Beckman Coulter Multisizer 4, User Manual

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PN A51387A
B
xvi
Introduction
About the Multisizer 4
By using the very latest in digital pulse measurement techniques, an entire analysis (which may
consist of many thousands of particle pulses) can be stored either in memory or on disk for recall
and reprocessing without the need to re-run the sample. Each pulse is stored at maximum
resolution so that, for the first time, the genuine resolution of an analysis can be increased up to a
hundred-fold in real-time by narrowing the size range of interest, eliminating the need to re-run
the sample. The Convert Pulses to Size feature in the software allows measurements from the lowest
to the highest possible resolution to be made on just one pass of sample through the aperture.
Storing the individual values of pulse heights means that it is not necessary to predetermine the
number of size classes (also called “channels” or “size bins”) into which any size distribution can be
divided. This choice is at the discretion of the operator and can be chosen either before or after the
analysis or even changed during analysis. Any number of channels from 4 up to 400 may represent
a partial or full range of an aperture. A smaller number may improve the appearance of a size
distribution by reducing statistical scatter in the results, while details in the results may be
enhanced by increasing the number of size classes in regions of particular interest. A higher number
of channels provides more detail about the size of the particles. The advanced digital electronics
used in the Multisizer 4 allow the number of channels to be changed in real time without losing any
of the information acquired with other channel spacing.
Results can also be stored in a fully processed (abridged) form that conserves disk space. Although
in this form the raw pulse data is lost and cannot be re-analyzed at a different resolution, the
processed results still can be enlarged, or a region of interest selected, using the Zoom facility in the
software.
Both number data and size distributions are corrected by proprietary algorithms for the occurrence
of multiple particle passage (coincidence) in the aperture. An indicator provides real time particle
concentration in the analysis suspension. The Multisizer 4 software includes a pulse monitor
window that offers a guide to the electronic behavior of the aperture. The time base of this window
can be adjusted to show either pulse concentration or the shapes of individual pulses. Electronic
pulse editing facilities ensure that very narrow size distributions can be highly resolved by
minimizing the effect of line width broadening in the sensing aperture.
Particle Size Determination
In industrial applications, historically it has been common practice to report particle “size ” in
linear terms, and so the volume of a particle is converted into an equivalent spherical diameter
(ESD). In this case, the “particle size ” is the diameter of a sphere whose volume is equal to that of
the particle. The biological and biomedical sciences traditionally (when reporting the results of
cellular analyses) are more accustomed to using actual volumetric metric units, and in these
applications “particle size ” is usually presented in terms such as femtoliters or cubic microns (fL,
or µm
3
).
Particle surface areas can be calculated, with the assumption that the surface area is that derived
from (and equates to) the surface area of a perfect sphere whose ESD is the same as that of the
volume of the particle.
The International Standard ISO 13319 Determination of Particle Size Distributions—Electrical
Sensing Zone Methods describes and gives guidance on the measurement of the size distribution of
particles using the Coulter Principle.