OBJECTIVE
·
To
determine the microalgal growth through different ways of measurements.
METHODOLOGY
1)
Estimation
of individual dry weight
o
3 duplicate counts of the concentration of the
algal culture [N] was determined accurately to be sampled for dry weight
analysis.
o
An exact volume [V] was filtered on pretared
glass microfibre filters [W] using a Buchner set up connected to a vacuum pump
(in triploicate).
o
The filter was washed with a solution of
ammonium formate (0.5 M) to remove salts.
o
The same procedure was followed with control
filters on which an equal volume of 0.22 μm
filtered seawater is filtered (in triplicate) [B].
o
The filters were dried at 100◦C for 4h to
volatilize the ammonium formate.
o
It was then weighed on an analytical balance
[W*-B*].
o
The dry weight per algal cell was calculated
according to the formula:
DW (g/cell)=DWwc-DWbc/N × V
2)
Optical
density reading
The optical density measurement
was done with a spectrophotometer at 670nm. The spectrophotometer is fitted
with a 10cm long cell. In this cell,we bring the sample to be measured. As a
blank measurement we take the culture medium=seawater.
When a bundle of light (I◦) is
sent through an absorbing material,the bundle of light will have a lower
intensity (I) when leaving the material. The absorption is dependent on the
absorbing material in the solution (the algal cells) but also on the
concentration and thickness of the layer (cell length).
This relation is described by the
Lambert-Beer law : OD or A (absorption) = log10 I◦/I
Practically,we measured the
absoprtion A of the seawater one time. We assume this value to be I◦ since we
are comparing it against the absorption of the algal cells in solution.then we
set up a series of algal dilutions at 100%,80%,60%,40%,20%,0. The absorption of
this series of dilutions is measured with the spectrophotometer and values are
calculated according to Lambert-Beer law. The dilutions are also counted for
number of algal cells with the haemacytometer counter chamber under the
microscope.
Using MS Excel we then put the
values in a graph; Haemacytometer counts on the X-axis and OD values on the
Y-axis. The a suggestion line is fitted and this can be used in the future to
calculate cell concentrations for certain OD value.
3)
Chlorophyll
analysis
o
50ml sample was filtered through GF/F filtered.
o
3 to 5 drops of MgCOᴈ was added to the sample as
it is being filtered.
o
The edges of filter which are not coated with
residue were trimed away.
o
The filter was homogenized with 5ml acetone for
1 minute. 5ml of acetone was added more and grinded for 30 seconds.
o
The sample extract was sampled in refrigerator
in the dark for 1 hr.
o
The sample was centrifuged at 3000 rpm for 10
minutes.
o
The absobance of sample extract was measured at
750nm,664nm,647nm, and 630nm.
RESULTS
1)
Estimation
of individual dry weight
Seawater filter
|
Microalgae filter
|
|
Before (g)
|
0.09
|
0.10
|
After (g)
|
0.10
|
0.11
|
2)
Optical
density reading
%
|
100
|
80
|
60
|
40
|
20
|
0
|
Cell/ml
|
592
|
560
|
539
|
261
|
67
|
0
|
OD
|
1.5684
|
0.6671
|
0.3852
|
1.1459
|
0.1403
|
0
|
3)
Chlorophyll
analysis
Chlorophyll wavelenght (nm)
|
750
|
664
|
647
|
630
|
Absorbance
|
0.083
|
2.1110
|
1.1353
|
0.5848
|
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