Chromatography Forum

I have recently started having a problem with our Waters I-Class UPLC in which the pressure shoots way up upon injection of a sample (as much as 5000 psi at 650 uL/min on top of the normal operating pressure). We used to see small increases in pressure, as would be expected, but this started a few days ago, and I am having a hard time tracing the problem in the instrument.

The pressure jumps as soon as the 6-port rheodyne valve in the autosampler switches into 'Load'. It isn't blocked (injection will still proceed without hitting max pressure at a lower flow rate), and back flushing through the valve doesn't lower the pressure any. I have also checked everything that comes after this valve, and there doesn't appear to be a problem with any of the fittings after the line leading into the column.

Any thoughts would be greatly appreciated.

Thanks.

Clean(sonicate, IPA and MeOH) the rotor and the stator of the 6-port valve, clean the needle seat, clean the needle and all the capillaries from/to needle/column/TCC/6-port valve.
You have a blockage in this area.
Good luck.

Clean(sonicate, IPA and MeOH) the rotor and the stator of the 6-port valve

I wouldn't recommend this... Taking apart a 6-port valve on a UPLC will cause leakage. As far as I know even Waters technicians don't attempt this, and a replacement will be your only option if you do take it apart.

You need to know what you've injected - i.e. what has blocked the valve etc.
When you/we know that as well as the mobile phase composition we may be able to suggest a solution.

Standard/universal rinsing/cleaning of systems as well as columns is sheer nonsense in my oppinion.

Best Regards