Calibrating Fluorometers for In Vivo Chlorophyll a Monitoring

Turner Designs fluorometers utilize a 'one-point' calibration method, and are calibrated using Secondary Standards to provide reliable and consistent readings. When data of actual chlorophyll a are required, a post-calibration procedure will need to be conducted (see below). Follow the links for instrument specific calibration procedures for in vivo chlorophyll calibration procedures and videos.

Fluorometers display a reading proportional to the chlorophyll concentration in water using a linear response established in the calibration by the calibration standard and response curve, see above example graph.

1. Calibration using a Secondary Standard:

Using a Secondary Standard to calibrate a fluorometer for in-vivo chlorophyll applications is often the most logical choice. It provides a stable and consistent signal level that can be correlated to actual chlorophyll a. The Secondary Standard can also be used for relative readings to provide a predictable and repeatable calibration reference point.

The secondary standard can either be a Solid Standard or a liquid solution, such as Rhodamine WT dye. Turner Designs calibration kits for flowthrough fluorometers include Rhodamine WT dye, and for discrete sample fluorometers the calibration kit includes a solid standard

2. 'Post Calibration' Method:

A "post calibration" method is used to correct for factors that influence the in vivo chlorophyll reading including changes in the environment or water conditions. This method requires that water samples be routinely collected during the course of the in-vivo monitoring,

For a given sample of water, in vivo chlorophyll readings are recorded, and then sub samples are stored for chlorophyll a extraction, (see EPA 445.0)

A 'calibration coefficient' is derived based on the relationship between the in vivo and the extracted levels for the collected sample. This calibration coefficient enables the in vivo chlorophyll data to be converted to absolute concentration levels in units of µg/L.