aoac官方方法920.156脂肪和fatty acids的熔點威利的方法_第1頁
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1、41.1.08AOACOfficialMethod920.156MeltingPointofFatsFattyAcidsWileyMethodFirstAction1920FinalActionA.ReagentAlcohol–watermixture.—Specificgravityshouldbesameasthatoffattobeexamined.PreparebyseparateboilingH2Oalcohol10minto

2、removedissolvedgases.WhilestillhotpourH2Ointotesttubeuntilitisalmosthalffull.Nearlyfilltesttubewithhotalcoholpouringitdownsideofinclinedtubetoavoidtoomuchmixing.IfalcoholisaddedaftertheH2Ohascooledairbubbleswillmakemixtu

3、reunfitfuse.B.DeterminationLetmeltedfilteredfatfall15–20cmfrompingtubeuponpieceoficeuponsurfaceofcoldHg.Disksthusfmedshouldbe1–1.5cmdiameterweighca200mg.Removediskswhensolidletst2–3htoobtainnmalmp.Alternativelydisksmaybe

4、preparedusingapparatusconsistingofAlplateca3mmthick100mmsqwithperfationsca10mmdiametersteelplateca10mmthick150mmsq.ThoughlychillsteelplateinrefrigeratplaceAlplateontop(surfacesshouldbeflush).Pourmeltedfilteredfatintohole

5、sofAlplateletstinrefrigerat≥2h.RemovefatabovesurfaceofAlplateremovedisks.Place303.5–3.8cmtesttubecontainingalcohol–H2Omixtureintall3510cmbeakercontainingiceH2Oleaveuntilmixtureiscold.diskoffatintotube.Itwillsinkimmediate

6、lytopointwheredensityofalcohol–H2Omixtureisexactlyequivalenttoitsown.Loweraccuratethermometerthatcanbereadto0.1Cintotesttubeuntilbulbisjustabovedisk.Tosecureeventemperatureinallpartsofalcohol–H2Omixturearounddiskstirgent

7、lywiththermometer.SlowlyheatH2Oinbeakerconstantlystirringwithairstreamothersuitabledevice.Whentemperatureofalcohol–H2Omixturerisestoca6Cbelowmpoffatdiskoffatbeginstoshrivelgraduallyrollsupintoirregularmass.Lowerthermomet

8、eruntilfatparticleisevenwithcenterofbulb.Rotatethermometerbulbgentlysoregulateheatthatca10minisrequiredflast2Cincreaseintemperature.Assoonasfatmassbecomessphericalreadthermometer.ThisisWileymp.Atthispointtemperatureofbat

9、hmustbe≤1.5Cabovempofsample.Conduct2additionaldeterminationsexactlyasabove.Secondthirdresultsshouldagreeclosely.Ifedgeofdisktouchessideoftubemakenewdetermination.?2000AOACINTERNATIONAL41.1.08AOACOfficialMethod920.156Melt

10、ingPointofFatsFattyAcidsWileyMethodFirstAction1920FinalActionA.ReagentAlcohol–watermixture.—Specificgravityshouldbesameasthatoffattobeexamined.PreparebyseparateboilingH2Oalcohol10mintoremovedissolvedgases.Whilestillhotpo

11、urH2Ointotesttubeuntilitisalmosthalffull.Nearlyfilltesttubewithhotalcoholpouringitdownsideofinclinedtubetoavoidtoomuchmixing.IfalcoholisaddedaftertheH2Ohascooledairbubbleswillmakemixtureunfitfuse.B.DeterminationLetmelted

12、filteredfatfall15–20cmfrompingtubeuponpieceoficeuponsurfaceofcoldHg.Disksthusfmedshouldbe1–1.5cmdiameterweighca200mg.Removediskswhensolidletst2–3htoobtainnmalmp.AlternativelydisksmaybepreparedusingapparatusconsistingofAl

13、plateca3mmthick100mmsqwithperfationsca10mmdiametersteelplateca10mmthick150mmsq.ThoughlychillsteelplateinrefrigeratplaceAlplateontop(surfacesshouldbeflush).PourmeltedfilteredfatintoholesofAlplateletstinrefrigerat≥2h.Remov

14、efatabovesurfaceofAlplateremovedisks.Place303.5–3.8cmtesttubecontainingalcohol–H2Omixtureintall3510cmbeakercontainingiceH2Oleaveuntilmixtureiscold.diskoffatintotube.Itwillsinkimmediatelytopointwheredensityofalcohol–H2Omi

15、xtureisexactlyequivalenttoitsown.Loweraccuratethermometerthatcanbereadto0.1Cintotesttubeuntilbulbisjustabovedisk.Tosecureeventemperatureinallpartsofalcohol–H2Omixturearounddiskstirgentlywiththermometer.SlowlyheatH2Oinbea

16、kerconstantlystirringwithairstreamothersuitabledevice.Whentemperatureofalcohol–H2Omixturerisestoca6Cbelowmpoffatdiskoffatbeginstoshrivelgraduallyrollsupintoirregularmass.Lowerthermometeruntilfatparticleisevenwithcenterof

17、bulb.Rotatethermometerbulbgentlysoregulateheatthatca10minisrequiredflast2Cincreaseintemperature.Assoonasfatmassbecomessphericalreadthermometer.ThisisWileymp.Atthispointtemperatureofbathmustbe≤1.5Cabovempofsample.Conduct2

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