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Calibration of Micropipettes through Gravimetric Solution and its Beneficial Impact on Research

Krishnan Usha Krishnan , Mangala Adisesh, Lakshmipriya Navaneethakrishnan and Reji Manjunathan

The use of high-quality precision liquid handling instruments such as pipettes demands more attention because it provides the user with a sense of confidence while dealing with those data whose applications are robust and rigorous. In order to identify and reduce possible errors in liquid handling, it is necessary to calibrate volume instruments using correct methods. At the highest level of acceptability, the accuracy can be determined by the primary method called a gravimetric method in which the contents of a suitable liquid are weighed by known temperature and density. On this background, in-house verification of pipettes within variable volumes such as 200 μl, 500 μl, and 1000 μl has been performed. The gravimetric method uses a balance to weigh liquid volumes. The balance reports a weight and that weight is converted to mass and then to volume using conversion factors, which may be found in tables, calculated from formulas, or produced by software packages. Corrections are made for the temperature and air pressure when the test is done as Z-factor. Statistical analysis was used to convert mass to volume (V=m*Z). The mean of ten measurements is calculated as V. Accuracy is calculated as A=V-Vs. Random error is expressed as standard deviation and coefficient of variability. In the house, verification findings are compared with those data published by ISO-8655 as Maximum Error Limits for pipettes. The analysis indicates that the performance of in-house pipettes especially the precision and accuracy was not within the tolerance limit that has given by the manufacturer. Hence, the pipettes were sent to manufactures for servicing and recalibration