HPLC and Ion Chromatography Back Pressure Primer

Apparent Location of Problem  

Possible Cause

*Probable Practical Solution


Mobile phase  

 Mobile phase contains particulates.

Use a 0.45 µm mobile phase filter/s.  Use HPLC grade solvents.  Change the pH.

Dust or particles in the mobile phase reservoir/s.

Lightly cover the mobile phase reservoir/s.

Particulates due to microbial growth in aqueous mobile phase/s.

Use an amber mobile phase container/s.  Store unused mobile phase/s in the refrigerator.  If possible, use 10 to 20% organic mobile phase.

Between pump and injection valve  

 

 

   

   

   


Buffer salts of the mobile phase/s, have precipitated.

Directly connect the pump outlet to waste and flush the pump with warmed 15%/85% methanol /water.


Back-flush the pump pistons.


(# If there are buffer salts within the mobile phase/s, do not let the pump lie unused for more than twenty minutes.


 When the system is not used for injections, ensure that the buffer solution is always circulated through the pumps at a low flow rate.  


When injections are not being run, if necessary and permitted, re-circulate the mobile phase/s.  

When you have finished using the buffer, flush the system with 15%/85% methanol /water for two hours.)

Excessively viscous mobile phase/s.

Experiment with a less viscous solvent or a combination of solvents.

The mixer is not performing.

Repair or change the mixer.

Pump flow rate is too high.

Reduce the pump flow rate.

Excessively long tubing.

Shorten the tubing.

Injection Valve and Needle .  


Particles from excessive wear to the rotary injection valve rotor seal.

 If the valve’s rotor seal is Vespel, avoid the use of high pH mobile phase/s.  In these circumstances, Tefzel valves would be more durable.


Injected solutions are not filtered.

Filter each injected solution, a 0.45 µm syringe filter may be used for each solution.

Buffer salts of the mobile phase, have precipitated.

Replace the needle.  Also see #.

Mobile phase is excessively viscous.

Experiment with a less viscous solvent or a combination of solvents, for example, methanol is less viscous than isopropanol (IPA).

Analytical and Guard column  


 Pump flow rate is too high.

Reduce the pump flow rate.


Precipitation of mobile phase buffer.

If possible backflush the analytical column.  Also see #.

 Mobile phase is too viscous.

Experiment with a less viscous solvent or a combination of solvents.

Particle size is too small.

Change to a column with a larger particle size.

The column temperature is too low.

Use a column heater to increase the column temperature.

Column is too long.

Change to a column of a shorter length.

Injected solutions not filtered.

Filter each injected solution, a 0.45 µm syringe filter may be used for each solution.

Injected solutions contain analytes which have not been eluted off the columns/.

Use a gradient to flush off analytes which are not of interest in the injected solutions.  If possible backflush the analytical column with an appropriate solvent or solution.  Use an efficient means of matrix reduction, during sample pre-treatment.

Mobile phase not filtered.

Use a 0.45 µm mobile phase filter/s.  Use HPLC grade solvents.

Normal/reverse phase mobile phase incompatibility.

Check for normal/reverse phase compatibility.  Flush column with intermediate miscible phase, then final phase.

Particulates in analytical column.

If possible backflush the analytical column.  Change the analytical column.

Guard column is blocked

Change the guard column.

Detector flow cell   

  

Detector’s waste outlet is blocked.

Check the detector’s outlet tubing for kinks or visible blockages.

Mobile phase salts have precipitated.

Clean or replace the flow cell.  Also see #.

Mobile phase is excessively viscous.

Experiment with a less viscous solvent or a combination of solvents.

Excessively High Back Pressures, in Analytical HPLC and Ion Chromatography

Some back pressure is necessary, to push mobile phase/s through the small particles packed into column/s.  However, when the column/s shows too high a back pressure, action is required.


*All the mentioned solutions must be used in consideration with the optimisation of a method.

Cecil Instruments Limited  

Milton Technical Centre, Cambridge  United Kingdom

www.cecilinstruments.com      telephone  +44 (0)1223 420 821          info@cecilinstruments.com