Pipette Calibration
The precision and accuracy of a pipette can be altered by mechanical or electronic failure, incorrect adjustment, the environment of the laboratory or poor technique. Just like torque wrenches, these instruments are of central importance, pipettes must be calibrated. The devices that do so are usually electronic and provide fast, automatic calibration and performance verification along with data and electronic documentation. They are usually unaffected by vibrations, wind currents, temperature or humidity and can be very portable. Some offer accuracies of less than 1% margin of error, even for low volumes used in micropipettes. Pipette calibration is used to safeguard against using flawed pipettes for critical procedures or when investigating a troublesome test result.
Pipettes can be made from plastic or glass and can be automatic, but most are handheld. The body contains a plunger that uses air- or positive-displacement to form a partial vacuum that creates enough suction to pull liquid up into the body of the pipette. A dial on the pipette allows the plunger to be adjusted, varying the maximum volume that the body can hold. Large electronic pipettes have plungers that require actuators. For
calibration that often takes place directly in the
laboratory, a sample is dispensed into a blank vial in the calibration machine. The blank vial contains a precisely-measured volume of a solution and the sample fluid is added to it. A light source releases a beam of light through a filter then into the sample; a detector on the other side of the sample fluid absorbs the light. The detector can read the difference in the absorbed light between from the blank volume and the sample volume. The results are displayed on the device's screen and, frequently, on a computer as well. Some calibration tests display whether or not the pipette passes or fails based on preexisting levels. The results are standardized and must usually meet the requirements of the International Measurement System which allows for direct comparison and consistency among all pipettes and laboratories.
