Troubleshooting
HPLC System Troubleshooting _____________________________________________________________
PEEK (Polyetheretherketone) Tubing
PEEK is a widely used alternative to stainless steel tubing in high-pressure
parts of the system. It is compatible with most LC solvents except THF
(tetrahydrofuran) and methylene chloride. It works well to a reasonably high
pressure, is easy to cut and route, and is less expensive than stainless steel.
PEEK is available in eight different internal diameters that are color-coded.
The four most commonly used diameters in LC/MS applications are shown
in Table 6-1.
Table 6-1. PEEK tubing color coding
Color
OD × ID
Max. Pressure
Orange
1/16" × 0.020"
6000 psig
Blue
1/16" × 0.010"
6000 psig
Yellow
1/16" × 0.007"
8000 psig
Red
1/16" × 0.005"
8000 psig
The choice of ID depends mainly on the LC flow. In general, avoid the red
0.005" ID tubing, as it is prone to blockage. It is mostly used for low flow
(<100 µL/min) applications.
Yellow 0.007" and blue 0.010" are most commonly used for flow rates
within the range of typical LC/MS applications; that is, 100 µL/min to
1.5 mL/min.
Cut PEEK tubing with a PEEK tubing cutter or scalpel to ensure a square
cut and no blockage. Flush PEEK tubing with solvent before use.
PEEK fittings used with PEEK tubing are one- or two-piece (with ferrule)
finger-tight compression fittings. Never over-tighten PEEK fittings, as this
can cause leaks.
Stainless steel fittings can also be used, but exercise care not to over-tighten,
as the tubing can become crushed and the flow restricted.
6-6
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