1、Designation: E2679 09 (Reapproved 2016)1Standard Test Method forAcidity in Mono-, Di-, Tri- and Tetraethylene Glycol byNon-Aqueous Potentiometric Titration1This standard is issued under the fixed designation E2679; the number immediately following the designation indicates the year oforiginal adopti
2、on 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.1NOTEMinor editorial changes were made in February 2016.1. Scope1.1 This test method c
3、overs the determination of totalacidity as acetic acid in commonly available grades of mono-ethylene glycol, diethylene glycol, triethylene glycol andtetraethylene glycol using a non-aqueous potentiometric titra-tion. This test method is useful for determining low levels ofacidity, below 200 mg/kg.1
4、.2 The mono-, di-, tri- and tetraethylene glycols can beanalyzed directly by this test method without any samplepreparation.1.3 Review the current appropriate Safety Data Sheets(SDS) for detailed information concerning toxicity, first aidprocedures, and safety precautions.1.4 The values stated in SI
5、 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 thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health
6、practices and determine the applica-bility of regulatory limitations prior to use. Specific hazardsstatements are given in the section on Hazards, Section 9.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE180 Practice for Determining the Precision of ASTMMethods for
7、Analysis and Testing of Industrial and Spe-cialty Chemicals (Withdrawn 2009)33. Terminology3.1 Definitions:3.1.1 aciditythe amount of total acid titrated with anaqueous base (KOH or NaOH) in a sample of ethylene glycol.The acidity is calculated as acetic acid in mg/kg.4. Summary of Test Method4.1 An
8、 aliquot of a mono-, di-, tri- or tetraethylene glycolsample is weighed and titrated potentiometrically with amonotonic or dynamic mode of titrant addition using anaqueous base (NaOH or KOH) solution to determine the acidcontent in milligrams of acid as acetic acid per kilogram ofsample.An ethylene
9、glycol sample can be analyzed directly bythis test method without any sample preparation using acombination pH electrode with an inert ethanol electrolytedesigned for non-aqueous titrations. The potentiometric titra-tion readings in millivolts are plotted automatically against therespective volumes
10、of the titrating solution and the end point isidentified by a well-defined inflection in the resulting curve.5. Significance and Use5.1 This test method provides for the quantitative determi-nation of total acidity in ethylene glycols by non-aqueouspotentiometric titration. The run time for titratio
11、n of ethyleneglycol samples ranges from 5 to 10 min with no samplepreparation required. The length of time for a titration dependson the amount of acidity in the sample and the acidity generallyincreases from monoethylene glycol to the higher glycols liketetraethylene glycol.5.2 Acceptable levels of
12、 acidity in ethylene glycols varywith the manufacturers specifications but are normally below200 mg/kg. Knowledge of the acidity in ethylene glycols isrequired to establish whether the product quality meets speci-fication requirements.1This test method is under the jurisdiction of ASTM Committee E15
13、 onIndustrial and Specialty Chemicals and is the direct responsibility of SubcommitteeE15.02 on Product Standards.Current edition approved Jan. 1, 2016. Published February 2016. Originallyapproved in 2009. Last previous edition approved in 2009 as E2679-09. DOI:10.1520/E2679-09R16E01.2For referenced
14、 ASTM standards, visit the ASTM website, 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.3The last approved version of this historical standard is referenced onwww.a
15、stm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16. Interferences6.1 Aqueous base solutions, such as the 0.01 mol/L KOH orNaOH titrant, may absorb carbon dioxide from the air toproduce carbonate ions in the titrant and change t
16、he concen-tration of the titrant. Care should be taken to minimizeexposure of basic titrants to the air. Verify the concentration ofthe titrant (standardize the titrant) if prolonged exposure to theair occurs.6.2 Minimize exposure of the ethylene glycol samples to theair to avoid contamination.7. Ap
17、paratus7.1 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.A
18、s aminimum, the automatic titration system shall meet the perfor-mance and specification requirements as warranted by themanufacturer.7.1.1 Amonotonic 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
19、of thesystem. The recommended minimum volume increment is0.02 mL for low acidity samples such as polyester grademonoethylene glycol and the recommended maximum volumeincrement is 0.05 mL. A signal drift of 10 mV/min andendpoint recognition set to greatest is also recommended toensure endpoint detect
20、ion. When using a monotonic titrantaddition the waiting time between increment additions needs tobe sufficient to allow for mixing and electrode response. It isrecommended to wait at least 10 s between additions.7.1.2 Buret, 5 mL capacity, capable of delivering titrant in0.02 mL or larger increments
21、. The buret tip should be able todeliver titrant directly into the titration vessel without exposureto the surrounding air. It is recommended that the buret usedfor aqueous base solutions should have a guard tube containinga carbon dioxide absorbing substance.7.1.3 Titration Stand, suitable for supp
22、orting the electrode,stirrer and buret tip.7.2 Combination pH ElectrodesSensing electrodes mayhave the Ag/AgCl reference electrode built into the sameelectrode body, which offers the convenience of working withand maintaining only one electrode. A combination pH elec-trode designed for non-aqueous t
23、itrations of organic solvents isneeded for titration of glycols. The combination pH electrodeshould have a sleeve junction on the reference compartmentand should use an inert ethanol electrolyte, 13 mol/L LiCl inethanol. Combination pH electrodes should have the same orbetter response than a dual el
24、ectrode system. They should havea movable sleeve for easy rinsing and addition of electrolyte.7.3 Titration Beaker, borosilicate glass or plastic beaker ofsuitable size for the titration.7.4 Stirrer, variable-speed mechanical stirrer, a suitabletype, equipped with a propeller-type stirring paddle.Th
25、e rate ofstirring shall be sufficient to produce vigorous agitation withoutspattering and without stirring air into the solution.Apropellerwith 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.7.4.1 If an electrical stirr
26、ing apparatus is used, it shall beelectrically correct and grounded so that connecting or discon-necting the power to the motor will not produce a permanentchange in the instrument reading during the course of thetitration.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall
27、beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.4Other grades may beused, provided it is first ascertained that the r
28、eagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.8.1.1 Commercially available solutions may be used inplace of laboratory preparations provided the solutions havebeen certified as being equivalent.8.1.2 Alternate volumes of the solutions may b
29、e prepared,provided the final solution concentration is equivalent.8.1.3 Purity of WaterUnless otherwise indicated, refer-ence to water shall be understood to mean reagent water thatmeets the requirements of either Type II or III of SpecificationD1193.8.1.4 50 % Potassium Hydroxide, carbonate free(W
30、arningCauses severe burns.)8.1.5 50 % Sodium Hydroxide, carbonate free (WarningCauses severe burns.)8.1.6 Potassium Hydrogen Phthalate (KHP) SolutionDry4to5gofKHPat110C in an oven for 2 h. Allow the driedKHP to cool to room temperature in a desiccator beforeweighing. Weigh approximately 1.0 g of dri
31、ed KHP and recordthe weight to the nearest 60.0001 g and make up to the markwith DI Type II water in a 500 mL Class A volumetric flask.Mix thoroughly to dissolve the KHP. Express the concentrationof KHP in solution as Molarity in moles of KHP per liter ofsolution (see 13.1). The use of a volumetric
32、flask can beavoided by weighing 1.0 g of dried KHP to the nearest0.0001 g into a beaker and adding 500 g of DI Type II water.Mix thoroughly to dissolve the KHP. Record the total weight ofwater and KHP to the nearest 60.01 g and express theconcentration of KHP in the solution as mg KHP per gram ofsol
33、ution (see 13.1). The KHP solution should be made freshbefore use.8.1.7 Commercial Aqueous pH 4 and pH 7 BufferSolutionsThese solutions shall be replaced at regular inter-vals consistent with their stability or when contamination issuspected. Information relating to their stability should beobtained
34、 from the manufacturer.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. 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 U
35、nited States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USP), Rockville,MD.E2679 09 (2016)128.1.8 Potassium Hydroxide (KOH) 0.01 mol/LWeigh1.122 6 0.02 g of 50 % KOH into a one liter volumetric flaskthat contains about 200 mL of Type II deionized water that hasbeen dega
36、ssed to remove dissolved CO2. Dilute to the one-litermark with additional deionized water. The KOH solutionshould be standardized using the KHP solution to determinethe titer. The titrant titer should be checked periodically due toabsorption of carbon dioxide with use over time. A titrant ofsodium h
37、ydroxide, 0.01 mol/L NaOH, made from 50 % NaOHmay be substituted for KOH.8.1.9 Lithium Chloride ElectrolytePrepare a 13 mol/Lsolution of lithium chloride (LiCl) in ethanol per the electrodemanufacturers recommendation.9. Hazards9.1 Each analyst must be acquainted with the potentialhazards of the equ
38、ipment, reagents, products, solvents andprocedures before beginning laboratory work. Sources ofinformation include: operation manuals, SDS, literature, andother related data. Safety information should be requested fromthe supplier. Disposal of waste materials, reagents, reactants,and solvents must b
39、e in compliance with laws and regulationsfrom all applicable governmental agencies.9.2 Ethylene glycol products are intended for industrial useonly. Before handling or using these products, read the currentSDS for each product (see 9.1).9.3 The following hazards are associated with the applica-tion
40、of this test method and the use of an automatic titrator.9.3.1 Chemical Hazard:9.3.1.1 A solution of 50 % potassium hydroxide or sodiumhydroxide is corrosive and should be handled in a fume hoodwith gloves, chemical goggles, and lab coat or chemical-resistant apron. Always add the base to water when
41、 diluting50 % KOH or NaOH.9.3.1.2 Ethanol is a flammable and toxic solvent that is usedto prepare the lithium chloride electrolyte solution for thecombination electrode. Be careful when handling a flammablesolvent and work in a well-ventilated area away from sourcesof ignition.10. Preparation of App
42、aratus10.1 Prepare the titrator in accordance with the manufactur-ers instructions. Care should be taken to see that there are noair bubbles in the buret tip which might be dispensed during thetitration and can lead to errors.10.2 Preparation of Electrodes:10.2.1 When the combination pH electrode co
43、ntains aAg/AgCl reference with an electrolyte which is not 13 mol/LLiCl in ethanol, the electrolyte must be replaced. Drain theelectrolyte from the electrode (vacuum suction), wash away allthe salt (if present) with water and then rinse with ethanol.Rinse several times with the LiCl electrolyte solu
44、tion and fillthe reference compartment with the LiCl/ethanol electrolyte.10.3 Maintenance and Storage of Electrodes:10.3.1 Follow the manufacturers instructions for storageand use of the electrode.10.3.2 Prior to each titration soak the prepared electrode inwater for at least 2 min. Rinse the electr
45、ode with deionizedwater immediately before use. The glass membrane needs to berehydrated after titration of glycol (non-aqueous) material.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 f
46、or anyappreciable period of time between titrations. While theelectrodes are not extremely fragile, handle them carefully atall times.11. Calibration and Standardization11.1 Calibration of Electrode:11.1.1 Select the correct electrode for the analysis (see 7.2).11.1.2 Verify that the electrode is fi
47、lled with 13 mol/LLiClin ethanol solution (see 7.2).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 manufacturers instruction
48、s. Immerse theelectrode in each buffer solution, adjust the stirring speed soadequate mixing occurs without forming a vortex and wait forthe instrument reading. When the reading is complete, rinse theelectrode in high purity water, wipe gently and repeat with theother buffer solution. Record the pH
49、value with an accuracy of0.01 and the temperature with an accuracy of 0.1C. Themeasured pH values should be within 60.05 pH units of thebuffers certified value.11.1.5 Verify that the calibration slope is between 0.95 and1.02.An ideal pH glass electrode has a slope of 1.00 (100 % ofthe Nernst slope) and an electrode zero point of 0 mV for pH7 at 25C. In practice, the electrode zero point potential shouldbe within 615 mV (corresponding to pH 6.75 to 7.25) and theslope should be 0.95 (56.2 mV per pH at 25C). Theelectrode zero point and the electrode slope ma
