ENZYME SUBSTRATE COLIFORM TEST
-By Method 10200 H
The concentration of photosynthetic pigments is used extensively to estimate phytoplankton biomass.1,2 All green plants contain chlorophyll a, which constitutes approximately 1 to 2% of the dry weight of planktonic algae. Other pigments that occur in phytoplankton include chlorophylls b and c, xanthophylls, phycobilins, and carotenes. The important chlorophyll degradation products found in the aquatic environment are the chlorophyllides, pheophorbides, and pheophytins. The presence or absence of the various photosynthetic pigments is used, among other features, to separate the major algal groups.
Pheophorbide a and pheophytin a, two common degradation products of chlorophyll a, can interfere with the determination of chlorophyll a because they absorb light and fluoresce in the same region of the spectrum as does chlorophyll a. If these pheopigments are present, significant errors in chlorophyll a values will result. Pheopigments can be measured either by spectrophotometry or fluorometry, but in marine and freshwater environments the fluorometric method is unreliable when chlorophyll b co-occurs. Upon acidification of chlorophyll b, the resulting fluorescence emission of pheophytin b is coincident with that of pheophytin a, thus producing underestimation and overestimation of chlorophyll a and pheopigments, respectively.
–Standard Methods For the Examination of Water and Wastewater
|Method 10200 H|
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