YSI ADV6600 - Manual (Page 189)

Appendix E. Chlorophyll Measurements
ADV6600
Y S I Environmental
Page 179
time of field measurement for the chlorophyll values determined by the two methods to
agree consistently. This level of synchronization is usually not practical.
The key point to remember is that in vivo chlorophyll determinations made with any
fluorometer are likely to be less accurate than those measured by laboratory analysis of
individual samples. The advantage of the in vivo method is its convenience and ability to
readily track changes in relative phytoplankton values via indirect fluorescence readings.
Can I use a dye standard to calibrate my 6025 chlorophyll sensor to increase the accuracy?
The use of the dye solutions will usually not significantly enhance the accuracy of your field
readings relative to extractive analysis of grab samples. The primary utility of the dye is to
check for sensor drift during deployment by reanalyzing the dye solution after sonde
recovery. The use of the 2-point dye calibration procedure may make it easier to quantify
the pre-deployment dye value and, if so, may be preferable. Remember, however, that no
real enhancement of sensor accuracy is attained by using dye as a calibration standard.
Will chlorophyll values determined in vivo with the YSI 6025 be reportable for compliance
purposes?
Probably not. Because of the limitations on the method there is always inaccuracy in the in
vivo method. It might be possible to work with a particular regulatory agency to develop
specific correlation protocols between in vivo and laboratory-determined chlorophyll
values for a particular site, but generation of this methodology is left to the user.
The Standard Methods procedure generates values designated as “chlorophyll a”. Is this
species the reporting unit for the YSI 6025?
No. The different types of chlorophyll cannot be differentiated by the YSI 6025, or by
virtually any in vivo fluorometer. The values from the YSI 6025 should be reported either
as relative fluorescence units or in ug/L of general chlorophyll as long as the method of
determination (and its limitations) is specified.
Is the YSI 6025 sensor linear with regard to changes in phytoplankton content?
Yes. The sensor is very linear as evidenced by the following plot that shows the results of
a serial dilution of a laboratory algae sample. This linearity on a particular algal species
maximizes the ability of the sensor to track relative phytoplankton changes from site to site
or during a monitoring study.