1、Designation: D7637 10 (Reapproved 2015)Standard Test Method forDetermination of Glycerin Assay by Titration (Sodium MetaPeriodate)1This standard is issued under the fixed designation D7637; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, 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 provides the quantitative determinationof glycerin by the titrimetric method. It i
3、s applicable to allglycerin or glycerin/water mixtures 75 %.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard may involve hazardous materials, opera-tions and equipment. This standard does not purport to addr
4、essall of the safety problems associated with its use. It is theresponsibility of whoever uses this standard to consult theestablished and appropriate safety and health practices anddetermine the applicability of regulatory limitations prior touse. Specific precautions are listed in Section 8.2. Ref
5、erenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4725 Terminology for Engine Coolants and Related FluidsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2
6、.2 Other Standards:The United States Pharmacopoeia 31 Glycerin Monograph Assay Method3AOCS Official Method EA 6-94 (Replaces AOCS EA 6-51),Determination of Crude Glycerin, Titrimetric Method4BS 5711: Part 3, 1979 Sampling and Test for Glycerol -Determination of Glycerol Content53. Terminology3.1 Def
7、initions:3.1.1 glycerinpropane-1,2,3-triol, C3H5(OH)3(alsoknown as glycerine), 1,2,3-propanetriol, 1,2,3-trihydroxypropane, glyceritol, glycyl alcohol, glycerol. CAS#56-81-5.3.1.2 SMPSodium Meta Periodate.3.1.3 For other definitions of terms used in thisspecification, refer to Terminology D4725.4. S
8、ignificance and Use4.1 This test method is based on the cold oxidation of theglycerol by sodium metaperiodate in a strong acidic medium.Formaldehyde and formic acid are produced in this reactionand the latter is used to measure the glycerol content bytitration with standard sodium hydroxide solution
9、, to a pH 8.16 0.1. The glycerol content is expressed as a percentage(m/m).CH2OH 2 CHOH 2 CH2OH12 NaIO4 (1)HCOOH12 HCHO12 NaIO31H2O4.2 InterferencesThe glycerin sample should be free oforganic compounds with more than two hydroxyl groups onadjacent carbon atoms (for example, sugars, glycols). Theset
10、ypes of compounds may produce formic acid which interfereswith the determination of the glycerol content.5. Apparatus5.1 Burette50 mL “Type A” unit that can deliver 30 dropsper mL and calibrated to meet the NIST standards.NOTE 1 It is critical that all glassware be “Type A” and thoroughlycleaned bef
11、ore use as dirty glassware will impact the analysis results.5.2 pH meter, fitted with glass electrode.NOTE 2The pH meter should be standardized with a minimum of two1This test method is under the jurisdiction of ASTM Committee D15 on EngineCoolants and Related Fluids and is the direct responsibility
12、 of SubcommitteeD15.93 on Research and Long Range Planning.Current edition approved May 1, 2015. Published June 2015. Originallyapproved in 2010. Last previous edition approved in 2010 as D763710. DOI:10.1520/D7637-10R15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact
13、 ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from U.S. Pharmacopeia (USP), 12601 Twinbrook Parkway,Rockville, MD 20852-1790, http:/www.usp.org.4Available from American Oil Ch
14、emists Society (AOCS), 2710 S. Boulder,Urbana, IL 61802-6996, http:/www.aocs.org.5Available from British Standards Institute (BSI), 389 Chiswick High Rd.,London W4 4AL, U.K., http:/.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1buff
15、er solutions at 10.0 and 7.0. (See 7.12.)5.3 Stirrerpreference should be given to a magnetic stir-rer. In this case, check that it does not influence the pH meter.6. Purity of Reagents and Water6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is
16、 intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available. Other grades may be usedprovided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without l
17、essening the accuracy ofthe determination.6.2 Purity of WaterUnless indicated otherwise, referencesto water shall be understood to mean Type II reagent water asdefined in Specification D1193.NOTE 3The presence of carbon dioxide can introduce errors; thereforeit is advisable to prepare 500 mL of wate
18、r by boiling for 5 min and coolingto room temperature. Check the pH of the distilled water before use. ThepH should be 7.0 6 0.1. If not, adjust the pH with 0.1 N sodium hydroxide(NaOH) or 0.1 N hydrogen chloride (HCl), whichever is appropriate. Storethe freshly boiled and neutralized water in a tig
19、htly closed container.7. Reagents7.1 Sodium Metaperiodate, NaIO4, acidic solutionDissolve 60 g of sodium metaperiodate in sufficient watercontaining 120 mL of 0.1 N sulfuric acid to make 1000 mL. Donot heat to dissolve the periodate. If the solution is not clear,pass it through a sintered-glass filt
20、er. Store the solution in aglass-stoppered, light-resistant container.7.2 Hydrochloric Acid, aqueous solution, approximately 0.1N.7.3 Sodium Hydroxide, aqueous solution, approximately0.05 N.7.4 Sodium Hydroxide, 0.1 N, Standardized Dissolve fourgrams of sodium hydroxide (NaOH) in water and dilute to
21、 oneliter. Standardize accurately to 60.0001 N. The standardizedsodium hydroxide solution should be protected against evapo-ration and absorption of carbon dioxide (CO2) from the air.7.5 Ethylene glycol (1,2-ethanediol, free from glycerol)solution in water. 1:1 (v/v).7.6 SulfuricAcid Solution, aqueo
22、us solution, approximately0.1 N.7.7 SulfuricAcid Solution, aqueous solution, approximately0.2 N.7.8 Sodium Thiosulfate, 0.1 N, aqueous solution.7.9 Potassium Iodide, aqueous solutionDissolve 16.5 g ofpotassium iodide in water to make 100 mL. Store tightlycapped in a light-resistant container.7.10 St
23、arch SolutionMix 1g of soluble starch with suffi-cient cold water to make a thin paste. Add 200 mL of boilingwater, and boil for 1 min with continuous stirring. Cool, anduse only the clear solution.NOTE 4It is recommended that freshly prepared starch solution beused to ensure a sharper endpoint. Com
24、mercially available, stabilizedstarch indicator solution may be also used in place of freshly preparedstarch.7.11 Bromothymol blue indicator solutionDissolve 100mg of bromothymol blue in 100 mL of water to make 100 mLof indicator solution.7.12 pH Buffers (7.0 6 0.01 and 10.0 6 0.01 at 25C)needed for
25、 pH meter standardization.7.13 Freshly boiled water, or equivalent. (See 6.2.)8. Precautions8.1 Sulfuric acid and sodium hydroxide solutions are cor-rosive. Avoid eye and skin contact.8.2 Please study and be aware of the Material Safety DataSheet and correct laboratory performance for the appropriat
26、ehealth and safety precautions that may apply to any of thechemicals and equipment prior to use.8.3 It is the responsibility of each organization to conduct ajob hazard analysis to assess safety risks and PPE needed forperformance of this test method.9. Procedure9.1 Sodium Periodate Solution Suitabi
27、lity TestPipet 10mL of the prepared sodium periodate solution (Reagent 7.1)into a 250-mL volumetric flask, dilute with water to volume,and mix.9.2 Weigh approximately 550 mg of glycerin into flask.Dissolve the sample in 50 mLof water and pipette 50 mLof thediluted periodate solution prepared in 9.1.
28、Allow the solution tostand for 30 min.9.3 Add 5 mL of hydrochloric acid solution (Reagent 7.2)and 10 mL of potassium iodide solution (Reagent 7.9), andgently swirl to mix. Allow the solution to stand for 5 min.9.4 Add 100 mL of water and 3 mL of starch solution(Reagent 7.10). Titrate slowly with 0.1
29、 N sodium thiosulfate(Reagent 7.8) to the starch endpoint, mixing continuously toensure the solution has stabilized after each addition.9.5 Blank Test for Sodium Periodate Solution SuitabilityTestFor the blank, pipet 50 mL of the diluted periodatesolution into a flask containing 50 mL of water. Carr
30、y out, atthe same time as the determination and under the sameconditions, a blank test without the glycerin test portion usingthe same quantities of reagents and diluting water for thedeterminations as outlined in 9.1 through 9.4.9.6 The ratio of the volume of 0.1 N sodium thiosulfate(Reagent 7.8) r
31、equired for the glycerin-periodate mixture tothat required for the blank should be between 0.750 and 0.765.9.7 Glycerol Assay DeterminationTransfer about 400mg of glycerin, accurately weighed on an analytical balance,into a 600 mL beaker.9.8 Dilute the sample in the beaker with 50 mL of water andadd
32、 approximately 3 mL of bromothymol blue indicator(Reagent 7.11). Carefully acidify with 0.2 N sulfuric acid(Reagent 7.7) to a definite green or greenish yellow color.Neutralize with 0.05 N sodium hydroxide (Reagent 7.3)toadefinite blue endpoint, free from green color.D7637 10 (2015)29.9 Pipette 50 m
33、L of sodium metaperiodate solution (Re-agent 7.1) into the beaker. Mix using moderate agitation andcover the beaker with a watch glass. Allow the beaker to standfor 30 min at room temperature (not exceeding 35C) in thedark or in subdued light.NOTE 5The presence of carbon dioxide can introduce errors
34、; thereforeit is advisable to cover the beaker containing the test solution with a watchglass during all standing periods.9.10 Add 10 mL of the ethylene glycol solution (Reagent7.5) into the beaker. Mix using moderate agitation and coverthe beaker with a watch glass. Allow the beaker to stand for 20
35、min at room temperature (not exceeding 35C) in the dark or insubdued light.9.11 Dilute the solution with water to about 300 mL.9.12 Insert the glass electrode and using moderate stirring,titrate slowly as the endpoint is approached with 0.1 N sodiumhydroxide (Reagent 7.4)toapHof8.16 0.1 for the spec
36、imenunder assay.NOTE 6When approaching the endpoint, it is critical that the titrationis conducted slowly and the solution is well mixed after each addition toensure a stable pH reading for the endpoint determination.9.13 Blank Determination for Glycerine AssayDeterminationCarry out, at the same tim
37、e as the assaydetermination and under the same conditions, a blank testwithout the test portion using the same quantities of reagentsand diluting water for the determinations as outlined in 9.5through 9.12. Titrate with 0.1 N sodium hydroxide to a pH of6.5 6 0.1 for the blank.9.14 Each mL of 0.1 N s
38、odium hydroxide, after correctionfor the blank, is equivalent to 9.210 mg of glycerol (C3H8O3).10. Calculation10.1 The glycerol content, expressed as a percentage, isgiven by the formula:Glycerol %! 5V12 VB! 3F 3NW(2)where:V1= number of mL of 0.1 N sodium hydroxide solutionused for the sample titrat
39、ion,VB= number of mL of 0.1 N sodium hydroxide solutionused for the blank titration,F = Factor = 9.210,N = exact normality of sodium hydroxide that was used forthe titration, andW = mass, in g, of glycerin subjected to the reaction withsodium metaperiodate solution.11. Report11.1 Report the glycerin
40、 content of the sample to the nearest0.1 %.12. Precision and Bias12.1 The precision of this test method is based on aninterlaboratory study conducted in 2009. Each of eight labora-tories tested two different materials. Every “test result” repre-sents an individual determination, and every laboratory
41、 re-ported two replicate test results for each of the materials.Except for the use of only two test materials, Practice E691was followed for the design and analysis of the data; the detailsare given in an ASTM Research Report.612.1.1 Repeatability Limit (r)Two test results obtainedwithin one laborat
42、ory shall be judged not equivalent if theydiffer by more than the “r” value for that material; “r”istheinterval representing the critical difference between two testresults for the same material, obtained by the same operatorusing the same equipment on the same day in the samelaboratory.12.1.1.1 Rep
43、eatability limits are listed in Table 1.12.1.2 Reproducibility Limit (R)Two test results shall bejudged not equivalent if they differ by more than the “R” valuefor that material; “R” is the interval representing the criticaldifference between two test results for the same material,obtained by differ
44、ent operators using different equipment indifferent laboratories.12.1.2.1 Reproducibility limits are listed in Table 1.12.1.3 The terms (repeatability limit and reproducibilitylimit) are used as specified in Practice E177.12.1.4 Any judgment in accordance with statements 12.1.1and 12.1.2 would have
45、an approximate 95 % probability ofbeing correct.12.2 BiasAt the time of the study, there was no acceptedreference material suitable for determining the bias for this testmethod, therefore no statement on bias is being made.12.3 The precision statement was determined through sta-tistical examination
46、of 26 results, from eight laboratories, ontwo materials. These two materials were described as thefollowing:Glycerin A: a 99.5 % pure glycerine (data fromseven laboratories included)Glycerin B: a 97.5 % solution of glycerine (datafrom six laboratories included)6Supporting data have been filed at AST
47、M International Headquarters and maybe obtained by requesting Research Report RR:D15-1025.TABLE 1 Glycerin (%)Material AverageARepeatabilityStandardDeviationReproducibilityStandardDeviationRepeatabilityLimitReproducibilityLimitx SxSrSRrRA 99.48 0.14 0.29 0.29 0.81 0.81B 97.48 0.36 0.17 0.38 0.48 1.0
48、5AThe average of the laboratories calculated averages.D7637 10 (2015)312.4 To judge the equivalency of two test results, it isrecommended to choose the type of glycerin closest in char-acteristics to the test fluid.13. Keywords13.1 antifreeze; engine coolant; ethylene; glycerin; glycer-ine; glycerol
49、; titrimetricASTM 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 validity 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 com
