Thermo Scientific TSQ 8000, Руководство пользователя

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4
Creating a Method
Creating a GC Method
Thermo Scientific TSQ 8000 Evo User Guide 81
b. Select the Split Flow check box to dilute high concentrations of sample. The split
flow is the amount of gas that is swept through the injector to the exhaust port.
Higher values will give more dilution. The split flow reduces the amount of
contamination that builds up in your system. The split flow ratio is the ratio of the
split flow to the carrier gas flow. It is effectively the dilution ratio of the sample. This
setting is typically turned on and set to a flow of 50 mL/min. However, more carrier
gas is used, so for your analysis, lower split flows may be more acceptable. If you set
the split ratio, the software calculates the correct split flow. The reverse is true also.
c. For best results, use the septum purge, which means additional carrier gas will go
through the injector. The default purge flow value is 5 mL/min. This reduces the
buildup of contaminants in the injector, on the column, and in the TSQ 8000
instrument. If you perform a splitless injection, even if the split flow is set, the split
flow turns off for the splitless time. The septum purge turns off for the stop purge
time. After these times, the split flow and septum purge are reactivated.
d. 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
as the viscosity of the carrier gas increases. 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 TSQ 8000 Evo instrument, which is
under vacuum, be sure the vacuum compensation is on to ensure accurate flow rates.
e. (Optional) Under Carrier Pressure, select the check box to use 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 feature is not commonly used, but may
be necessary if you have a particularly challenging separation.
f. In an effort to reduce the amount of carrier gas used, select the Carrier Gas Saver
option under Carrier Gas Options. When used, the split flow is 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
TSQ 8000 instrument, which can affect the system performance.
g. 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, use the surge pressure to increase the column flow for the surge duration
time.