ASTM_D_7638_-_10_2015.pdf

Designation:D763810(Reapproved 2015)Standard Test Method forDetermination of Fatty Acids and Esters in Glycerin1This standard is issued under the fixed designation D7638;the number immediately following the designation indicates the year oforiginal adoption 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.Scope1.1 This test method provides the quantitative determinationof the fatty acid and ester content in purified glycerin by thetitrimetric method.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 addressall of the safety concerns,if any,associated with its use.It isthe responsibility of the user of this standard to establishappropriate safety and health practices and determine theapplicability of regulatory limitations prior to use.Specificprecautions are listed in Section 8.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4725 Terminology for Engine Coolants and Related Fluids2.2 Other Standard:The United States Pharmacopoeia 31 Glycerin Monograph Fatty Acids and Esters33.Terminology3.1 Definitions:3.1.1 glycerinpropane-1,2,3-Triol,C3H5(OH)3(alsoknownasglycerine),1,2,3-propanetriol,1,2,3-trihydroxypropane,glyceritol,glycyl alcohol.CAS#56-81-53.1.2 FA&EFatty acid and Esters3.1.3 Forotherdefinitionsoftermsusedinthisspecification,refer to Terminology D4725.4.Significance and Use4.1 Any residual fatty acid and esters(FA&E)should bepresent only at very low levels in purified glycerine.4.2 This procedure requires the addition of a measuredvolume of sodium hydroxide,in excess of the amount actuallyneeded to react with FA&E in the glycerine sample.Afterboiling,the excess sodium hydroxide is back titrated withstandardized hydrochloric acid.The quantity of the substancebeing titrated is calculated as the difference between thevolumes of the sodium hydroxide solution originally added,corrected by means of a blank titration,and that was consumedby the titrant in the back titration.NOTE1The standardized solutions for sodium hydroxide and hydro-chloric acid are commercially available.5.Apparatus5.1 Standard Type A Glassware.5.2 Erlenmeyer flask,200 to 250 mL,alkali-resistant with astandard tapered 24/40 ground glass neck joint,or equivalent.5.3 Microburette having a capacity of 5 mL,graduated to0.02 mL and calibrated to meet the NIST specification.Anautomatic titrator with a minimum capacity of 5 mLcan also beused.5.4 Pipette,standard or automatic that can accurately de-liver 5 6 0.01 mL.5.5 Air reflux condenser with standard taper ground glassjoint which fits the Erlenmeyer flask in 5.1.Minimum length,550 mm.6.Purity of Reagents and Water6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.Unless 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.Other grades may be usedprovided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening 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 D1193.1This test method is under the jurisdiction of ASTM Committee D15 on EngineCoolants and Related Fluids and is the direct responsibility 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 D763810.DOI:10.1520/D763810R15.2For referenced 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.3Available from U.S.Pharmacopeia(USP),12601 Twinbrook Parkway,Rockville,MD 20852-1790,http:/www.usp.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 NOTE2The presence of carbon dioxide can introduce errors;thereforeit is advisable to prepare 500 mL of water by boiling for 5 min.Cool toroom temperature.Check the pH of the distilled water before use.The pHshould 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.Store the freshly boiled and neutralized water in a tightly closed container.7.Reagents7.1 Phenolphthalein Solution(See Note 2.)Dissolve 1 gof phenolphthalein in 100 mL of ethanol(95%),methanol orisopropanol.This solution can be purchased.7.2 Hydrochloric Acid,0.5 N,aqueous solution(See Note1 and Note 2.)To a 1000-mL volume