for oxygenate blending(BOB), natural gasoline, or other hydrocarbons in the gasoline boiling range. The hydrocarbon blend components will also containtrace quantities of other elements.3.3 Definitions of Terms Specific to This Standard:3.3.1 coulometric titrati
19、on, nin reference to Karl Fischer titration methods, a process of measuring the water content of asample using an electrolytic process to generate iodine in situ.3.3.2 pre-titration, nthe process of adding titrant to react with any water in the Karl Fischer system so the system is totallydry prior t
20、o addition of a test sample.3.3.3 volumetric titration, nin reference to Karl Fischer titration methods, a process of measuring the water content of asample by the physical delivery of a titration reagent containing iodine.4. Summary of Test Method4.1 This test method is based on the Karl Fischer (K
21、F) reaction for determining water. Iodine is consumed by water in a oneto one molar ratio in the presence of sulfur dioxide, organic base, and methanol or other alcohols. The coulometric methodgenerates iodine from iodide by anodic oxidation while the iodine is already present in the volumetric KF r
22、eagents.5. Significance and Use5.1 Blends of fuel ethanol and hydrocarbon have a limited solvency for water that is dependent upon temperature and the ratioof ethanol to hydrocarbon. Good handling practices are important during the blending, storage, and transportation of fuel to avoidwater contamin
23、ation. High concentrations of water can cause haze or phase separation in ethanol and hydrocarbon blends and leadto freezing problems at low temperatures. Water has also been associated with corrosion and filter plugging.6. Interferences6.1 A number of functional groups are known to interfere with K
24、arl Fischer titrations. In hydrocarbons, the most commoninterferences are mercaptans and sulfides. In ethanol, aldehydes and ketones are known to interfere with the Karl Fischer reagent.Some interferences can be mitigated with the use of applicable reagents. For fuel grade ethanol and gasoline in ar
25、eas with stringentenvironmental regulations, the magnitude of the interference should be negligible under most circumstances. A list of severaladditional functional groups that can interfere with Karl Fischer titrations is included in the Appendix (X1.1.1).7. Apparatus7.1 Automatic Titrator:7.1.1 Co
26、ulometric Automatic Titrator, consisting of a control unit, titration vessel, dual platinum sensing electrode, generatorelectrode assembly, and magnetic stirrer. The instrument is designed to coulometrically generate iodine that reacts stoichiometri-cally with the water present in the sample solutio
27、n. The coulombs of electricity required to generate the reagent are converted tomicrograms of water, which is obtained as a direct digital readout.7.1.2 Volumetric Automatic Titrator, consisting of a control unit, titration vessel, dual platinum sensing electrode, dispensingburet, and magnetic stirr
28、er. The instrument is designed to accurately dose an iodine containing titrant into the titration vessel thatreacts stoichiometrically with the water present in the sample solution. The titrant solution is standardized to determine milligramsof water per milliliter of Karl Fischer reagent it will ne
29、utralize in the sample.7.2 Gas-tight Syringe, fitted with a cannula needle of appropriate length and gauge for introducing sample into the titrationchamber or removing excess solution from titration chamber (see Note 1). The syringe shall be made of glass or other suitably inertmaterial. The volume
30、of the syringe will depend on the sample size. When injecting by volume, the sample should occupy at least25 % of the syringe volume.7.2.1 Rinse all glass syringes and needles with dry methanol or ethanol after cleaning, then dry in an oven at 100 C for at least1 h and store in a desiccator.7.3 Samp
31、le Bottle, suitable for collecting sample and maintaining an air-tight enclosure to prevent intrusion of atmosphericmoisture.D7923 1727.4 Oven, temperature 100 C 6 5 C.7.5 Desiccator, standard laboratory type with desiccant containing color change indicator.7.6 Analytical Balance, capable of weighin
32、g to 60.0001 g.8. Safety Precautions8.1 The reagents contain one or more of the following: iodine, organic base, sulfur dioxide, and methanol or other alcohol. Wearchemically resistant gloves when mixing the reagents and removing solution from the titration chamber. Exercise care to avoidinhalation
33、of reagent vapors, or direct contact of the reagent with the skin.9. Sampling9.1 Sampling is defined as all of the steps required to obtain an aliquot representative of the contents of any pipe, tank or othersystem and to place the sample into a container for analysis by a laboratory or test facilit
34、y. Sampling practices are covered inPractices D4057 and D4177.9.2 Due to the low concentration of water to be measured, and the hygroscopic nature of ethanol, exercise care at all times toavoid contaminating the sample with moisture from the sample container, the atmosphere, or transfer equipment.9.
35、3 Samples shall be at room temperature at time of analysis.9.4 Verify that samples are single phase before taking an aliquot to test. Water or water/ethanol blend will separate fromhydrocarbon if the solubility limit is exceeded. The solubility limit depends on the gasoline makeup, concentration of
36、ethanol orother emulsifiers, and sample temperature. Water is infinitely soluble in ethanol.9.4.1 For a transparent container, this observation can be determined by visual inspection. If the material has two phases, shakethe sample vigorously to combine. If the separate layer re-forms, the sample is
37、 not suitable for testing.9.4.2 If the sample is contained in a non-transparent container, mix the sample and immediately pour a portion of the remainingsample into a clear glass container and observe for evidence of phase separation. If the separate layer forms, the sample is notsuitable for testin
38、g.9.4.3 Because of the volatile and hygroscopic nature of the samples, mixing with a mechanical or electronic mixer is notrecommended.9.5 Remove the test specimens for analysis from the sample bottle with a dry, inert gas-tight syringe.PROCEDURE A (COULOMETRIC)10. Reagents10.1 Purity of ReagentsUnle
39、ss otherwise indicated, it is intended that all reagents shall conform to the specifications of theCommittee onAnalytical Reagents of theAmerican Chemical Society, where such specifications are available.3 Other grades maybe used, provided it is first ascertained that the reagent is of sufficiently
40、high purity to permit its use without lessening the accuracyof the determination.10.2 Purity of WaterUnless otherwise indicated, reference to water shall be understood to mean Type II or Type III reagentwater, conforming to Specification D1193, or better.10.3 Karl Fischer ReagentsCommercial coulomet
41、ric KF reagents and reagent systems of various types are available for usewith autotitrators for water determination. Traditionally, pyridine was the organic base used in KF reagents. Pyridine-freeformulations are available and are preferred by most KF instrument manufacturers for use with their equ
42、ipment. The pyridine-freereagents are less toxic, less odorous, and more stable than those containing pyridine. The use of pyridine-free reagents isrecommended whenever possible. Coulometric titrations normally require two reagent solutions: an anolyte and a catholyte orgenerator solution. However,
43、with the use of an integrated or diaphragm-less cell, a single solution that contains all of the reagentsneeded for a KF titration may be used.10.3.1 Catholyte solution, contains ammonium salts and methanol.10.3.2 Anolyte solution, contains iodide, sulfur dioxide and imidazole buffer in a suitable s
44、olvent.10.3.3 One component solution, iodide, sulfur dioxide, imidazole buffer, and bases in a suitable solvent. This solution may beused as the only solution in a coulometric system with a diaphragm-less generator cell or as the anolyte solution in a diaphragmcell if specified by the manufacturer.1
45、0.3.4 Water Standards, 0.1 % by mass and 1 % by mass, commercially prepared in organic solvent recommended for thismethod.3 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed bythe American Che
46、mical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D7923 17311. Preparation of Apparatus11.1 Clean, dry, and assemble the titration chamber as
47、 directed in the manufacturers instructions. Care should be taken toensure the vessel is sealed from atmospheric moisture. Replace the desiccant if saturated. Connect the leads from the sensing andgenerator electrodes to the titrator.11.2 Add catholyte solution (10.3.1) to the generator electrode as
48、sembly 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 catholyte solutionin the inner chamber shall be maintained slightly below the level of the anolyte solution to prevent bac
49、kflow contamination of thetitration (anolyte) solution. The anolyteAs samples are analyzed, the volume of the anolyte will increase. This may slow reactivityof the catholyte due to increased pressure across the membrane. A portion of the anolyte solution may have to be removedperiodically to maintain the lowercorrect level. (Note 1)NOTE 1A coulometric system with a diaphragm-less generator electrode should be filled with the appropriate one component solution.11.4 Agitate the titration solution by gently swirling the titration chamber to remove any residual moist
