A GUIDE FOR LABORATORIES Pure - Water Purification

7Dedicated to DiscoveryPU RE LABWATER GUIDEABOUT THISSECTIONIn this section we highlight somecommon applications and provideguidance on the water qualityrequired. We also provide someguidance on what purificationtechnologies you should be lookingfor in your water purification system.There are many water qualitystandards published throughout theworld, however only a few are relevantto specific research applications. Thishas resulted in the majority of waterpurification companies, including ELGA,adopting broad generic classificationsdefined by measurable physical andchemical limits. Throughout this guidewe will refer to the “Types” of purifiedwater referred to in this chart (seebelow).Grade of waterResistivity MΩ-cmTOC (PPB)BacteriaEndotoxin (EU/mL)Type I 18.2 5 1 0.03Type I 18 10 1 0.03Type II 10 50 10n/aType II 1 50 100n/aType III 0.05 200 1000n/aTable 1: Details of various water grades and typical applications. TOC, total organic carbon; ppb, parts per billion; CFU, colony forming units; EU, endotoxin units.TYPE I TYPE ITYPE II TYPE IITYPE IIIGoes beyondthe purityrequirements ofType 1 water’Often referred to as ultra pure, this gradeis required for some of the most watercritical applications such as HPLC (HighPerformance Liquid Chromatography)mobile phase preparation, as well asblanks and sample dilution for other keyanalytical techniques; such as GC (GasChromatography), AAS (Atomic AbsorptionSpectrophotometry) and ICP-MS (InductivelyCoupled Plasma Mass Spectrometry). Type I isalso required for molecular and microbiologyapplications as well as mammalian cellculture and IVF (In Vitro Fertilisation).is the grade forgeneral laboratoryapplicationsrequiring higherinorganic purity.The grade forgeneral laboratoryapplications. Thismay include mediapreparation, pHsolutions andbuffers and forcertain clinicalanalysers. It is alsocommon for Type IIsystems to be usedas a feed to a TypeI system*.The graderecommended fornon-critical workwhich may includeglassware rinsing,water baths, autoclaveand disinfector feed aswell as environmentalchambers and plantgrowth rooms. Thesesystems can also beused to feed Type Isystems**The production of ultra pure water (18.2 MΩ-cm resistivity, 5 ppb TOC) from tap water is usually carried out in two stages – pretreatment and polishing. Ideally,pretreatment reduces all the major types of impurities – inorganic, organic, microbiological and particulate – by over 95%. This can be most effectively achieved usingreverse osmosis or reverse osmosis combined with ion exchange or EDI. Alternatively ion exchange can be used but this cannot reduce the levels of organic, bacterial andparticulate impurities to the same extent. The better the pretreatment the higher potential quality of the final ultra pure water.

8Dedicated to DiscoveryPU RE LABWATER GUIDEAnalyticaland generalapplications ofpurified waterSummarised on P13ELECTROC H E M IST RYSince these techniques rely on thesensitive measurement of tinyelectrical signals, it is vital thatthe water used produces minimalinterference due to backgroundcontamination. ASMT Type II water,typically with a TOC (Total OrganicCarbon) 50 ppb and a bacterial countbelow 1 CFU/ml (Colony FormingUnits per millilitre) is recommendedfor electrochemistry applications. Forultra trace electrochemical analysesType I (ultra pure) water is required.TECHNIQUES INCLUDEPotentiometryPotentiometry measures the potentialof a solution between two electrodes.This is a passive technique, affectingthe solution very little in the process.The potential is then related tothe concentration of one or moreanalytes. The cell structure used isoften referred to as an electrode eventhough it contains two electrodes: anindicator electrode and a referenceelectrode (distinct from the referenceelectrode used in the three electrodesystem). Only demineralised wateris used with electrodes sincemineralic water contaminats willinterfere with the electric potentialof the electrodes. Potentiometry isusually conducted in an ion selectiveway with a different electrodefor each ion. The most commonpotentiometric electrode is the glasspH electrode.pH measurementpH is a subclass of potentiometryand is used to measure the acidity oralkalinity of a liquid. Measurementof pH in pure water is problematicdue to the low ionic strength ofthe solution and because the rapiduptake of carbon dioxide affects theobserved reading.CoulometryCoulometry uses applied current orpotential to completely convert ananalyte from one oxidation state toanother. In these experiments thetotal current passed is measureddirectly or indirectly to determinethe number of electrons passed. Thiscan indicate the concentration of theanalyte or, when the concentrationis known, the number of electronsinvolved with a redox couple. Bulkelectrolysis, also known as controlledpotential coulometry, or some hybridof the two names, is perhaps the mostcommon form of coulometry.VoltammetryVoltammetry applies a constant and/or varying potential at an electrode’ssurface and measures the resultingcurrent with a three electrodesystem. This method can reveal thereduction potential of an analyte andelectrochemical reactivity amongother things. This method in practicalterms is nondestructive since only avery, small amount of the analyte isconsumed at the two-dimensionalsurface of the working andauxiliary electrode.

9Dedicated to DiscoveryPU RE LABWATER GUIDEPolarographyPolarography is a subclass ofvoltammetry that employs adropping mercury electrode as theworking electrode and often usesthe resulting mercury pool as theauxiliary electrode. Concern overthe toxicity of mercury, combinedwith the development of affordable,inert, easily cleaned, high qualityelectrodes made of materials such asnoble metals and glass carbon, hascaused a great reduction in the use ofmercury electrodes.AmperometryAmperometry is a subclassof voltammetry in which theelectrode is held at constantpotentials for various lengthsof time. This is mostly a historicdistinction that still results insome confusion, for example,differential pulse voltammetryis also referred to as differentialpulse amperometry, which canbe seen as the combination oflinear sweep voltammetry andchronoamperometry. One thing thatdistinguishes amperometry fromother forms of voltammetry is thatit is common to sum the currentsover a given time period ratherthan considering them at individualpotentials. This summing can resultin larger data sets and reducederror. Amperometric titration is atechnique that would be consideredamperometry since it measures thecurrent, but would not be consideredvoltammetry since the entire solutionis transformed duringthe experiment.I D E N T I F Y I N G Y O U R D R I N K I N G W AT E R Q U A L I T YOver 70 years of experience in the lab water industry, combined with Veolia’s expertise in running many municipaltreatment plants, gives ELGA unsurpassed knowledge about feedwater qualities throughout the world. On our firstvisit to your laboratory we will carry out a test, on site, to analyse your feed water quality. Armed with data about yourlaboratory’s water quality, required applications, lab design and budget, our sales team will deliver an informed proposalabout the best water purification solutions to suit your needs.SPECTROSCOPY& S P E C T ROM E T RYSpectroscopy was historically thestudy of the interaction betweenradiation and matter as a functionof wavelength (l), and it referredto the use of visible light dispersedaccording to its wavelength, i.e.by a prism. Later the concept wasfurther expanded to comprise anymeasurement of a quantity as afunction of either wavelength orfrequency. Thus it also can refer tointeractions with particle radiationor a response to an alternating fieldor varying frequency (v). Once thevery close relationship betweenphoton energy and frequency (E hv)was realised, where h is the Plankconstant, a further extension ofthe definition added energy (E) as avariable. A plot of the response as afunction of wavelength — or morecommonly frequency — is referred toas a spectrum.Spectrometry is the spectroscopictechnique that is employed to assessthe concentration or amount of agiven substances and the instrumentthat performs such measurements isa spectrometer or spectrograph.

10Dedicated to DiscoveryPU RE LABWATER GUIDETECHNIQUES INCLUDEFlame Atomic AbsorptionSpectrophotometry (F-AAS)Although somewhat eclipsed byICP-MS and ICP-ES for multielementanalyses, the relatively modest costof AAS ensures its use in smallerlaboratories or for specific analyses.Depending on the element, detectionlimits vary from low ppb to ppmlevels. ASTM Type II water is usuallypure enough for most routine AAS andthere is no requirement for low levelsof organic compounds or bacteria.Gas Chromatography – MassSpectrometry (GC-MS)For GC, purified water is used toprepare blanks, standards andsample pretreatments, e.g. solidphase extraction. Since highsensitivity can be achieved in GCMS, the requirement for waterpurity is extremely stringent. Verylow TOC levels, i.e. less than 3 ppb,are required and this can best beachieved by using a top-of-the-rangepolisher that is fed with water thathas been pre-treated by ReverseOsmosis for removal of ions andorganic compounds.Graphite Furnace Atomic AbsorptionSpectrophotometry (GFAAS) alsoknown as Carbon Furnace AtomicAbsorption Spectrophotometry (CFAAS)This variant of AAS in which the flameis replaced with an electrically heatedgraphite tube or rod can achieve veryhigh sensitivity in elemental analysis.A top of the range ASTM Type I waterpolisher is required that ensures pptlevels of elemental impurities, 18.2MΩ-cm resistivity ultra pure and lowtotal organic content (TOC), whilemulti-stage monitoring (as deliveredby the ELGA PureSure system – seeabove) provides the best guaranteeof purity. Ultimate performanceis achieved when enhanced pretreatment is followed by continuousrecirculation and repurification ofthe purified water.Mass spectrometryThis highly sensitive techniqueThe PureSure SystemAt ELGA LabWater we fit an extra sensor betweenthe two purification stages of an ultra puresystem. This ensures that the second purificationpack can be changed before weakly chargedimpurities contaminate your application.permits trace analysis of complexmixtures and therefore requireshigh purity water. All samplepretreatments such as solid phaseextraction and sample preparationsteps require ASTM Type I (ultrapure) water, which is produced bya top of the range water ‘polisher’system. This gives ppt levels ofelemental impurities, 18.2 MΩ-cmresistivity water and an extremelylow TOC, typically 3 ppb. Multi-stagemonitoring (see above) is the onlymethod that guarantees this level ofpurity and the ultimate performanceis achieved with enhancedpretreatment followed by continuousrecirculation and repurification of thepolished water.Inductively Coupled Plasma AtomicEmission Spectrometry (ICP-AES)In ICP-AES, sensitivity differs markedlyfor different elements, howevermetals, semi-metals, phosphorousand Sulphur have detection limitsin the ppb (μg/l) range and requiresfairly stringent water purity. A highpurity Type I water system (polisher),is preferred, giving 18 MΩ-cmresistivity, however TOC requirementsare generally not critical and pretreatment can be by reverse osmosisor ion exchange.Inductively Coupled Plasma MassSpectrometry (ICP-MS)Advances in modern analyticalinstrumentation have continued toimprove the sensitivity of trace metalanalysis. These elements are nowmeasured at ppt and sub-ppt levelsusing techniques such as ICP-MS.Trace analytical work requires waterthat is free from the components tobe measured and demands the sameextremely stringent water purityfor the most sensitive ICP-MS work.

11Dedicated to DiscoveryPU RE LABWATER GUIDEwith enhanced pre-treatment from arecirculating ASTM Type II system.CHROMATOG RAPHYsample pretreatment require extremely stringent, high quality pure water(HPLC grade water), where the lowestpossible TOC levels are typically lessthan 3 ppb (see graph). This can be bestachieved with a top-of the-range TypeI water system (polisher) especiallydesigned for the purpose, fed with TypeII or Type III water pre-treated by RO(reverse osmosis).Chromatography may bepreparative or analytical, but thetwo are not mutually exclusive.Preparative chromatography seeksto separate the components of amixture for further use. Analyticalchromatography normally operateswith smaller amounts of materialand seeks to measure the relativeproportions of analytes in a mixture.High Performance LiquidChromatography (HPLC)HPLC can be used for the direct analysisand determination of minor and majorcomponents in a complex mixture. Inthe mobile phase, purified water ofgeneral laboratory grade (ASTM Type II)with a TOC of typically 50 ppb and aresistivity 1 MΩ-cm is used to prepare blanks, standards and for samplepre-treatment.Gradient HPLC is capable of extremelylow detection limits, e.g. well below 1ppb, therefore blanks, standards andSpectrophotometryPurified water for spectrophotometricapplications is recommended to beat least of Type II quality with a lowlevel of inorganic, organic or colloidalcontaminants. Typically, the waterhas a resistivity 1 MΩ-cm and hasbeen micro-filtered. Low TOC contentIon Chromatography (IC)IC determines minor and majorcomponents in a range of substancesdown to 0.1 ppm by direct injectionof 10 to 50 microlitre samples. Highlypurified water is needed for blanks,standards and to prepare eluents.While ASTM Type I water is preferred,Type II water is often adequate, especially if price is an issue. Extremely lowlimits of detection (down to low pptlevels) can be achieved using IC if theions are preconcentrated on a shortion exchange column and then elutedinto the eluent stream for separationand analysis. 50 or 100 ml of sample( 50 ppb) is of particular importancein techniques where UV detectionsystems are used, as dissolvedorganics may interfere with detection.can be analyzed in this way. A top ofthe range Type I (preferably Type I )water system is essential for obtainingppt levels of elemental impurities, 18.2MΩ-cm resistivity ultra pure and lowTOC. Multi-stage monitoring providesa guarantee of purity not offered byalternatives (see PureSure diagram,page 10). The ultimate performance isachieved with enhanced pre-treatmentfollowed by continuous recirculationand repurification of Type I water.Trace gradient HPLC of primarygrade and ultra pure waterRO permeateUltra-pure watermAUTypically cleanroom facilities arepreferred for preparing high-qualityreagents for blank analysis, standarddilutions and sample preparations.The water purifying system specifiedshould be a purpose-designed ASTMType I system. This should includea form of multi-stage monitoring(see PureSure Diagram, page 10)to guarantee these levels of purity.Ultimate performance is achievedBlankTime

12Dedicated to DiscoveryPU RE LABWATER GUIDEGENERALL A B O R AT O R YA P P L I C AT I O N SGeneral chemistryLaboratory grade purified water withresistivity 1 MΩ-cm, TOC less than50 ppb and bacterial count of 10CFU/ml is recommended for generalchemistry applications.Glassware washing/ rinsingGlassware washing is a routine practicein most laboratories and the gradeof water required depends on thenature of the applications. To minimizecosts (and depending upon your localdrinking water quality), most generalpurpose glassware can be washed withASTM Type III water. For more sensitiveanalytical or research techniques,Type II water with a resistivity of 1 to15 MΩ-cm should be used. For criticalapplications, such as trace analyticaltechniques (e.g. ICP-MS), cell cultureor stringent clinical methods (likeDNA sequencing or extraction),glassware should be washed withultra pure water, especially for thefinal rinse to ensure that the ultrapure buffers, media or diluents arecontained in “noncontaminated”glassware. For this, Type I (ultra pure)water, inorganics should be 18.2MΩ-cm, TOC 10 ppb and bacterialcounts 1 CFU/ml.Qualitative analysesMost qualitative analysis methods formajor or minor constituents requiregeneral laboratory grade purifiedwater with resistivity 1 MΩ-cm, aTOC less than 50 ppb, low particulatesand bacterial counts. However, formore sensitive techniques such asICP-MS, ultra pure water from a top ofthe range water polisher is requiredto produce ppt levels of elementalimpurities, 18.2 MΩ-cm resistivitywater and low TOC.Sample dilutionand reagent preparationThe water required for dilutingsamples, blanks, reagents andstandards must be of sufficientpurity that subsequent analysesare not affected. Preparing generalpurpose buffers, blanks andstandards for general chemistrytechniques, and for analyses 1ppm the use of a general laboratorygrade purified water with a typicalresistivity of 1 MΩ-cm, a TOC of 50ppb and low bacteria will enableaccurate results. For trace analysisat ppb levels or lower, ASTM TypeI (ultra pure) water is required forpreparing blanks and standards.SPE – Solid Phase ExtractionThis technique is widely used intrace organic determinations as apretreatment to separate the tracecomponents of interest from themajor components of the matrix.For trace analysis water of thehighest organic purity is neededto prepare blanks and standards,and to rinse the solid phase. Thiscan best be achieved with a top ofthe range Type I water system thathas a minimum TOC specification(especially designed for thispurpose), and is fed with waterpre-treated by reverse osmosis (RO).Additional operational protocolsmay be needed to ensure continualhigh performance.Steam generatorsSteam generators are used in arange of applications including cleanroom humidification, moisturisation,direct steam heating, injection andin autoclaves and sterilisers. Moststeam generators benefit frompre-treatment of the water supplyto avoid build-up, precipitation orcontamination in order to reducemaintenance, improve performanceand enhance hygiene levels. Steamgenerators can use ASTM Type IIIquality water with conductivity inthe range of 1–50 μS/cm (0.02 to 1.0MΩ-cm resistivity), which is typicallyproduced by reverse osmosisafter suitable pre-treatment.Some authorities now apply strictspecifications for the water usedto produce ‘pure steam’ for used indisinfection services in healthcareenvironments.Total Organic Carbon (TOC) analysisThis non-specific method is capableof quantifying the overall carboncontent of materials. Applicationsrange from high levels in effluentsand process streams to sub-ppblevels in ultra pure water. Samplesare diluted and reagents andstandards prepared with water.For high level measurement Type IIwater is adequate, while trace workrequires Type I (ultra pure) water.Water analysisWater analyses are required for awide range of different purposes,e.g. ensuring that drinking watermeets current standards, check

systems. The comprehensive Pure LabWater Guide is an amalgamation of our original Pure LabWater Guide and Pure Clinical LabWater Guide, first published in 1991 and . types of purified water required for each category of application. SECTION 2 CLINICAL DIAGNOSTICS Highlights the importance of us