Metrohm 774 Oven Sample Processor - Manual (Page 44)

4 Oven control and gas flow
774 Oven Sample Processor, Instructions for use 38
• Programmable HEATER command – the HEATER command can be
used as a part step in the processing sequence of a method. This
means that it is possible to alter the program-controlled oven tempera-
ture whenever this is necessary. If the HEATER command is used the
heating-up period can be freely selected so that it is possible to carefully
warm up a sensitive sample. Temperature profiles or ramps within a se-
quence can be followed by repeated use of the HEATER command.
This allows the realization of complex applications, e.g. the determina-
tion of surface moisture and the water of crystallization content of solid
samples in the same run.
parameters
>sample sequence
1 HEATER: 110°C 10 min
…
10 HEATER: 180°C 15 min
…
15 HEATER:init°C min
Method:
– controlled heat-up (moisture)
– controlled heat-up (water of crystallization)
– rapid cooling to initial temperature
T [°C]
t [min]
10 min 15 min ? min
HEATER: 110°C 10 min
HEATER: 180°C 15 min
HEATER:init°C min
110°C
180°C
4.2 Gas flow
In order to drive out moisture quantitatively from a sample it is necessary to
remove the vapors formed on heating with a stream of gas. This stream of
gas is also used to lead the vapors into a reaction solution contained in a
measuring cell.
With thermally stable, unproblematic sample substances, such as oils, air
can be used as the carrier gas; this can be supplied by the pump built into
the tower of the 774 Oven Sample Processor. However, it is necessary to
dry the air with a desiccant such as molecular sieve before it can be used.
In the Oven Sample Processor tower the flow of air is led through a pres-
sure regulator and a flowmeter. An excess pressure valve ensures a con-
stant overpressure of approx. 60…80 mbar in the tubing system.
With thermally unstable samples or samples which are sensitive to air it is
recommended that nitrogen or helium is used as an inert carrier gas. As
these gases are available in gas cylinders or pressure lines they can be
connected directly to the tower of the Oven Sample Processor via the sole-
noid valve. A pressure reduction valve must be used to ensure that the gas
pressure is less than 1 bar. The required value can also be set here with
gas flow regulator.
initial temperature initial temperature