Across industries and around theglobe, speed and flexibility areparamount — particularly in product development. The expert individuals that makethis possible need the support notjust of capable staff, but ofsophisticated instrumentation toincrease their effectiveness.At the same time, regulatorycompliance demands more rigour in the measurement ofparameters linked to productperformance. Traceable analysis,repeatable measurement andsystems validation are all essential.Laser diffraction — the techniquepioneered and advanced byMalvern Instruments — has alwaysprovided a powerful analyticalapproach to particle sizing.

INTR

ODUC

TION

Contents Page

One comprehensive system for particle sizing 3

Repeatable measurements around the globe . 4–5

The system approach . . . . . . . . . . . . . . . . . . . . 6–7

Making a measurement . . . . . . . . . . . . . . . . . . 8–9

Setting the standards . . . . . . . . . . . . . . . . . . . . . 10–11

Performance inside and out . . . . . . . . . . . . . . 12–13

Laser diffraction theory . . . . . . . . . . . . . . . . . . 14–15

Mie theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16–17

An all round view . . . . . . . . . . . . . . . . . . . . . . . 18–19

Software — bringing the system together . . . 20–21

Standard Operating Procedures . . . . . . . . . . . . 22

Technical specifications . . . . . . . . . . . . . . . . . . . 23

One comprehensive system

Two or more dispersion units canbe connected to the optical unit atany time. Changeover from one tothe other is virtually instantaneous.The system automatically recognisesand configures the new sampledispersion unit.The family of sample dispersionunits includes the Hydro 2000Micro Precision, a small volumehigh performance liquid dispersionunit designed to handle mostsolvents. With a capacity of only 18 ml, this unit is ideal for themeasurement of expensive, scarceor toxic materials.The Dry Powder Feeder, theScirocco, also has the capability ofmeasuring very small quantities ofmaterial and has a sealed cell tomaximise the respiratory safety ofthe user.Both these units as well as the largevolume sample dispersion unit, theHydro 2000G and the fullyautomated Small Volume sampledispersion unit, the Hydro 2000S,can be operated completelyautomatically by the use of standardoperating procedures embedded inthe operating software.Now, more than ever, making ameasurement is truly routine,repeatable, validatable and reliable.The Mastersizer 2000 systemprovides the complete systemsolution to particle sizing.

With the Mastersizer 2000, Malvern Instruments has further refined its characteristicsystem approach to sampledispersion, instrument control and measurement. Software provides not only controlbut management, enabling thesystem administrator to establishStandard Operating Procedures(SOPs) for all staff. These SOPs caneven be relayed from site to site viae-mail, so that procedures can beimplemented or adjusted worldwidewithin minutes. Any variability inmeasurement can thus be taken outof the hands of individual users.Advanced instrumentation featuresunder software control ensure thatmeasurement is simple andrepeatable. Set-up and optimisationare made invisible to the user byextensive software control and afixed optical system. The system measurement capability,size range and resolution have allbeen enhanced by an expandedarray of focal plane, wide angle andbackscatter detectors, as well as bythe use of red and blue light.The system comprises a single opticalunit supported by a comprehensivefamily of sample dispersion units tocondition and present a wide range ofwet and dry samples to the opticalunit for measurement.

for particle sizing

■ Simplified changeover between wet

and dry measurement with new

optics design.

■ Plug and Play dispersion units

for all sample types.

■ Assured user-to-user and

site-to-site reproducibility

through transferable Standard

Operating Procedures.

■ Software controlled configuration,

set-up and operation leaves

nothing to chance.

■ Measures materials from

0.02 μm to 2000 μm.

■ High resolution.

■ Full QSpec validation

documentation and Malvern

Quality Audit Standards

ensure highest levels of

Regulatory compliance.

Proven effectiveness for measurement of:

■ Pharmaceuticals

■ Chemicals

■ Surface coatings

■ Food and beverages

■ Mining and minerals

■ Paints and inks

■ Plastics

■ Petrochemicals

Consistency and comparability ofresults from sample to sample andfrom day to day are essential to anyQuality Control or QualityAssurance programme. However,increasingly global businessesrequire more than this.Measurements performed on aWednesday in Stockholm must becomparable with those performed onThursday in New York.Instrumentation and methods mustnot only be consistent withinthemselves, but must also berepeatable from site to site.

Day-to-day

The choice of instrumentation isvital. Only with rugged hardwareand fully integrated software canmethods and results be standardized.The Mastersizer 2000 includessystem features such as softwarewizards to lead the user through the measurement process from first principles. With a new sample material, this eases method development.

The system provides for step-by-step establishment of multipleStandard Operating Procedures(SOPs) for different samples. Agrowing library of standard SOPs issupplied for many routine analyses. All measurement variables arerecorded in the software to providefull traceability.

Person-to-person

With the Mastersizer 2000, fullyautomated measurement isprovided for routine users. Evennew personnel can be confident asthey deal with a variety of sampletypes, interchanging dispersionunits and switching from one typeof measurement to another.Running a sample can almost bereduced to a single-buttonoperation. Training time for newstaff is reduced. The requirementfor troubleshooting support fromkey personnel is minimized.

Repeatable measurement around the globe

Overplot of 18 separate measurements ofcornflour by 3 experts and 15 complete novicesusing a standard SOP

Size (microns)

0

10

20Percent in Band

Result 1

17.8

25

Result 10

Result 18

15

5

3.16

98

31.6

979

5.63

68

10.0

237

Sample-to-sample

Correct sample dispersion is vital to accurate particle sizing. By providing fully automatedsample dispersion units undersoftware control, the variationsintroduced by individual operators are eliminated. SOPs can be used to define not justthe selection of sample dispersionunits but also their particularsettings. For each type of sample,you can define all the controlparameters such as pump and stirrerspeeds and ultrasonication durationand intensity on wet dispersionunits, as well as air pressure andfeed rates on the dry powderfeeder.

Site-to-site

By establishing software-drivenSOPs, Malvern allows you toensure that the same methods areused consistently at different sites.Measurement and set-upparameters can be pre-defined,down to the detail of cleaningroutines, multiple measurementsand print out of results. For standard samples, repeatablemeasurements can be carried out inseconds with exactly the sameinstrument configuration. The SOP used to create anymeasurement record can beextracted from that record with asingle mouse-click for criticalappraisal, adaptation or further use. You can adjust the SOP or establish a new SOP for a newsample type, then simply e-mail itto colleagues around the world toensure that measurements at all sites are consistent. If a result file is e-mailed, therecipient can not only view the sizedata, but can extract the SOP usedto produce that result and can alsoreplicate it or review it.Remote operation is a furtheroption which allows user sites tocommunicate with each other andwith Malvern’s Help Desk andsupport personnel.

Technique-to-technique

Although different particle sizingtechniques are not absolutelycomparable, the Mastersizer 2000includes Result Emulation softwarewhich can model the likely sizedistribution which would be givenby other methods. This allows comparison with sizingmethods used by a company inprevious years, or still perhaps usedin remote sites or outside thelaboratory environment.

Standard Operating Procedurescan be used to define:

■ Sampler selection

■ Material to be measured, withoptical properties

■ Dispersant, with optical properties

■ Length of measurement time

■ Calculation type

■ Labelling protocols

■ Operator on-screen instructions

Report format

■ Number of measurements per sample

■ Upper and lower alarm limits on size

■ Sampler settings such as:– pump speed – stirrer speed– ultrasonics duration and intensity– dry powder feeder dispersive air pressure

– dry powder feeder feed rate

■ Automation cycles

The key to quality particle sizemeasurement is the ability topresent a well-dispersed,homogeneous sample to the laserbeam, at an appropriateconcentration and with a minimumof bias. Sample dispersion isessential for achieving optimalmeasurement. Malvern’s range ofsampling accessories is designed tomeet this requirement to the full. Across a range of industries,including pharmaceuticals,chemicals and paints, products are supplied in a variety of formsfrom dry powders and tablets tosuspensions and emulsions. The Mastersizer 2000 has theflexibility to allow wet and drymeasurement in rapid succession, aswell as enabling the user to changerapidly from aqueous to solvent-based dispersions. Many materials need to bemeasured in a wet dispersion.These include any materials that areused wet in the manufacturingprocess, sticky materials such as clayor kaolinite, or materials whichhave a tendency to agglomeratewhen dry, such as titanium dioxide.A suspension of particles in wateror other liquid media is created andoptimised using ultrasonics andsurfactants where necessary. Particles in the range from 0.26 to1500 microns can be measuredusing dry analysis dependent on thedensity and cohesiveness of thematerial being measured. By veryprecise control of air pressure, theuser can optimise dispersion so that“difficult” materials such asmagnesium stearate can bemeasured with ease. The ability tocontrol dispersive air pressure to anaccuracy of 0.1 bar allows users tomeasure fragile materials such asfreeze dried coffee and dried milkvery successfully.The Mastersizer 2000 user canchoose from a wide variety of sampledispersion units, for both wet anddry measurement modes. Any ofthese units can be plugged in at amoment’s notice and immediatelyrecognised by the system.

Hydro 2000 Micro Precision

Only the smallest quantities of extremely high value materials may beavailable to measure, particularly in the pharmaceutical and chemicalindustries. Malvern has developed a unique unit to deal with these materialsin the widest possible range of dispersants. The Hydro 2000 Micro Precision sample dispersion unit works with just 18 ml dispersant to allow the measurement of minute sample quantities. Thisprovides savings both in solvent disposal costs and in the use of expensivematerials. The unit has been designed to maximise sample recovery.Crucially, this can reduce time to market for new drugs, by allowing preciseparticle size measurement and method development at an earlier stage inproduct development. By using high efficiency ultrasonication, the unit provides maximumdispersion efficiency. This, together with the specially designed impellerpump/stirrer, helps to keep all the particles in suspension, ensuring thatsample conditioning is consistent from sample to sample. Complete computer control ensuresprecise replication of measurementroutines, both on a single instrument and,through transferable SOPs, at othercompany sites around the world. The Hydro 2000 Micro Precisionprovides quicker routes to validation,saving time and money in pharmaceuticaland chemical product development.

Scirocco 2000 Dry Powder Feeder

The Scirocco dry powder feeder features a sealed flow cell to ensure no lossof materials to the environment. This safety measure is essential, not just forknown toxic materials and active pharmaceuticals but even with powderssuch as flour, to which operator sensitization is known to occur and towhich exposure must be minimized. Scirocco’s improved air cell design eliminates velocity bias, which can leadto overestimation of fine particles in a sample and also allows efficientdispersion to be achieved at lower air pressures. This not only enablesScirocco to disperse cohesive powders more efficiently but also helps tominimise noise levels.Dispersive air pressure is precisely controlled and monitored to better than0.1 bar. This ensures that it can be used with fragile materials such as milkpowders without attrition, as well as having the power to disperse

notoriously cohesive materials such as magnesium stearate. Vacuummonitoring helps to maintainrepeatability of results. For the measurement of cements and abrasive samples, an erosionresistant ceramic venturi is available as an option.Driven by Standard OperatingProcedures, operator variability isminimised to ensure consistent,reproducible results wherever andwhenever the measurement is made.

INST

RUM

ENT

SELE

CTIO

N GU

IDE Mastersizer 2000 — the system approach

Scirocco 2000 Dry Powder Feeder withmicro and macro feed trays

The Hydro 2000 Micro Precision smallvolume sample dispersion unit

The Mastersizer 2000 Autosampler

The value of the SOP mode of operationof the Mastersizer 2000 comes to a peakwith the Mastersizer 2000 Autosampler.With a capacity of 36 50ml sample potsto hold wet or dry sample material, thisunit is equipped with an automaticbarcode reader to enable it to recognisethe contents of each pot andautomatically apply the appropriatemeasurement protocol to it.Two different additives can beautomatically injected into each sample as required to condition thesample and ensure that it is perfectlydispersed for measurement.■ For operation with Mastersizer 2000

Hydro 2000G or Hydro 2000S sampledispersion units.

■ Users can create or schedule measurementstandard operating procedures for eachindividual pot loaded.

■ Capability of dispersing dry powdersamples as well as handling suspensionsor emulsions.

■ Sample autorecognition gives the ultimatein flexibility.

■ If the lid of the autosampler is raised toremove or add samples or if samples aremoved, the autosampler simply rescansthe contents of the tray and less than aminute later is back on track with arevised schedule.

■ Instant ability to re-schedule urgent samples.

■ Offline scheduling allows preparation ofsample trays in advance for uninterruptedoperation of the autosampler station.

■ Autorecognition of previously programmed samples — even months after programming

■ Database facility with powerful search,sort and filter utility to access all recordson the system.

Hydro 2000S and Hydro 2000G

With a capacity of 50–170 ml, the Hydro 2000S employs built-in ultrasonic probe dispersion under full software control by SOPs with an in-line pump and stirrer. In the minerals, chemical, metal powder refining and cement industries,measurements of larger sample volumes are often most appropriate forquality control of the manufacturing process and finished product. TheHydro 2000G has an 800 ml capacity for the measurement of largermaterials having broader size distributions.The Hydro 2000G’s ability to suspend larger, denser material is enhanced bya contra-rotating pump and stirrer design. This allows the pump and stirrerto be operated at high speeds without vortexing and the introduction of airbubbles into the sample.Both the Hydro 2000S and the Hydro 2000G offer programmableautocleaning routines when they are connected to the dispersant supply.

Manual sample dispersion units

Not all users require full automation of their measurements. Two manualsample dispersion units are available for them: The Hydro 2000MU uses a 1000 ml beaker as the sample container forrapid and simplified sampling. A dip-in pumpand stir head continuously agitates the sampleand automatically circulates it through themeasuring system, while a built-in ultrasonicprobe provides consistent control ofdispersion. For smaller sample volumes from 50–120 ml,the low cost Hydro 2000SM uses a manuallyoperated control unit with an in-line pumpand stirrer.

Hydro 2000G Hydro 2000S

Hydro 2000MU Autosampler

USAG

E

The day at Acme PharmaceuticalsInc. Products Laboratory starts witha batch of twenty different samplesof lactose being delivered to thewarehouse. You need to rapidlyverify their particle size distributionbefore unloading can begin. You have already establishedStandard Operating Procedures forthese, using a dry powder feeder.You remove the cell cassette forthe Hydro 2000S wet sampledispersion unit from the Mastersizer2000 and insert the cell cassette forthe Scirocco dry powder feeder.The Mastersizer 2000 softwareinstantly recognises the new cassetteand automatically reconfigures fordry powder measurement with theScirocco unit. Selecting “Measure Automatic”you choose the appropriate SOP for lactose from the menu andcommence the measurementprocedure, following the on-screenprompts and instructions as they appear.The Mastersizer software sets thedispersion pressure of the Sciroccodry powder feeder, as defined inthe SOP. You enter the sampledetails. The system automaticallychecks and adjusts alignment andmeasures the background. Whenthe background measurement iscomplete, the sample is fedautomatically to the sizer.On completion of the measurement,data is automatically printed out inthe pre-selected format and is sent toa central LIMS system.All the samples are within theexpected size range but, out ofcuriosity, you decide to see if there has been any regular variation over time. You key in a database searchroutine to call up all lactosemeasurements over the last sixmonths. Running a Trend Graphreveals, as you suspected, that,although the material is still withinspecification, there has been agradual increase in the median size.

Making a measurementWhilst the material is still withinrange, you can give an earlywarning call to the supplier andadvise them to check theirproduction procedures. Manufacturing then send up abatch of emulsions being prepared.You remove the dry powder cellcassette and slot in the Hydro2000S for small volume samples.The system reconfigures itself andagain you select the appropriateSOP for the emulsion and select“Measure Automatic”. As defined in the chosen SOP, theMastersizer runs five successivemeasurements of 10 seconds, with

10 seconds pause between eachmeasurement. In this particularSOP, each measurement includes10,000 data scans or ‘snaps’.Now R&D bring in a selection of new formulations. These are trial batches of an experimentaldrug produced using a small scale bio-production process, and consequently are very costly and scarce.Fortunately, you can use the HydroMicro Precision unit to make anaccurate measurement using just 50mg of sample with 18 ml ofdispersant and can also recover thesample for further analysis.

With the weekend coming up, you want to set up some furthertesting to run unattended using the Autosampler. Using Malvern’s sampleRegistration and Scheduler utility, you enter samples formeasurement into theAutosampler’s sample database.You can put in sample details andselect the appropriate measurementSOP for each sample. Measurement priorities can beupgraded on screen at any time bysimply dragging them up the list ofthe scheduler.After entering the details, a barcode label is printed to be attachedto the sample pot. Pots do not needto be loaded into the carousel ofthe Autosampler immediately butcan be pre-programmed in largenumbers in advance of a night orweekend shift. Programming canbe carried out off-line so that theoperation of the Autosampler cancontinue uninterrupted. After loading a tray full of samples,the security lid on the Autosampleris lowered. The sample traycontents are automatically scannedand within 30 seconds the systemrecognises and prioritises each pot.When a pot is sampled, thesampling head of the Autosampleris lowered into the pot and a

quantity of dispersant is injected,together with any additives thatmay have been specified in theSOP for the sample. The sample is agitated in the pot toachieve a homogenous dispersionand a pre-determined quantity ofthe dispersion is withdrawn andinjected into the sample dispersionunit of the Mastersizer 2000.The resulting concentration of thesample in the sizer is then assessedand, if necessary, a predictiveconcentration routine in thesoftware adds any additional samplewhich may be required to arrive atthe correct concentration.Once the correct concentration ofsample has been delivered to thesizer, the sampling probe moves toa wash position and is thoroughlyrinsed before moving back to the sampling position for the next sample.Whether the Autosampler is beingused to free analytical staff for moredemanding tasks or to allow roundthe clock measurement to auniformly high standard, theMastersizer 2000 Autosampler has aplace in your laboratory.If you want to leave it in charge at night, simply set it up and turnthe lights out when you leave —it doesn’t need light, or refreshment breaks!

Working with the lights out…Autosampling in practice…You take out the Scirocco cassette

and insert the Hydro MicroPrecision cell. With a meeting togo to, you ask a colleague to takeover. They have not carried outthis particular analysis before, butcan just log on and follow the SOPyou have already set up. On screenadvice guides them through theprocedure, prompting the necessarydata entry and the systemimplements pumping andultrasonication to disperse thesample, before carrying out themeasurements and printing out the data……and then the night shift takes over…

What is ISO 13320?

ISO 13320-1 is the first formalInternational Standard for particlesize analysis by laser diffraction. It has been introduced to provide a methodology for adequate quality control. It provides a clear and independentguide to users on what they shouldlook for in system features andperformance, measurementcalculations, reference materials and validation

Quality Audit Standards

Different particle sizing techniquesderive particle size values fromdifferent properties of the particlesbeing measured. Some, such assedimentation and cascadeimpaction, are based on the surfaceof the particle and will vary withparticle roughness and shape.Sieving measures the seconddimension of a particle so thatneedle-shaped particles of the same thickness but varying lengthswill not be discriminated by theirsize differences.

Even microscopy, which is oftenregarded by the layman as theultimate tool for determining thetrue size of a particle, uses abewildering array of differentinterpretive formulae to derive sizeinformation. Such formulaeinclude Feret’s diameter, Martin’sdiameter, the unrolled diameterand the maximum length of theparticle, each of which gives adifferent particle size value.Because the key determinant ofdifferences between particle sizingtechniques is the variation in theshape of the particles, the onlymeaningful cross-referencebetween techniques is a sphere. For this reason, MalvernInstruments Quality AuditStandard is a spherical glass beadmaterial. Its refractive index (RI) at

BASI

C PR

INCI

PLES Setting the Standards Sphere of

same weightSphere of same

maximum length

dmax

ds

dv

dw

dsieve

dsed

dmin

Sphere ofsame volume

Sphere of samesurface area

Sphere passingsame sieve aperture

Sphere having samesedimentation rate

Sphere of sameminimum length

Particle Size (μm)0.1 1 10 100 1000 2000

Overplot showing a pressure titration on a fragile pharmaceutical material

1.54 and an absorption of 0.0,ensures that it provides anappropriate challenge to proveeffective wet or dry measurementfor the broad range of materialswith similar or higher RIs. The Quality Audit Standard has asize distribution of 10 to 120 μm,which is sufficiently broad tochallenge the sample handlingcapabilities of the sample dispersionunits. To eliminate sampling errors,it is packaged in single-use bottleswith a typical bottle-to-bottlevariation of ± 0.3 μm on the Dv50.These bottles are available in foursizes to suit the different sampledispersion units. They have beenproduced from a master batch of250 kg of material. This is theworld’s largest batch of particle sizereference material ever producedand ensures that, once adopted, thestandards will be available for manyyears to come.

Validation support

As a leading instrument supplier tothe pharmaceutical industry and

other highly regulated industries,Malvern Instruments supports thevalidation process with acomprehensive package. Quality isdesigned into the product from theoutset and is followed throughoutconstruction, installation,operation, performance andongoing customer support. Full lifecycle documentation,viewable as part of Malvern’sunique QSpec Validation Contract,provides complete traceability forthe design, production andfunctionality of Mastersizerhardware and software. Keyfeatures of the QSpec validationpackage include IQ/OQdocumentation, escrow contractsand a QSpec logbook as a primaryrecord for presentation atregulatory audit.

With a refractive index of 1.54, similar to common materials such asgypsum and quartz, Malvern’s Quality Audit Standards are a true‘Real World’ sample material

Material Refractive AbsorptionIndex

Haematite 3.0 1.0Rutile Titanium Oxide 2.75 3.0Silicon Carbide 2.64 1.0Barium yellow 1.96 3.0Carbon Black 1.8 3.0Graphite 1.8 3.0Corundum 1.76 0.1Spinel 1.71 0.1Polycarbonate 1.59 0.1Brucite 1.58 0.1Chalk 1.58 0.1China Clay 1.56 0.1Soda Glass Spheres 1.54 0.0Urea 1.54 0.1Potash Feldspar 1.54 0.1Silica 1.54 0.1Quartz 1.54 0.1Aluminium Hydroxide 1.53 0.1Calcium Carbonate 1.53 0.1Gypsum 1.53 0.1Mica 1.53 0.1Wood Flour 1.53 0.1Sodium Chloride 1.52 0.1Sugar 1.51 0.1Talc 1.51 0.1Methyl Methacrylate 1.50 0.1Zeolite 1.50 0.1Polypropylene 1.49 0.1Aluminium 1.48 1.0Intralipid 1.46 0Borax 1.45 0.1Natural Rubber Latex 1.43 0.0PVA 1.39 0.0PTFE 1.35 0.1Lactose 1.34 0.1Sorbitol 1.33 0.1

“Small differences in the assumed complex refractive index may causesignificant differences in the resulting particle size distributions.”

Average of 87 individual pots of MalvernQuality Audit Standard (red lines indicatelimits of variation)

Particle d

iameter

(μm)

100908070605040302010

0

20

10

0

10.0

100.0

Volume (%), 8

7 Results, Stats: 1# S.D.

Trend graph showing agreement between 25 Hydro 2000S sample dispersion units

DEVE

LOPM

ENT Performance inside and out

The reverse Fourier design with a550 mm cell to detector distanceallows a single lens to be used forboth wet and dry measurementswith no loss of resolution. The usersimply removes the wet cassettefrom the sizer and inserts the drycassette. Any re-configuration iscarried out automatically by system software. The superior beam stability of thepolarized He-Ne laser gives better power stability thanalternative sources.Dual wavelength detection withboth red and blue light providesthe additional information tomeasure reliably below 0.2 μm. A solid state short wavelength bluelight source is used in conjunctionwith forward and backscatterdetectors to give enhanced sizing performance.

Perfect optical alignment ismaintained by a unique software-controlled RapidAlign system,whereby the detector system isadjusted to balance light intensityacross an array of dedicatedalignment pads. Optimisedalignment is achieved in secondswithout any user involvement. Alignment can be carried outtogether with an automatedmeasurement of electronicbackground with a single mouseclick on-screen.

How Laser Diffraction Works

Blue LED

He-Ne laser

Spatial filter

Flow cell

Focal planedetector

Obscurationdetector and signal

processing

Wide angledetector array

Backscatter detectors

THEORY

The diagram on the left shows asimplified schematic of a laserdiffraction particle size analyser.This comprises a collimated heliumneon laser beam which is broughtto a focus by a reverse Fourier lensto a point at the centre of a focalplane detector array. This arrayconsists of a large number ofphotosensitive elements radiatingfrom a central point and increasingin area as they do so.

At the centre of the array is apinhole through which the laserbeam passes and falls on a seconddetector known as an obscurationdetector. If no particles are presentin the laser beam, all the laser lightwill fall on this second detector.However, as soon as particles enterthe laser beam, they block andscatter light away from this detectorand onto the other elements of thedetector array. The angle at which the light isscattered by a particle is inverselyproportional to the size of theparticle so that small particles willgive rise to large angles of scatterand large particles will give rise tosmaller angles of scatter. Thereverse Fourier lens has theproperty of collecting the scatteredlight from an ensemble of particlesand overlaying common angles of

How much or how many?

A small number of large particlescan form a very high proportion ofthe total volume of a sample. Asingle 100 μm diameter particle hasthe same volume as one million 1 μm diameter particles. That iswhy volume-based measurement isessential for all measurementsrelating to product formulationwhich is always performed in termsof weight/volume.The Mastersizer produces volume-based measurements based on themeasurement of ensembles ofparticles sampled at the rate of 1000data grabs per second. This meansthat the system is exceptionallysuitable for tracking transientchanges or detecting rogue coarseparticles in real time.

“I have yet to meet a chemist or manufacturer who formulates or

manufactures a product in terms of number.”

“If you formulate, manufacture andsell by volume, then volume is the true

expression for success.”

The fundamental measurement produced by the Mastersizer

2000 is a size/volumedistribution.

scatter onto the same portions ofthe detector array. There is thus adirect relationship between theintensity distribution of thisoverlaid light and the particle sizedistribution. By a correctunderstanding of this relationship(Mie Theory), it is possible toobtain an extremely rapid,repeatable and accuratemeasurement of particles in liquids or in air.This means that laser diffraction iscapable of measuring sprays,smokes, dry powders or particles inliquid suspension. It is thisversatility, combined with thereproducibility of themeasurements obtained, whichcontinues to give laser diffraction its significant lead in the field ofparticle size measurement.

The importance of large particles

1 million 1μm particles 100μm

Detection and measurement of transient effects is a major benefit offered by the Mastersizer 2000

Using Mie theory has never been easierMie theory is the key to absolute accuracy in particle sizing by laserdiffraction. It is the full rigorous theory providing a complete and exactsolution of the Maxwell’s field equations for the interaction of a plane wave with a spherical body.

In the 1970s when Malvern first pioneered the development of particle sizers using laser diffraction, the computers then available only had16KB of RAM — the equivalent of a single page of formatted Word script.

At that time, it also took eighthours on a mainframe computerto create a light scattering matrixto predict the light scatteringcreated by a single material witha particular set of optics.

Consequently the Fraunhoferapproximation, which was muchless demanding, was used insteadof Mie theory. For theinstruments of the day, thisproved to be perfectly adequatesince there was no expectation ofmeasuring particle sizes belowone or two microns.

As the demand for greateraccuracy coupled with sub-micron measurement capability intensified,the use of Mie theory became highly desirable. More powerful desk-top computers made it feasible.

In 1987, Malvern Instruments introduced the first of the Mastersizerrange of instruments. These used Mie theory and featured a newdetector array designed to extract the greatest benefit from this change.This required a considerableinvestment in computing tocalculate the light scatteringmatrices for all the materials tobe measured. But it meant thatthe Mastersizer was even able toprovide accurate measurementsof transparent sub-micron materials —something which is impossible using the Fraunhofer approximation.

Now, with 128 MB of RAMbeing commonplace, there is nojustification for reliance on theFraunhofer approximation. Incommon with all the Mastersizerrange of instruments which preceded it, the Mastersizer 2000 has adetector array optimised to exploit Mie theory to the full.

Light scattering library

The Mastersizer 2000 softwarefeatures a comprehensive library ofmaterials from acrylic to zirconiawhose light scattering properties areautomatically picked up when oneof them is selected for measurement.

If a new material needs to beintroduced into this library forfurther use, this can be done in lessthan two minutes. Once a material is in the library,SOPs in the software can call it upand use its scattering matrix.

There are no further demands on the user other than to select the appropriate SOP for the new material. The optical properties which formthe basis of a Mie calculationappear on the standard print-out for Validation purposes.

61 2 3 4 5

0.1 0.2 0.3 0.4 0.5

5

4

3

2

1Scat

terin

g C

oeffi

cient

(K)

Particle Diameter (μm)

true scattering coefficient

area of significant error

Fraunhofer approximation

Variation of scattering coefficient of rutile titanium dioxide below 0.45 microns

THEORY

Mie Theory

Mie theory provides a completeand exact solution of the Maxwell’sfield equations for the interaction ofa plane wave with a spherical body. It holds good for all particulatematerials in transparent media —liquids or gases or even transparentsolids. The Mastersizer 2000 is thus suitable for the measurementof suspensions, emulsions or dry powders.

Fraunhofer Approximation

The Fraunhofer approximation(named after the physicist Josef vonFraunhofer, 1787–1826) assumesthat particles are infinitelyabsorbing disks and only predictslow angle scattering up to 30°. It also assumes that all particleshave an extinction coefficient of2.0, regardless of their size. In fact,below 1 micron, this variesconsiderably and can be as much as5 at 1.5 microns for materials suchas titanium dioxide. Paint andpaper manufacturers actuallycapitalise on this since this increasein scattering efficiency increases theperceived opacity of the materialwhen it is ground to 1.5 μm.

Scattering Angle Particle Diameter (μm)

FRAUNHOFER APPROXIMATION

Light energy plotted against Particle size and Scattering angle for equal volumes of particles

MIE THEORY

Light energy plotted against Particle size and Scattering angle for equal volumes of particles

Latex particles RI = 1.6-0.0 in water

Energy

Scattering Angle

2.5+i1 Chromium Oxide, Metals

1.59+i0 Calcium Carbonate

1.59+i0

1.37+i0

Error is X10 for this material

PolystyreneSpheres

Volume Normalised Extinction Behaviour

0 0.1 1 10 100

Particle Diameter (μm)

Fraunhofer approximation

0

9

18

27

36

Energy

0

20

40

60

80

100

120

0.25

14.9

22.5

103475

21

2.5

0.3

21

2.5

0.3

Particle Diameter (μm)

0.25

14.9

22.5

103

475

Variation of extinction coefficients of some common materials compared withthe Fraunhofer approximation

Pushing the frontiers — providing an all round view

Different sizes of particle scatterlight differently. As particlesbecome smaller, they scatter light atlarger angles. However, as the sizereduces below one micron, thedifference in intensity withscattering angle diminishes. As theparticles reduce below 0.1 μm insize, these differences becomealmost non-existent.

In addition, the intensity of thescattering from these particles isvery low in relation to thescattering from larger particles. The scattering from a 0.1 μm latexparticle is less than 100th of thatfrom a 0.5 μm particle. The detector array must thereforeobtain as much signal as possible atlarger angles to differentiate the data successfully.

This can be achieved by increasingthe area of the silicon detectorelements — resolution would not be enhanced by cramming the wide angles of the detector arraywith small elements withcorrespondingly poor sensitivityand low signal-to-noise.

Large particles, on the other hand,scatter light at narrow forwardangles. Resolving differences in thesize of large particles does requirediscrimination of the variation inscattered light intensities at verysmall angular differences. Thismeans that the forward angles need to be well populated withdetector elements to give theresolution required.

Fortunately, owing to the fact thatlarge particles scatter light muchmore strongly than small particles, the size of the silicondetector elements in this part of the array can usefully be reduced in size. This gives a response more proportional to the scattering received by the wideangle detectors.

The balancing of these designcriteria has led Malvern Instrumentsto the creation of an optimiseddetector array that gives the bestangular resolution and amplitudeconsistent with obtaining reliablemeasurements as well as allowingthe best implementation of Mie theory.

“In view of the

characteristic features of

the scattering patterns, it

is advantageous to sample

the light intensities over a

wide range of angles…”

When complete sizing information is available from 0˚ to 360˚ why would you settle for less?

ISO13320

THEORY

There is an inverse relationshipbetween the size of a particle andthe angle at which that particlescatters light. Consequently, muchuseful information about thepresence and size of sub-micronparticles can be derived bysupplementing a focal planedetector array with wide-angle side and backscatter detectors.

The first 30° of scattering canprovide only a limited vision of any sub-micron fraction in a particlesize distribution (see fig.1).

By adding additional detectors outto 90°, a much fuller view of theenergy distribution is obtained(see fig.2).

The addition of backscatteringinformation together with dualwavelength extinction complete the picture (see fig.3).

The use of a wide angle detectorarray optimised to give uniformityof response, together with the useof two wavelengths of light andaccurate modelling of backscatterand cell window reflections, givesthe Mastersizer 2000 the power toaccurately measure complexparticle size distributions down to 0.02 μm.

Further optimisation is gained byhaving large surface area detectorsat the wider angles to compensatefor the lower scattering intensitiesfrom smaller particles. Placingprogressively smaller detectors atthe narrow angles of scatteringallows these detectors to be packedmore densely to give greaterangular resolution where it is really needed.

100000

10000

1000

100

10

1

0° 30° 60° 90° 120° 150° 180°

AngleR

elat

ive

Inte

nsity

RI is 1.59,0 in 1.33 for 633nm laser VERTICAL POLARISATION

Latex Scattering Plot

100000

10000

1000

100

10

1

0° 30° 60° 90° 120° 150° 180°

Angle

Rel

ativ

e In

tens

ity

RI is 1.59,0 in 1.33 for 633nm laser VERTICAL POLARISATION

Latex Scattering Plot

100000

10000

1000

100

10

1

0° 30° 60° 90° 120° 150° 180°

Angle

Rel

ativ

e In

tens

ity

RI is 1.59,0 in 1.33 for 633nm laser VERTICAL POLARISATION

Latex Scattering Plot

fig.1

fig.2

fig.3

0.5 μm0.3 μm0.2 μm0.1 μm

0.5 μm0.3 μm0.2 μm0.1 μm

0.5 μm0.3 μm0.2 μm0.1 μm

Bringing the system togetherMalvern Mastersizer softwareprovides the user-friendlyframework within which samplingand measurement, data handlingand reporting, as well as regulatoryrequirements and procedures are allbrought together.New graphing power includes allthe expected features such as filledfrequency plots, frequency andcumulative plots on screen and addsrefinements such as a zoom facilityto magnify a selected part of thegraph and give precise values.Graphs can be cut and pasted intoother applications.Trend graphs can be used to display information on dynamicprocesses such as milling and can beused to analyse the effects ofdifferent milling times, differentmachine settings, or unexplainedproduct variability.

Trend graph limits can be set, sothat measurement values outsidethe limits are automaticallyhighlighted. A Result Emulation feature allows the sizer to estimate theresults that would be obtainedfrom a particular sample usingother techniques such as sieving.

Security

Layered access allows differentgroups of users such as productionor QC departments to have differentaccess rights, to give maximumfreedom of access or tamper-proofmeasurement procedures. Traceability is enhanced with arecord page numbering systemwhich refers uniquely to onerecord within one file. If thatrecord is deleted, the recordnumbers will not close up toconceal the fact.

If a record is edited, that record is not changed but a “clone” iscreated for editing proposes and is automatically saved at the end of the file. Each record has aunique date/time stamp that cannot be changed. Customisable record pages allowat-a-glance comparisons of keyparticle size parameters. Data can be exported to any DDEor Active X compatible softwaresuch as Excel®. It is possible toconfigure the system so that data isautomatically exported after repeatmeasurement or re-calculation. Special data calculations includeGrade efficiency (Tromp) curves,Rosin Rammler fits, Phi plots andtables. It is also possible to measurethe aspect ratio of disks andmicaceous particles by the use of a custom calculation which isfully documented in the systemHelp file together with many other examples.

The tightness of overplots can be criticallyexamined using the zoom feature in thesoftware to try and separate the componentelements. In this example, very little separationis evident even after three progressive zooms.Zooming is achieved by a simple marqueeselect operation directly on the graph.

Records on the Record View can be highlighted and averaged. The Average dialogue allows theuser to name the average result and record a note to show the point which the averaging issupposed to show. The average result is then stored as a separate record.

The Record View is user configurable to show desired parameters at a glance. This powerfultool acts as a “ready extrapolated” graph where variations between measurements can beinstantly evaluated.

THEORY

Refractive Index database

Malvern Mastersizer calculationsare based on the real RefractiveIndex and absorption of thematerials measured. Actual RIvalues for a wide range of materialsare held in the comprehensiveMastersizer 2000 software database.The Mastersizer 2000 records andreports Refractive Index valueswith each measurement and aunique method of Refractive Indexconfirmation is provided.Where a default value for therelative refractive index is used, adiagnostic fit curve can be accessedso that the appropriateness of thisvalue can be critically assessed.

Customising Reports

Mastersizer 2000 Report Designergives you complete control of theoutput obtained from yourMastersizer 2000.Whether you are interested inadding your own key parameters tothe measurement print out usingthe powerful custom calculationutility or simplifying the standardreport for ease of assimilation,Report Designer gives you exactly what you require withoutthe need to learn any specialprogramming techniques.

Sample material input. The window on the left gives access to a comprehensivelibrary of materials and their optical properties. The window on the right containsthe user’s most frequently measured materials.

The powerful Report Designer utility allows users todesign the exact style and content that they require. ACustom Expressions tool allows key parameters to becalculated, displayed and printed out together with statusindicators such as “Pass”, “Fail” or “Call supervisor”.

S.O.

P.s Setting up a Standard Operating Procedure

SOPs are easily established with aWizard — a step by step decision-making tool providing advice atevery stage. In less than ten minutes you canestablish a detailed SOP for globaladoption. These SOPs can be astightly or loosely defined as youwish. Once established, an SOP can be saved on the system andtransferred to other Malvernsystems by e-mail. Because an SOPis automatically embedded in ameasurement record, the recordcan be e-mailed and the recipientcan not only extract the SOP butcan see the expected result.

Sampling/Dispersion (fig.1)

A choice of sample dispersion unitsis presented on screen. Advicescreens guide you through thechoice of wet or dry dispersion,aqueous or solvent-based, to suityour particular sample.

Material — optical propertiesand analysis (fig.2)

Select the sample material beingmeasured from the extensive

database that includes detailsof the optical properties ofthe material. With the aid ofthe built-in advice, select theanalysis required.

Sample Identification andReport Printing/Saving

Define the procedure forsample identification. The sample identifier —including source of thesample, its location andsample number — may beinput by the user or pre-set tominimise keyboard entry.

Select the report format from standard optionsor from those that havebeen created with theCustom ReportDesigner. You candefine formats for file saving andexporting to othersoftware packages.

Measurement andalarms (fig.3)

Set the length ofmeasurement time and

any alarm limits which maybe required on diameter, as well ascleanliness and optical alignment.

Calculate parameters

Limits can be assigned to define the acceptable size range withpass or fail criteria andappropriate messages.

Sampler Settings (fig.4)

Set up all the relevant controlparameters for the dispersionunit that you have selected.For dry powder feeders, youcan specify your choice ofgeneral purpose, small volume or micro volumesample feed tray.

You can also specify dispersive airpressure to 0.1 bar and sample feedrate to 1%.

For automated wet sampledispersion units, you can specifypump and stir rates as well asultrasonics intensity and duration.For manually operated dispersionunits, the preferred settings can beentered in the SOP and the userwill be advised to use them duringa measurement.

Measurement cycles

Repeat doses and measurementscan be selected, together withprocedures for cleaning or flushingof the sample dispersion unit, aswell as degassing of dispersantsbefore measurement.

fig.1

fig.2

fig.3

fig.4

SPECIFICATIONS

Des

igned

& p

roduce

d b

y C

•Forc

e C

om

munic

atio

ns

Lim

ited

, H

unge

rford

, U

K.

ww

w.c

forc

e.co

.uk

Malvern service and supportValidation and traceability

Malvern Instruments seeks innovation not only in product design anddevelopment, but in every area of business. As many of our systems

are used in highly regulated environments, product validation andR&D traceability are key commitments to our customers. We have

therefore invested to achieve ISO9001 with TickIt accreditation andare able to provide full traceability of changes in software and design.

Applications expertise

Malvern Instruments’ trained specialists are available on the ground inmore than 50 countries around the world to assist with applications

development and advise on and analyze difficult samples. We have ourown laboratory facilities with extensive applications experience derived

both from our own work and that of our extensive user base.Malvern’s own Applications Laboratories in the UK as well as North

and South America, Europe and Asia routinely run thousands ofcustomer samples each year. We can offer advice on how to measuredifficult materials, optimise sample dispersion and eliminate causes of

error in sample preparation.

Remote diagnosis

Our innovative approach to customer service is illustrated by the development of after-sales remote diagnostics. Malvern Instruments’

service specialists can access and control instruments worldwide viamodem links in order to minimize downtime and improve payback.

Ongoing development

In many industries, particle size analysis has become a key QCparameter. The need to obtain data as close to the production line as

possible and to react to that data as quickly as possible, is becoming increasingly important. Malvern Instruments applies its

expertise to meeting this challenge through continued research andapplications development.

Trends in regulatory requirements are watched closely and we aredeveloping the tools to support customers in electronic data protection

and submission.

For a full description of all Malvern Instruments’ products, services andsupport contact your nearest office.