User`s guide

Method Development
209
they burn. Residual solvents are often locked (occluded) inside
the crystal structure of the solid drug. You must ensure that
molten pharmaceuticals do not move out of the sample tube and
contaminate the system flow path.
• Do not heat samples containing mercaptans above 200°C.
Trap Low Temperature—The cold trap is cooled with a Peltier
cooler to temperatures between -30°C and +150°C. A temperature of
-30°C is usually sufficient for quantitative retention of the
components of interest, provided a suitable trap packing is selected.
For more information on trap packing selection, see Selecting
Packing Material for the Cold Trap on page 227.
Even samples covering a wide boiling range, such as C
3
to saturated
n-C
40
alkane, can be retained by the cold trap at -30°C and desorbed,
provided a sandwich packing of increasing adsorbent strength is
used.
The LN2 accessory lowers the minimum trap temperature to -100°C.
See Liquid Nitrogen Accessory (LN2) on page 189 for details. A
temperature of -100°C is required for the retention of some
permanent air gases. Methane and other more volatile components
that are being collected onto a trap packed with a weak adsorbent or
with glass wool may also required extreme low temperatures.
In some applications, selective retention is required in the cold trap.
Example: For the analysis of water-based paints, the cold trap is
packed with approximately 20 mg of Tenax and the trap low
temperature is set at about 4°C.
At this temperature, the aromatic hydrocarbon components of
interest are quantitatively retained while the water passes through
the trap during the primary desorption process. In this way, the water
has passed through the system and is out of the way before the start
of the GC analysis.
Trap Heating Rate—The trap-heating rate is selectable. Set the
heating rate to any value between 5, 20, 40 and 99 ºC/sec (ballistic).
A setting of 40 ºC/sec. ensures that volatile compounds are
transferred to the GC column in a narrow band over approximately
1.5 seconds. A slower heating rate will increase the sample transfer