Preventing Leaks
Leaks are a common problem in HPLC analyses. Avoid interchanging hardware and fittings from different manufacturers to minimize leaks in your system. Incompatible fittings can be forced to fit initially, but the separation may show problems and repeated connections may eventually cause the fitting to leak. If interchanging is necessary, use appropriate adapters and check all connections for leaks before proceeding.
Highly concentrated salts (>0.2 M) and caustic mobile phases can reduce pump seal efficiency. The lifetime of injector rotor seals also depends on mobile phase conditions, particularly operation at high pH. In some cases, prolonged use of ion-pair reagents has a lubricating effect on pump pistons that may produce small leaks at the seal. Some seals do not perform well with certain solvents.
Before using a pump under adverse conditions, read the instrument manufacturer’s specifications. To replace seals, refer to the maintenance section of the pump manual.
Unclogging the Column Frit
A clogged column frit is another common HPLC problem. To minimize this problem from the start, use a pre-column filter and a guard column.
To clean the inlet, first, disconnect and reverse the column. Connect it to the pump (but not to the detector), and pump solvent through at twice the standard flow rate. About 5-10 column volumes of solvent should be sufficient to dislodge small amounts of particulate material on the inlet frit. Evaluate the performance of the cleaned column using a standard test mixture.
Replacing a Frit at the Column Inlet
Sometimes neither solvent flushing nor restoration procedures restore a column’s performance. If you’ve isolated the column as the problem source, and other restorative procedures have failed, a void in the packing or a persistent obstruction on the inlet frit may exist.
As a last resort, open the inlet end of the column.
Caution: Opening the inlet end, and more so opening the outlet end, can permanently damage the packing bed. Before opening columns, consult the manufacturer’s literature. (Never open either end of a resin-filled column).
Use the following procedure to open a column.
- Disconnect the column from the system. To prevent the packing from oozing out of the column, perform subsequent steps as quickly as possible.
- Using a vise and wrench, or two wrenches, carefully remove the inlet end fitting. If the frit remains in the fitting, dislodge it by tapping the fitting on a hard surface. If the frit stays on the column, slide it off rather than lift it off. This will help preserve the integrity of the packing bed. Modular columns may require a special tool, to remove the frit cap.
- Examine the old frit. Compression of the frit against the stainless steel tubing will leave a ring around the edge on the column side of a properly seated frit. No ring can mean the ferrule is seated too near the tubing end. The resulting loose connection can leak silica or act as a mixing chamber.
- Examine the packing bed. If it is depressed or fractured, you need a new column.
- Replace the frit.
- Replace the end fitting. Screw it down finger-tight, then tighten 1/4 turn with a wrench.
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