[kpamorn]

How can we solve the problem about the pressure in HPLC pump are not stable or fluctuate around 500 psi ?

  I used HPLC-UV (Water) to analyte. The problem will occur when I run the sample around 8-10 hour.

[kevins]

Please try to degas or purge the eluent.

[Moroni]

Try to clean the bottle´s filters (from possibles fungis) and valves (from incrustantions of salts) with hot water (80ºC) + isopropilic alcohol  (80/20).

Moroni

[chiralic]

The causes of pressure changes in your HPLC equipment could be from mechanics and/or chemical origin.

If the Pressure changes, check the flow rate indirectly with measurement Dead Time (tm), in this way you can pinpoint the cause: FLOW or CHEMISTRY. Also you must check LEAKS.

If you have permanent small fluctations you must check:
+ Air bubles (in the pump, in pump head seal defect , frit of suction is clogged)
+ Pump head seal defect

If your pressure increases, deacreses, increases you must check:
+ Inlet valve is clogged (you must check pump head malfunction)

NOTE: Check in your system defect on pressure sensor

Regards,

Chiralic