Pipetting method and apparatus

Claim 1

A pipetting apparatus for accurately pipetting a predetermined quantity of a liquid, comprising: a. probe means for receiving and dispensing the predetermined quantity of a liquid; b. a fluid line connected to the probe means; c. pump means connected to the fluid line for drawing air and the predetermined quantity of liquid into the probe means during an intake phase and expelling the air and predetermined quantity of liquid from the probe means during a delivery phase; d. flow control means interposed in said fluid line between the probe means and pump means for permitting the air and predetermined quantity of liquid to flow therethrough when said flow control means is in an open state and hindering flow of the air and predetermined quantity of liquid therethrough when said flow control means is in a closed state; and e. controller means connected to said pump means and flow control means for controlling the intake phase and delivery phase of said pump means and the open state and closed state of said flow control means, such that (i) the flow control means is in the open state during the intake phase of the pump means, whereby the air and predetermined quantity of liquid may be drawn into the probe means during the intake phase; (ii) the flow control means is in the closed state for a portion of the delivery phase of the pump means to hinder flow of the air and predetermined quantity of liquid there through thereby compressing the air and retaining a portion of the predetermined quantity of liquid; and (iii) the flow control means is returned to the open state during the delivery phase of the pump after compression of the air to thereby cause the pipetting apparatus to rapidly expel the compressed air through the probe means creating an air stream which entrains the retained portion of the predetermined quantity of liquid not previously expelled, thereby accurately pipetting the predetermined quantity of liquid.