1、Designation: D7591 12 (Reapproved 2017)Standard 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 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.1. Scope1.1 This test method covers and describes an anion ex-change chromatography pr
3、ocedure 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
4、containing between 0.5 mg kg to50 mg 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 theresponsibili
5、ty 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.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the
6、 Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D975 Specification for Diesel Fuel OilsD1193 Specification for Reagent Water
7、D4057 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 Specificatio
8、n for Biodiesel Fuel Blend Stock (B100)for Middle Distillate FuelsD6792 Practice for Quality Management Systems in Petro-leum Products, Liquid Fuels, and Lubricants TestingLaboratoriesE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlabora
9、tory 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
10、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 ther
11、esins 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 glycer
12、in (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 s
13、ites 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%.1This test method is under the j
14、urisdiction 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 May 1, 2017. Published July 2017. Originally approvedin 2012. Last previous edition approved in 2012 as D75
15、91 12.DOI:10.1520 D7591-12R17.2For 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.Copyright ASTM International, 1
16、00 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and
17、Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1Calibration 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 level
18、s 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.6. Interferences6.1 Interferences can be caused by substances
19、 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 gly
20、cerin 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, negative peak as shown inFig. 1) can cause interference with some integrators. This dipcan be eliminated by dilution with the eluent. The water dipshould
21、 not be a problem since the glycerin peak is resolvedfrom the void peak.6.3 Interferences can be caused by contamination ofglassware, eluent, reagents, etc. Take care to ensure thatcontamination is kept at the lowest possible levels. The use ofnitrile gloves is highly recommended to prevent contamin
22、ationduring sample preparation.6.4 There are several known additives based on naturalproducts that might have similar retention times and detectorresponse similar to glycerin. In the case of higher thanexpected values for biodiesel blends, it is highly recommendedthat the user needs to verify these
23、higher than expected valuesfor glycerin using a different analytical technique.6.5 Pre-rinsing of the sample preparation containers withdeionized water is mandatory.7. Apparatus7.1 Analytical Balancecapable of weighing up to 200 gaccurately to 60.0001 g.7.2 Desiccatorcontaining freshly activated sil
24、ica gel (orequivalent desiccant) with moisture content indicator.7.3 Pipettes or Volumetric Transfer Devices 1 mL and5 mL class A volumetric pipettes or calibrated variable volumeautomatic pipettes fitted with disposable polypropylene tips.7.4 Volumetric Flasks25 mL, 50 mL, 100 mL, and1000 mL class
25、A volumetric flasks.7.5 Containerstandard HDPE plastic 100 mL bottle withcap.7.6 Ion ChromatographAnalytical system with all re-quired accessories including syringes, columns, high-pressuredual piston pump, and detector.7.6.1 Injection Systemcapable of delivering 5 L to 25 Lwith a precision better t
26、han 1 %.7.6.2 Pumping Systemcapable of delivering mobile phaseflows between 0.1 mL min and 5.0 mL min with a precisionbetter than 2 %. Due to the corrosive nature of the eluent, aPEEK pump head is recommended.7.6.3 Guard Columnfor protection of the analytical col-umn from strongly retained constitue
27、nts.7.6.4 Anion Exchange Columncapable of producing sat-isfactory analyte separation.7.6.5 Electrochemical Detectorintegrated, temperaturecontrolled to 0.1 C, capable of measuring at least 0 A to200 A on a linear scale. Detector has a pulsed amperometricdetection mode for required sensitivity. Consu
28、lt with themanufacturer for optimal cell settings.7.6.6 Electrochemical Detector Cellminimum 3 mm goldworking electrode surface with wall jet design, solid statereference and counter electrodes. Ensure a minimal volume inthe cell for enhanced sensitivity. A platinum working electrodemay also be used
29、.FIG. 1 Typical Chromatogram of a Solution Containing 0.7 mg kg of GlycerinD7591 12 (2017)27.6.7 Integrator or Chromatography Data SystemSoftwarecapable of measuring peak areas and retentiontimes, and performing a baseline correction.7.6.8 Sample Digestion Systemcapable of heating, andstirring with
30、integrated reflux. Reflux is needed to minimizeloss of petroleum diesel in biodiesel blend samples. A chiller isrecommended for providing water to the reflux condenser forefficiency and to conserve water resources.7.7 Mechanical Wrist Shaker.7.8 Gloves, nitrile.8. Reagents and Materials8.1 Purity of
31、 ReagentsReagent grade or higher puritychemicals shall be used for the preparation of all samples,standards and eluent solutions. Unless otherwise indicated, it isintended that all reagents conform to the specifications of theCommittee on Analytical Reagents of the American ChemicalSociety, where su
32、ch specifications are available.3Other gradesmay be used, provided it is first ascertained that the reagent isof sufficiently high purity to permit its use without lesseningthe accuracy of the determination.8.2 Water QualityUnless otherwise indicated, reference towater shall be understood to mean re
33、agent water as defined byType II in Specification D1193 or better. For eluent preparationand handling, comply with all ion chromatograph instrumentand column vendor requirements (for example, filtering,degassing, etc.).8.3 Eluent Stock Solution, sodium hydroxide (NaOH, 50 %certified, ACS).8.3.1 Elue
34、nt Preparation, 0.10 M NaOH. Weigh 8.00 g 60.02 g of 50 % NaOH in reagent water in a 1 Lvolumetric flaskand dilute to volume with degassed reagent water. The eluentsolution used may be different if other systems or analyticalcolumns are used. Other volumes of stock solution may beprepared using appr
35、opriate ratios of reagents. Ready to usereagents may be used. Consult with the instrument manufac-turer for guidance and use. Do not store sodium hydroxidesolutions in glass.8.4 Potassium Hydroxide Solution for Total Glycerin, 1.0 MKOH. Weigh out 56.1 g of ACS grade potassium hydroxidepellets. Disso
36、lve the pellets in approximately 250 mL DI waterin a 1 L volumetric flask. Use caution when handling the flaskdue to the heat produced during the dissolution of the potas-sium hydroxide. Dilute to the mark with DI water. Preparedready to use 1.0 M potassium hydroxide solutions made withacceptable pu
37、rity materials may also be used. Keep containerstightly closed when not in use to minimize carbonate formationfrom atmospheric carbon dioxide.9. Preparation of Standard Solutions9.1 Stock and working solutions.9.1.1 Glycerin Stock Solution, 1000 mg/LAccuratelyweigh 1 g of 99.5+ % glycerin to the nea
38、rest tenth of amilligram (0.0001 g) and transfer to a 1 L volumetric flask.Dilute to the mark with water. Shake or swirl to mix thestandard for homogeneity. Other volumes of stock solutionmay be prepared using the appropriate ratio of reagents.9.2 Working StandardsPrepare glycerin working stan-dards
39、 according to Table 1.9.2.1 Alternatively, commercial stock calibration solutionscan be used, provided that the solutions are traceable toprimary stock solutions or certified reference materials, and arefree from other analytes.10. Calibration10.1 Set up the ion chromatograph according to the manu-f
40、acturers instructions. No specific parameters are given heresince different manufacturers equipment might requirechanges in eluent, flow conditions, and instrument settings toperform the separation and obtain the results. Calibrate the ionchromatograph with at least five concentration levels ofglyce
41、rin, starting near but above the minimum detection limit,and covering the expected working range of samples subse-quently to be analyzed. Select concentrations of calibrantsolutions used that bracket the expected range for the samplesto be analyzed. Use one or more mid-range standards to verifythe l
42、inearity of the calibration plot.10.1.1 Typical ion chromatographic conditions:Flow: 1.0 mL minSample loop: 10 LOther analytical conditions may be used per the manufac-turers instructions.NOTE 1The sample loop volume will vary based on the columncapacity, sensitivity, and other factors. Refer to ion
43、 chromatographyequipment manuals and column information for instrument/column-specific details.10.1.2 Establish analytical curves with only one detectorscale setting. This will prevent a change of slope affecting theanalytical curve.10.2 Verify the analytical calibration plot daily or wheneversample
44、s are to be run, prior to the analysis of samples to verifythe system resolution, calibration, and sensitivity as part of thequality verification process (see Section 14).10.3 Repeat calibration after any change of the ion chroma-tography eluent solution from 8.3, to reestablish ion retentiontimes a
45、nd resolution. Use a check standard to verifycalibration, retention times, and resolution after any change inthe IC eluent solution from 8.3. Recalibrate if needed.3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing o
46、f reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.TABLE 1 Preparation of Glycerin Standards in WaterGly
47、cerin Standard,mg/kgWater(final weight), gGlycerin StockSolution, g50 100 5.020 100 2.010 100 1.05 100 0.51 100 0.10.5 100 0.05D7591 12 (2017)310.4 Measurement of the Calibration StandardsInject10 L of each calibration solution from 9.2 into the ionchromatograph, and measure the areas of the peaks c
48、orre-sponding to glycerin. Generally, one injection per sample issufficient. Refer to Section 14 for quality control discussion.10.5 Construct the glycerin calibration plots by plotting thepeak areas against the glycerin concentrations. Use linearregression to determine the best straight-line calibr
49、ation. Alinear least squares correlation coefficient of 0.99 or greater isrequired (see Fig. 2). The response factor for glycerin, Rf, isthe slope of the calibration plot straight line, in mg/kg/(areacount).10.5.1 If the plot of the peak area values against the ionconcentrations is not linear (the correlation factor should be atleast 0.99), the procedure should be checked for errors, and ifnecessary, the calibration should be repeated starting fromSection 9.11. Procedure11.1 For Free Glycerin in Biodiesel and its Blends:11.1.1 Obtain sa
