二氧化硫检测方法.doc

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1、ASTAANALYTICALMETHODSMethod30.0DeterminationofAddedSulfitesinDriedAllium(ModifiedMonier-WilliamsMethod)Purpose:ThismodificationoftheMonier-Williamsmethodissuitablespecificallyfordetectionofsulfitesindriedallium(i.e.garlic,onion,shallot,leek,andchive)

2、(Reference1).Organosulfurcomponentsareremovedinatoluenetrapbeforesulfurdioxideiscollectedandoxidizedtosulfuricacidwithhydrogenperoxideinasecondtrap.Sulfuricacidistitratedwithstandardsodiumhydroxidesolution.Thelimitofquantitationis10μg/g.Sulfitesinnon

3、-alliumfoodsshouldbeanalyzedbytheoptimizedMonier-WilliamsmethodasdescribedinAOAC990.28orEN1988-1.A.Apparatus1.Distillationapparatus:asdescribedinEN1988-1(1998)orAOAC990.28(2000)andwithadualbubble-throughsystem(seeFigure).2.1000mLround-bottomflaskwith

4、three29/32(or24/40)taperedjoints(verticalarms)andappropriateheatingmantle.3.250mLdroppingfunnelwithstopcockandtaperedjointtofitroundbottomflask.4.25mLburet.5.Graduatedcylindersof25,50,100and500mL.6.1Lvolumetricflask.7.3mLgraduatedpipet.8.Cryostatseta

5、t-5°C.9.pHmeter.B.Reagents1.Deionizedwater.2.0.01NNaOHsolution.3.Indicator:Dissolve250mgofmethylredin100mLofethanol(analyticalgrade).ThisindicatorisredforpH<4.4andyellowforpHvalue>6.2.4.30%w/wor3%w/whydrogenperoxideH2O2solution,analyticalgrade.5.37%c

6、oncentratedhydrochloricacidHClforanalysis.6.85%phosphoricacidH3PO4foranalysis.Page6of6October2010ASTAANALYTICALMETHODSMethod30.07.85%potassiumhydroxideKOHinpelletsforanalysis.8.PotassiumdihydrogenphosphateKH2PO4ofpurity>99%foranalysis.9.Toluene,analy

7、ticalgrade.10.Cryostatcirculatingfluid:mixtureofmonopropyleneglycol/water(2/1).11.Nitrogenflowwithprecisionvalveallowingaflowrateofabout200mL/minute.12.BuffersolutionSolutionA(acidpart):0.59MH3PO4and0.96MHClsolution.Introduceapproximately200mLofwater

8、intoa1Lvolumetricflask,carefullyadd40mLof85%H3PO4followedby80mLof37%HClwith,respectively,a50and100mLgraduatedcylinderand,finally,dilutetovolumewithwater.SolutionBbasepart:0.25MKH2PO4and0.258MKOHsolution.Introduce34gKH2PO4and17gKOHintoa1Lvolumetricfla