At least one liquid access port is formed in each of the sample liquid storage part and the buffer liquid storage parts.

The temperature may be sensed by a probe in a sample holder containing an evaporating liquid sample, or in an adjoining sample holder containing a buffer liquid.

An inlet capillary (2) is provided for supplying a buffer liquid (9) to an outlet end (6) arranged in the pressure chamber.

Also, an outlet capillary (3) is provided for discharging buffer liquid and/or sample from the pressure chamber.

The vessel may be double walled, and the space between the two walls be filled by a low attenuation buffer liquid (36) whose cavitation threshold is above that of the liquid to be treated.