Volume comparison on Calibration of micropipettes – Gravimetric and photometric methods

Project Description

The purpose of the comparison is to compare the results of the participating laboratories regarding the calibration of several micropipettes of different nominal volume using the gravimetric method and the photometric method.

Final Report 2016-02-01

The project has been completed and the report can be downloaded here>>.

This bilateral comparison between IPQ and Artel comprised the calibration of four different micropipettes in five volume points, IPQ acting as the pilot laboratory determined the reference value.
The volume results obtained by Artel are 86 % consistent with the reference value for the gravimetric method and 98 % consistent for the photometric method. 
The values obtained for higher volumes had the most percentage of inconsistent results, this may be due to a larger operator effect or the balance characteristics.
The value obtained for the expanded uncertainty for the 1000 microliter, 100 microliter and 10 microliter volumes is quite similar in both laboratories however for the smaller volumes the uncertainty of the reference value in both methods is smaller than Artel claims.

The uncertainty component that has a major contribution to the final uncertainty depends on the volume determined. In the photometric method for small volumes the repeatability will be the largest uncertainty component but for large volumes, bigger than 100 microliter, the instrument will be the most significant source of uncertainty. This is the opposite of the results obtained by the gravimetric method. Conclusion the best method to be used for volumes smaller than 100 microliter is the photometric method.
The variability found between the operators for large volumes reflects the need to include the operator-to-operator standard deviation in the calibration uncertainty and calibration measurement capability.
In this report it was as also determined the equivalence of results for both laboratories between the gravimetric method and the photometric method. The results obtained for all micropipettes for both laboratories had an En value lower than 1.