Automatic pipetting apparatus

An automatic pipetting apparatus is disclosed having a base on which is mounted a vertical frame supporting a row of positive displacement pipettes which are driven in the up or down direction by an electromechanical mechanism under microprocessor controls. The apparatus includes a base, a track and a carriage longitudinally movable beneath the row of pipettes. The carriage includes an independent translating and position signal generation mechanism. The carriage carries a tray which includes sample chambers, a space to receive a microporous electrophoresis support medium, such as a cellulose acetate strip, a wash well, rinse well and a space to receive blotting paper. The pipettes include a barrel and a plunger capable of aspirating and dispensing from 0.5 to 5 mu l of liquid. The barrels move up and down with respect to the base by means of another independent translating and signal generating mechanism. The barrels may be easily replaced from the mechanism if they become damaged or worn from many operating cycles. The apparatus under microprocessor program control, washes, rinses, blots the barrels before and after each application or engagement of the barrels with a liquid or contaminant.