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available . . . in Syringe Filters 0.45 and 0.22um 13, 25, 33mm Diameter CA, PES, Nylon, PP, PVDF, PTFE Non-sterile STERILE Normal single filter GF preFilter 1um / Main multiLayer 10,1.0,0.7um / Main
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Whatman GD/X PVDF
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Membrane Disc Filters  BottleFilters and Glass Funnels 0.45um Nylon, PVDF, Glass Fibre 1um 47mm Diam
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Filtration Speed - micron size of filter media 0.45um > 0.22um >>0.1um - surface area of media 33 > 25 > 13mm Syringe Filter 90mm VacuCap > 70mm >50mm BottleTop Filter - source of pressure Positive pressure OR Vacuum
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“how long is a piece of string” . . . it All depends . . . it IS VERY sample dependant . . . Trial and Error required - particulate matter; how dirty and NOT just visible dirt but from product manufacture re crude paper filter methods - “invisible fibres” etc Factors : Viscosity . . . temperature dependant / dilution if possible oils/solvents warm fluid . . . in extreme cases use Syringe Pump and heated Syringe Jacket Chemical Compatability / wettability sample fluid & filtration media and equipment Specifics : Teflon and PVDF may need to be prewetted - isopropanol Structure of different OEM filter media for same nominal pore size may be different random fibres vs mesh type : pore size is a average pore size measurement and porosity depends on dispersion of pores about a mean size
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some Equipment Limitations
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BottleTop Filter preferred for aqueous media and medium Vac < 250mm Hg - higher vacuum can collapse plastic vacuum bottles - plastic bottles can be softened with “oils” particularly if media has to be warmed ) - aggressive solvents can soften filter housing material (PP/syringe filters ) - filter fibres can swell ( close off pores ) if filter media and fludis are ”less” compatible match hydrophyllic with hydrophyllic and hydrophobic with hydrophobic - non polar oils use PP, Teflon PVDF - essential oils/ fatty acids ester oil PVDF, Nylon perhaps - aqueous solution, high speed PES (polyetherSulfone), Nylon Glass Filtration Equipment - requires Heavy Duty Glass receiver - more expensive . . . initial cost - very robust ( but NOT unbreakable ) - safer for higher vacuum if required ( use safety shield as glass can implode if scratched or cracked ) - can be easily cleaned . . . sterilised in needed - will handle most aggressive fluids and solvents Vacu-Cap - for large batches ( 100ml to 1000ml )of fast fluids, generally aqueous and often HandVacuum pump adequate and controllable /managable.
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Vacuum System
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Hand Vacuum Pump : can develop higher vacuum at slow filtration speeds and collapse plastic filtration vacuum bottles - use small filter flasks less pumping required - can be tedious/tiresome for large batches and fast flow fluids Motorised Vacuum Pump : for large batches, vacuum can be regulated and filtration pumps 250mm HG is adequate for most fluids - takes tedium out of slow filtration fluids ie set and “forget”
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Syringe Filter 
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- pressurised by thumb pressure ( syringe dispenser ) 33mm for 50 to 200ml, 25mm 25 to 100ml, 13ml 5 to 25ml - depending for large through puts - tedious and thumb soreness are issues - slow fluids use a Syringe Pump - for viscous fluids either dilute with a solvent or use a Syringe Heater jacket ( can easily develop 100psi ) Syringe Filters are rated only to 50-75psi max Use Heavy Duty Glass Syringe or SS syringe if necessary - come in a variety of filter materials; CA, Nylon, PES, PP, PVDF, Teflon
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Prefilters
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- are used to speed up flow and SF capacity coarser layer traps large particles and helps protect the main filter material - Glass Fibre preFilter usually 1umlayer built-in ( Membrane Solutions ) - multiLayer preFilter : 10um, 1um , 0.7um layers then main filter 0.45um or 0.22um - Glass Fibre preFilter can also be used with Filter Funnel systems - either stand-alone GF Filter or separate membrane filter added on top of main filter / combined Whatman GD/X PVDF Syringe Filters . . . are AGAIN now available from Chromalytic Tech
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re “Sterility”
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This is not to be regarded as advice re TGA implications - see Chromalytic DISCLAIMER Sterile equipment; filters etc WILL NOT sterilise unsterile fluids Where originally STERILE Fluids need to be filtered AND Sterility needs to be maintained then ALL filtration equipment including Filter Media must be purchased sterile or suitably sterilised in-situ and recommended handling proceedures / asceptic conditions
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some methods
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disinfectants, boiling water, dry heat 300deg C ( borosilicate glass ) (steam) autoclaving ( 130degC ) industrial , ethylene oxide gas; gamma irradiation . . . with clean room handling/packaging to strict TGA requirements . . . for pharmaceuticals and medical use MicroFiltration : 0.45um sterile filters - only part successful ( arbitrary 60% ) 0.22um sterile filters much more effective ( 90% ) 0.1um sterile filters - 98% - but NO GUARANTEES !
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