Sample dispersion method
The second thing to consider when choosing a lens is the way the sample is
dispersed. Because of the physical arrangement of the 45mm and 300RF lenses it
is not possible to measure samples dispersed in air (i.e. using one of the dry
powder feeder accessories or performing spray measurements) using these lenses.
Due to “lens cut off” (discussed next) the 100mm lens on the Mastersizer X is
also unlikely to be used for spray measurements.
As general advice:
.
Spray measurements should only be performed on the 300mm or
1000mm* lens.
.
Samples dispersed in a liquid should initially be tried using the 45mm lens
on the Mastersizer X or the 300RF lens on the Mastersizer S. If the size
range of the sample is then found to be outside the ranges for these lenses
then try another lens.
Avoiding lens cut off (Vignetting)
Care should be taken when measuring spray samples. It should be noted that
there is a physical measurement zone - an area in front of the range lens that the
spray must be confined to. If you spray outside this area then the scattering
information will not be picked up by the detector.
This measurement zone is defined by the “cut off point”, a distance from the face
of the range lens along the analyser beam.
The chart below gives the cut off point for the lenses. (The 45mm and 300RF
lens have not been included as it is not possible to measure spray samples with
these lenses).
Mastersizer X Mastersizer S
Lens Cut off
.
(mm) Lens Cut off. (mm)
100mm 24 300mm 36
300mm 84 1000mm* 290
1000mm* 290
(* Used on the long bench Mastersizers only.)
CHAPTER 4
GETTING STARTED
Page 4.5
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