STUDIES ON THE DETERMINATION OF MEASUREME NT INACCURACY FOR PISTON-OPERATED PIPETTES WITH VOLUMES OF 1 TO 50 MICROLITERS

A gravimetric measurement concept for the verification of piston-opera ted pipettes has been developed. With specially fabricated flasks surr ounded by a ring-shaped evaporation vessel inside the housing of a 5 g balance, measurement uncertainties of less than 10 nl were achieved. The influence of prior wetting and repeated use on devices with ''air displacement'' was investigated The filling and dispensing capacity of the pipettes is significantly influenced by the various parts of the handling process such as stripping. The influence of the stripping len gth was therefore determined in both cases. Effects related to heating due to the human body temperature were also studied. The method was u sed for testing twelve piston-operated pipettes of different design an d capacity from two manufacturers. Deviations from the specified measu rement uncertainties were found in two cases.