Device for reducing loss of liquid during fraction collection

1. A method for avoiding loss of liquid during fraction collection of a liquid flow when switching from one collecting receptacle to the next in a fraction collector, comprising the steps:

actuating an expandable chamber to accumulate the liquid flow during the time interval for switching from one collecting receptacle to the next receptacle,

locating the fluid front at a dispensing nozzle,

controlling the actuation of the expandable chamber to keep the fluid front at a predetermined position,

actuating the expandable chamber to dispense the accumulated liquid into the second receptacle.

2. A fraction collector comprising: a liquid holder including an expandable chamber; a dispensing nozzle in fluid communication with said chamber; a fluid front sensor at said nozzle for sensing a fluid front; and a fluid front control arrangement arranged to control the liquid holder to keep the fluid front at a predetermined position at the nozzle.

3. The fraction collector of claim 2 , wherein the fluid front sensor comprises an optical fluid front detector.

4. The fraction collector of claim 3 , wherein the optical fluid front detector comprises a light source directing light across a fluid flow path at the nozzle and an optical detector arranged to receive said light.

5. The fraction collector of claim 4 , wherein the light source and the optical fluid front detector are arranged off axis with respect to the center of the nozzle.

6. The fraction collector of claim 3 , wherein the optical fluid front detector comprises a light source arranged to couple light to an optical sensor fiber arranged with a terminating end surface in the fluid flow path at the dispensing nozzle, and an optical detector arranged to register the reflected intensity of light from the end surface.

7. The fraction collector of claim 2 , wherein the fluid front sensor comprises a conductivity fluid front detector ( 40 ).