1、Designation: D7795 12Standard Test Method forAcidity in Ethanol and Ethanol Blends by Titration1This standard is issued under the fixed designation D7795; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、 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 acidity asacetic acid (see Specification D4806) in commonly availablegrades of denatured
3、ethanol, and ethanol blends with gasolineranging from E95 to E30. This test method is used fordetermining low levels of acidity, below 200 mg/kg (ppmmass), with the exclusion of carbon dioxide.1.1.1 Test Method ADeveloped specifically for measure-ment of acidity by potentiometric titration. This is
4、the refereemethod.1.1.2 Test Method BDeveloped specifically for measure-ment of acidity by color end point titration.1.2 The ethanol and ethanol blends may be analyzed di-rectly by this test method without any sample preparation.1.3 Review the current and appropriate Material Safety DataSheets (MSDS
5、) for detailed information concerning toxicity,first aid procedures, and safety precautions and proper personalprotective equipments.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 addre
6、ss 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 limitations prior to use. Some specifichazards statements are given in Section 7 on
7、 Hazards.2. Referenced Documents2.1 ASTM Standards:2D770 Specification for Isopropyl AlcoholD1193 Specification for Reagent WaterD4175 Terminology Relating to Petroleum, PetroleumProducts, and LubricantsD4806 Specification for Denatured Fuel Ethanol for Blend-ing with Gasolines for Use as Automotive
8、 Spark-IgnitionEngine FuelD6300 Practice for Determination of Precision and BiasData for Use in Test Methods for Petroleum Products andLubricantsE200 Practice for Preparation, Standardization, and Storageof Standard and Reagent Solutions for Chemical Analysis3. Terminology3.1 Definitions:3.1.1 acidi
9、ty, nthe quality, state, or degree of being acid.D41753.1.1.1 DiscussionThe amount of acid titrated with a base(NaOH or KOH) in a sample of ethanol or ethanol blend withgasoline, calculated as acetic acid in mg/kg (ppm mass).3.2 Abbreviations:3.2.1 KHC8H4O4KHP-Potassium Acid Phthalate4. Summary of T
10、est Method4.1 Samples are purged with nitrogen prior to and duringtitration for the elimination of carbon dioxide and then a knownamount of ethanol or ethanol blend sample is analyzed poten-tiometrically either using a monotonic or dynamic end pointtitrant addition, as specified in Test Method A, or
11、 by color endpoint titration, as specified in Test Method B, using a base(NaOH) solution. Acid content is calculated as milligrams ofacetic acid per kilogram of sample.5. Significance and Use5.1 This test method measures acidity in ethanol or ethanolblends quantitatively. Denatured fuel ethanol may
12、containadditives such as corrosion inhibitors and detergents as well ascontaminants from manufacturing that can affect the acidity offinished ethanol fuel. Very dilute aqueous solutions of lowmolecular mass organic acids, such as acetic acid, are highlycorrosive to many metals. It is important to ke
13、ep such acids ata very low level.5.2 Acceptable levels of acidity in Ethanol or Ethanolblends can vary with different specifications but in general it isbelow 200 mg/kg (ppm). Knowledge of the acidity can berequired to establish whether the product quality meets speci-fication.1This test method is u
14、nder the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.06 on Analysis of Lubricants.Current edition approved Dec. 1, 2012. Published February 2013. DOI: 10.1520/D7795-12.2For referenced ASTM standards, visit the ASTM websit
15、e, 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1
16、6. Interferences6.1 Basic solutions will absorb carbon dioxide from the airto produce carbonate ions in the titrant and change theconcentration of the titrant. Care should be taken to minimizeexposure of basic titrants to the air as much as possible. Verifythe concentration of the titrant (standardi
17、ze the titrant) fre-quently enough to detect concentration changes of 0.0005 Mand especially if prolonged exposure to the air occurs.6.2 Minimize exposure of the ethanol or ethanol blendsamples to the air to avoid contamination by carbon dioxide.7. Hazards7.1 Each analyst shall be acquainted with th
18、e potentialhazards of the equipment, reagents, products, solvents andprocedures before beginning laboratory work. Sources ofinformation include: instrument manuals, MSDS, variousliterature, and other related sources. Safety information shouldbe requested from the supplier. Disposal of waste material
19、s,reagents, reactants, and solvents shall comply with all the lawsand regulations from all applicable governmental agencies.7.2 Ethanol or ethanol blend products are intended forindustrial use only.7.3 The following hazards are associated with the applica-tion of this test method and the use of an a
20、utomatic titrator.7.3.1 Chemical Hazard:7.3.1.1 A solution of potassium hydroxide or sodium hy-droxide is corrosive and shall be handled with the appropriatepersonal protective equipment such as gloves, chemicalgoggles, and lab coat or chemical-resistant apron. Always addthe base to water when dilut
21、ing 50 % NaOH.7.3.1.2 Ethanol is a flammable and toxic solvent that is usedto prepare the lithium chloride electrolyte solution for thereference electrode. When handling a flammable solvent, workin a well-ventilated area away from all sources of ignition.TEST METHOD APOTENTIOMETRIC TITRATION8. Appar
22、atus8.1 Potentiometric TitratorAutomatic titration systemscapable of adding fixed increments of titrant at fixed timeintervals (monotonic) or variable titrant increments with elec-trode stability between increment additions (dynamic) withendpoint seeking capabilities as prescribed in the method. Att
23、he very least, the automatic titration system shall meet theperformance and specification requirements as warranted bythe manufacturer.8.2 A monotonic or dynamic mode of titrant addition shallbe used. During the titration, the speed and volume of theaddition may vary depending on the rate of change
24、of thesystem. The recommended minimum volume increment is 0.05mL for low acidity samples such as E30, and the recommendedmaximum volume increment is 0.1 mL. A signal drift of 10mV/min and endpoint recognition set to last is recommended toensure endpoint detection. When using a monotonic titrantaddit
25、ion the waiting time between increment additions shall besufficient to allow for mixing and a stable electrode response.Wait at least 10 s between additions.8.3 Buret, 5 mL capacity, capable of delivering titrant in0.02 mL or larger increments. The buret tip shall deliver titrantdirectly into the ti
26、tration vessel without exposure to thesurrounding air. The buret used for base solutions shall have aguard tube containing carbon dioxide absorbent.8.4 Titration Stand, suitable for supporting the electrode,stirrer and buret tip.8.5 Sensing Electrode, standard pH, suitable for non-aqueous titrations
27、.8.6 Reference ElectrodeSilver/Silver Chloride (Ag/AgCl)Reference Electrode, filled with 1M-3M LiCl in ethanol.8.7 Combination pH ElectrodesSensing electrodes mayhave the Ag/AgCl reference electrode built into the sameelectrode body, which offers the convenience of working withand maintaining only o
28、ne electrode. A combination pH elec-trode designed for nonaqueous titrations of organic solvents isneeded for titration of ethanol and ethanol blends. The combi-nation pH electrode shall have a sleeve junction on thereference compartment and shall use an inert ethanolelectrolyte, 1 to 3 mol/L (M) Li
29、Cl in ethanol. Combination pHelectrodes shall have the same or better response than a dualelectrode system. They shall have a movable sleeve for easyrinsing and addition of electrolyte.8.8 Titration Beaker, borosilicate glass or plastic beaker ofsuitable size for the titration.8.9 Sparging System, a
30、 gas delivery system suitable todeliver directly into the liquid sample, with an externalpressure of 10 psi (69 kPa).8.10 Variable-Speed Mechanical Stirrer, a suitable type,equipped with a propellertype stirring paddle. The rate ofstirring shall be sufficient to produce vigorous agitation withoutspa
31、ttering and without stirring air into the solution. A propellerwith blades 6 mm in radius and set at a pitch of 30 to 45 issatisfactory. A magnetic stirrer and stirring bars is also satis-factory.8.10.1 If an electrical stirring apparatus is used, it shall beelectrically correct and grounded so that
32、 connecting or discon-necting the power to the motor will not produce a permanentchange in the instrument reading during the course of thetitration.9. Reagents and Materials9.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall rea
33、gents shall conform to the specifications of the commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.3Other grades may be3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on t
34、he 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. (USPC), Rockville,MD.D7795 122used, provided it is pure enough
35、 to be used without lesseningthe accuracy of the determination.9.1.1 Commercially-available solutions may be used inplace of laboratory preparations provided the solutions havebeen certified as being equivalent.9.1.2 Alternate volumes of the solutions may be prepared,provided the final solution conc
36、entration is equivalent.9.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean reagent water that meetsthe requirements of either Type II or III of SpecificationD1193.9.2.1 Prepare CO2free water by sparging 1 L of water (9.2)with nitrogen (9.8) for no less than
37、3 min.9.3 Potassium Acid Phthalate (KHC8H4O4), primarystandard, driedPlace 4-5 g of primary standard potassiumacid phthalate KHC8H4O4of 100-mesh fineness, in a weighingbottle at 120C for 2 h. Stopper the container and cool it in adesiccator.9.4 Potassium hydrogen phthalate (KHP) SolutionAccurately w
38、eigh approximately 1.0 g of dried KHPand recordthe mass to the nearest 60.0001 g and transfer it to a 500 mLClassAvolumetric flask swept free of carbon dioxide.Add 200mL of Type II DI water that is free of carbon dioxide, stopperand swirl gently until it is dissolved. Dilute to 500 mL and mixthoroug
39、hly. Express the concentration of KHP in solution asMolarity in moles of KHP per litre of solution. The use of avolumetric flask can be avoided by weighing 1.0 g of driedKHP to the nearest 0.0001 g into a beaker and adding 500 g ofType II carbon dioxide free DI water. Record the total mass ofwater a
40、nd KHP to the nearest 60.01 g and express theconcentration of KHP in the solution as mg KHP per gram ofsolution. Mix thoroughly to dissolve the KHP and store it in aclosed container.9.5 Sodium Hydroxide, Standard Solution (0.01 N)Prepare and standardize a 0.01N sodium hydroxide (NaOH)solution in acc
41、ordance with the Preparation and Standardiza-tion of Solutions, Precision and Bias, Preparation of 50 % ofNaOH Solutions and standardizations section of Practice E200.9.5.1 Alternatively, KOH (0.01 N) in isopropyl alcoholsolution may be used instead of 0.01 N) NaOH.9.6 Alcohols, refined, ethyl or is
42、opropyl.NOTE 1Isopropyl alcohol (99 % grade) conforming to SpecificationD770, or 190 proof ethyl alcohol conforming to formula No. 3A of theU.S, Bureau of Alcohol, Tobacco, and Firearms as defined in Title 27,Code of Federal Regulations (or equivalent regulations in other jurisdic-tions) is suitable
43、 for use as the solvent. The use of methyl alcohol is notrecommended.9.7 Lithium Chloride ElectrolytePrepare a 1-3 mol/L (M)solution of lithium chloride (LiCl) in ethanol per the electrodemanufacturers recommendation.9.8 Nitrogen, 99.9 % pure.9.9 Commercial Aqueous pH 4 and pH 7 Buffer SolutionsThes
44、e solutions shall be replaced at regular intervals consistentwith their stability or when contamination is suspected. Infor-mation relating to their stability is provided by the manufac-turer.10. Preparation of Apparatus10.1 Prepare the titrator in accordance with the manufactur-ers instructions. An
45、y visible air bubbles in the buret tip shallbe eliminated prior to titration since this can lead to errors.10.2 Preparation of ElectrodesWhen the combination pHelectrode contains Ag/AgCl reference with an electrolytewhich is not 1 to 3 mol/L (M) LiCl in ethanol, the electrolyteshall be replaced. Dra
46、in the electrolyte from the electrode(vacuum suction), wash away all the salt (if present) with waterand then rinse with ethanol. Rinse several times with LiClelectrolyte solution. Finally, replace the sleeve and fill theelectrode with the LiCl electrolyte to the filling hole. Whenrefitting the slee
47、ve, ensure that there will be a free flow ofelectrolyte into the system.10.3 Maintenance and Storage of Electrodes:10.3.1 Follow the manufacturers instructions for storageand use of the electrode10.3.2 Prior to each titration soak the prepared electrode inwater for at least 2 min. Rinse the electrod
48、e with deionizedwater immediately prior to use. The glass membrane needs tobe rehydrated after titration of non-aqueous solutions.10.3.3 When not in use, immerse the lower half of thecombination electrode in LiCl electrolyte. Do not allow elec-trodes to remain immersed in a titrated sample solution
49、for anylonger than it is necessary. While the electrodes are notextremely fragile, handle them carefully at all times.11. Calibration and Standardization11.1 Calibration of Electrode:11.1.1 Select the correct electrode for the analysis (see10.2).11.1.2 Verify that the electrode is filled with 1 to 3 mol/L(M) LiCl in ethanol solution (see 10.2).11.1.3 Prepare the two buffer solutions, pH 7.0 and pH 4.0by placing approximately 50 mL of each solution in individual125-mL disposable beakers.11.1.4 Calibrate the electrode using the two buffer solutionsaccording to the
