Before starting any type of lab work, it is important to check the accuracy of the micropipettes that will be used for the duration of the semester. Water provides a simple way to do this, since it has a density of 1 kg/L. Thus, by recording the weights of different volumes of water, it is easy and quick to evaluate the accuracy of the pipette, given the reliability of the balance.
Use the protocol below to fill out the following table for each pipette:
Micropipette # _______ Micropipette Maximum Volume: _____ mL
Volume setting: _____ mL (max) Volume setting: _____ mL (1/4 max)
Mass of distilled H2O (mg) Mass of distilled H2O (mg)
- Using a balance capable of reading in milligrams or smaller, tare a plastic weighing boat on the pan of the balance.
- Set the micropipette to its maximum capacity and carefully transfer that volume of distilled water to the weighing boat.
- Repeat the operation four times recording in the table below the weight of the distilled water transferred each time.
- Set the micropipette to transfer 20-25% of its maximum volume and repeat step 3.
- Calculate the average (x-bar) and the standard deviation (s) for each set of measurements, using the appropriate button on a calculator.
- Calibrate the 3 micropipettes and fill out a table for each as shown above.
- Using the parameters that were calculated, assess the accuracy of the pipettes.