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GE Healthcare Life Sciences

December 2014

Fundamentals of Lab filtrationFactors to consider when selecting a filter

Content

The main uses of filters in the laboratory

Importance of filter selection

The basics of selecting a filter

Filter materials

Selecting a filter paper

Selecting a membrane filter

Selecting a filter for HPLC/UHPLC

The main uses of filters in the laboratory

Three main uses of filters in the laboratory

1. General laboratory filtration –

Isolating a solid from a liquid phase,

degassing, clarification etc.

2. Sample preparation prior to

analysis by an instrumental analytical

method such as HPLC/UHPLC/IC/ICP.

3. Instrument protection – for

example hydrophobic filter in a

pipette, vacuum pump protection

filters.

Importance of filter selection

Incorrect filter use may lead to:

• Increased time to filter a sample

• Need for multiple filters to obtain the required volume

for the analysis instead of one

• Increased pressure to push liquid through the syringe

filter

• Bursting the membrane and/or filter housing

• Observation of leachable in the results due to solvent

incompatibility

Filtration can become a bottleneck

What can be the benefits of choosing an optimal filter?

• Increase filtration speed

• Simplified workflow

• Reduce time taken for filtration step

• Reduce the need for troubleshooting and repeat

analysis due to observation of leachables

• Improved ergonomics during filtration step

The basics of selecting a filter

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What is a filter?

In this context “a filter is a material

that will remove solids or liquid

droplets from a fluid stream”

Note: There are filters that work at

the molecular scale.

These types of filters will not be

considered here.

Factors to consider when selecting a filter

• What is to be filtered?

Liquid or gas

• What is the desired product?

Filtrate or solid

• What size particles are to be removed?

May or may not know the answer to this question. For

example if trying to remove bacteria, will need a filter with

pore size that is 0.2 µm or smaller

• Chemical compatibility & leachables

Aqueous or organic solvents

Click on this image to

select your filter online

Factors to consider when selecting a filter

• What volumes are to be filtered?

• What flow rates are required?

• Is a sterile filter needed?

• Regulatory requirements?

(e.g. USP Class VI, Food Contact etc.)

• What type of filter housing is required?

Click on this image to

select your filter online

Filter materials

Main filter materials and their formats

Cellulose filters

• Flat

• Prepleated

Glass fiber filters• Flat

• Syringe filters

• Filter vials

Membranes

• Flat

• Syringe filters

• Filter vials

Filter materials - differences

High loading capacity

Depth Filter Surface Capture

Low loading capacity

Cellulose & Glass Membranes

(Glass > Cellulose)

Differences between depth filters and membranes

Membranes

• Microporous structure

• Pore size range (typical) : 5 µm to 0.2

µm

• Surface retention of particles

• Limited loading capacity

• Do not release fibers

• Stable to 130 ºC

• Some membranes sensitive to organic

solvents

Depth filters (glass & cellulose)

• Retention rating based on 98% of

particles retained by filter

• Cellulose limit ~2 µm, Glass

microfiber limit ~0.7 µm

• Random fibrous matrix

• Particles trapped within filter

• High particle loading capacity

• May release fibers

• Stable to 500°C (glass microfibre)

• Resistant to organic solvents

Depth filters: differences between cellulose and glass fiber filters

Cellulose filters

• Lower loading capacity

• Larger retention rating

• Good temp. stability (up to 140 ºC)

• Good chemical compatibility

• Strong

• Can be ashed

• Can be folded

Glass fiber filters

• Higher loading capacity

• Smaller retention rating

• High temp. stability (up to 500 ºC)

• Excellent chemical compatibility

• Relatively fragile

• May bind proteins & DNA

What type of filtration media?

Consider your requirements against

the characteristics of each media

type.

Click on this image to

download the solvent

compatibility table

Selecting a filter paper

The filter paper families

• Glass fiber filters (e.g. GF/CTM)

• Cellulose filter papers

Qualitative (e.g. Grade 1)

Qualitative wet strengthened (e.g. Grade 113)

Quantitative ashless (e.g. Grade 40)

Hardened low ash (e.g. Grade 50)

Hardened ashless (e.g. Grade 540)

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Use selection tools available to select the most suitable filter paper for your needs

Use these tools to select filter papers

Filter paper selection chart

Click on image to download

Online filter selectorTo select your filter online, click on image or visit

www.gelifesciences.com/LabFilterSelector

The filter selection tool provides

simple guides to choosing the correct

WhatmanTM filter and help take the

guesswork out of filter selection.

Selecting a membrane filter

The membrane filter range

Cast membranesRegenerated cellulose, Cellulose acetate, Cellulose

nitrate, PVDF, PES.

Stretched membranesePTFE .

Track etched membranesPolycarbonate, polyester

CycloporeTM, NucleporeTM

Inorganic membranesAnoporeTM

Pore size distribution ofTrack-etch membranes, Anopore™, cast membranes

Anopore and

Track-etch have

narrow pore size

distribution

compared to cast

or stretched

membranes

Cast membranes

(track-etch)

Stretched membrane

To select a membrane, check:

• Pore size (0.1µm, 0.2µm, 0.45µm

etc)

• Solvent compatibility

• Membrane diameter

Solvent compatibility

Hydrophilic membranes

• Easy to push water through a hydrophilic membrane –very low back pressure

• Examples

Nylon, PES, Regenerated cellulose (RC)

Hydrophobic membranes

• Hard to push water through a hydrophobic membrane –lot of back pressure.

• Examples

PTFE, Polypropylene membranes

Solvent compatibility

Hydrophobic membranes

• These membranes are suitable or use with organic solvents or organic/aqueous mixtures

Hydrophilic membranes

• Can filter organic solvents through hydrophilic membranes as long as the membrane is compatible with the solvent.

e.g. Regenerated Cellulose membrane is

compatible with all common HPLC

solvents. So can be used with water,

methanol and acetonitrile.

Solvent compatibility

Use published solvent compatibility tables to determine if

the solvent you are using is compatible with the

membrane.

Click on this image to

download the solvent

compatibility table

Use these tools to select membrane filters

Solvent compatibility tableClick on image to download

Online filter selector

To select your filter online, click on image or

visit www.gelifesciences.com/LabFilterSelector

The filter selection tool provides simple

guides to choosing the correct

WhatmanTM filter and help take the

guesswork out of filter selection.

Selecting a filter for HPLC/UHPLC sample preparation (Syringe filter/ filter vial)

Sample flow in HPLC/UHPLC analysis

Guard column should not be used as a solid removal

filter:

Need to filter the sample before injection in to the

instrument.

Guard column should not be used as a solid removal filter:

Need to filter the sample before injection in to the instrument.

Sample Injector

Guard

Separator

DetectorAutosampler

Need to filter

before injection

Sample filtration prior to HPLC or UHPLC

Filtration of the sample to remove solids improves

column life

Filtration of the sample to remove solids improves column life

1.7 μm

Critical radius = 0.35μm

• Filtration removes solids from the

sample: it improves column life &

instrument down time

• Chose pore size according to

column packing particle size:

If >3μm use 0.45μm filter

If <3μm use 0.2μm filter

HPLC/UHPLC sample filtrationwhat type of filter to use?

Number of options available for sample filtration. The option

chosen depends on a number of factors such as workflow,

number of samples analyzed per day and available

hardware.

Syringe filters Syringeless filters (filter

vials)

Use these tools to select syringe filters and filter vials

Syringe filter and filter vial

selection chart

Click on image to download

Online filter selector

To select your filter online, click on image

or visit

www.gelifesciences.com/LabFilterSelector

The filter selection tool provides

simple guides to choosing the correct

WhatmanTM filter and help take the

guesswork out of filter selection.

For latest updates about WhatmanTM filters and tools

www.gelifesciences.com/LaboratoryFiltration

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Anopore, Anodisc, Cyclopore, Nuclepore, Mini-UniPrep, GF/C, Whatman are trade marks of GE

Healthcare companies.

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All goods and services are sold subject to the terms and conditions of sale of the company within

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and contractual approval, if required, to make changes in specifications and features shown

herein, or discontinue the product described at any time without notice or obligation. Contact your

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© 2014 General Electric Company – All rights reserved

First published November 2014

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