1、Designation: D 6423 08An American National StandardStandard Test Method forDetermination of pHe of Ethanol, Denatured Fuel Ethanol,and Fuel Ethanol (Ed75-Ed85)1This standard is issued under the fixed designation D 6423; the number immediately following the designation indicates the year oforiginal a
2、doption or, 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. Scope*1.1 This test method covers a procedure to determine ameasure of the aci
3、d strength of high ethanol content fuels.These include ethanol, denatured fuel ethanol, and fuel ethanol(Ed75-Ed85). The test method is applicable to fuels containingnominally 70 volume % ethanol, or higher, as described inSpecifications D 4806 and D 5798.1.2 Acid strength as measured in this test m
4、ethod is definedas pHe. A pHe value for alcohol solutions is not comparable topH values of water solutions. For example, a 1.5310-5M (18ppm) solution of H2SO4gives a pH of about 5.5 in watersolution, but, depending on buffering strength, a pHe as low as1 to 2 in unadditized alcohol fuel.1.3 The valu
5、e of pHe measured will depend somewhat onthe fuel blend, the stirring rate, and the time the electrode is inthe fuel.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesaf
6、ety 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.2. Referenced Documents2.1 ASTM Standards:2D 4806 Specification for Denatu
7、red Fuel Ethanol for Blend-ing with Gasolines for Use as Automotive Spark-IgnitionEngine FuelD 5798 Specification for Fuel Ethanol (Ed75-Ed85) forAutomotive Spark-Ignition Engines3. Terminology3.1 Definitions:3.1.1 denaturants, nnatural gasoline, gasoline compo-nents, unleaded gasoline, or toxic or
8、noxious materials added tofuel ethanol to make it unsuitable for beverage use but notunsuitable for automotive fuel use.3.1.2 denatured fuel ethanol, nfuel ethanol made unfit forbeverage use by the addition of denaturants.3.1.3 ethanol, nethyl alcohol, the chemical compound,C2H5OH.3.1.4 fuel ethanol
9、 (Ed75-Ed85), na blend of ethanol andhydrocarbons of which the ethanol portion is nominally 75 to85 volume % denatured ethanol.3.2 Definitions of Terms Specific to This Standard:3.2.1 pHe, na measure of the acid strength of alcoholfuels defined by this apparatus and procedure.4. Summary of Test Meth
10、od4.1 The sample is analyzed at room temperature using aspecified electrode system and a pH meter with an inputimpedance 1012ohms. Meters designed for use wtih ion-specific electrodes normally meet this criteria.4.2 Readings are taken at exactly 30 s because the meterreading will change throughout t
11、he analysis due to glass-electrode voltage drift caused by dehydration of the glass-electrode membrane. Because alcohol dehydrates the glass-electrode membrane, time spent soaking in alcohol solutionshould be minimized.4.3 The electrode is soaked in water-based pH 7 bufferbetween readings to prepare
12、 it for the next sample. Thisrehydrates the glass electrode, a necessary step to preserve theelectrodes response characteristics.4.4 The electrodes are cleaned/rehydrated at least every tensamples by alternately soaking several times in 1 M NaOHsolution and1MH2SO4(or 1 M HCl) for about 30 s each. Ne
13、welectrodes are treated by this procedure before first use.5. Significance and Use5.1 The acid strength, as measured by pHe, is a goodpredictor of the corrosion potential of ethanol fuels. It ispreferable to total acidity because total acidity does notmeasure acid strength; overestimates the contrib
14、ution of weakacids, such as carbonic acid; and may underestimate thecorrosion potential of low concentrations of strong acids, suchas sulfuric acid.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD0
15、2.A0.01 on Gasoline and Gasoline-Oxygenate Blends.Current edition approved Dec. 15, 2008. Published February 2009. Originallyapproved in 1999. Last previous edition approved in 2004 as D 642399(2004).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
16、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.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-
17、2959, United States.6. Apparatus6.1 pH meterAs recommended for use with ion-specificelectrodes, commercially available pH meters with an input of1012ohms are acceptable for this test method. Temperaturecompensation and readability to 0.01 pH unit are recom-mended.6.2 ElectrodeORION Ross Sure-Flow co
18、mbination elec-trode3with a glass body shall be used. Because the measure-ment is (of necessity) not made at equilibrium, it is essentialthat this exact electrode pair be used to ensure the reproduc-ibility of results. Critical features of this electrode include ahigh leak-rate sleeve-junction refer
19、ence electrode and a largemembrane glass measuring electrode. High leak-rate referenceelectrodes minimize salt-bridge junction potential drift, espe-cially in extremely low conductivity solutions like fuel alco-hols. For similar reasons, large membrane glass electrodes(measuring electrodes) were fou
20、nd to perform better and havelonger life in alcohol fuels. Since this is a method-basedparameter, other electrodes (even those of similar design) willlikely give different results under some or all conditions due tothe use of a different size or type of glass membrane for the pHelectrode, a differen
21、t type of salt bridge junction, or other smalldifferences, which may affect their nonequilibrium response.6.3 Reference Electrode Filling SolutionAlthough somereferences suggest alcoholic filling solutions for measurementsin alcohol, this test method was developed using an aqueousKCl filling solutio
22、n and aqueous buffer calibration solutions.The effect of alcoholic filling solution was not investigated.6.4 Temperature CompensatorThe thermocompensator isa temperature-sensitive resistance element immersed in thesample with the electrodes. The thermocompensator automati-cally corrects for the chan
23、ge in slope of the glass electroderesponse (with change in temperature) but does not correct foractual changes in sample pH with temperature. Becausetemperature compensation corrects only for changes in pHelectrode response with temperature, the fuel sample must be at22 6 2C.6.5 Beakers, borosilicat
24、e glass, 100 mL.6.6 Magnetic StirrerAny laboratory magnetic stirrer canbe used, along with a TFE-fluorocarbon-coated stirring barapproximately 19 to 25-mm long.6.7 Timer, capable of measuring seconds.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Un
25、less otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.4Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh pu
26、rity to permit its use without lessening the accuracy ofthe determination.7.2 Buffer SolutionsCommercially available, waterbasedbuffer solutions (pH=4.00 and pH=7.00) are acceptable for thestandardization.7.3 1 M Hydrochloric Acid (HCl)Mix one volume ofconcentrated (12 M) HCl with eleven volumes of
27、distilledwater.7.4 3 M Potassium Chloride (KCl)The electrode isshipped with this filling solution already prepared.7.5 1 M Sodium Hydroxide (NaOH)Dissolve4gofNaOHpellets in 100 mL of distilled water.7.6 1 M Sulfuric Acid (H2SO4)Mix one volume of con-centrated (18 M) H2SO4with 17 volumes of distilled
28、 water.8. Sample Containers8.1 Care must be used in sample container selection to avoidreactions that change the pHe of the sample. Do not use steel,plated steel, or epoxy-coated steel containers or PVC-coatedglass bottles for samples. Avoid closures with a paper seal.Fluorinated high-density polyet
29、hylene and spun aluminumsample containers with polyethylene or TFE-fluorocarbonclosures are acceptable. Glass bottles without an external PVCcoating and utilizing TFE-fluorocarbon or polyethylene capseals are also acceptable.8.2 Rinse the container with a portion of the fuel to besampled before taki
30、ng the sample.9. Standardization of Assembly9.1 Turn on the pH meter and allow it to warm upthoroughly in accordance with the manufacturers instructions.Note the temperature of the sample to be tested. If temperaturecompensation is to be manual, adjust the temperature dial ofthe meter to correspond
31、to the temperature of the sample to betested and allow time for all buffers, solutions, and theelectrode to equilibrate thermally.9.2 Clean/rehydrate the electrode after every ten samplesand new electrodes before first use by alternately soakingseveral times in 1 M NaOH solution and 1 M H2SO4(or1MHC
32、l) for about 30 s each. Remove the electrode and rinse itwell with distilled water into a waste container.9.3 Calibrate the pH meter to pH=7.00 with a water-basedpH=7.00 buffer solution. Remove the electrode and rinse itwith distilled water into a waste container.9.4 Calibrate the pH meter to pH=4.0
33、0 with a water-basedpH=4.00 buffer solution, using the slope adjustment. The slopemust be in the 95 to 100 % range, or the electrode will have tobe cleaned or replaced. Remove the electrode and rinse it withdistilled water into a waste container. Return the electrode tothe pH=7.00 buffer.10. Procedu
34、re10.1 Fill the electrode as needed with 3M aqueous KClsolution, supplied with the electrode.10.2 Standardize the assembly with two reference buffersolutions, as described in 9.3 and 9.4.10.3 Start with a new aliquot (fresh portion) of ethanolsample for each measurement. Since many fuel alcohols are
35、3The specified electrode (ORION Cat. No. 8172BN) is available from manylaboratory supply companies or from the manufacturer: Orion Research Incorpo-rated, Laboratory Products Group, The Schrafft Center, 529 Main Street, Boston,MA 02129.4Reagent Chemicals, American Chemical Society Specifications , A
36、mericanChemical Society, Washington, D.C. 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, Inc.
37、(USPC), Rockville,MD.D6423082poorly buffered and have low ionic strength, it is important touse a new aliquot for each measurement for best accuracy.10.4 Place about 50 mL of sample in a 100-mL beakercontaining a magnetic stirring bar and either a thermometer oran ATC probe to ensure the sample is a
38、t 22 6 2C.10.5 Remove the electrode from the pH=7.00 buffer, andrinse the electrode with distilled water into a waste container.10.6 Blot the electrode to remove excess water.10.7 Insert the electrode into the room-temperature stirredethanol sample, start the timer, and measure the pHe at exactly30
39、6 1 s. Stirring must be rapid enough to cause a small tomoderate vortex about 6 to 8 mm deep. Note that the readingwill still be changing slowly at 30 s due to dehydration of theglass pH electrode, which causes a shift in its output. If thereading is not rising at the 30-s point for low pHe fuels(pH
40、e5), or gives poor repeatability in some solutions (thosewith low buffering capacity), the electrode probably needs tobe cleaned or replaced.10.8 Remove the electrode from the sample and rinse it withdistilled water into a waste container. Return the electrode tothe pH=7.00 buffer to rehydrate the g
41、lass pH electrode.10.9 Soak the electrode in the buffer until the reading fallsbelow 7.05, but soak for at least 20 s. Recalibrate to pH=7.00if the pH is still above 7.05 after 5 min.10.10 Clean/rehydrate the electrode as described in 9.2 afterten alcohol samples have been measured. The electrode ma
42、ygive poor repeatability or high results (in alcohols) if notperiodically cleaned/rehydrated in acid and base before use.10.11 Start with 10.3 for the next sample.11. Precision and Bias11.1 PrecisionThe precision of this test method as deter-mined by statistical examination of the interlaboratory te
43、stresults is as follows:11.1.1 RepeatabilityThe difference between successivetest results, obtained by the same operator using the sameapparatus under constant operating conditions on identical testmaterial, would in the long run, in the normal and correctoperation of this test method, exceed 0.29 p
44、He in only one casein twenty.11.1.2 ReproducibilityThe difference between two singleand independent test results, obtained by different operatorsworking in different laboratories on identical test material,would in the long run, in the normal and correct operation ofthis test method, exceed 0.52 pHe
45、 in only one case in twenty.11.2 BiasSince there is no material having an acceptedreference value for pHe, bias cannot be determined.12. Keywords12.1 acid strength; automotive spark ignition engine fuel;corrosion potential; denatured fuel ethanol; ethanol; fuel etha-nol; pHeSUMMARY OF CHANGESSubcomm
46、ittee D02.A0 has identified the location of selected changes to this standard since the last issue(D 642399(2004) that may impact the use of this standard.(1) Revised to add an example showing the difference betweenpHe and PH.(2) Revised to clarify instructions.(3) Revised to provide background for
47、procedural details.(4) Revised to better describe electrode and meterrequirements.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the v
48、alidity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your c
49、omments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. In
