半微量测定法-欧洲药典

Thesemi-microdeterminationofwaterisbaseduponthequantitativereactionofwaterwithsulphurdioxideandiodineinasuitableanhydrousmediuminthepresenceofabasewithsufficientbufferingcapacity.ApparatusTheapparatusconsistsofatitrationvesselwith:2identicalplatinumelectrodes;tightinletsforintroductionofsolventandtitrant;aninletforintroductionofairviaadesiccant;asampleinletfittedwithastopperor,forliquids,aseptum.Inletsystemsforintroductionofdrynitrogenorforaspirationofsolventsmayalsobefitted.Thetitrationiscarriedoutaccordingtotheinstrumentsupplier’sinstructions.Careistakenthroughoutthedeterminationtoavoidexposureofreagentsandsolventstoatmosphericmoisture.Theend-pointisdeterminedusing2identicalindicatorelectrodesconnectedtoanelectricalsourcethatmaintainsbetweentheelectrodeseitheraconstantcurrentoraconstantvoltage.Wheredirecttitrationisused(methodA),additionoftitrantcauseseitheradecreaseinvoltagewhereconstantcurrentismaintainedoranincreaseincurrentwhereconstantvoltageismaintained,untiltheend-pointisreached.Instrumentswithautomaticend-pointdetectionarecommonlyused.水分的半微量测定法是基于水与二氧化硫和碘在无水的具有足够缓冲性能的介质中的反应。设备该设备是由2个相同的铂电极，引入溶剂和滴定剂的密封入口，引入空气的干燥通道和引入样品的通道(引入固体物质的通道装有塞子，引入液体物质的通道装有隔膜)。入口系统中也装有引入氮气的通道或引入溶剂的通道。其滴定操作是根据仪器供应商的说明书执行。整个测定过程需细心以防止试剂或溶剂散入到空气中。其终端用2个相同的检测电极连接电源以保持电极间稳定的电流或稳定的电压。其直接滴定法见方法A，滴定标准液的加入导致稳定电流下的电压的减少或增加，直到达到反应终点。将用到自动的终点检测仪器。StandardisatiorTothetitrationvessel,addmethanolR,driedifnecessary,orthesolventrecommendedbythesupplierofthetitrant.Whereapplicablefortheapparatusused,eliminateresidualwaterfromthemeasurementcellorcarryoutapre-titration.Introduceasuitableamountofwaterinanappropriateform(waterRoracertifiedreferencematerial)andcarryoutthetitration,stirringforthenecessarytime.Thewaterequivalentisnotlessthan80percentofthatindicatedbythesupplier.Standardisethetitrantbeforethefirstuseandatsuitableintervalsthereafter.Unlessotherwiseprescribed,useMethodA.标准化。于滴定容器中加入甲醇，如有必要，进行干燥或使用其他的支持滴定的溶剂。消除设备中的残留水或实行预滴定。以合适的形式引入适量的水来进行滴定，搅拌一定的时间。第一次使用时，或间隔一段时间后，水的等量不少于标准滴定的80%，除运用方法A测量以外。MethodA.IntroduceintothetitrationvesselmethanolR,orthesolventindicatedinthemonographorrecommendedbythesupplierofthetitrant.Whereapplicablefortheapparatusused,eliminateresidualwaterfromthemeasurementcellorcarryoutapre-titration.Introducethesubstancetobeexaminedrapidlyandcarryoutthetitration,stirringforthenecessaryextractiontime.方法A。在滴定容器中引入甲醇或者专论中所规定的支持滴定的溶剂。除去设备中的残留水或实行预滴定。迅速引入检测物质并实行滴定，在提取期间实行搅拌。MethodB.IntroduceintothetitrationvesselmethanolR,orthesolventindicatedinthemonographorrecommendedbythesupplierofthetitrant.Whereapplicablefortheapparatusused,eliminateresidualwaterfromthemeasurementcellorcarryoutapre-titration.Introducethesubstancetobeexaminedrapidlyandinasuitablestateofdivision.Addanaccuratelymeasuredvolumeofthetitrant,sufficienttogiveanexcessofabout1mlortheprescribedvolume.Allowtostandprotectedfromlightfor1minortheprescribedtime,withstirring.TitratetheexcessofreagentusingmethanolRortheprescribedsolvent,containinganaccuratelyknownquantityofwater.方法B。于滴定容器中引入甲醇或专论中所规定的支持滴定的溶剂。除去设备中的残留水或实行预滴定。于合适的位置迅速引入需检测的物质。加入精确量取的滴定剂，超过所需要的滴定剂的量1ml或按照规定的量。避光1分钟或一段时间后，搅拌。用甲醇或规定的溶剂滴定过量的试剂，这包括已知量的水分。Suitability.Theaccuracyofthedeterminationwiththechosentitrantmustbeverifiedforeachsubstancetobeexamined.Thefollowingprocedure,givenasanexample,issuitableforsamplescontaining2.5-25mgofwater.Thewatercontentofthesubstancetobeexaminedisdeterminedusingthereagent/solventsystemchosen.Thereafter,sequentialknownamountsofwaterRareaddedinanappropriateform(atleast5additions)andthecumulativewatercontentdeterminedaftereachaddition.Calculatethepercentagerecovery(r)ateachpointusingthefollowingexpression:W1=amountofwateradded,inmilligrams;W2=amountofwaterfound,inmilligrams.

Calculatetheregressionlineofthecumulativewaterdeterminedagainstthewateradded.Calculatetheslope(b),theinterceptwiththey-axis(a)andtheinterceptoftheextrapolatedcalibrationlinewiththex-axis(d).Calculatethepercentagemeanrecovery(=).Calculatethepercentageerrors(e1ande2)usingthefollowingexpressions:◄a=they-axisintercept,inmilligramsofwater;d=thex-axisintercept,inmilligramsofwater;M=watercontentofthesubstance,inmilligramsofwater.Thereagent/solventsystemisconsideredtobeacceptableif:一IIandIIarenotgreaterthan2.5percent;—bisbetween0.975and1.025(deviation+2.5percent);—-isbetween97.5percentand102.5percent.稳定性。滴定所选的滴定剂对所检测物质的准确性需查清楚。以下操作，如样品中含有2.5-25mg水分是合适的。检测物质的含水量用所选的试剂/溶剂系统。随后，将水以合适的形式加入已知量的水（至少滴定5次）。累计每次滴定的水的含量。按照以下公式计算恢复率：叫=加入水的含量，用毫克表示；W2=所检测到的水的含量