Xylem 6-Series Multiparameter - Manual (Page 336)

Chlorophyll Measurements Appendix I
YSI Incorporated Environmental Monitoring Systems Operations Manual I-9
Do I have to worry about the effect of variable temperature on my field readings?
This factor is definitely a consideration depending on the level of reliability you require if the water at your
site is at a significantly different temperature from that of calibration. YSI studies show that, while the
optics and electronics of the sensor show very little temperature effect, the fluorescence of phytoplankton
samples does vary significantly with temperature. Generally, the chlorophyll in biological samples shows
increased fluorescence at lower temperatures with a factor of 1-2 % per degree Celsius. In practice, this
means that if, for example, the calibration temperature is 25 C and the water temperature at the site is 10 C,
the observed chlorophyll readings will be erroneously high by 15-30 %. The “Chl Tempco” factor in the
Advanced|Sensor menu can be used to partially compensate for this error, if the user has some knowledge
of the temperature effect on the particular phytoplankton at the site. The factor can be empirically
determined by bringing a sample of the environmental water to the laboratory and determining its
fluorescence at ambient temperature and low temperature. (Simply cool the sample in a refrigerator for the
latter reading.) The calculated factor can then be entered into the sonde software. See the example in
Section 5, Principles of Operation.
I suspect that my YSI 6025 chlorophyll sensor is not performing properly. What should I do before
contacting YSI Technical Support to facilitate resolving the problem?
You should perform two diagnostic tests to help YSI personnel determine if the YSI 6025 is
malfunctioning.
First, determine whether the wiper system of the probe is working by interfacing the sonde containing the
sensor to a computer on a 650 MDS display/logger, beginning a Discrete Sample study, and manually
activating the wiper. Determine if the wiper turns at all, and, if it does, whether it reverses direction and
parks approximately 180 degrees from the optical face.
Second, determine the sensitivity of the probe by measuring its sensitivity under factory default conditions
in a dye solution prepared as described in Section 5, Principles of Operation. Place the sonde containing
the probe in question into the dye solution. Enter the Calibrate menu and then the Chlorophyll submenu
and choose a “1-point Chl ug/L” protocol. Instead of entering a value at the prompt, type the work “uncal”
and press Enter. This returns the sonde software to the factory default sensitivity. Begin a Discrete
Sample study and record the chlorophyll ug/L reading displayed. Finally, place the sonde in deionized
water and record the chlorophyll ug/L reading displayed in Discrete Sample.
Record the results of these two tests and report them, along with any other symptoms, to a YSI Technical
Support Group representative.