TOPwave
Operating
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6
Operating
6.1
Setup Methods
6.1.1
General Notes
The applied microwave energy causes the sample material to heat rapidly. The speed of
this heating process depends on the total volume of liquid in the oven as well as on the
amount of microwave radiation applied (power). The TOPwave is controlled by continu-
ously adjusting the microwave power. Sample temperature and sample pressure in each
vessel are simultaneously acquired in a contactless process during every rotation of the
sample turntable, and the microwave power level is adjusted accordingly. In addition,
microwave power is also controlled on the basis of the number of samples actually pre-
sent in the turntable. This graduated regulation concept leads to reproducible heating
curves and therefore to reproducible results.
A vapor pressure strongly dependent on the temperature arises from the warming of the
acid mixture. All digestion vessels have a maximum permissible pressure. If this maxi-
mum pressure is exceeded, the rupture disc in the pressure vessel activates, providing a
rapid pressure release into the collection vessel.
In addition to the vapor pressure, reaction gases (primarily carbon dioxide generated by
samples containing carbon) also produce pressure. This pressure is therefore dependent
on the sample amount, the vessel volume, as well as the carbon content of the sample.
Together with the applied microwave radiation, digestion of organic substances also re-
leases reaction heat. These types of reactions frequently begin in the temperature range
between 120 – 150 °C (266 – 302 °F). We therefore recommend holding the samples at
this temperature for some time (3-5 minutes), in order to allow this reaction heat to
subside somewhat. The temperature should then be increased to the desired maximum
in a second stage in order to obtain optimum digestion vessel.
CAUTION
Reaching the maximum pressure!
Note that the reaction pressure is only reached during the course of the reaction, in
other words, several minutes after the maximum temperature has been reached. There-
fore, an activation of the rupture discs may be anticipated even after the temperature
has reached a constant level.
Optionally the TOPwave can be equipped with pressure monitoring. With this option
the, internal vessel pressure determined and, when the preset maximum pressure is
reached, the unit automatically switches to a pressure-controlled mode. In this mode the
microwave output is controlled so that the internal pressure of the vessel does not
exceed the maximum pressure.