Thermo Scientific ISQ, Руководство пользователя

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4
Creating a Method
Creating a Method for the GC
46 ISQ User Guide Thermo Scientific
b. You can set the carrier mode to Constant Flow , Constant Pressure , Programmed
Flow , or Programmed Pressure . The gas flow and the oven temperature work
together to determine how well the analytes are separated and how long the analysis
will take. If you use constant pressure, as the column is heated in the oven, the flow
rate will fall because the hotter column is more resistant to carrier gas flow. If you use
constant flow, the carrier gas pressure will increase as the column temperature
increases to keep the flow constant. Constant flow is more common. Typical flow
rates are 1-3 mL/min. The pressure depends on the column length and internal
dimensions, so there is not a typical value. Because the outlet of the column is in the
ISQ instrument, which is under vacuum, the vacuum compensation
must be on to
ensure accurate flow rates.
c. The flow can also be operated in programmed flow or programmed pressure modes.
In these modes, you may have up to three flow rates or pressures to use during an
analytical run. This is not commonly used, but may be necessary if you have a
particularly challenging separation.
d. In an effort to reduce the amount of carrier gas used, check Carrier Gas Saver . When
used, the split flow will be reduced to the gas saver flow after the gas saver time. It is
not recommended to use a flow of less than 20 mL/min because contaminants can
build up in the injector, column, and ISQ instrument, which can affect the system
performance. It is also possible for air to diffuse back into the column with low split
flows when the column head pressure is low.
e. Finally, if your analysis requires a higher flow to quickly sweep the analytes into the
column, which may be needed with high temperature injectors and thermally labile
compounds, you can use the surge pressure to increase the column flow for the surge
duration time.