Sample Tube Prepurge At Elevated Temperature; Securetd-Q™ - Re-Collection For Repeat Analysis - Markes International Unity 2 User Manual

3.6.4 Sample tube prepurge at elevated temperature

The elevated purge option is used for selectively eliminating water and/or high levels of unwanted volatile
components. The trap is, by definition, almost always out of line during elevated temperature purge,
which means that the split flow must be on. The elevated temperature purge immediately follows, and
does not replace, the ambient temperature purge.
Example applications are:
 Eliminating high levels of water collected on sorbent tubes when monitoring humid atmospheres.
 Eliminating high levels of ethanol from a sample of the flavour profile of potable spirits when the
components of interest are higher boiling esters and ketones.
 Eliminating high levels of volatile solvent from higher boiling (e.g. aromatic) standards introduced onto
sorbent tubes as droplets of liquid solution.
It is the entry of the second tube desorb time (Time 2) in the appropriate box, which indicates to the
system that an elevated temperature purge is required. When a value is entered for Time 2 an extra Trap
In Line check box appears in the line referring to stage 1 of tube desorb. As stage 1 of tube desorb is now,
effectively, an elevated temperature purge, it becomes appropriate, as in ambient temperature purge, to
deselect the cold trap. The cold trap is invariably selected off-line and the split flow on during elevated
temperature purge because the purpose of elevated temperature purge is generally to eliminate volaties
from the tube and system before analysis of higher boiling target analytes.
Gas flows during elevated temperature purge are controlled as described in Section 2.6.2 for the ambient
temperature purge.
When using 2 stages of tube desorption, remember to place a check in the second split on box if an inlet
split is required for the analysis. The gas flow through the hot tube during its analytical desorption = the
flow through the cold trap (the so-called desorb flow - controlled via needle valve) + the inlet split flow i.e.
the flow through the split vent (also controlled via needle valve), if any.
3.6.5 SecureTD-Q™ - Re-collection for repeat analysis
UNITY 2 facilitates the quantitative re-collection of the split portion of a sample onto a clean sorbent tube
thus facilitating repeat analysis. This is of real benefit in situations where it is not possible, or prohibitively
expensive, to collect replicate samples.
To re-collect the split effluent, the normal charcoal-packed split filter tube (SERUTD-5065) supplied with
UNITY 2 must be replaced with a conditioned sorbent tube - the SecureTD-Q tube.
NOTE: This procedure should only be carried out with the system in standby mode.
In order to access the tube on the split side (charcoal or SecureTD-Q), the exchange split tube icon (
must be selected. This will isolate the split tube from the carrier gas supply without disrupting the flow to
the analytical column allowing chromatography to continue uninterrupted as the SecureTD-Q and charcoal
tubes are exchanged.
Once 'exchange split tube' has been selected, lift the right-hand levered tube cover to release the charcoal
split tube from one of its seals. Use your fingers or the tube extractor tool to gently pull the tube free from
the other seal. Once the charcoal tube has been removed, the clean (SecureTD-Q) sorbent tube should be
inserted with its sampling (grooved) end pointing to the rear of the instrument. Lower the right-hand
Markes International Ltd
T: +44 (0)1443 230935 F: +44 (0)1443 231531 E: enquiries@markes.com
www.markes.com
QUI-1057
Page 43
)