32
The Radiocarbon Method to Estimate Primary Production
drops of 0.2% its solution in 70% alcohol) sequenced by 0.1 % KOH solution
added drop by drop until a weak rose color appears. If an intensive red color
appears instantly after addition of the indicator, the subsample should be
titrated with 0.05N HCl until its coloration decreases to a weak rose (without
recording the volume of HCl in the solution thus used). On such coloration
by phenolphthalein, all forms of CO2 are presented in the water sample in the
bicarbonate form (HCO)). The subsample with pH adjusted to (8.5) is then
titrated with 0.05 N HCl in the presence of the mixed indicator methyl red +
methylene blue until its green color changes to red. The mixed indicator is prepared by dissolving 100mg methyl red +20mg methylene blue in 50ml of 70%
ethanol. Then the Ci value is calculated: Cj = V 6 mg C 1- 1 , if V is the volume of
0.05N HCl used for titration. The same procedure can be used to measure Ci
in freshwaters.
During acid titration, some other bases present in the sample may also be
titrated, thus resulting in some overestimation. To be safe, the titration method
may be controlled and corrected by the analysis content of hydro carbonates
+ CO2 in water via CO2 distillation from acidified samples in an apparatus as
shown in Fig. 2.3 (Sorokin 1959b). A sample of 100mi is placed into flask 1 of
the apparatus. The absorber is filled with exactly 10ml of 0.1 N NaOH free of
carbonates. Then a weak flow of air free of CO2 is arranged and 3-5ml 5%
H 2S04 is added into the flask. The water sample acidified in the flask is boiled
for 2-3 min to extract the CO2• Then the flow of air in the apparatus is
increased. After 10-15-min distillation, all taps are closed, the alkaline solution is washed out quantitatively from the absorber into the 50-ml flask with
boiled hot distilled water, and 1 ml of 10% BaCb solution is added. The contents of the flask while still hot are titrated with a 0.05 N HCl solution in the
presence of phenolphthalein as indicator. The value of Ci is then calculated as
follows: Ci = (Vb - Vi) x 3 mg C 1-1, if: Vb and Vi the volumes of 0.05 N HCI used
for titration of the blank and sample distillations, correspondingly. The blank
distillation is made with the freshly boiled distilled water instead of the sample.
As alternative, more technically advanced methods of total CO2 contents in
water (C;), if available, such as infrared gas analysis coulometric titration or
gas chromatography, can be employed (Stanton 1973; Johnson et al. 1987).
These are especially efficient in waters with low alkalinity.
2.3.2.3 Selection of Bottles for Experiments and Their Preparation
The minimal volume of bottles to be used safely for primary phytoplankton
production measurements without serious bottle effects (see below) depends
upon the kinds of water bodies to be studied. In oligotrophic tropical oceanic
waters, it should be not less than 0.51, in eutrophic and mesotrophic marine
basins, as in mesotrophic freshwaters, not less than 0.251, in eutrophic freshwaters and eutrophic lagoons not less than 0.151 (Sorokin 1987). Use of bottles
with volumes greater than these for a given kind of water does not give higher
The Radiocarbon Method to Estimate Primary Production
drops of 0.2% its solution in 70% alcohol) sequenced by 0.1 % KOH solution
added drop by drop until a weak rose color appears. If an intensive red color
appears instantly after addition of the indicator, the subsample should be
titrated with 0.05N HCl until its coloration decreases to a weak rose (without
recording the volume of HCl in the solution thus used). On such coloration
by phenolphthalein, all forms of CO2 are presented in the water sample in the
bicarbonate form (HCO)). The subsample with pH adjusted to (8.5) is then
titrated with 0.05 N HCl in the presence of the mixed indicator methyl red +
methylene blue until its green color changes to red. The mixed indicator is prepared by dissolving 100mg methyl red +20mg methylene blue in 50ml of 70%
ethanol. Then the Ci value is calculated: Cj = V 6 mg C 1- 1 , if V is the volume of
0.05N HCl used for titration. The same procedure can be used to measure Ci
in freshwaters.
During acid titration, some other bases present in the sample may also be
titrated, thus resulting in some overestimation. To be safe, the titration method
may be controlled and corrected by the analysis content of hydro carbonates
+ CO2 in water via CO2 distillation from acidified samples in an apparatus as
shown in Fig. 2.3 (Sorokin 1959b). A sample of 100mi is placed into flask 1 of
the apparatus. The absorber is filled with exactly 10ml of 0.1 N NaOH free of
carbonates. Then a weak flow of air free of CO2 is arranged and 3-5ml 5%
H 2S04 is added into the flask. The water sample acidified in the flask is boiled
for 2-3 min to extract the CO2• Then the flow of air in the apparatus is
increased. After 10-15-min distillation, all taps are closed, the alkaline solution is washed out quantitatively from the absorber into the 50-ml flask with
boiled hot distilled water, and 1 ml of 10% BaCb solution is added. The contents of the flask while still hot are titrated with a 0.05 N HCl solution in the
presence of phenolphthalein as indicator. The value of Ci is then calculated as
follows: Ci = (Vb - Vi) x 3 mg C 1-1, if: Vb and Vi the volumes of 0.05 N HCI used
for titration of the blank and sample distillations, correspondingly. The blank
distillation is made with the freshly boiled distilled water instead of the sample.
As alternative, more technically advanced methods of total CO2 contents in
water (C;), if available, such as infrared gas analysis coulometric titration or
gas chromatography, can be employed (Stanton 1973; Johnson et al. 1987).
These are especially efficient in waters with low alkalinity.
2.3.2.3 Selection of Bottles for Experiments and Their Preparation
The minimal volume of bottles to be used safely for primary phytoplankton
production measurements without serious bottle effects (see below) depends
upon the kinds of water bodies to be studied. In oligotrophic tropical oceanic
waters, it should be not less than 0.51, in eutrophic and mesotrophic marine
basins, as in mesotrophic freshwaters, not less than 0.251, in eutrophic freshwaters and eutrophic lagoons not less than 0.151 (Sorokin 1987). Use of bottles
with volumes greater than these for a given kind of water does not give higher