Getting Started in HPLC

Section 2B. HPLC Pumps

   
What can go wrogn ?

Outside of failures in the control electronics, there are only a few things that can go wrong with a reciprocating piston pump:

  • Check valves may fail because of wear, overtightening, or particulate contamination (dirt). This can allow some liquid to flow the "wrong way", decreasing the net flow from the pump.
  • Air bubbles can get into the head and interfere with proper opening and closing of the check valves (air is more compressible than liquids, so the pressure change resulting from piston movement is smaller).
  • Seals eventually wear and allow mobile phase to leak out behind the pump head. A certain amount of leakage (very small!) is normal, but seal wear is aggravated by crystallization of buffer salts as solvent evaporates. In general, mobile phases that contain nonvolatile buffers or salts should never be left stagnant in an HPLC system; the system should be flushed with buffer- or salt-free mobile phase before it is shut down.


 
Preventive Maintenance

As is true of any instrument, consistent preventive maintenance can go a long way to ensure reliable, trouble-free operation. Standard preventive maintenance for HPLC pumps includes:

  • degassing the mobile phase. Any solvent in contact with the atmosphere contains an equilibrium level of dissolved air. As it happens, the solubility of air in the kind of solvent mixtures typically used for HPLC is lower than it is in the pure solvents. When we mix the solvents to prepare the mobile phase, the excess dissolved air forms bubbles. Bubbles can interfere with proper pump operation; they can also contribute to baseline noise problems with our detectors. All of these problems can be minimized by degassing the HPLC mobile phase before it gets to the pump.
  • flushing the system with buffer- and salt-free mobile phase before shutting down. This minimizes corrosion of the stainless steel in the pump head and fittings, the possibility of bacterial growth in the mobile phase, the precipitation of salts in the pump head or check valves, and the deposition of salt crystals under and behind the pump seals.
  • periodic seal changes. Pump seals are a consumable item. Like tires on a car, they will eventually wear and have to be replaced. It is far more effective to replace seals on a scheduled basis than to wait for a catastrophic failure


 
   
 

 


2000, LC Resources Inc. All rights reserved.
Last revised: April 06, 2001.