Xylem 6-Series Multiparameter - Manual (Page 329)

Chlorophyll Measurements Appendix I
YSI Incorporated Environmental Monitoring Systems Operations Manual I-2
6025 should approximately track the chlorophyll trends in the environmental water being analyzed. For
example, if the user deploys the sensor and acquires readings over time at a standard sampling interval
(e.g., every 15 minutes), the changes in the chlorophyll data will usually reflect increases or decreases in
the phytoplankton content at the site over a long period of time. If the user makes horizontal or vertical
profiling spot readings in the same body of water, then the sensor output will usually indicate the presence
of more or less phytoplankton at the various sampling sites. The figure below shows the tracking of the
chlorophyll content at various sites by both the YSI 6025 and a good quality single parameter commercial
fluorometer.
It is important for the user to remember that, because of the limitations defined in this appendix and in
Section 5, Principles of Operation, YSI is unable to quote an accuracy specification for the in vivo
measurement of chlorophyll.
What calibration methods are available for the YSI 6025?
There is only one real method of calibration for the 6025 sensor if accuracy is to be assured versus the true
chlorophyll content of the water: The sensor must be calibrated with a phytoplankton suspension for which
the chlorophyll content is known from extractive analysis in the laboratory.
This methodology requires the
user to collect water samples of the environmental water in question during sampling or monitoring studies,
analyze the samples in the laboratory after cell disruption, and use the chlorophyll values determined by
this method to adjust the data acquired with the YSI 6025. Discrete steps for this procedure are found in
Section 5. Principles of Operation.
Using this method, the field data must be adjusted, either manually or in a spreadsheet, according to the
laboratory value. For example, if the YSI 6025 value for a particular site is15.6 ug/L chlorophyll and the
laboratory value is 10.8 ug/L, then all of the values for the study should be multiplied by .69 (10.8/15.6).
This can easily be done in a spreadsheet, such as Excel, as shown below.