What type of calibration should be performed after an electrode is changed?

a. Quality control c. Two-point
b. Three-point d. One-point

ANS: B
A three-point calibration should be performed every 6 months or whenever an electrode is re-placed. A two-point calibration is usually performed at least three times daily, typically every 8 hours. In many cases, analyzers can be programmed to perform a two-point calibration at prede-termined intervals. The one-point calibration involves adjusting the electronic output to a single, known standard and should be performed before an unknown sample is analyzed, unless the an-alyzer is programmed to perform a one-point calibration automatically at regular intervals, such as every 20 to 30 minutes. Quality control is the system that includes the analysis of control samples and assessment of the measurements against defined limits, identification of problems, and spec-ification of corrective actions.