Understanding the views Chapter 6
Mastersizer 2000 Page 6-5
D(v, 0.5), D(v, 0.1) and D(v, 0.9) are standard percentile readings from the
analysis.
D(v, 0.5) is the size in microns at which 50% of the sample is smaller and
50% is larger. This value is also known as the Mass Median Diameter
(MMD) or the median of the volume distribution. The v in the expression
D(v, 0.5) shows that this refers to the volume distribution. This can be
replaced by s for surface, l for length or n for number distributions.
D(v, 0.1) is the size of particle below which 10% of the sample lies.
D(v, 0.9) is the size of particle below which 90% of the sample lies.
D[4,3] is the Volume Weighted Mean or Mass Moment Mean Diameter.
D[3,2] is the Surface Weighted Mean, also known as the Surface Area
Moment Mean Diameter or Sauter mean.
The Span is the measurement of the width of the distribution. The narrower
the distribution, the smaller the span becomes. The span is calculated as:
The x is replaced by any of the letters v, s, l or n that define the distribution
type.
Concentration – the volume concentration. This is calculated using Beer-
Lambert’s law. For full details see the following section.
Obscuration – this helps the user to set the concentration of the sample when
it is added to the dispersant. It is a measure of the amount of laser light lost due
to the introduction of the sample into the analyser beam.
The obscuration term can be expressed mathematically:
L
s
is the light intensity measured in the central detector when a sample is
present in the cell, L
b
is the same but with clean dispersant (i.e. with no sam-
ple). Obscuration is usually expressed as a percentage: 100 x Ob.
An ideal range is between 3 and 20%, depending on the sample and dispersion
unit used.
Span
dx0.9,()dx0.1,()–
dx0.5,()
------------------------------------------------=
Ob 1
L
s
L
b
-----–=
MAN0384-1.0 Mastersizer 2000.book Page 5 Tuesday, March 20, 2007 8:56 AM
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