USP645水电导率.docx
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USP645水电导率.docx
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USP645水电导率
645
WATERCONDUCTIVITY
<645>水电导率
水中的电导率是离子形成电流的一种度量。
水分子离解成离子,作为pH计和温度的一个函数,且能产生可预测的电导率。
一些气体,尤其是二氧化碳,很容易溶在水中且与形成的离子相互作用,这些可以用pH来预测对电导率的影响。
讨论此问题的目的,这些离子和它们所产生的电导率可以被认为是水本身固有的。
水电导率也可以被存在的外来离子影响,在下面所描述模拟电导率标准中所用的外来离子是氯离子和钠离子。
普遍存在的氯离子的电导率(在USPXXII或更早期的修定本中,当它是所必需的一个属性时,理论终点浓度为0.47ppm)限度为0.3ppm的氨离子代表绝大部分所允许的水的杂质范围。
为保持电中性,阳离子的平衡数量(例如钠离子)被包括在允许的杂质范围。
这些外来离子可能对水的化学纯度和制药应用的适用性有明显的影响。
固有的和外来的离子的混合电导率随pH值的变化而变化,是在进行测试法的第三阶段时附表中所描述和使用的电导率标准的依据。
在测试法中包括两个预备阶段,如果在任何一个预备阶段中,符合测试条件和电导率限度,则认为水符合检查要求,在此条件下进行第三阶段的实验是没必要的,仅在最后的测试步骤中出现不合格时,才可以判定供试品不符合测试要求。
Electricalconductivityinwaterisameasureoftheion-facilitatedelectronflowthroughit.WatermoleculesdissociateintoionsasafunctionofpHandtemperatureandresultinaverypredictableconductivity.Somegases,mostnotablycarbondioxide,readilydissolveinwaterandinteracttoformions,whichpredictablyaffectconductivityaswellaspH.Forthepurposeofthisdiscussion,theseionsandtheirresultingconductivitycanbeconsideredintrinsictothewater.
Waterconductivityisalsoaffectedbythepresenceofextraneousions.Theextraneousionsusedinmodelingtheconductivityspecificationsdescribedbelowarethechlorideandsodiumions.Theconductivityoftheubiquitouschlorideion(atthetheoreticalendpointconcentrationof0.47ppmwhenitwasarequiredattributetestinUSPXXIIandearlierrevisions)andtheammoniumion(atthelimitof0.3ppm)representamajorportionoftheallowedwaterimpuritylevel.Abalancingquantityofcations,suchassodiumions,isincludedinthisallowedimpurityleveltomaintainelectroneutrality.Extraneousionssuchasthesemayhavesignificantimpactonthewater'schemicalpurityandsuitabilityforuseinpharmaceuticalapplications.TheproceduredescribedinthesectionBulkWaterisdesignedformeasuringtheconductivityofwaterssuchasPurifiedWater,WaterforInjection,WaterforHemodialysis,andthecondensateofPureSteamproducedinbulk.ForwaterpackagedinbulkbutmanufacturedelsewhereorforSterilePurifiedWater,SterileWaterforInjection,SterileWaterforInhalation,andSterileWaterforIrrigation,someadditionalconductivitytestsmayberequired.SuchtestsaredescribedinthesectionPackagedWater.
Onlineconductivitytestingprovidesreal-timemeasurementsandopportunitiesforreal-timeprocesscontrol,decision,andintervention.Precautionshouldbetakenwhilecollectingwatersamplesforoff-lineconductivitymeasurements.Thesamplemaybeaffectedbythesamplingmethod,thesamplingcontainer,andenvironmentalfactorssuchasambientcarbondioxideconcentrationandorganicvapors.
INSTRUMENTSPECIFICATIONSANDOPERATINGPARAMETERS
Waterconductivitymustbemeasuredaccuratelyusingcalibratedinstrumentation.Theconductivitycellconstant,afactorthatrepresentsthegeometricalpropertiesoftheconductivitysensor,mustbeknownwithin±2%.Thecellconstantcanbeverifieddirectlybyusingasolutionofknownortraceableconductivity,orindirectlybycomparingtheinstrumentreadingtakenwiththeconductivitysensorinquestiontoreadingsfromaconductivitysensorofknownortraceablecellconstant.
MetercalibrationisaccomplishedbyreplacingtheconductivitysensorwithNIST(orequivalentlocalnationalauthority)-traceableprecisionresistors(accurateto±0.1%ofthestatedvalue)oranequivalentlyaccurateadjustableresistancedevice,suchasaWheatstoneBridge,togiveapredictedinstrumentresponse.Eachscaleonthemetermayrequireseparatecalibrationpriortouse.Thefrequencyofrecalibrationisafunctionofinstrumentdesign,degreeofuse,etc.However,becausesomemultiple-scaleinstrumentshaveasinglecalibrationadjustment,recalibrationmayberequiredbetweeneachuseofadifferentscale.Excludingtheconductivitysensorcellconstantaccuracy,theinstrumentaccuracymustbe±0.1µS/cm.
Inordertoincreasethemeasurementaccuracyontheconductivityrangesused,whichcanbelarge,andtoensureacompleteequipmentcalibration,itissuggestedthatperiodicverificationoftheentireequipmentbeperformed.Thiscouldbedonebycomparingtheconductivity/resistivityvaluesdisplayedbythemeasuringequipmentwiththoseofanexternalcalibratedconductivity-measuringdevice.Thetwonontemperature-compensatedconductivityorresistivityvaluesmustbeequivalenttowithin±20%ofeachother,oratadifferencethatisacceptableonthebasisofproductwatercriticalityand/orthewaterconductivityrangesinwhichthemeasurementsaretaken.Thetwoconductivitysensorsshouldbepositionedcloseenoughtogethertomeasurethesamewatersampleinthesameenvironmentalconditions.
Inadditiontotheverificationmethodperformedinnon-temperature-compensatedmode,asimilarverificationperformedintemperature-compensatedmodecouldbeperformedtoensureanappropriateaccuracyoftheequipmentwhensuchamodeisusedfortrendingorotherpurposes.
Becausetemperaturehasasubstantialimpactonconductivityreadingsofspecimensathighandlowtemperatures,manyinstrumentsautomaticallycorrecttheactualreadingtodisplaythevaluethattheoreticallywouldbeobservedatthenominaltemperatureof25
.Thisistypicallydoneusingatemperaturesensorembeddedintheconductivitysensorandanalgorithmintheinstrument'scircuitry.Thistemperaturecompensationalgorithmmaynotbeaccurate.Conductivityvaluesusedinthismethodarenontemperature-compensatedmeasurements.TemperaturemeasurementisrequiredfortheperformanceoftheStage1test.Itmaybemadeusingthetemperaturesensorembeddedintheconductivitycellsensor.Anexternaltemperaturesensorpositionedneartheconductivitysensorisalsoacceptable.Accuracyofthetemperaturemeasurementmustbe±2
.
仪器装置说明与操作参数
水电导率必须使用经校准过的仪器准确测定。
电导池常数,常用作仪表刻度读数的放大器,在已知数的±2%范围内。
电导池常数可以通过已知电导率的溶液直接检验,或通过将已知的或经检验过的电导池常数与有问题的仪器电导池读数进行对比而间接得到。
仪表校准通过用可追踪的能斯特精密电阻(精确到标示值的±0.1%)或等效的精密调节的电阻装置(例如惠斯通电桥),给出预期的仪器响应值来完成。
再校准的频率是仪器设计、使用程度等因素的函数。
然而,由于一些多刻度仪器有单一的校准调节器,再校准可以在使用不同刻度时进行。
仪器必须在最低量程内有0.1µS/cm的最小分辨率。
除了电导池精确度,仪器精确度必须是±0.1µS/cm。
在高温和低温下,由于温度对供试品的电导率读数有很大的影响,因此许多仪器可自动纠正实际读数,以显示在正常温度25℃下观察到的理论值。
这可以通过使用在电导池探针中的温度传感器和仪器线路中的运算来实现。
这种温度补偿可能是不准确的。
在这种方法中使用的电导率值是非温度补偿的测量值。
温度测量的准确度必须为±2℃。
下面所描述的操作法是用于测量“纯化水与注射用水”的电导率。
下面操作法中的阶段1可用在线检测仪器(已经过适当校准)替代(对阶段1进行适当的修改),在线仪器的电导池常数已被精确地测定且温度补偿功能已无效。
这样的在线质量控制仪器的适用性也取决于它在水系统中的位置。
所选择的仪器位置必须反映所监测的水的质量。
操作法
BULKWATER
Theprocedurebelowshallbeperformedusinginstrumentationthathasbeencalibrated,hasconductivitysensorcellconstantsthathavebeenaccuratelydetermined,andhastemperaturecompensationfunctionthathasbeendisabled.Forbothonlineandofflinemeasurements,thesuitabilityofinstrumentationforqualitycontroltestingisalsodependentonthesamplinglocation(s)inthewatersystem.Theselectedsamplinginstrumentlocation(s)mustreflectthequalityofthewaterused.
ThecombinedconductivitiesoftheintrinsicandextraneousionsvaryasafunctionofpHandarethebasisfortheconductivityspecificationsdescribedintheStage3—pHandConductivityRequirementstableandusedwhenperformingStage3ofthetestmethod.Twopreliminarystagesareincludedinthetestmethod.Ifthetestconditionsandconductivitylimitsaremetateitherofthesepreliminarystages,thewatermeetstherequirementsofthistest.Proceedingtothethirdstageofthetestinthesecircumstancesisunnecessary.Onlyintheeventoffailureatthefinalteststageisthesamplejudgednoncompliantwiththerequirementsofthetest.
Procedure
Stage1
Stage1isintendedforonlinemeasurementormaybeperformedofflineinasuitablecontainer.
1.Determinethetemperatureofthewaterandtheconductivityofthewaterusinganontemperature-compensatedconductivityreading.
2.UsingtheStage1—TemperatureandConductivityRequirementstable,findthetemperaturevaluethatisnotgreaterthanthemeasuredtemperature,i.e.,thenextlowertemperature.Thecorrespondingconductivityvalueonthistableisthelimit.[Note—Donotinterpolate.]
3.Ifthemeasuredconductivityisnotgreaterthanthetablevalue,thewatermeetstherequirementsofthetestforconductivity.Iftheconductivityishigherthanthetablevalue,proceedwithStage2.
Stage1—TemperatureandConductivityRequirements
(fornontemperature-compensatedconductivitymeasurementsonly)
Temperature
ConductivityRequirement(µS/cm)
0
0.6
5
0.8
10
0.9
15
1.0
20
1.1
25
1.3
30
1.4
35
1.5
40
1.7
45
1.8
50
1.9
55
2.1
60
2.2
65
2.4
70
2.5
75
2.7
80
2.7
85
2.7
90
2.7
95
2.9
100
3.1
阶段1
1.用非温度补偿的电导仪测定水的温度和电导率,可以在适当的容器中测量或在线测量。
2.使用“阶段1-温度与电导率要求表”,找到不高于所测温度的温度值,也就是相邻的较低的温度,在表中相应的电导率值是限度值。
[注:
不可以内插]。
3.如果测量的电导率不大于表中的数值,则水符合电导率检查的要求。
如果电导率高于表中的数值,按阶段2进行。
阶段1-温度与电导率要求
(仅对非温度补偿的电导率测定)
温度
电导率要求(µS/cm)
温度
电导率要求(µS/cm)
0
0.6
55
2.1
5
0.8
60
2.2
10
0.9
65
2.4
15
1.0
70
2.5
20
1.1
75
2.7
25
1.3
80
2.7
30
1.4
85
2.7
35
1.5
90
2.7
40
1.7
95
2.9
45
1.8
100
3.1
50
1.9
Stage2
4.Transferasufficientamountofwater(100mLormore)toasuitablecontainer,andstirthetestspecimen.Adjustthetemperature,ifnecessary,and,whilemaintainingitat25±1
beginvigorouslyagitatingthetestspecimenwhileperiodicallyobservingtheconductivity.Whenthechangeinconductivity(duetouptakeofatmosphericcarbondioxide)islessthananetof0.1µS/cmper5minutes,notetheconductivity.
5.Iftheconductivityisnotgreaterthan2.1µS/cm,thewatermeetstherequirementsofthetestforconductivity.Iftheconductivityisgreaterthan2.1µS/cm,proceedwithStage3.
阶段2
4.将足量的水(100ml或多于100ml)转移至一个适宜的容器中,并搅拌供试品。
必要时调节温度,当温度保持在25±1℃,开始剧烈的搅拌供试品,并定期观察电导率
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- USP645 水电