Instruction Manual for ZetaPALS, Zeta Potential Analyzer
Contents
1. Brookhaven Instruments PALS Zeta Potential Analyzer ojx BITES File Graphs pH Conductance Setup Help a m t ar al r 2 Set Parameters ____ _ gt Measured Parematers Wavelength 675 0 net 15 16 d EI Voltage Conductance Unknown BS Auto Unknown Electric Field Unknown VZem CUse 5 0 r Frequency hz Peed Signal Strength Auto Unknown Sample Count Rate Unknown User 5 0 Ref Count Rate Unknown r Drive Mode _ Sine wave C Square wave Iv Show status on Main Screen M Autotrack l OK Cancel z E 2 5 24 gt Page 6 Sec 64 Ati5m in2 Coi 1211 REC MAK ExT OVR WPH start Microsoft Office ZE Microsoft Word ZPALSM IE Brookhaven Instrume f 1221 If you are not2. and voltage in the Setup Instrument dialogue to allow the user to control the voltage applied to the cell during the measurements See Electrophoretic Mobility See Sample ID and Operator ID In the parameters dialogue the user can enter text for this purpose Values set by the user that describe the characteristics of the sample and the duration of the measurement process The dialogue box where these values are supplied is brought up by clicking the Parameters command button Include sample ID operator ID dielectric constant viscosity etc A field in the parameters dialogue where the particle size in nanometers can be entered This could be the value measured with the PSDW software on the ZetaPALS itself This is purely a label at present Some methods of calculating the zeta potential can use this information so it is included for convenience in the database It can be left set to 0 in many cases as it is not used with current Brookhaven software The phase signal measured by the ZetaPALS is plotted on the main screen Phase is the integral of frequency so the plot of phase against time is a track of the changing value of the Doppler frequency shift as the AC field changes The ZetaPlus is fitted with a BNC connector to which a pH probe can be attached The software allows the probe to be calibrated and measurements of pH performed under manual control This pH value is then inserted into the parameter lis
3. value of viscosity in centipoise cP of the suspending liquid at the set temperature The database under Liquid in the Parameters dialogue has some useful values for a range of common liquids including water The viscosity is calculated for a modest range of temperature 5 70 C The wavelength of the laser source in nanometers Displayed in the Setup Instrument dialogue A quantity expressed in mV calculated from the electrophoretic mobility Depends on the viscosity and dielectric constant of the medium and the choice of H ckel or Smoluchowsky models See ZetaPlus Manual section IV and the Appendices for more details This value is calculated because it can be used in theoretical predictions of dispersion stability Expand the graph of the experimental and fitted phase data to fill the main form
4. zeta potential from electrophoretic mobility This is entered in the Parameters dialogue A table of values for common liquids is installed in the software The value for this quantity depends slightly on temperature so you may need to operate the instrument at a temperature for which it is available If not otherwise stated operate at 25 C A field is generated when a voltage is applied across the electrodes in the cell This causes the particles in the dispersion to move allowing the electrophoretic mobility to be measured The value is computed allowing for the applied voltage the gap between the electrodes and the characteristics of the drive circuitry It is stated in Volts cm and ranges from 0 600 V cm nominally Electrode s Electrophoretic Mobility Frequency Graphs Hiickel Liquid Log File Manual The electrodes consist of a noble metal usually palladium mounted on a machined support The standard electrodes are mounted on an acrylic support and are compatible with hydrophilic liquids and some inert organic liquids such as paraffins Aggressive solvent requires the use of Kevlar or ceramic supported electrodes The support also contains a temperature sensor to measure the temperature near the sample The electrodes connect to the instrument via a multi way connector mounted on top of the assembly The basic quantity that is measured in microelectrophoresis It is the average velocity that the particle
5. Instruction Manual for ZetaPALS Zeta Potential Analyzer Brookhaven Instruments Corporation Brookhaven Corporate Park 750 Blue Point Road Holtsville New York 11742 USA Telephone 1 631 758 3200 Fax 1 631 758 3255 e mail tech bic com web www bic com Please Read This is your instruction manual for the Brookhaven ZetaPALS Please read it carefully before making measurements You should also read the instruction manual for the ZetaPlus instrument since the basic theory underlying the measurement of zeta potential using electrophoretic mobility is common to both variants and is not reproduced here Sections I Introduction IV Theory VII Sample Preparation and the Appendices are especially relevant The ZetaPALS option consists of hardware and software that extends the capabilities of the Brookhaven Instruments ZetaPlus zeta potential analyser or the 90Plus particle size analyzer to provide another method of measuring electrophoretic mobility and hence determining zeta potential This method is referred to as PALS or Phase Analysis Light Scattering and is a far more sensitive technique than the laser Doppler method used in the basic ZetaPlus This extra sensitivity is particularly useful though not limited to the measurement of low electrophoretic mobilities Such mobilities can arise in a variety of situations but particularly when a dispersion of particles in media of low dielectric constant or high viscosity must be cha
6. an experienced user go to Setup Instrument Parameters and check that Auto has been selected for voltage and frequency Normally leave the default settings of sine wave and Autotracking unchanged You may now begin the measurement by clicking the Start button The instrument will first measure the conductance then adjust the laser beam intensity passing through the sample to optimize the sample s count rate also referred to as the scattered light signal When data collection begins you will see the cycles counter increasing and mobility values will appear in the upper portion of the main screen When the run is complete number of cycles completed or relative residual achieved the results will appear in the tabulation chart The next run then starts When the designated set is complete the mean values for the measured quantities are calculated and displayed Also the combined value of the total data recorded is summed together In most instances if the mean and combined values for mobility and zeta potential agree to about the standard error of the measurement it is taken to be satisfactory The residual of the combined value will usually be less than any of the individual runs These criteria can be taken to indicate a reliable measurement If a trend of increasing or decreasing mobility 1s seen it is probable that thermal equilibrium has not yet been reached and the measurement should be repeated Ordinarily we expect t
7. cing the voltage and frequency in order to compensate With such samples it is a good idea to inspect the electrodes frequently perhaps making 3 single runs of 10 cycles then changing the sample and cleaning the electrodes as the passage of high current can lead to electrode blackening and the production of bubbles If this happens excessively it may be worth using manual settings of 3 volts and 20 Hz to reduce polarization effects Also extending the cycles to 20 or even 30 will assist but be prepared to change the sample after each run if necessary I 4 RESULTS INTERPRETATION Listed below are important quantities determined by the PALS Although the following terms are defined in depth in the glossary portion of the manual a basic knowledge of these quantities will assist the user in data interpretation The quantities are Electrophoretic mobility microns second volt cm Zeta potential millivolts mV e Relative residual a dimensionless number characterizing the fitted data Il 4a MORE ADVANCED INTERPRETATION When performing PALS analysis there are a number of indicators that reveal valueable information regarding the nature of a sample especially if the sample is unknown Two of these are the width of the phase graph and the sample s measured conductance Width is determined directly from a sample s mobility The mobility is measured from the amplitude weighted phase difference function AWPD The square of the m
8. cy eventually gives rise to a change in phase between the signals This phase change Q t can be related to the Doppler shift and hence the electrophoretic mobility in the following way Measure a phase Q t in the scattered light field at scattering vector q which changes due the movement of particles with mobility u in an electric field E t Given that the scattered light has an amplitude of A QA Q 0 4 gu Eat For the case of a sinusoidal field the integral gives the following result Qc O 0 4 au cos d costat d o 5 where o is the frequency of the applied electric field The ZetaPALS hardware incorporates a digital signal processor which can extract Q t directly from the Doppler signal The other quantities are known or controlled so the mobility can be determined and an estimate of zeta potential by applying equation 1 in either the Smoluchowsky f ka 1 5 or H ckel f ka 1 limits One of the problems with microelectrophoresis is the presence of small thermal drifts in the sample These manifest themselves as a collective velocity component added to the electrophoretic motion Over short periods of time this component may be taken to be constant but unknown If we add the effect of a constant velocity V we obtain equation 4 QC Q0 4 au cos amp cosCot o V 4 The effect of the constant velocity is to add a slope to the phase signal This can be removed experimentally by adjust
9. d Most nonaqueous media with the exception of alcohol require H ckel If in doubt contact Brookhaven for advice Note that you also set the temperature for the measurement on this screen As the viscosity and maybe the dielectric constant are quoted at specific values of temperature be careful that you use an appropriate one The database is set up for automatic calculation as a function of temperature for the aqueous case and it is suggested that this be used when possible Note that the suspensions used are dilute and the pure liquid values generally apply For dispersions in ordinary acids and alkalis and inorganic salts use the pure liquid water value automatically calculated when Aqueous is selected Note that under Run Time the number of cycles can be set by selecting Manual or Automatic In the former case simply enter the number required typically 10 20 The number of cycles and runs is not critical but at least 3 runs of 10 cycles should be performed so that an assessment of reproducibility can be made In the Automatic mode the measurement will continue until the relative residual calculated for the data is less than the value entered here A typical value would be 0 01 Close the dialogue box The values selected will be stored and used until another entry is made and saved I 2 The Instrument Parameters Dialogue
10. express written permission of Brookhaven Instruments Corporation Brookhaven Corporate Park 750 Blue Point Road Holtsville New York 11742 USA iii WARRANTY Brookhaven Instruments Corporation hereinafter known as BIC warrants that the product is free from defective material and workmanship Under the terms of the warranty BIC agrees to correct by repair or at BIC s election by replacement any parts which prove to be defective through no fault of the user This warranty is limited to the original purchaser of the product The product shall be shipped freight prepaid and insured in full or delivered to a facility authorized by BIC to render the service provided thereunder in either the original package or in a similar package affording an equal degree of protection The purchaser must contact BIC for instruction prior to returning the product The product shall not have been previously altered repaired or serviced by anyone other than a service facility authorized by BIC The product shall not have been subjected to accident misuse or abuse or operated contrary to the instructions contained in the instruction manual or manuals BIC shall not be liable for direct indirect incidental consequential or other type of damages resulting from use of this product other than the liability stated above These warranties are in lieu of all other warranties expressed or implied including but not limited to the implied warranties of
11. f moving particles that scatter laser light PALS is interesting because it is much more sensitive than conventional ELS It has been shown that using PALS one can measure velocities that are as little as 1000 times smaller In the BIC ZetaPALS the benefits of PALS are applied to the measurement of electrophoretic mobility EPM and the calculation of zeta potential The velocity that is measured here is the product of the EPM and the electric field The ordinary ZetaPlus measures the EPM by conventional ELS The ELS technique can measure samples of EPM greater than about 0 2 microns second volt cm and greater and salt concentrations as high as about 20 mM ofa 1 1 electrolyte like NaNO3 Lower EPMs are found in media of low dielectric constant high viscosity or higher salt molarity or where the zeta potential itself is low close to the IEP for example The ZetaPALS is useful in such cases It too has the ability to perform measurements on samples that are within the capability of the ZetaPlus although the greater sensitivity leads to more accurate measurements in a given experiment duration Externally the ZetaPALS is identical to the ZetaPlus Internally extra electronic modules are added that provide the phase analysis and field drive functions In addition an interlock is provided that prevents the application of high voltage fields when the sample door is open The instruments range is as follows lowrange 0 28 V cm 1 to 250 Hz s
12. functions you will use to save delete recall print or archive your data from a specified folder These folders can be created or deleted It is suggested that each user experiment have their own folder This will assist in keeping data in an orderly manner Data can also be archived and restored from backup disks Report files containing summaries of measured and calculated quantities can also be created and saved as text Each file contains a set of runs Multiple files can be selected and compared using the Graph menu main menu bar to plot an SPC statistical process control chart or to make two variable graphs can be made These tools are often useful for example if you make runs at a number of different pH values and wish to plot mobility or zeta potential against pH The isoelectric point IEP is defined as the pH at which the zeta potential mobility I zero Not all systems has an IEP even in water and certainly the IEP has no meaning in any liquid where pH is not well defined IV Theory The reason for performing a phase analysis measurement may be understood by examining the relationship shown as equation 1 This is the relationship between mobility and zeta potential as a function of the parameters of the suspending liquid the dielectric constant g and the viscosity n The factor f ka is of the order unity For a discussion of f ka see the appendices to the ZetaPlus instruction manual w 6 f ka 1 7 u is electrop
13. he software by clicking on the ZetaPALS icon Before starting a measurement click Parameters to bring up the dialogue in which these values can be viewed and altered Enter a description or sample title in the text boxes provided Particularly check that the sample s suspending liquid has been correctly identified under Liquid Clicking the down arrow to the right of the Liquid text entry box will display a list of common liquids for which information has been stored in the database Selecting the liquid you are using will automatically set the parameter values for viscosity dielectric constant and refractive index Note that these values are used in the calculation of zeta potential from mobility and they are also used by the automatic mode s field setting to select an appropriate applied electric field If you are simply interested in the electrophoretic mobility the correct values are not necessary If the liquid you wish to use is not present in the data base you may manually enter the viscosity and dielectric constant values into the correct fields by selecting Unspecified You may add other values to the database yourself by editing the file PALSDB TXT using Notepad If you plan to do particle sizing also get the value for refractive index Use the ID and notes fields so that the sample run can be correctly identified later Take care to also select either Smoluchowsky or H ckel for the calculation metho
14. his go to the Setup Instrument Parameters dialogue click the voltage selection to User and enter 200 You may also reduce the frequency so the field is established for a longer time period this will also assist in determining very low mobilities Click the frequency button to User and enter 2 Hz the lowest recommended operating frequency You may also increase the number of runs by setting runtime to Manual Accumulation time is determined by the number of cycles the voltage is applied A cycle consists of a burst of two field periods If the field frequency is 10 Hz this takes 0 2 seconds Typically about 10 cycles are enough for a single measurement of a good sample Very low mobilities or unnedessarily low fields and high frequencies can lead to small signals require more cycles The limit is 500 cycles though in Automatic mode the limit is 100 cycles Once in the Automatic mode after performing 5 cycles additional ones are added until the Relative Residual a measure of data fit quality falls to less than a target value typically 0 1 A poor fit will generally have a residual gt 1 0 1 for a good fit For ZetaPALS ver 1 22 and higher the default settings are 5 Volts and 5 Hz default settings for unknown samples The manual settings may assist in achieving better reproducibility for samples such as those in high salt of conductance gt 10 000 uS The automatic field settings deal with such cases by redu
15. horetic mobility It is often expressed in practical units of micron second Volt cm which for typical colloids in polar liquids like water is typically in the range of 1 to 5 The correct SI formulation of meters Volt second gives these values scaled by a factor of 10 G is zeta potential usually expressed in millivolts mV Table 1 Ratios of n For A Few Common Liquids Ratio To Water Ethylene Glycol Oleic Acid 0 095 0 001 If we now consider a particle system in which the zeta potential is constant despite the fact that very different liquids see Table 1 are used to make the dispersion we see that the mobility that will arise can be much smaller than the value when water is used In general dispersions in organic liquids may have mobilities lower by several factors of 10 than aqueous based systems Low mobilities can also occur in dispersions of high salt content in higher viscosity liquids or close to an isoelectric point Conventional laser Doppler electrophoresis is limited to mobilities of the order of 0 5 x 10 m V s and cannot readily be used to measure such low mobilities due to limits of frequency resolution and background drifts in the sample due to thermal fluctuations However direct frequency analysis is not the only way of measuring the Doppler shift If the Doppler signal is compared to a reference signal corresponding to stationary particles using phase quadrature any small change in frequen
16. ine or square wave high range 29 555 V cm same timing characteristics Measurements using many nonaqueous media require the use of glass or quartz cells and the Kevlar supported electrodes The cells are 1cm square however be careful when using non BIC supplied cuvettes as the exact dimensions vary between suppliers For most aqueous based samples disposable acrylic cells and Plexiglas also known as Perspex or Lucite based electrodes may be used II Making A Measurement Sample preparation is undoubtedly the most important consideration in making use of the ZetaPALS A good dispersion at an appropriate concentration in the chosen medium must be presented to the instrument The cell and electrodes must be clean and appropriate for the chosen medium Guidance on sample preparation is given in section VII of the ZetaPlus manual Exactly the same considerations apply to the ZetaPALS Make sure that you are aware of and adopt the proper handling precautions necessary for the sample and medium you are using Many nonaqueous media should be handled in a fume hood solvents such as concentrated acids and alkalis can be corrosive Disperse your sample in the chosen media and select a cell and electrode combination that is suitable for the medium A typical concentration results in a slightly turbid sample The instrument automatically adjusts the light intensity to cope with a wide range of concentrations so precision is not required Place abo
17. ing the reference frequency appropriately This is known as Autotracking and improves the precision of the system Autotracking is a useful feature that minimizes convection effects due to sample heating and other parasitic flows by tuning the phase analysis to remove any collective velocity This shows up as a slope superimposed on the oscillating phase AWPD function It should be left selected checked in normal circumstances V Glossary The most important words and terms you will find when using the ZetaPALS are listed and briefly described in this section These are terms that are specific to the ZetaPALS in most cases Familiarity with the operation of Microsoft Windows is assumed so terms like command button menu item dialogue box are used without further explanation Auto In the Parameters dialogue this is associated with automatically setting the run time or number of cycles of each run In Setup Instrument Parameters Auto buttons instruct the instrument to choose the appropriate values for voltage and frequency based on the sample characteristics Autosave A Check box in the parameters dialogue If checked results will automatically be saved in the current folder in the file database Autotracking A method by which the ZetaPALS improves the precision by continually adjusting the reference signal to remove the effect of thermal drifts in the sample Cell The measurement cell in
18. justing the voltage and frequency It is reported in microSiemens uS Typical values for aqueous based samples will range from 30 uS to 30 000 uS Many solvents will show values of 1 or less 1 uS is the maximum precision for this quantity in the ZetaPALS Conductance can also be measured by the clicking Conductance on the main menu without then proceeding to a complete measurement of electrophoretic mobility Conductance must not be confused with conductivity conductance does not include a cell constant A measurement that has been stopped can be continued If the original total of runs and cycles is complete the number of ions can be increased and the measurement continued A cycle consists of the application of the voltage to the sample and the recording of the change A run may consist of any number of cycles up to a max of 500 though 10 50 are typical values for this The reason that more than one cycle is needed is that except for very large mobilities a single application of the voltage does not produce a sufficient signal to noise ratio and hence a reliable value for mobility The number of cycles in a run is set in the Parameters dialogue If Auto is selected for Run Time on the parameters dialogue cycles will be collected and added until the relative residual is less than the target A value for the dielectric constant of the medium in which the sample is dispersed is needed in the calculation of
19. merchantability or fitness for a particular purpose The BIC warranty extends for a period of 90 days This period from the date of receipt of the equipment and it applies only to the original purchaser The warranty period is automatically extended to 1 year except as noted below from the date of receipt of the equipment provided all invoices for said equipment including transportation if applicable are paid within 30 days after receipt of invoice The BIC warranty extends for a period not exceeding the warranty period of the Original Equipment Manufacturer where applicable The typical warranty period on printers and computer peripherals is 90 days Please contact BIC for copies of applicable OEM warranties This warranty does not cover replacement of fiber optic probes or connectors damaged by dropping or from corrosion caused by lack of cleaning Please refer to the relevant section for information on caring for your ZetaPALS and its accessories iv Software License Agreement Carefully read the following terms before using the software provided with this system Use of the software indicates your acceptance of these terms If you do not agree with the terms promptly return the software and system BIC refers to Brookhaven Instruments Corporation Terms l In purchasing this software you are granted a nonexclusive license to use the software product on one computer 2 BIC retains title to and ownership of the software pr
20. n on the screen after a measurement Before making another run clear the previous one by clicking on Clear If the data has not yet been saved the user will be warned at this point IIL 3 More Advanced Measurements The Automatic mode settings for applied voltage frequency and runtime are intended to deal with most samples but you may need to consider changing these parameters for some situations The instrument utilizes the values for the dielectric constant and the measured conductance in deciding if it is appropriate to apply a high or low voltage in order to establish a high or low electric field A high field is appropriate when the ratio of dielectric constant to viscosity for the suspending medium is 20 see Table 1 in the Theory Section of this manual This ratio predicts 1f the mobility is low A high field is only applied if the sample s conductance is less than 5 uS This threshold can be adjusted if necessary but seek advice before attempting to do this If the user has selected a value for the dielectric constant and viscosity that indicate expectations of low mobility the instrument will select the high voltage range defaulting to 100 V yielding a field of 278 V cm Having measured such a sample if the mobility is very low in absolute magnitude lt 05 you may wish to establish the highest field possible which corresponds to an applied voltage of 200 V across the electrode gap of 3 6 mm 600 V cm To do t
21. o obtain reproducibility of 5 or better on a well dispersed sample If a large number of runs 75 have been performed you may wish to exclude the highest and lowest values and recalculate the mean and combined results This can be done by clicking on the run or runs in the tabulated list The runs removed are greyed out Clicking on a greyed out run will restore it Detailed reports are saved in the database folder selected by the user automatically done if Auto Save is checked in Parameters If you wish to save it somewhere else as well File Save As gives you the opportunity to select a different folder and also amend the sample ID Entering a file name ending in pal eg mysample pal runl pal This is the standard file extension for measurements analyzed by PALS Data can later be reloaded by clicking on File Database and selecting the folder and file name required If the data is to be re analyzed this would usually be required if the values for dielectric constant or viscosity had been wrongly set go to the Parameter dialog and alter the values and title if required Click OK and the data records in memory will be re analyzed with the new values If the new results are to be saved they should be Saved into a new file Results can be printed using File Print possibly using File Printer Setup first to establish a printer selection A standard page format can hold the information see
22. obility is measured by the amplitude weighted phase structure function AWPS If the population of particles studied has a spread in mobilities the square root of the AWPS mobility will be larger and the difference measures the standard deviation of that spread The width quoted here is defined as Mobility AWPS Mobility AWPD A width less than 0 1 indicates an essentially narrow distribution of mobility The AWPS is more sensitive to outliers and measurement noise Therefore the value for width is only calculated for the combined data set rather than each run The conductance of the sample is displayed in the Measurement Parameters table In the case of aqueous samples and other polar liquids conductance is a useful measure of the concentration of the free salt ions if their concentration is not known in advance With the current electrode geometry a 1mM 1 1 electrolyte yields a conductance in the range of 300 to 330 uS The relationship between concentration and conductance is very roughly linear up to 10 to 20 mM but then the conductance rises less rapidly HI Data Handling In this section we outline the facilities for data handling This will give the user an idea of what is possible and where to find it The controls used are standard Windows features so detailed instructions on how to use them are not given The most important data handling functions are collected under the File menu Under Database are the
23. oduct The software product may not be modified without the written consent of BIC 3 Duplication of the software product for any purpose other than backup protection including duplication for any commercial use is a violation of the copyright laws of the United States of America and of other countries Information produced by using BIC software and it s manual including the resulting displays reports and plots are believed to be accurate and reliable However no responsibility is assumed by Brookhaven Instruments Corporation for any changes errors or omissions Table of Contents I Introduction ner taber idus bnt ea SER RI I 1 Il Making a Measurement essere II 1 The Paramelers Dialoge erede ipte aeg onte II 1 The Instrument Parameters Dialogue sesssss II 3 More Advanced Measurements sese II 5 Results Inte rpteldtigfis s soie cata ota ta tet GU dotis II 6 II Data Handling ies mc spe pleno rebote e epe predios ane III 1 IV Theon co petu hie ee Gee eet eae aee IV 1 I INTRODUCTION This document describes the Brookhaven Instruments Corporation ZetaPALS It is intended to supplement the user manual supplied with the B C ZetaPlus covering those aspects that are specific to PALS operation PALS is an acronym for Phase Analysis Light Scattering this is an extension of laser electrophoretic light scattering ELS ELS is used to the measurement of the velocity o
24. racterized Another case is that of a dispersion in a highly conductive medium when the high concentration of ions leads to strong electrostatic shielding of the particles and limits the electric field that may be applied Yet another case is when the mobility is low simply because the zeta potential itself is very low close to an isoelectric point for example The additional components making up a ZetaPALS unit are 1 PALS plug in electronic card This plugs into the CPU bus next to the standard ZetaPlus card and connects to it via a 40 way ribbon cable which also extends to the power distribution board 2 PALS HV high voltage module Mounted beneath the optics table 3 Cables 4 PALS Zeta Potential Analyzer Software This requires Windows 3 X or higher and 8 Mb of RAM 5 This manual Optionally you may have purchased the ceramic or Kevlar supported solvent resistant electrodes The units above will have been factory fitted unless an in field upgrade has been agreed upon The parts should only be fitted by Brookhaven personnel or an appointed representative ii Copyright Notice Copyright 1999 by Brookhaven Instruments Corporation All Rights Reserved Worldwide No part of this manual may be reproduced transmitted transcribed stored in a retrieval system or translated into any human or computer language in any form or by any means electronic mechanical optical chemical manual or otherwise without the
25. s of the sample dispersion would maintain in an electric field of 1V cm Also referred to simply as mobility The electric field is an AC waveform that switches direction at a rate set by the frequency control Typical values are 2 20 Hz The lower the frequency the further the particles travel before they reverse direction so the larger the phase signal becomes Typically this will be selected automatically by the software if the Auto button on the Setup Instrument Parameters dialogue is enabled The Graphs menu item allows the user to produce two variable plots e g mobility versus pH and the statistical process control or SPC plot which is essentially mobility or zeta potential vs time One limit for calculating zeta potential from the measured mobility using the dielectric constant and viscosity of the suspending fluid the H ckel equation applies to non aqueous based systems or very small particles See the discussion in section IV of the ZetaPlus manual The parameters dialogue has a database of different liquids to provide parameters such as viscosity dielectric constant and refractive index The user can specify which quantities are stored in a simple text summary of all that the instrument has measured since the log file was reset This file normally c bicw palsw data logfile txt can be printed viewed or plotted using standard software or locally produced programs Setting for frequency
26. sidual are analyzed statistically to calculate the mean and standard error of the mean using the normal definitions of these quantities Standard error equals the standard deviation divided by the square root of the number of measurements Start collecting data Initially the sample conductance is checked then the strength of the scattering and reference signal The intensity of the laser beam that produces the scattering signal is adjusted to an optimal value if possible The reference beam should be between 2 and 20 times stronger than the scattering signal ideally Stop collecting data During data collection as each cycle is collected it is added to the previous total and the data reanalysed If Runtime has been set as Auto then the relative residual must be less than the target value before the run stops The number of cycles collected must also be gt 5 and lt 100 The set temperature that the instrument regulates Since viscosity and other parameters vary with temperature it is important that the sample temperature is stabilized to better than 0 5 C Changed under Parameters dialogue Buttons on the Setup Instrument Parameters dialogue that enable the user to enter values for the voltage and frequency The voltage across the electrodes that generates the electric field Ranges from 0 to 200 volts Typically 5 V max 10 V for aqueous samples 100 Vor more for non polar liquids The
27. t and is saved in the database and optionally in the log and report files The current measurement on the screen is sent to the system printer The intensity of the reference beam expressed in 1000 s of photon detections second The reference beam is optically mixed with the scattered light from the sample to produce the total optical signal on which the phase analysis is performed In effect the reference beam provides a signal corresponding to fixed speed virtual particles Moving particles in the sample produce a relative change in optical phase that is synchronous with the driving electric field and this synchronous movement can be distinguished from random thermal and other movements by the PALS processing Refractive Index Relative Residual Report File Runs Sample ID Smoluchowsky Standard Error A value for the suspending liquid can be entered in the parameters dialogue It is also recalled from the Liquid database It is used in calculating the q vector and true scattering angle in the sample medium The phase function consisting of discrete values of phase plotted at regular measured intervals along a time axis is fitted to the experimentally measured phase points in order to extract the mobility of the scattering sample The sum of squares of the difference between measured and fitted data divided by the total amplitude of the fitted data represents the quality of the fit and is therefore defined here as
28. the relative residual A small relative residual of the order of 0 01 represents a good fit and a reliable result Large values of residual imply that the experimental data is noisy and longer measurements more cycles or a larger voltage or lower frequency may be necessary The user can select individual runs from the database and include a selection of the measured quantities and parameters in simple text file suitable for import into spreadsheets and word processor documents When Start is clicked the instrument performs a measurement consisting of a number of runs each divided into a number of cycles The main reason for dividing a measurement into several runs is to demonstrate the reproducibility of the measurement All the runs can be added together and analyzed as if they were a single run to obtain a single result Individual runs can be excluded by clicking on the values given in the tabulation on the main display A text string to identify the sample currently in the instrument and to use as a useful tag for later identifying the data One limit for calculating zeta potential from the measured mobility using the dielectric constant and viscosity of the suspending fluid the Smoluchowsky equation usually applies to aqueous based systems with large particles and at least a moderate salt concentration See the discussion in section IV of the ZetaPlus manual The tabulated quantities mobility zeta potential relative re
29. ut 1 5 ml in the cuvette carefully insert the electrodes catching any spillage Open the trap door connect the lead to the top of the electrode and place the cuvette in the holder with the lead going to the right as you face the front of the instrument II 1 The Parameters Dialogue Brookhaven Instruments PALS Zeta Potential Analyzer nl xl 18 x B5 coc X 2 Unkn sanpie 1 Operator ID Unknown perator Notes 100 Jeet 1536 rire j Runs B omg Temperature deg C Run Time Liquid Aqueous Ral Bun Manual 7 E rs 1 rN pena Gr nown Ret inde C Automatic A pou ielectric nown Target 1 0000e 01 Constant mun sann D JS Useri 0 00 E Mean User2 0 00 Concentration mg mL Zeta Potential Model A _ Particle Size nm E Smoluchowski C H ckel C f Auto Save Results V Li OK Cancel X B z gt Page 5 Sec 1 5 10 At Stem tn 15 Cod 1 1640 REC MAK EXT OVR WPH Start Microsoft Office ZK Microsoft Word ZPALSM IE Brookhaven Instrume QE 1641 Load t
30. which the sample dispersion is placed Into this the electrodes are inserted About 1 5 ml of dispersion is needed Cells can be plastic or glass quartz The latter are needed for some aggressive solvents in which case Kevlar or ceramic electrode supports must also be used Cell Holder Opening the sliding hatch reveals the square opening into which the cell is placed The electrode connection lead is also just inside the hatch and should be attached when the cell is inserted The cell is oriented in the holder with the connector facing the right side of the instrument Clear Remove the current data from memory to allow a new measurement to start Combined A measurement of several runs has all the data unless specifically excluded by the user added together to produce a single result This is the combined run Individual or combined data can be graphed in the small or Zoomed graph Concentration A field in the Parameters dialogue where the user can enter a value for concentration in mg ml of the sample This is not measured by the instrument or required in the calculation of results but may be used as a dependant plotting variable in the two variable plots Conductance Continue Cycle s Dielectric Constant Electric Field The conductance of the sample is determined at the start of a measurement to assist in optimising the instrument settings and in calculating the characteristics of electric field to use by ad
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