实验室用水的种类和区别_精品文档Word格式文档下载.docx
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实验室常见的水的种类:
1、蒸馏水(DistilledWater):
实验室最常用的一种纯水,虽设备便宜,但极其耗能和费水且速度慢,应用会逐渐减少。
蒸馏水能去除自来水内大部分的污染物,但挥发性的杂质无法去除,如二氧化碳、氨、二氧化硅以及一些有机物。
新鲜的蒸馏水是无菌的,但储存后细菌易繁殖;
此外,储存的容器也很讲究,若是非惰性的物质,离子和容器的塑形物质会析出造成二次污染。
2、去离子水(DeionizedWater):
应用离子交换树脂去除水中的阴离子和阳离子,但水中仍然存在可溶性的有机物,可以污染离子交换柱从而降低其功效,去离子水存放后也容易引起细菌的繁殖。
3、反渗水(ReverseosmosisWater):
其生成的原理是水分子在压力的作用下,通过反渗透膜成为纯水,水中的杂质被反渗透膜截留排出。
反渗水克服了蒸馏水和去离子水的许多缺点,利用反渗透技术可以有效的去除水中的溶解盐、胶体,细菌、病毒、细菌内毒素和大部分有机物等杂质,但不同厂家生产的反渗透膜对反渗水的质量影响很大。
4、超纯水(Ultra-puregradewater):
其标准是水电阻率为18.2MΩ-cm。
但超纯水在TOC、细菌、内毒素等指标方面并不相同,要根据实验的要求来确定,如细胞培养则对细菌和内毒素有要求,而HPLC则要求TOC低。
评价水质的常用指标:
1、电阻率(electricalresistivity):
衡量实验室用水导电性能的指标,单位为MΩ-cm,随着水内无机离子的减少电阻加大则数值逐渐变大,实验室超纯水的标准:
电阻率为18.2MΩ-cm。
2、总有机碳(TotalOrganicCarbon,TOC):
水中碳的的浓度,反映水中氧化的有机化合物的含量,单位为ppm或ppb。
3、内毒素(Endotoxin):
革兰氏阴性细菌的脂多糖细胞壁碎片,又称之为“热原”,单位cuf/ml。
1、自来水(Tapwater)
Tapwaterisusuallyofuncontrolledquality,mayhaveseasonalvariationssuchaslevelofsuspendedsedimentdependingonthesource(municipalreservoir,river,well),maycontainotherchem-icalspurposelyaddedtodrinkingwater(chlorine,fluoride),andisgenerallyunsuitableforuseinimportantexperiments.Tapwaterisfineforwashingglasswarebutshouldalwaysbefollowedbyarinsewithahigher-gradewater(distilled,deionized,etc.).
2、蒸馏水(DistilledWater)
Distillationgenerallyeliminatesmuchoftheinorganiccon-taminationandparticularlysedimentspresentintapwaterfeedstock.Itwillalsohelpreducethelevelofsomeorganiccon-taminantsinthewater.Doubledistillingsimplygivesaslightlyhighergradedistilledwater,butcannoteliminateeitherinorganicororganiccontaminants.
Distilledwaterisoftenproducedinlargestillsthatserveanentiredepartment,orbuilding.Thequalityofthewaterisdependentonhowwelltheequipmentismaintained.Asignificantstiroccurredwithinalargeuniversity’sbiochemistrydepartmentwhenthefirstmentionofaproblemwiththehousedistilledwaterwasamemothatcameoutfromthemaintenancedepartmentthatstated:
“Wewouldliketoinformyouthattherepairshavebeenmadetothestillservingthedepartment.Thereisnolongeranyradiuminthewater.”Thenextday,afollow-upmemowasissuedthatstated:
“Correction—thereisnolongeranysodiuminthedis-tilledwater.”
3、去离子水(DeionizedWater)
Deionizedwatercanvarygreatlyinqualitydependingonthetypeandefficiencyofthedeionizingcartridgesused.Ionexchangebedsusedinhomesystems,forinstance,areusedprimarilytoreducethe“hardness”ofthewaterusuallyduetohighlevelsofdivalentcationssuchasmagnesiumandcalcium.Theresinbedconsistsofacationexchanger,usuallyinthesodiumform,whichreleasessodiumintothewaterinexchangeforremovingthediva-lentions.(Rememberthatwhenyouattempttoreduceyoursodiumintake!
)Thesebedsthereforedonotreducetheioniccontentofthewaterbutratherexchangeonetypeofionforanother.
Laboratorydeionizingcartridgesareusuallymixed-bedcartridgesdesignedtoeliminatebothanionsandcationsfromthewater.Thisisaccomplishedbypreparingtheanion-exchangebedinthehydroxide(OH-)formandthecation-exchangeresinintheacid(H+)form.Anionsorcationsinthewater(includingmonovalent)areexchangedforOH-orH+,respectively,whichcombinetoformneutralwater.AnyimbalanceintheremovaloftheionscanresultinapHchangeofthewater.Typicallywaterfromdeion-izingbedsisslightlyacidic,oftenbetweenpH5.5to6.5.
Thedeionizingresinscanthemselvesincreasetheorganiccon-taminantlevelinthewaterbyleachingofresincontaminants,monomer,andsoon,andshouldalwaysbefollowedbyabedofactivatedcarbontoeliminatetheorganicssointroduced.
4、18MΩ水(ReverseOsmosis/MilliQTM)
Thehighestgradeofwateravailableisgenerallyreferredtoas18MWwater.Thisisbecausewhentheinorganicionsarecompletelyremoved,theabilityofthewatertoconductelectriccurrentdecreasesdramatically,givingaresistanceof18MW.Com-mercialsystemsthatproducethisgradeofwaterusuallyapplyamultiple-stepcleanupprocessincludingreverseosmosis,mixed-bedionexchangers,carbonbeds,andfilterdisksforparticulates.Somemayincludefiltersthatexcludemicroorganisms,resultinginasterilewaterstream.High-grade18MWwatertendstobefairlyacidic—nearpH5.NecessarypHadjustmentsofdilutebuffersolutionspreparedusing18MWwatercouldcausediscrep-anciesinthefinalionicconcentrationofthebuffersaltsrelativetobufferspreparedusingotherwatersources.
5、WhenIs18MΩWaterNot18MΩWater?
Supposethatyourresearchrequires18MWwater,andyoupur-chasedthesystemthatproduces500ml/mininsteadofthe2L/minversion.Ifyourresearchdoesn’trequireaconstantflowofwater,youcanconnecta20Lcarboytoyoursystemtostoreyourpris-tinewater.BadMove.
18MWisnotthemosti