ISO 13319:2007
(Main)Determination of particle size distributions — Electrical sensing zone method
Determination of particle size distributions — Electrical sensing zone method
ISO 13319:2007 gives guidance on the measurement of the size distribution of particles dispersed in an electrolyte solution using the electrical sensing zone method. The method measures pulse heights and their relationship to particle volumes or diameters, and it reports in the range from approximately 0,4 micrometres to approximately 1 200 micrometres. It does not address the specific requirements of the measurement of specific materials. However, guidance on the measurements of conducting materials such as porous materials and metal powders is given.
Détermination des répartitions granulométriques — Méthode de la zone de détection électrique
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 13319
Second edition
2007-07-01
Corrected version
2007-09-01
Determination of particle size
distributions — Electrical sensing zone
method
Détermination des répartitions granulométriques — Méthode de la zone
de détection électrique
Reference number
ISO 13319:2007(E)
©
ISO 2007
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ISO 13319:2007(E)
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ISO 13319:2007(E)
Contents Page
Foreword. iv
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols .2
5 Principle.3
6 General operation .4
6.1 Response.4
6.2 Size limits .4
6.3 Effect of coincident particle passage .4
6.4 Dead time.5
7 Repeatability of counts .6
8 Operational procedures .6
8.1 Instrument location.6
8.2 Linearity of the aperture/amplifier system .6
8.3 Linearity of the counting system .7
8.4 Choice of electrolyte solution .7
8.5 Preparation of electrolyte solution .7
8.6 Recommended sampling, sample splitting, sample preparation and dispersion .8
8.7 Choice of aperture(s) and analysis volume(s).9
8.8 Clearing an aperture blockage .10
8.9 Stability of dispersion .10
8.10 Calibration .11
9 Analysis .11
10 Calculation of results .12
11 Instrument qualification .12
11.1 General.12
11.2 Report .12
Annex A (informative) Calibration for the measurement of porous and conductive particles .13
Annex B (informative) Technique using two (or more) apertures.16
Annex C (informative) Chi-squared test of the correctness of instrument operation or sample
preparation .18
Annex D (informative) Table of materials and electrolyte solutions.20
Annex E (informative) Mass integration method.30
Annex F (informative) Calibration and control of frequently used apertures .36
Bibliography .37
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ISO 13319:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 13319 was prepared by Technical Committee ISO/TC 24, Sieves, sieving, and other sizing methods,
Subcommittee SC 4, Sizing by methods other than sieving.
This second edition cancels and replaces the first edition (ISO 13319:2000), which has been technically
revised.
This corrected version of ISO 13319:2007 incorporates the following corrections:
[13] [11], [12]
— in 8.10.1, paragraph 2, line 2, “ ” has been deleted, and “ ” inserted;
— in E.2.4, the factor “K ” has been added to the right hand side of Equation (E.1).
d a
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INTERNATIONAL STANDARD ISO 13319:2007(E)
Determination of particle size distributions — Electrical sensing
zone method
1 Scope
This International Standard gives guidance on the measurement of the size distribution of particles dispersed
in an electrolyte solution using the electrical sensing zone method. The method measures pulse heights and
their relationship to particle volumes or diameters, and it reports in the range from approximately 0,4 µm to
approximately 1 200 µm. It does not address the specific requirements of the measurement of specific
materials. However, guidance on the measurements of conducting materials such as porous materials and
metal powders is given.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 787-10, General methods of test for pigments and extenders — Part 10: Determination of density —
Pyknometer method
ISO 9276-2:2001, Representation of results of particle size analysis — Part 2: Calculation of average
particle sizes/diameters and moments from particle size distributions
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
dead time
time during which the electronics are not able to detect particles due to the signal processing of a previous
pulse
3.2
aperture
small-diameter hole through which suspension is drawn
3.3
sensing zone
volume of electrolyte solution within, and around, the aperture in which a particle is detected
3.3
sampling volume
volume of suspension that is analysed
3.4
channel
size interval
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ISO 13319:2007(E)
3.5
envelope size
external size of a particle as seen in a microscope
3.6
envelope volume
volume of the envelope given by the three-dimensional boundary of the particle to the surrounding medium
4 Symbols
For the purposes of this document, the following symbols apply.
A amplitude of the most frequent pulse
p
A amplitude of the electrical pulse generated by an arbitrary particle
x
d modal diameter of a certified particle size reference material
p
d mean particle diameter of a size interval or channel
d particle diameter at the lower boundary of a size interval or channel
L
d particle diameter at the upper boundary of a size interval or channel
U
D aperture diameter
K calibration constant of diameter
d
K mean calibration constant of diameter
d
K arbitrary calibration constant of diameter
d a
m mass of sample
∆N number of counts in a size interval i
i
V volume of electrolyte solution in which a mass, m, is dispersed
T
V analysis volume
m
V arithmetic mean volume for a particular size interval i
i
V volume of the particle obtained from a threshold or channel boundary
i
x diameter of a sphere with volume equivalent to that of the particle
xx,,x values of x corresponding to the 50 %, 10 % and 90 % points of the cumulative percent
50 10 90
undersize distributions
ρ mass of the particles per volume of the electrolyte displaced
σ standard deviation of mean calibration constant
K
d
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ISO 13319:2007(E)
5 Principle
A dilute suspension of particles dispersed in an electrolyte solution is stirred to provide a homogeneous
mixture and is drawn through an aperture in an insulating wall. A current applied across two electrodes,
placed on each side of the aperture, enables the particles to be sensed by the electrical impedance changes
as they pass through the aperture. The particle pulses thus generated are amplified and counted, and the
pulse height is analysed. After employing a calibration factor, a distribution of the number of particles against
the volume-equivalent diameter is obtained. This distribution is usually converted to percentage by mass
versus particle size, where the size parameter is expressed as the diameter of a sphere of volume and density
equal to that of the particle. See Figure 1.
Key
1 volumetric metering device 7 output
2 valve 8 stirred suspension of particles in electrolyte solution
3 pulse amplifier 9 aperture
4 oscilloscope pulse display 10 counter start/stop triggered by the volumetric device
5 counting circuit 11 electrodes
6 pulse-height analyser
Figure 1 — Diagram illustrating the principle of the electrical sensing zone method
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ISO 13319:2007(E)
6 General operation
6.1 Response
The response (i.e. the electrical pulse generated when a particle passes through the aperture) has been found
both experimentally and theoretically to be proportional to the particle volume if the particles are
[1]-[3]
spherical .This has also been shown to be true for particles of other shapes; however, the constant of
[4]
proportionality (i.e. the instrument’s calibration constant) may be different . In general, particles should have
a low conductivity with respect to the electrolyte solution, but particles with high conductivity can be measured
[5] [6] [7], [8]
e.g. metals , carbon , silicon and many types of cells and organisms, such as blood cells . For porous
[9], [10]
particles, the response may vary with the porosity . Recommendations for the measurement of
conducting particles and porous particles are given in Annex A.
As the response is proportional to the volume of particles, the pulse amplitude provides a relative scale of
particle volumes. By calibration, this scale may be converted to spherical diameter. The calibration constant
based on diameter may be calculated by Equation (1):
d
p
K = (1)
d
3
A
p
The size, x, of any particle can be calculated by Equation (2):
3
xK=⋅ A (2)
dx
6.2 Size limits
The lower size limit of the electrical sensing zone method is generally considered to be restricted only by
thermal and electronic noise. It is normally stated to be about 0,6 µm but, under favourable conditions, 0,4 µm
is possible. There is no theoretical upper size limit, and for particles having a density similar to that of the
electrolyte solution, the largest aperture available (normally 2 000 µm) may be used. The practical upper size
limit is about 1 200 µm, limited by particle density. In order to increase the possibility of keeping the particles
in homogeneous suspension, the viscosity and the density of the electrolyte solution may be increased, for
example by addition of glycerol or sucrose. The homogeneity may be checked by repeated analyses at a
range of stirrer speeds. The results of this should be compared to establish the lowest speed at which
recovery of the largest particles is maintained.
The size range for a single aperture is related to the aperture diameter, D. The response has been found to
depend linearly in volume on D, within about 5 % under optimum conditions, over a range from 0,015 D to
0,8 D (i.e. 1,5 µm to 80 µm for a 100 µm aperture) although the aperture may become prone to blockage at
particle sizes below the maximum size where the particles are non-spherical. In practice, the limitation of
thermal and electronic noise and the physical limitation of non-spherical particles passing through the aperture
usually restricts the operating range to 2 % to 60 % of the aperture size. This size range can be extended by
using two or more apertures (see Annex B). In practice, this procedure can be avoided by the careful selection
of the diameter of one aperture, to achieve an acceptable range.
6.3 Effect of coincident particle passage
Ideal data would result if particles traversed the aperture singly, when each particle would produce a single
pulse. When two or more particles arrive in the sensing zone together, the resulting pulse will be complex.
Either a single large pulse will be obtained, resulting in a loss of count and effectively registering a single
larger particle, or the count will be correct but the reported size of each will be increased, or some particles will
not be counted. These effects will distort the size distribution obtained but can be minimized by using low
concentrations. Table 1 shows counts per millilitre for the coincidence probability to be 5 %.
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ISO 13319:2007(E)
Table 1 — Counts for 5 % coincidence probability for typical aperture diameters
Aperture diameter Analysis Count for 5 %
a b
D
volume coincidence
V N
m
µm
ml
1 000 2 80
560 2 455
400 2 1 250
280 2 3 645
200 2 10 000
140 2 29 150
100 0,5 20 000
70 0,5 58 500
50 0,05 16 000
30 0,05 74 000
20 0,05 250 000
a
For other sampling volumes, use pro rata values.
10
41× 0 V
m
b
Calculated using the equation N =
3
D
Counts per millilitre should always be less than these quoted values. Since particle size distributions should
not be a function of concentration, the effect of coincidence can be tested by obtaining a distribution at one
concentration and comparing it with that obtained when the concentration is halved. In such a test, repeat
such dilutions until the reduction in count in a channel with the largest number decreases in proportion to the
dilution. This should always be done when analysing very narrow size distributions, as this is where the effect
of coincidence is most noticeable.
6.4 Dead time
In instruments using digital pulse processing routines, to analyse the signal it is scanned at high frequency.
Information on pulse parameters, such as maximum pulse height, maximum pulse width, mid-pulse height,
mid-pulse width and pulse area, is stored for subsequent analysis. In this case, analog-to-digital conversion of
the pulse with storage of the size value for the pulse is not performed in real time and dead time losses are
avoided.
In instruments in which pulse-height analysis routines are used in real time to process the data, it is possible
that the analyser may not count particles for a given time after receiving a pulse, since it takes a finite time to
process each pulse. Dead time is not a function of pulse height. Therefore, the loss will be proportional to the
counts in each channel and will not affect the size distribution.
To minimize the effect of dead time, the analyser should be used with the lower threshold set to exclude
thermal and electronic noise, as indicated at A in Figure 2. Additionally, the concentration of particles should
be maintained below 5 % coincidence levels.
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ISO 13319:2007(E)
Key
X channels
Y counts
NOTE Counts at channels below A are noise counts. True particle counts are at the higher channels.
Figure 2 — Typical results
7 Repeatability of counts
In a correctly performed analysis, the number of counts in a size interval is a random variable which follows a
Poisson distribution. In this, the variance is equal to the expected (mean) value. This indicates that the
standard deviation of a number of counts, n, with mean, N, approximates to N . Both the variance and the
standard deviation can be used in statistical tests on the correctness of instrument operation or sample
preparation. The statistical chi-squared test can be used to test whether obtained data follow a Poisson
distribution or not. In this, the apparent and the theoretical variance for a given number of measurements and
a given probability are related. An example is given in Annex C. This statistical test can be performed on
single size intervals, groups of size intervals, or on the total particle count.
8 Operational procedures
8.1 Instrument location
The instrument should be sited in a clean environment that is free from electrical interference and vibration. If
organic solvents are to be used, the area should be well ventilated.
8.2 Linearity of the aperture/amplifier system
The linearity of the aperture/amplifier system can be checked using four materials consisting of near mono-
sized particles with a certified modal diameter. In a suitable electrolyte solution, the instrument is calibrated
with particles at about 0,3 D (see 8.10.2). Three further sizes of particles are then added to the suspension,
one of size of about 0,1 D, one of size of about 0,2, D and one of size about 0,5 D. The suspension is re-
analysed and the size corresponding to these extra peaks must correspond to the quoted size of the particles
to within 5 %.
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ISO 13319:2007(E)
8.3 Linearity of the counting system
The linearity of the counting system can be tested by obtaining three counts at an arbitrary concentration. The
concentration is then reduced and three further counts obtained. Coincidence-corrected counts shall be used.
The ratio of the mean of the counts should be the same as the dilution. If the agreement is not within 5 %, the
test should be repeated comparing the two lowest dilutions. Subsequent analyses should be carried out at the
dilution giving the best results.
8.4 Choice of electrolyte solution
8.4.1 General
An electrolyte solution should be selected in which the sample is stable. The electrolyte solution should not
dissolve, flocculate, react or, once a good dispersion is achieved, not change the state of dispersion of the
sample in the measurement time, typically up to five minutes. Particles insoluble in water can be analyzed in a
variety of aqueous electrolyte solutions. Particles soluble in water can often be analyzed in methanol or in Iso-
propanol. See Annex D for recommended electrolyte solutions. When using small apertures (20 µm, 30 µm
and 50 µm) or large apertures (400 µm, 560 µm, 1 000 µm and 2 000 µm), special care shall be taken due to
their particular characteristics.
8.4.2 Special considerations for small apertures (D u 50 µm)
Where possible, the electrolyte solution should consist of a 4 % sodium chloride solution or one of equivalent
conductivity. It should be membrane filtered twice at 0,2 µm.
8.4.3 Special considerations for large apertures (D W 400 µm)
To prevent turbulence that can cause noise signals due to fast flow through the aperture, the viscosity of the
electrolyte solution may be increased by the addition of glucose or glycerol; 10 % glycerol is recommended for
560 µm and 400 µm apertures, and 30 % glycerol for the 2 000 µm and 1 000 µm apertures.
8.5 Preparation of electrolyte solution
An electrolyte solution should be well filtered with a membrane filter for which the pore size is less than the
diameter of the smallest particle measured, as it is essential that its background count should be as low as
practicable. It should be noted that quoted values for filters are not absolute. Usually a mean pore size is
given. The width of the distribution of pores around this mean varies depending on filter type and
manufacturer. This will affect the choice of filter size used. All glassware and apparatus used should be pre-
rinsed with filtered electrolyte solution or other suitable liquids. Background counts should not exceed the
values given in Table 2 or yield a total equivalent volume in excess of 0,1 % of the total volume of particles
subsequently measured in the analysis volume.
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ISO 13319:2007(E)
Table 2 — Counts for background for typical aperture diameters
b
Aperture diameter Analysis
Background counts
a
D
volume
V
m
µm ml
1 000 2 2
560 2 10
400 2 25
280 2 75
200 2 200
140 2 600
100 0,5 400
70 0,5 1 200
50 0,05 300
30 0,05 1 500
20 0,05 5 000
a
For other analysis volumes, use pro rata values.
b
Suggested maximum counts.
8.6 Recommended sampling, sample splitting, sample preparation and dispersion
8.6.1 General
See ISO 14488 for guidance on the sampling and sample-splitting procedure. Select a dispersant and a
dispersion method from the recommendations in ISO 14887 or Annex D. The expertise of the laboratory
performing the analysis with respect to the sample under test may also be utilized.
8.6.2 Method 1: Using a paste
3
The sample should be subdivided to about 0,2 cm . If the sample is in the form of a powder, it should be
worked and kneaded gently with a flexible spatula with a few drops of suitable dispersant to break down
agglomerates. Transfer a mass of about 20 mg to 50 mg of the paste to a round-bottomed beaker and thin it
with dispersant, followed by a few drops of electrolyte solution. Almost fill the beaker with electrolyte solution
and place it in an ultrasonic bath with suitable power and frequency for 1 min, stirring occasionally. A stop
watch is recommended for a reproducible dispersion technique. One suitable design of beaker of 400 ml
capacity with a baffle is shown in Figure 3. If the sample is not required to be fully dispersed, it may be added
to the electrolyte solution and dispersant while stirring.
NOTE The use of high energy ultrasonic baths and probes, blenders and mixers can cause both agglomeration and
fracture of particles.
8.6.3 Method 2: Alternative method applicable to low-density particles of less than 50 µm
Subdivide the sample into portions of about 1 g. Mix a portion with the dispersant and add it to the electrolyte
solution. Then place the beaker (see Figure 3) containing the suspension in an ultrasonic bath for about 45 s.
After stirring this stock suspension well, withdraw 5 ml using a pipette and add to approximately 400 ml of
electrolyte solution. Place in the ultrasonic bath for a further 15 s. When using this method, it is important that
at least two samples are withdrawn from the stock suspension and analysed to ensure repeatability of the
aliquot sampling and the analysis.
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ISO 13319:2007(E)
Key
1 aperture tube
2 stirrer
3 baffle
Figure 3 — Example of a beaker with baffle and stirrer
8.6.4 Suspensions and emulsions
Suspensions and emulsions should be diluted by addition of smaller volumes of diluent to the emulsion, not by
addition of the emulsion to a larger volume of diluent. Dilution should be performed stepwise with mixing
performed at each step. To avoid “dilution shock”, oil-in-water emulsions may be initially diluted with distilled
or de-ionized water.
8.6.5 Verification of the dispersion
A small sample of the dispersion may be placed on a microscope slide and used to verify the degree of
dispersion and to estimate the size range of the particles using an optical microscope.
8.7 Choice of aperture(s) and analysis volume(s)
From the microscope examination (8.6.5), estimate the diameter of the largest particles present. Choose an
aperture for the size analysis such that the diameter of the largest particles to be analysed is less than
approximately 60 % of the diameter of the aperture, selected to reduce the possibility of blocking the aperture.
For particles that are spherical or nearly spherical, an aperture such that the diameter of the largest particles
is less than 80 % of the diameter of the aperture may be chosen. If there is a considerable proportion of
sample below the lower size limit of that aperture (1,5 % of its diameter), a second and possibly a third smaller
aperture will be needed (see Annex B). An alternative method to determine the amount of particles not
accounted for with a specific aperture is to perform a mass balance (see Annex E).
Select a suitable analysis volume with reference to Table 1 or select a suitable time of accumulation. It may be
necessary to analyse a number of analysis volumes or to accumulate for a long time to obtain an acceptable
precision, e.g. 50 000 particles will yield a precision (relative standard deviation) of 0,4 %. Counting fewer
particles will reduce the precision, but this may be necessary when using the larger apertures (see Clause 7
and Annex C).
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ISO 13319:2007(E)
8.8 Clearing an aperture blockage
Apertures below 100 µm in diameter may become blocked with extraneous particles, particularly if care is not
exercised in the clean handling, careful filtration and thorough rinsing of beakers and associated equipment. A
...
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