Markes International Unity 2 User Manual page 41

Min Carrier Pressure
GC Cycle Time
Split Ratios – split
flow calculator
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temperature (e.g. system default temperature of 140°C) is often preferred.
Whenever analysing labile compounds use a low (<100°C) flow path
temperature and, where possible, increase gas flow rates (linear gas velocities)
inside the system.
Use the highest possible flow path temperature (200 - 210°C) for analysing
semi volatile organics.
Set a minimum carrier gas pressure below that at which UNITY 2 is normally
operated. If the carrier gas pressure drops below this minimum pressure, UNITY
2 status will change to Low Carrier Pressure and UNITY 2 status will read Not
Ready. If the carrier gas pressure drops below the minimum pressure during a
run, UNITY 2 will enter Low Carrier Gas status and the tube oven (if heating) and
trap heater (if heating) will start to cool down.
The GC Cycle Time = GC Run Time + GC Cool Down Time + Equilibration (if
appropriate).
If a GC Cycle Time is entered, UNITY 2 will calculate the time at which it can
begin the next tube desorption stage such that at the end of that tube
desorption and at the time the trap is ready to heat, the GC will have just come
ready from the previous analysis. To enter a GC Cycle Time click in the relevant
box and type in the required value.
NOTE: This tool only calculates the split flows – it does not set them.
The inlet, outlet and total split ratios can be viewed, when applicable, in the box
at the bottom right hand corner of the method page once the measured flows
have been entered into the method.
Flows may be entered by clicking on the Confirm/Enter Flows button to bring
up the relevant dialogue box.
Once the values have been entered and confirmed by pressing OK, the split
ratios are automatically calculated and displayed.
For measurement of gas flows see Section 1.4.4.
QUI-1057
Page 41