How Frequently Should an Instrument Be Calibrated?
The simple answer to this question, although not a very helpful one, is “when it needs it.” From a more practical standpoint, daily or periodically testing the control solutions of known values can provide a quantitative indication of instrument performance, which can be used to establish a history. If the controls data indicate that instrument performance is stable, or is varying randomly well within the acceptable range of values, then there is no need to recalibrate the instrument. However, if the historical data indicates a trend toward, or beyond, the acceptable range limits, or if the instrument displays a short-term pronounced shift (due to operation at a different ambient temperature, for example), then recalibration is warranted. Realize also that specific laboratory standard operating procedures or regulatory requirements may require instrument recalibration even when no action is warranted from a results standpoint. These requirements should always take precedence, and the above guidance used at times when there is uncertainty as to whether instrument recalibration should be performed to improve accuracy.