HPLC column structure and connection
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A typical HPLC column has a structure as shown in the figure above.
At both ends of the column pipe, which is filled with the
packing materials responsible for compound separation, there are
porous disks called 'frits'. These are held in place by
end-fittings.
The role of the 'frit' is to prevent the
packing materials from escaping the column pipe, not to act as a
'filter' as commonly mentioned.
The 'end-fitting' serves two
roles. One is to press the frit against the column pipe to prevent
the packing materials from spilling out, and the other is to connect
the tubing to allow the mobile phase and solutes to pass through the
column without leaking.
HPLC tubing is typically made of PEEK
or stainless steel, with an outer diameter of 1/16 inch and an inner
diameter of 0.1-0.3mm. To connect HPLC tubing to the column, a male
nut is required. In addition, at the tip, there is a cone-shaped
structure called a 'ferrule' which firmly grips the tubing to
prevent leakage under high pressure.
For the solutes flowing
inside the tubing to be accurately and fully injected into the
column, the tip of the tubing needs to make firm contact with the
bottom surface of the column's end-fitting. Therefore, when
tightening the male nut, the tubing's tip must protrude 2-3mm from
the ferrule. If the tubing is not tightly adhered to the bottom
surface of the end-fitting, the solutes may linger there, causing
peak tailing or, in the worst-case scenario, mobile phase leakage.
The tip of the tubing must also be flat.
Maintenance of the
tubing connecting the column is also an important task in HPLC.
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