Detecting and preventing leakage in your HPLC system
Causes, detection methods and preventive maintenance for analytical systems
Leakage in an HPLC system is one of the most common faults in the analytical laboratory. A leak introduces air into the system, changes the volume ratio and can create dangerous situations when volatile solvents are used. Yet leakage in an HPLC system can almost always be traced back to a limited number of locations and causes.
This article explains where leaks come from, how to track them down quickly and how to prevent them structurally with preventive maintenance of couplings and fittings.
⏱ approx. 5 minutes reading time
Where does leakage in an HPLC system occur most often?
Virtually all leakage in an HPLC system is found in the same locations. Systematically checking these points saves a lot of search time and prevents prolonged downtime.
| Location | Cause of leakage | Signal |
| Pump (plungers) | Worn plunger seals or a damaged plunger | Drops or moisture around the pump head |
| Injector / autosampler | Worn rotor seal or stator | Leak around the injection block, variable peak height |
| Column connections (inlet) | Incorrectly tightened HPLC fitting or wrong ferrule position | Leak at the front, where the highest pressure is present |
| Fittings throughout the system | Not properly tightened, damaged ferrule | Drops or white salt crystals around the fitting |
| Detector | Leakage from the flow cell or connecting capillaries | Moisture around the detector connection |
| Check valves | Blocked or worn; internal leak, not always visible | Pressure instability, uneven flow, pump knocking |
Tracking down leakage in your HPLC system: three methods
Visual inspection
Always start with a visual round of the system. Look for drops, traces of liquid or salt and buffer deposits. White crystal formation around a fitting is a reliable sign of an older or intermittent leak in your HPLC system that previously went unnoticed.
Soapy water or leak detection fluid
Apply a small amount of soapy liquid to the connection to be checked. If the amount of foam increases or bubbles form, there is leakage. This method is particularly effective for small leaks that are difficult to see visually and also works at low pressures.
Absorbent paper under the system
Place white paper or an absorbent cloth under the system and let it run at working pressure. Stains on the paper indicate the location of the leak. Combine with visual inspection to find the exact location.
Increasing pressure as a detection tool
Temporarily increase the system pressure (within the safe specification) and inspect visually. Small leaks that are barely visible at working pressure become more obvious at higher pressure. Only do this if the system safely allows it and the manufacturer permits it.
Common installation errors that cause leakage
Most leakage in HPLC systems is caused by installation errors, not by defective parts. These are the most common:
Fittings tightened too loosely or too tightly
PEEK fittings are tightened by hand and then given an extra quarter turn. Overtightening damages the PEEK material and the instrument port and causes leakage due to deformation. Tightening too loosely causes immediate leakage. Stainless steel fittings require a wrench and a specific tightening torque.
Incorrect ferrule position
The ferrule must be positioned at the right point on the capillary before final tightening. With stainless steel ferrules, this is irreversible: the ferrule sets in the position of the first installation. If you then place it in a different port, the sealing surface no longer fits and leakage is unavoidable. PEEK ferrules and fingertight fittings can be repositioned.
Wrong capillary and fitting combination
Every HPLC fitting is designed for a specific capillary outer diameter. A 10-32 fitting for 1/16 inch OD does not work correctly with a 1/8 inch OD capillary. Always check that the fitting, ferrule and capillary have the same nominal outer diameter.
Salt deposits as a hidden sign of leakage
White crystal formation around an HPLC fitting after using buffers or salt solutions indicates a small or intermittent leak. Replace the fitting and ferrule even if no active leak is visible at that moment. Salt deposits corrode steel fittings and disrupt the measurement.
Preventive maintenance to prevent leakage in your HPLC system
Systematic preventive maintenance reduces leakage in your HPLC system, extends the life of fittings and improves the reproducibility of analyses. Include these points in your maintenance schedule:
- Visually inspect all connections at every system start-up or after a shutdown of more than a week
- Replace ferrules every time a capillary or fitting in the high-pressure zone is replaced
- Check check valves in the event of unexplained pressure instability or uneven flow
- Do not loosen and retighten HPLC fittings in the high-pressure zone unnecessarily: every cycle wears the seal
- Record the installation date of plunger seals and rotor seals and replace them at fixed intervals
- Never use Teflon tape or sealants on HPLC fittings: this causes dead volume and contamination
