Back in the good old days, glass pipettes didn't have moving parts and didn't require calibration. But these days, mechanical action pipettes might corrode, pop a leak in a seal, or deteriorate in the shaft ends. In short, you might begin with top notch equipment and still end up with gross measurement inaccuracies. Thus pipette calibration is a vital step in getting accurate lab results. If you perform pipette calibration frequently, you are more likely to detect problems early on.
As you decide how frequently to perform pipette calibration, determine the mean time before failure. The mean time before failure is the average time that elapses before failure. You'll want to use a group of pipettes and record how much time elapses before each one fails. Then add all the times up, divide by the number of pipettes and you'll have the mean time before failure. This will give you a good idea of long you can expect a pipette to remain accurate, and how frequently you should perform pipette calibration.
Along with the mean time before failure, to determine how frequently to perform pipette calibration, keep the following points in mind:
- The nature of the liquid used in the pipettes (Is it corrosive?)
- How the pipettes are stored (Are they stored properly in a vertical position?)
- How frequently the pipettes are used
- The degree of accuracy required (The more accuracy required, the more frequent the calibration.)
- The skill of the pipette operator
- The specifications of your particular lab.
Manufacturers establish their own tolerance limits for pipettes but your lab will have unique performance requirements. The tolerance limits you choose will be influenced by several different factors, most especially the skill and experience of the operator. You need to regularly test both single channel and multi-channel pipettes to ensure that you are working within defined tolerances. As a general rule, most pipettes can be calibrated every six months and perform satisfactorily. If you need to adhere to Food and Drug Administration or other stringent standards, then you should perform pipette calibration more frequently.
Choosing a pipette calibration provider is obviously an important step in calibrating your pipettes. A good way to choose the right laboratory is to look for one that is certified to national or international standards. These labs must follow strict protocols, including having a quality testing system in place, standardized and published lab operator procedures, using only established and approved methods of calibration, an approved system for training and supervising employees, and so on. Additionally, these calibration service providers must be certified by institutions chosen by the standard creators' governing body.