Malvern Mastersizer 2000, User Manual

Page: 77 / 154

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
d x 0.9
, ( )
d x 0.1
, ( )
–
d x 0.5
, ( )
------------------------------------------------ =
Ob 1
L
s
L
b
----- – =
MAN0384-1.0 Mastersizer 2000.book Page 5 Tuesday, March 20, 2007 8:56 AM