November 16, 2016, 715004521 Rev. C
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Figure 2–9: Step 7: The SM-FL washes the outside and inside of the needle
With the injection and auxiliary valves in the inject position, after injecting the sample, the SM-FL
washes the outside and inside of the sample needle. The wash syringes dispense the
programmed amount of strong and weak washes through a single trace in the injection valve and
out through the needle.
2.5 Performing column screening
Before running separations, best practice requires that you first screen the various UPC
2
column
chemistries, to determine the most suitable one to use for the compounds you want to separate.
A typical column screening workflow involves these actions:
• Create a method for each column that you want to screen.
• In each method, create a gradient consisting of two or three injections. Specify the first
injection, to equilibrate the column, and the second and third injections, to inject the sample.
• Run the gradient for 5 minutes, starting with a mobile phase mixture of 5% organic solvent
and 95% CO
2
, and ending with a maximum of 40% organic solvent and 60% CO
2
.
• Run the 40% organic solvent for at least 1 minute to wash the column.
Waste
Waste
Auxiliary valve (inject position)
Injection valve (inject position)
Sample
Liquid mobile phase (CO
2)
Gas mobile phase (CO
2)
Air gap
Buffer volume
Sample
Weak wash
From pump
To column
Sample loop
Metering syringe
Wash
syringes
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