Scope: The purpose of this Standard Operating Procedure (SOP) is to describe methods for verifying and inspecting pipettes to ensure that pipettes are dispensed with the expected accuracy. This determines the difference between the dispensed volume and the selected volume.

Materials: For a quick check, the following materials are required: pipette, pipette tips (manufacturer recommendation), appropriate calibrated laboratory balance, evaporation trap (or suitable weighing container), test liquid ( deionized water), thermometer, pressure gauge, gloves, worksheet, or software.

The ISO 8655 standard has very strict minimum requirements for the weighing equipment used, which for practical purposes depend on the nominal capacity of the pipette being tested.

Frequency of quick checks, test volume and number of repetitions The higher the risk of failure, the more frequently the pipettes should be quick checked.

Pipettes should be inspected at least once completely (nominal volume). Depending on the criteria implemented, a larger number (10%, 50%) of testing is required.

A standard pipette quick check procedure typically follows the following 10 steps for a quick check:

1. Place the prepared vessel on the balance, tare, adjust the pipette to 100% of its nominal capacity and install the manufacturer's recommended tip.
2. Pre-rinse by repeatedly inhaling and draining the specified volume of deionized water.
3. Hold the pipette vertically, immerse the tip to the appropriate depth and aspirate deionized water.
4. Carefully move the pipette over the container on the balance and dispense the liquid. Slide the tip up along the side wall to remove any remaining liquid from the tip.
5. To avoid evaporation effects, the mass of water should be recorded in mg as soon as the balance has stabilized.
6. Repeat this process three more times using the same tip, recording the mass each time.
7. Eject the tip after final dispensing.
8. Adjust pipette down to 10% of nominal volume. Rinse the new tip three times and repeat steps 3-7.
9. The collected data were used to calculate the average volume, accuracy (mean error), and precision (standard deviation) of the pipette; the formulas, equations, and Z-factors (Table 2) are shown below.
10. The results are compared with technical parameters (Table 3). If the results do not match, the pipette may require maintenance or the operator may require further technical training.

Formulas, Z-Factors, and Calculations Formulas for calculating the average volume, accuracy (mean error), and precision (standard deviation) of a pipette:

Tolerance, maximum allowable error (ISO 8655) ISO 8655 clearly defines maximum error limits for piston-operated pipettes. This standard describes the maximum allowable systematic error and the maximum allowable random error limits for devices with specific volumes in the range 1–10,000 μL. These errors are doubled for multichannel pipettes. Most pipette manufacturers specify tolerances well below these limits, but when making low-volume measurements, meeting ISO8655 tolerances can become a challenge for many service providers.

If your results do not match your pipette's specifications, your pipette needs maintenance or calibration.