ASTM_D_7591_-_12.pdf

Designation:D759112Standard Test Method forDetermination of Free and Total Glycerin in BiodieselBlends by Anion Exchange Chromatography1This standard is issued under the fixed designation D7591;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 covers and describes an anion ex-change chromatography procedure for determining free andtotal glycerin content of biodiesel(B100)and blends(B0 toB20)with diesel fuel oils defined by Specification D975Grades 1-D,2-D,and low sulfur 1-D and 2-D and SpecificationD6751(for B100 feedstocks).It is intended for the analysis ofbiodiesel and blend samples containing between 0.5 to 50mg/kg glycerin.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 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 limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D975 Specification for Diesel Fuel OilsD1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System PerformanceD6751 Specification for Biodiesel Fuel Blend Stock(B100)for Middle Distillate FuelsD6792 Practice for Quality System in Petroleum Productsand Lubricants Testing LaboratoriesE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions:3.1.1 free glycerin,nmeasure of the amount of glycerinremaining in the fuel.3.1.2 total glycerin,nsum of the free glycerin and theglycerin portion of any unreacted or partially reacted oil or fat.4.Summary of Test Method4.1 Free GlycerinA small volume of an extract of theblend sample is directly injected into an ion chromatographconsisting of appropriate ion exchange columns and into anelectrochemical detector.Glycerin is separated based on itsaffinity for ion exchange sites of the resin with respect to theresins affinity for the eluent.An electrochemical detector isemployed for detection of glycerin.Glycerin is quantified bypeak area based on an external calibration curve,and isreported as g/g(mg/kg),or may be converted to wt%.Calibration standards are prepared from commercially avail-able glycerin(99+%purity)in an aqueous solution.4.2 Total GlycerinA small volume extract of a saponifiedblend sample is directly injected into an ion chromatographconsisting of appropriate ion exchange columns and into anelectrochemical detector.Glycerin is separated based on itsaffinity for ion exchange sites of the resin with respect to theresins affinity for the eluent.An electrochemical detector isemployed for detection of glycerin.Glycerin is quantified bypeak area based on an external calibration curve,and isreported as g/g(mg/kg),or may be converted to wt%.Calibration standards are prepared from commercially avail-able glycerin(99+%purity)in an aqueous solution.5.Significance and Use5.1 Petroleum-based diesel may be blended with biodiesel.High levels of free glycerin in biodiesel can cause injectordeposits(“gel effect”),as well as clogging fuel systems.Highlevels of unreacted glycerides can cause injector deposits andcan adversely affect cold weather operation and filter plugging.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,Liquid Fuels,and Lubricants and is the direct responsibility ofSubcommittee D02.04.0C on Liquid Chromatography.Current edition approved Jan.1,2012.Published March 2012.DOI:10.1520/D7591122For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.Interferences6.1 Interferences can be caused by substances with similarion chromatographic retention times,especially if they are inhigh concentration compared to the analyte of interest.Sampledilution can be used to minimize or resolve most interferenceproblems.Also,an excess of unreacted hydroxide(base)duringthe sample preparation step for total glycerin can cause a pHimbalance on the anion exchange column,resulting in anegative dip in front of the glycerin peak.6.2 A water dip(system void,n