Positive-displacement sampling device designed to improve the grasping of the piston of a piston-capillary system

A positive-displacement sampling device, comprising:

• an endpiece intended to carry a capillary of a piston-capillary system the endpiece being hollow, centred on a longitudinal central axis of the endpiece;
• an ejector intended to eject the piston-capillary system movable relative to the endpiece according to an ejection axial stroke between a rest high extreme position and an ejection low extreme position, the ejector comprising an ejection end intended to be in axial contact with a capillary end during the ejection stroke;
• a fixed body secured to the endpiece
• a movable pipetting equipment movable in translation relative to the fixed body, the equipment comprising a movable main body and a clamp system for gripping a piston upper end, the clamp system comprising grasping members secured to a lower end of the movable main body, as well as a clamping ring of the grasping members, the ring being itself movable in translation relative to the grasping members between a radial clamping low position of the grasping members, in which these members urged radially inwards allow gripping the upper end of the piston located between these grasping members, and a radial loosening high position of the grasping members,
• wherein
• the movable pipetting equipment further includes a piston driving member lower end of which is intended to contact the upper end of the piston during an operation of grasping the piston with the capillary fitted on the endpiece, the driving member arranged between the grasping members being mounted movable in translation relative to the movable main body between a maximum projection position and a minimum projection position, a first elastic return means forcing the driving member downwards relative to the movable main body, towards its maximum projection position,
• the sampling device further comprising a control system of the clamping ring of the clamp system, the control system comprising a second elastic return means arranged between the clamping ring and the movable main body, this control system being designed so that during the operation of grasping the piston upon an axial movement of the movable pipetting equipment causing the movable main body in a predetermined axial position with respect to the fixed body, the clamping ring automatically moves from its loosening high position to its clamping low position under the effect of the second elastic return means,
• said predetermined axial position of the movable main body being accessible, during the axial movement of the movable pipetting equipment only after the driving member has been moved relative to the movable main body towards its minimum projection position, by bearing thereof on the piston accommodated in the bottom of the capillary fitted on the endpiece, and by countering the force generated by the first elastic return means.