1、Designation: E 2679 09Standard Test Method forAcidity in Mono-, Di-, Tri- and Tetraethylene Glycol byNon-Aqueous Potentiometric Titration1This standard is issued under the fixed designation E 2679; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e 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. Scope1.1 This test method covers the determination of totalacidity as acetic acid in commonly availa
3、ble 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.1.2 The mono-, di-, tri- and tetraethylene glycols can beanalyzed directly
4、 by this test method without any samplepreparation.1.3 Review the current appropriate Material Safety DataSheets (MSDS) for detailed information concerning toxicity,first aid procedures, and safety precautions.1.4 The values stated in SI units are to be regarded asstandard. No other units of measure
5、ment 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 practices and determine the applica-bility of regulatory limita
6、tions prior to use. Specific hazardsstatements are given in the section on Hazards, Section 9.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterE 180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals3.
7、 Terminology3.1 Definition: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 aliquot of a mono-, di-, tri- or tetraethylene glycolsample is weighed and titr
8、ated 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 glycol sample can be analyzed directly bythis test method without any sample pr
9、eparation 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 of the titrating solution and the end point isidentified by a well-defined infl
10、ection 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 titration of ethyleneglycol samples ranges from 5 to 10 min with no samplepreparation r
11、equired. 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 acidity in ethylene glycols varywith the manufacturers specifications but are
12、normally below200 mg/kg. Knowledge of the acidity in ethylene glycols isrequired to establish whether the product quality meets speci-fication requirements.6. Interferences6.1 Aqueous base solutions, such as the 0.01 mol/L KOH orNaOH titrant, may absorb carbon dioxide from the air toproduce carbonat
13、e ions in the titrant and change the 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.1This test method is under the jurisdiction of ASTM Commi
14、ttee E15 onIndustrial and Specialty Chemicals and is the direct responsibility of SubcommitteeE15.02 on Product Standards.Current edition approved April 1, 2009. Published May 2009.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.or
15、g. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.2 Minimize exposure of the ethylene glycol samples to theair to
16、 avoid contamination.7. Apparatus7.1 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
17、prescribed in the method. As 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 depen
18、ding on the rate of change of thesystem. The recommended minimum volume increment is 0.02mL for low acidity samples such as polyester grade monoeth-ylene glycol and the recommended maximum volume incre-ment is 0.05 mL. A signal drift of 10 mV/min and endpointrecognition set to greatest is also recom
19、mended to ensureendpoint detection. When using a monotonic titrant additionthe waiting time between increment additions needs to besufficient 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
20、 in0.02 mL or larger increments. 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 Tit
21、ration Stand, suitable for supporting 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-t
22、rode designed for non-aqueous titrations 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 o
23、rbetter response than a dual electrode 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 pr
24、opeller-type stirring paddle. The rate ofstirring shall be sufficient to produce vigorous agitation withoutspattering 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-fa
25、ctory.7.4.1 If an electrical stirring 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 Reag
26、entsReagent grade chemicals shall 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.3Other grades may beused, provided
27、it is first ascertained that the reagent 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 Altern
28、ate volumes of the solutions may be 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 SpecificationD 1193.8.1.4 50 % Po
29、tassium Hydroxide, carbonate free(WarningCauses 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 beforeweighin
30、g. Weigh approximately 1.0 g of dried KHP and recordthe weight to the nearest 6 0.0001 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
31、(see 13.1). The use of a volumetric flask can beavoided by weighing 1.0 g of dried KHP to the nearest 0.0001g into a beaker and adding 500 g of DI Type II water. Mixthoroughly to dissolve the KHP. Record the total weight ofwater and KHP to the nearest 60.01 g and express theconcentration of KHP in t
32、he solution as mg KHP per gram ofsolution (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
33、to their stability should beobtained from the manufacturer.8.1.8 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 degassed to remove dissolved CO2. Dilute to the one-litermark with
34、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 of3Reagent Chemicals, American Chemical Society Specifications, AmericanC
35、hemical 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 United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), R
36、ockville,MD.E2679092sodium hydroxide, 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
37、 potentialhazards of the equipment, reagents, products, solvents andprocedures before beginning laboratory work. Sources ofinformation include: operation manuals, MSDS, literature, andother related data. Safety information should be requested fromthe supplier. Disposal of waste materials, reagents,
38、reactants,and solvents must be 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 currentMSDS for each product (see 9.1).9.3 The following hazards are ass
39、ociated with the applica-tion 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. Alw
40、ays add the base to water when 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 i
41、gnition.10. Preparation of Apparatus10.1 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 t
42、he combination pH electrode contains 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
43、with the LiCl electrolyte solution 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
44、 least 2 min. Rinse the electrode 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 i
45、mmersed in a titrated sample for 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 V
46、erify that the electrode is filled with 13 mol/L LiClin 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 t
47、o the manufacturers instructions. 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
48、buffer solution. Record the pH 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
49、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 may change as aresult of the aging of the glass membrane or contamination ofthe diaphragm. If the electrode slope falls below 0.95 youshould follow the electrode manufactures instructions forelectrode maintenance or replace the electrode. The pH elec-trode must be calibrate
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