YSI 600DW-B Sonde - Manual (Page 229)

Principles of Operation Section 5
unattended studies. The user should determine from experience whether its activation is also appropriate
for spot sampling studies at particular sites.
5.12 CHLOROPHYLL
INTRODUCTION
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 those from the certified extractive analysis procedure.
The limitations of the in vivo method are outlined below and should be carefully considered before making
chlorophyll determinations with your YSI sonde and sensor. Some of the sources of inaccuracy can be
minimized by combining the data from the YSI 6025 with data from extractive analysis of a few samples
acquired during a sampling or monitoring study. However, the in vivo studies will never replace the
standard procedure. Rather, the estimates of chlorophyll concentration from the easy-to-use YSI
chlorophyll system are designed to complement the more accurate (but more difficult to obtain) results
from more traditional methods of chlorophyll determination.
MEASUREMENT OF CHLOROPHYLL IN VIVO
One key characteristic of chlorophyll is that it fluoresces, that is, when irradiated with light of a particular
wavelength, it emits light of a higher wavelength (or lower energy). The ability of chlorophyll to fluoresce
YSI Incorporated Drinking Water Monitoring Systems Operation Manual 5-16