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To Measure Column Flow Linear Velocity
With capillary columns, such as those used with the MSD, linear velocity is
often measured rather than volumetric flow rate.
Procedure
1 Set Data Acquisition for splitless manual injection and selected ion
2 Press Prep Run on the LCP keypad.
3 Inject 1 µL of air into the GC inlet and press Start Run.
4 Wait until a peak elutes at m/z 28. Note the retention time.
5 Calculate the average linear velocity.
6 Use this velocity to verify the MSD ChemStation flow calculations
7 To calculate the volumetric flow rate.
5975T LTM GC/MSD Operation Manual
monitoring (SIM) of m/z 28.
Average linear velocity (cm/s)
where:
L = Length of the column in meters
t = Retention time in seconds
Be sure to account for any pieces of column broken off. A 1-meter section
missing from a 25-meter column can yield a 4% error.
If the numbers disagree, click Change to calibrate the column dimensions.
Volumetric flow rate (mL/min) =
where:
D = Internal column diameter in millimeters
L = Column length in meters
t = Retention time in minutes
Operating in Electron Impact (EI) Mode
100 L
=
------------- -
t
2
0.785 D
L
--------------------------- -
t
3
(page
88).
87
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