YSI ADV6600 - Manual (Page 127)

Section 9. Principles of Operation
ADV6600
Y S I
Environmental
Page 117
particles in the optical path at the instant of measurement. For example, in long-term studies this
effect can be seen with spikes of up to 10 NTU sometimes observed. This apparent jumpiness is not
observed for freshly prepared turbidity standards, since the particle size in these suspensions is
homogeneous. The sonde turbidity system allows the user to either observe these real turbidity
events, while obtaining somewhat jumpy readings, or to activate the Turb Spike Filter, which
allows for a better presentation of the average turbidity during deployment.
9-16. Chlorophyll
Chlorophyll, in various forms, is bound within the living cells of algae, phytoplankton, and other
plant matter found in environmental water. Chlorophyll is a key biochemical component in the
molecular apparatus that is responsible for photosynthesis, the critical process in which the energy
from sunlight is used to produce life-sustaining oxygen. In general, the amount of chlorophyll in a
collected water sample is used as a measure of the concentration of suspended phytoplankton, the
magnitude of which can significantly affect the overall quality of the water.
The use of the measurement of phytoplankton as an indicator of water quality is described in
Section 10200 A. of Standard Methods for the Examination of Water and Wastewater. The classical
method of determining the quantity of chlorophyll at a particular site is to collect a fairly large water
sample and analyze it in the laboratory. The procedure involves filtration of the sample to
concentrate the chlorophyll containing organisms, mechanical rupturing of the collected cells, and
extraction of the chlorophyll from the disrupted cells into the organic solvent, acetone. The extract
is then analyzed by either a spectrophotometric method using the known optical properties of
chlorophyll or by high performance liquid chromatography (HPLC). This general method is
detailed in Section 10200 H. of Standard Method and has been shown to be accurate in multiple
tests and applications as long as a competent laboratory analyst carries out the protocol. The
procedure is generally accepted for reporting in scientific literature. The method is time-consuming,
however, and usually requires an experienced, efficient analyst to generate consistently accurate and
reproducible results. It also does not lend itself readily to continuous monitoring of chlorophyll, and
thus phytoplankton, since the collection of samples at reasonable time intervals, e.g., every hour,
would be extremely tedious.
YSI has developed the YSI 6025 chlorophyll sensor for the determination of chlorophyll in spot
sampling and continuous monitoring applications. It is based on an alternative method for the
measurement of chlorophyll which overcomes these disadvantages, albeit with the potential loss of
accuracy. In this procedure, chlorophyll is determined in vivo, i.e., without disrupting the cells as in
the extractive analysis. The YSI 6025 chlorophyll sensor is designed for these in vivo applications
and its use allows the facile collection of large quantities of chlorophyll data in either spot sampling
or continuous monitoring applications. It is important to remember, however, that the results of in
vivo analysis will not be as accurate as results obtained from the certified extractive analysis
procedure.