Calibration of micropipettes using the photometric method

Project Description

During the EURAMET TC-F meeting 2017 it was discussed in the volume subgroup the possibility of having a comparison on calibration of micropipettes using the photometric method. Artel, one of the manufacturers of a photometer volunteered to cooperate with EURAMET in this comparison. Since the majority of the laboratories does not have this method implemented in the laboratory it was decided to register this project as a comparison (pilot study). Artel will supply the photometer, the micropipettes and the tips. Training will be given to the participants prior to the measurements.
The Volume and Flow Laboratory of Portuguese Institute for Quality (IPQ) - National Laboratory of Metrology (NMI), acting as the pilot laboratory will perform the initial and final measurements of the micropipettes. Artel will also perform these measurements in order to access the stability of the devices.
Four micropipettes (transfer package) will be tested at different volume capacities.
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 photometric method. 

Final Report 2018-10-08

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

IPQ has implemented the photometric method at its volume laboratory in 2016 [6], following a bilateral comparison in the frame of EURAMET project 1353 "Volume comparison on Calibration of micropipettes – Gravimetric and photometric methods" which supported the publication of CMCs at BIPM webpage. This method" allowed IPQ to increase the range and to reduce uncertainty claims in the calibration of micropipettes with a volume lower than 100 μl. In order to verify that this can be accomplished by other laboratories, a pilot study was performed by seven Europeans NMI’s. Four micropipettes were calibrated at different nominal volumes.

The obtained results were 88% consistent with the reference value for all micropipettes. There was some variation found in the expanded uncertainty declared by the participants and that was mainly due to the repeatability of the measurements. For the majority of the participants this was a first contact with a new method so it is expected that some variation in the results and the uncertainty would arise due to limited or non-existent experience in this method.

The photometric method has certain advantages compared to the gravimetric method which make it favourable especially at smaller volumes. In particular, due to its principle of operation the photometric method offers low uncertainties at the low volume range. On the contrary the gravimetric method's highest uncertainty component arises from the balance itself, has a fixed value and weighs significantly in the low volume range. Moreover, the photometric method is not affected by environmental conditions usually prevailing in the laboratory like temperature, humidity, static electricity, vibrations, etc. However, it has a higher cost of consumables therefore it becomes less favourable compared to the gravimetric method in the range over 100 microliters due to higher uncertainty and it cannot be applied for the determination of volumes higher than 5000 microliters.