Chapter 3 Software features
Page 3-8 MAN 0386
Tray selection
This lists all the sample trays available. All systems the SOP is distributed to must
have the tray selected in the list fitted.
Vibration Feed Rate control
The Scirocco 2000 uses a vibrating tray to feed the sample into the dispersion sys-
tem. The rate at which sample is fed is governed by the vibration amplitude and the
type of tray fitted.
Adjust the feed rate to produce a steady flow of sample into the dispersion system
and to obtain the optimum sample concentration through the measurement cell. If
the feed rate is too high the sample concentration may become too high and any
agglomerates may not disperse correctly. If the feed rate is too low the concentra-
tion may become too low and/or the sample flow may become intermittent. The
General Purpose tray has an adjustable slit to help maintain a steady sample feed.
Sample concentration is monitored using the obscuration reading in the Meas-
urement Display dialogue.
Dispersive Air Pressure control
The Scirocco 2000 uses compressed air to transport and suspend the particles of the
sample as they pass through the air cell. High air pressure settings can also help
break up agglomerates. The air pressure can be controlled over the range 0 to 4 bar
(atmospheric pressure is approximately one bar).
The optimum air pressure setting depends on the sample, so a few trial measure-
ments are recommended. A typical starting air pressure is between 1 and 3 bar. If
the sample is fragile, for example freeze dried coffee, use a lower pressure. If the
sample is dense or cohesive use a higher pressure.
If the air pressure is set too high this may physically change the particle size, giving
an incorrect result. One of the following methods may be used to ensure that the
correct air pressure is being used:
If the sample can also be measured using a wet dispersion unit, and there is no
significant difference in the result, the air pressure setting is acceptable.
Perform a number of measurements at different air pressures and look for a
‘plateau’ of stable results. Choose the lowest air pressure commensurate with a
stable result.
Note
Application Notes available at www.Malvern.com describe the process
of method development for dry powder dispersion.
MAN0386-1.0 Scirocco 2000.book Page 8 Friday, March 16, 2007 4:15 PM
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