274
Assay of Some Common Hydrobiological Techniques
2. The method of phytoplankton concentration by inverse filtration through
Nucleopore membranes
This method provides gentle inverse filtration with a very slow flow of water
through a large Nucleopore membrane 60-65 mm in diameter with i-11m pores
(Sorokin 1979). It prevents sticking the cells into the pores as well as their
destruction. The motile algae at such a low flow speed may easily escape direct
collision with the solid surface of the filter. The concentration procedure is
accomplished with fresh living samples. In this case, the small naked flagellates
still preserve their natural durability against mechanical destruction, which is
not undermined by the fixatives.
The funnel for inverse filtration is made of Plexiglas (Fig. 6.1). Its inner
chamber (5) of some 30-cm3 capacity, is formed by the body (C) and the cup
(B) fixed with the brass bolts (10). The chamber is divided by the filtering
membrane fixed between the body and the cup. The body is supported by the
/(7
( A
z
~
9
f
/
.f
/ (7
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.f
B
/
5-E
Fig. 6.1 A-C. Scheme of a funnel by Sorokin for inverse filtration at the Nucleopore
filtering membrane. A Side and top views of combined funnel. B The same of the cup.
C The same of the body (without 8). I Exit connection of the upper chamber; 2 exit
tube of the lower chamber; 3 entrance connection of the lower chamber; 4 the upper
chamber over the filtering membrane; 5 lower chamber; 6 body; 7 cup; 8 prop; 9 rubber
layer; 10 nut; II cross wires supporting the membrane