Malvern Mastersizer 2000, User Manual

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Making measurements - a tutorial Chapter 4
Mastersizer 2000 Page 4-3
Cleanliness of the optical system
Laser scattering is a high resolution optical method in which the detectors and win-
dows are an integral part of the measurement zone. Dust or smears on the windows
will scatter light that will be measured with the sample scattering. In general the
process of measuring both a background and a sample and then subtracting the
background corrects for such contributions. However, this correction is first order
only and excessive dirt on the optics will degrade the instrument's sensitivity.
We recommend ensuring that detectors and windows are clean at all times. See the
Essentials Manual for advice on cleaning the system. If in doubt about the optical
cleanliness, the user can use the live display of the background measurement. By
viewing this screen they can judge whether the optics are clean or not.
The basics of making a measurement
There are two ways to make a measurement:
„
Using a Standard Operating Procedure (SOP) – SOPs are user defined
procedures that are easily programmed into the software to allow the same type
of sample to be measured in a consistent way with all the difficult decisions on
measurement strategy already having been made.
When the SOP is run, it automatically runs through the defined measurement
procedure, prompting the operator to perform tasks such as adding the sample.
The SOP takes full control of the dispersion unit (unless it’s a manual unit),
making all adjustments and settings (such as pump speeds and ultrasonic
power). This is the recommended method of operation and is suited to begin-
ners or when routinely measuring the same type of sample.
„
Manual measurements – used either to make one-off measurements or to
try out a sample prior to defining an SOP for it.
Follow the section below for the instrument used.
Obscuration
range (%) Obscuration
graph colour
Notes
<5 red Add more sample.
5-10 orange Low but usable with a good signal to back-
ground ratio.
10-20 green Ideal.
20-50 orange Usable but try to add more dispersant -
there’s a danger of multiple scattering.
>50 red Too high.
MAN0384-1.0 Mastersizer 2000.book Page 3 Tuesday, March 20, 2007 8:56 AM