Key comparison confirms top position of pipette testing facility

10.10.2006

PTB has participated in the CIPM key comparison CCM.FF-K4 and has determined the volumes of three 20 liters stainless steel pipettes. The relative uncertainties obtained, < 2·10^-5, and particularly the small deviations of the measured volumes from the Key Comparison Reference Values (KCRV) of 1·10^-6 (as an average) underpin the top position of the PTB pipette test facility.

Within the scope of the CIPM key comparison CCM.FF-K4, the volumes of three stainless steel pipettes with a nominal volume of 20 liters and six pycnometers with a nominal volume of 100 ml were determined. A total of eight NMIs took part in the comparison; at PTB, however, only the pipettes were investigated. CENAM in Mexico provided the pipettes (see Fig. 1) and coordinated and analyzed the comparison as pilot laboratory. Besides CENAM and PTB, the other participants were: NIST/USA, MC/Canada, SP/Sweden, IMGC/Italy, NMIA/Australia and INMETRO/Brazil. The measurements took place at the respective NMIs between December 2003 and March 2005. The final report was published in BIPM’s Key Comparison Database in March 2006.

20 l stainless steel pipette

Figure 1: 20 l stainless steel pipette

PTB’s pipette testing facility achieved a more than satisfying overall result. Besides relatively small measurement uncertainties, volume values were determined for the three pipettes which were very close to their respective reference values (KCRV) (see Fig. 2). The excellent agreement with the reference values is reflected especially by the average value of these deviations (“overall degree of equivalence”) of 1·10^-6. Related to 20 l, this small deviation corresponds to approximately one third of the volume of a drop of water.

Deviations of measured volume values from the KCRV of the three pipettes (open blue signs; the length of the bars corresponds to the range of uncertainty) and means of the deviations (red signs). Note: one of the SP results was desclared as an outlier which was not taken into account.

Figure 2: Deviations of measured volume values from the KCRV of the three pipettes (open blue signs; the length of the bars corresponds to the range of uncertainty) and means of the deviations (red signs). Note: one of the SP results was desclared as an outlier which was not taken into account.

Contact person:

Helmut Többen, FB 1.5, AG 1.53, e-mail: helmut.toebben@ptb.de