ISO 2448-1998 Fruit and vegetable products - Determination of ethanol content《水果和蔬菜制品 乙醇含量的测定》.pdf

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1、A Referencenumbe r ISO2448:1998 (E) INTERNATIONAL STANDARD ISO 2448 Secondedition 19980801 Fruitandvegetableproducts Determinationofethanolcontent ProduitsdrivsdesfruitsetlgumesDterminationdelateneur enthanolISO2448:1998(E) ISO1998 Allrightsreserved.Unlessotherwisespecified,nopartofthispublicationma

2、ybereproducedorutilizedinanyformorbyan ymeans,electronic ormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromthepublisher. InternationalOrganizationforStandardization Casepostale56 CH1211Genve20 Switzerland Internet isoiso.ch PrintedinSwitzerland ii Foreword ISO(theInternati

3、onalOrganizationforStandardization)isaworldwidefederationofnationalstandardsbodies(ISO memberbodies).TheworkofpreparingInternationalStandardsisnormallycarriedoutthroughISOtechnical committees.Eachmemberbodyinterestedinasubjectforwhichatechnicalcommitteehasbeenestablishedhas therighttoberepresentedon

4、thatcommittee.Internationalorganizations,governmentalandnongovernmental,in liaisonwithISO,alsotakepartinthework.ISOcollaboratescloselywiththeInternationalElectrotechnical Commission(IEC)onallmattersofelectrotechnicalstandardization. DraftInternationalStandardsadoptedbythetechnicalcommitteesarecircul

5、atedtothememberbodiesforvoting. PublicationasanInternationalStandardrequiresapprovalbyatleast75%ofthememberbodiescastingavote. InternationalStandardISO2448waspreparedbyTechnicalCommiteeISO/TC34,Agriculturalfoodproducts, SubcommitteeSC3, Fruitandvegetableproducts. Thissecondeditioncancelsandreplacest

6、hefirstedition(ISO2448:1973),whichhasbeentechnicallyrevised. AnnexAformsanintegralpartofthisInternationalStandard.INTERNATIONALSTANDARD ISO ISO2448:1998(E) 1 FruitandvegetableproductsDeterminationofethanolcontent 1Scope ThisInternationalStandardspecifiesamethodforthechemicaldeterminationofethanolinf

7、ruitandvegetable products. Themethodisnotapplicabletoproductscontainingmorethan5%( m/m)ofethanol. Inthecaseofproductscontainingessentialoils,itisnecessarytoremovethelatter(seeannexA). 2Definition ForthepurposesofthisInternationalStandard,thefollowingdefinitionapplies. 2.1 ethanolcontent massofthesub

8、stancesdeterminedbythemethodspecifiedinthisInternationalStandard,expressedasa percentagebymassforsolidproductsorasgramsper100mlforliquidproducts 3Principle Separationoftheethanolbydistillation,followedbyoxidationbypotassiumdichromateinasulfuricacidmedium. Determinationoftheexcessdichromatebyammonium

9、iron( II)sulfateinthepresenceofiron( II)1,10 phenanthrolineasindicator. 4Reagents Useonlyreagentsofrecognizedanalyticalgrade,unlessotherwisespecified,anddistilledordemineralizedwateror waterofequivalentpurity. 4.1 Sulfuricacid (H 2 SO 4 ), r 20 =1,84g/ml. 4.2 Dilutesulfuricacid, r 20 =1,49g/ml,conta

10、ining500mlofsulfuricacid(4.1)perlitre. 4.3 Calciumhydroxide Ca(OH) 2 ,suspensionobtainedbyshaking110gto112gofcalciumoxidein1litreof water. 4.4 Potassiumdichromatesolution, containing42,572gofK 2 Cr 2 O 7 perlitre.1mlofthissolutionisequivalentto 0,01gofethanol. 4.5 Potassiumpermanganatesolution, cont

11、aining1,372gofKMnO 4 perlitre.10mlofthissolutionisequivalent to1mlofammoniumiron( II)sulfatesolution(4.6). 4.6 Ammoniumiron( II)sulfatesolution (NH 4 ) 2 Fe(SO 4 ).ISO2448:1998(E) ISO 2 Dissolve170,2gofammoniumiron( II)sulfate hexahydrateinwater.Add20mlofsulfuricacid(4.1)anddiluteto 1litrewithwater.

12、 Stabilizebytheadditionofaluminiumchips.2mlofthissolutionisequivalentto1mlofpotassiumdichromate solution(4.4). 4.7 Iron(II)1,10phenanthrolinesolution . Dissolve0,695gofiron( II)sulfateheptahydrate(FeSO 4 . 7H 2 O)in100mlofwater.Add1,485gof 1,10phenanthrolinemonohydrate(C 12 H 8 N 2 . H 2 O)andheatto

13、aidsolution. Thesolutionkeepswell. 5Apparatus Usuallaboratoryapparatusand,inparticular,thefollowing. 5.1 Distillationapparatus,comprisinga500mlflasksurmountedbyafractionationcolumnandacondenser endinginaslightlytaperedextensionpiecelongenoughtoreachtothebottomofa100mlvolumetricflask. Anyothersteamdi

14、stillationapparatusmaybeused,providedthatitsatisfiesthefollowingcriterion. Nolossofethanolgreaterthan0,02%shalloccurinthecourseofadistillation;i.e.200mlofa10%(V/V) ethanol/watermixturedistilledfivetimesinsuccessionshallcontainatleast9,9 %ofethanolafterthelast distillation. 5.2 Heatingapparatus, whic

15、hdoesnotcauseevenslightdecompositionoftheextractablematerialscontainedin theflask. 5.3 Volumetricflasks, ofcapacity100ml. 5.4 Pipettes,ofcapacities5ml,10mland20ml. 5.5 Burettes, of capacity50ml,fittedwithastopcock. 5.6 Wideneckedflasks, ofcapacity250ml,fittedwithgroundglassstoppers,clean,dry,freefro

16、mgreaseand airtight(absolutetightnesscanbeensuredwiththeaidofapolytetrafluorethylenesleeve). 5.7 Blender. 5.8 Balance, capableofweighingtothenearest0,01g. 6Sampling Itisimportantthelaboratoryreceiveasamplewhichistrulyrepresentativeandhasnotbeendamagedorchanged duringtransportorstorage. Samplingisnot

17、partofthemethodspecifiedinthisInternationalStandard.AsthereisnospecificInternational Standarddealingwithfruitandvegetableproducts,itisrecommendedthatthepartiesconcernedcometoan agreementonthesubject. 7 Preparationoftestsample 7.1 Solidorthickproducts (pure,marmaladeorjam,fruits,vegetables) Blendmech

18、anicallythewholeofthesamplesupplied.Takecarethatthetemperatureoftheproductdoesnotrise. Takeasufficientquantityoftheproducttoenabletwoparalleldeterminationstobecarriedout.ISO ISO2448:1998(E) 3 7.2 Liquidproducts (juices,pulpsandsyrups) Thoroughlymixthesample.Takeasufficientquantityoftheproducttoenabl

19、etwoparalleldeterminationstobe carriedout. 8Procedure NOTE Ifitisrequiredtocheckwhethertherepeatabilityrequirement(clause10)ismet,carryouttwodeterminationsin accordancewith8.2.1to8.2.3. 8.1Test portion Weigh,tothenearest0,01g,amassofthepreparedsample,ortakeavolumeofitsuchthatthequantityofethanol col

20、lectedin100mlofdistillateislessthan1g. 8.2Determination 8.2.1Distillation Dilutethetestportionwithabout50mlofwaterandtransferitquantitativelytotheflaskofthedistillationapparatus (5.1).Rinsethevesselusedtotakethetestportionwithnotmorethan120mlofwater,collectingtherinsingwater intheflask. Maketheprodu

21、ctslightlyalkaline(pH8 0,2)withthecalciumhydroxidesuspension(4.3),shakenbeforeuse. Addglassbeadsorpiecesofporcelaintocontroltherateofboiling.Pour10mlofwaterintoa100mlvolumetric flask(5.3)andinserttheendofthetaperedextensionofthedistillationapparatussothatitisimmersedintheliquid. Distilthedilutedtest

22、portion(previouslymadealkaline)insuchawaythatthedistillate,whenitreachesthe volumetricflask,isatarelativelylowtemperature(15 Cto20 C). Collectabout80mlto85mlofdistillate.Stopthedistillationandrinsethecondenserandextensionwithafew millilitresofwater. Shakethevolumetricflasktomixthecontents.Ifnecessar

23、y,immersetheflaskincoldwater(15 Cto20 C)fora fewminutes. Dilutethecontentsofthevolumetricflasktothemarkwithwaterandshake. 8.2.2Oxidation Pour20ml( V 1 )ofpotassiumdichromatesolution(4.4),accuratelymeasured(seenote),and20mlofdilutesulfuric acid(4.2)intoa250mlflaskwithagroundglassstopper(5.6)andshake.

24、 Add10ml( V 0 )ofdistillate(8.2.1),accuratelymeasured.Stoppertheflask,moisteningthestopperwithadropof sulfuricacid(4.1).Shaketheflaskandwaitforatleast30min,shakingtheflaskfromtimetotime. Theresultantmixtureshouldinnocaseassumethegreencolorationofthechromiumcationasthiswouldindicate thattheethanolcon

25、tentofthetestportionwastoohigh.Ifthisoccurs,recommencetheoxidationtakingasmaller amountofdistillate(forexample5ml).Ifnecessary,recommencebothdistillationandoxidationtakingasmallertest portion.Takeaccountofanysuchchangesinthecalculations. Ifthetestportioncontainstoolittleethanol,asmalleramountofpotas

26、siumdichromatesolution(4.4)maybeused, i.e.10mlor5mlofthissolution,dilutedwith10mlor15mlofdistilledwater,respectively.Takeaccountofany suchchangeinthecalculations.ISO2448:1998(E) ISO 4 8.2.3Titration Titratetheexcessofdichromate,usingtheammoniumiron( II)sulfatesolution(4.6).Theexcessofdichromate shou

27、ldbeatleastequalto20%ofthequantityusedfortheblanktest.Shaketheflaskaftereachaddition. Whenthecolourchangestogreenishblue,add4dropsofiron( II)1,10phenanthrolinesolution(4.7).(Another appropriatecolouredindicatormaybeused,atthediscretionoftheoperator,seenote.)Continuetheadditionofthe ammoniumiron( II)

28、sulfatesolution(4.6)untilthecolourofthemediumchangesfromgreenishbluetobrown.Ifthe endpointispassed,returntoitpreciselybyaddingpotassiumpermanganatesolution(4.5). Deduct,fromthevolumeoftheammoniumiron( II)sulfatesolutionused,onetenthofthevolumeofpotassium permanganatesolutionadded.Let V 2 bethevolume

29、remainingafterthisdeduction,whichrepresentstheexact volumeofammoniumiron( II)sulfatesolutionequivalenttotheexcesspotassiumdichromate. NOTEThetitrationoftheexcessofdichromatewiththesolutionofammoniumiron( II)sulfate(4.6)canalsobecarriedoutin thepresenceofamixtureof 1mloforthophosphoricacid(85%), r 20

30、 =1,71g/ml;and 1mlofasolutionofbariumdiphenylaminesulfonatecontaining0,5gper100ml. Carryouttwodeterminationsonthesamepreparedsample. 8.2.4Blank test Carryoutablanktestunderthesameconditionsasforthetitration,replacingthevolume, V 0 ,ofdistillatebythe samevolumeofdistilledwater.Let V 3 bethevolumeofam

31、moniumiron( II)sulfatesolution(4.6)used,followingthe procedureof8.2.2and8.2.3. 9 Expressionofresults 9.1Solid products Theethanolcontent,expressedasapercentagebymass,isequalto 0,01 V 1 VV VV 32 30 100 - 100 m where m isthemass,ingrams,ofthetestportion; V 0 isthevolume,inmillilitres,ofdistillatetaken

32、forthetitration; V 1 isthevolume,inmillilitres,ofpotassiumdichromatesolutionusedfortheoxidation; V 2 isthevolume,inmillilitres,ofammoniumiron(II)sulfatesolutionusedforthebacktitrationofthe dichromate; V 3 isthevolume,inmillilitres,ofammoniumiron( II)sulfatesolutionusedintheblanktest. 9.2Liquid produ

33、cts Theethanolcontent,expressedingramsper100mlofproduct,isequalto 0,01 V 1 VV VVV 32 304 100 100 - ISO ISO2448:1998(E) 5 where V 0 , V 1 , V 2 and V 3 havethesamemeaningasin9.1; V 4 isthevolume,inmillilitres,ofthetestportion. 10Repeatability Theabsolutedifferencebetweentwoindependentsingletestresult

34、s,obtainedusingthesamemethodonidentical testmaterialinthesamelaboratorybythesameoperatorusingthesameequipmentwithinashortintervaloftime, willinnotmorethan5%ofcasesbegreaterthan1%ofthearithmeticmeanofthetworesults. 11Test report Thetestreportshallspecify: allinformationnecessaryforthecompleteidentifi

35、cationofthesample; thesamplingmethodused,ifknown; thetestmethodused,togetherwithreferencetothisInternationalStandard; alloperatingdetailsnotspecifiedinthisInternationalStandard,orregardedasoptional,togetherwithdetailsof anyincidentswhichmayhaveinfluencedthetestresult(s); thetestresult(s)obtained; if

36、therepeatabilityhasbeenchecked,thefinalquotedresultobtained.ISO2448:1998(E) ISO 6 AnnexA (normative) Modifiedprocedureforproductscontainingessentialoils Inthepresenceofessentialoils,thedistillateisturbid,withdropsofessentialoilfloatingonthesurface.Insuch casestheprocedureshallbemodifiedasfollows. Co

37、llectthedistillateina100mlvolumetricflaskandallowittostandfor2h.Dilutetothemarkwithwater,the interfacebetweenthetwophases(essentialoilandwater)beingatthelevelofthemark.Allowtostandforafurther 1hto2h.Discardthesmallquantityofessentialoilcollectedonthesurface,eitherbysuctionwithafinepipetteor byfiltra

38、tionthroughpaperinacoveredfunnel. Transferthestillturbidfiltratetoa150mlflaskandadd10gofpolystyrenegranules(granulesize1mmto2mm). Shakethestopperedflaskfor15minandthenfilterthemixturethroughgauzeinacoveredfunnel.Theliquid shouldthenhavebecomeclearandhavelostitsodouralmostcompletely. Proceedwiththedeterminationonthisliquid.ISO2448:1998(E) ISO ICS67.080.01 Descriptors: agriculturalproducts,foodproducts,plantproducts,fruitandvegetableproducts,chemicalanalysis,determinationofco ntent, ethanol,volumetricanalysis. Pricebasedon6pages