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Diagnostics Tips and Tricks for System Pressure Problems in HPLC

Pressure Problem in HPLC
Continuous use of HPLC columns under high pressure can cause deterioration and overload of the equipment. Therefore, it is important to monitor column back pressure regularly and solve the problem timely. The back pressure increase can be due to clogging of a column or clogging of the equipment.



What causes low pressure in HPLC?
The most common causes of no/low pressure are the solvent inlet lines not being immersed in solvent, no solvent in the reservoir and leaks. The most common cause of fluctuating pressure is poorly primed lines with badly degassed solvents. Baseline irregularities can be non-cyclic or cyclic.

What causes high pressure in HPLC?
High back pressure in LC instruments is usually caused by foreign material blocking the flow of mobile phase. Although crimped PEEK or stainless steel tubing will occasionally be the culprit, particulates clogging the system are most often the cause.

What is back pressure in HPLC?
It's called backpressure because it's established by the column/lines and depends on the fluid viscosity, flow rate, temperature etc., not directly controlled by the pump setting, as the pressure is a consequence of the actual pump setting for the system resistance to flow.


How can back pressure be handled in HPLC?
An increase in back-pressure usually suggests either a guard or analytical column problem. To find exactly where the problem lies It suggest that remove the guard column (if you are using one) and replace the old cartridge with a new one. If the original pressure is restored, you solved the problem.

System Pressure Problems

  1. To identify a pressure change from normal operation, create a pressure reference point.
  2. System Pressure is affected by the column, mobile phase, flow rate, temperature and can vary greatly with different methods Erratic flow rates/pressure pulsations
  3. Overpressure
  4. No or low pressure
Erratic flow rates/pressure pulsations
  • Air in system: Prime the pump (methanol or IPA to remove air)
  • Air in solvent lines. Not enough solvent in bottle: Replace the solvent bottle
  • Air in solvent lines. Bottle filters dirty: Remove the bottle filters
  • Air in solvent lines. Not enough degas: Degas the mobile phase
  • Problem with check valves: Sonicate or replace the check valves
  • Problem with seals or plungers: Replace the seals or plungers


Overpressure
  • Check if pressure has risen gradually or suddenly: If pressure has risen gradually particulates are accumulated in inline filter, columns frits or column. If pressure has risen suddenly something could be a obstruction in system or column.
  • Check if something has changed (column, mobile phase, temperature)
  • If nothing has changed, remove the column and replace it with a union to check if the system pressure is the usual.
  • If system pressure is high loosen fittings beginning with the last connection in line and working backward to the pump
  • After loosening each fitting observes if pressure stays the same or reduces. Replace or clean the appropriate part
Caution: Do not loosen fittings under high pressure

Low pressure
  • Check if something has changed (column, mobile phase, temperature, method)
  • If nothing has changed, check for leaks.

No pressure
Air in system: Prime the pump (methanol or IPA to remove air)
Air in solvent lines. Not enough solvent in bottle: Replace the solvent bottle
Problem with check valves: Sonicate or replace the check valves
Problem with seals or plungers: Replace the seals or plungers

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