If a regulator requires that a calibration be performed on a colorimeter or spectrophotometer is this a good idea?

Document ID

Document ID TE777

Published Date

Published Date 11/06/2018
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Question
If a regulator requires that a calibration be performed on a colorimeter or spectrophotometer is this a good idea?
Summary
Performing a calibration on a colorimeter or spectrophotometer
Answer
First make sure that the regulator requires a new calibration and not just a calibration check for the test that is being performed.

A new calibration is time-consuming and has the potential to introduce error, resulting in inaccurate data. Hach instruments are calibrated by experienced chemists using multiple lots of reagent, standard, and multiple instruments and are independently verified to ensure accuracy. 

Hach recommends using a standard solution to verify the existing calibration curve in an instrument rather than enter a new calibration into the instrument. If the correct result is obtained using a standard solution, a new calibration is not necessary. If the resulting concentration is significantly different from that of the standard (more than 10-20 %), make sure the procedure for performing the test and the prepararation of the standard was followed exactly. Verify that the correct program number on the instrument is used, that the correct sample cells and specified reagents are used, that glassware has been cleaned thoroughly, and that the correct glassware is used. Verify that the chemical form on the standard solution matches that of the result, for example if the label on a phosphorus standard solution reads as PO4, be sure the result from the instrument or kit is also displayed as PO4 and not as P.

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