46
The Radiocarbon Method to Estimate Primary Production
in the flask is air-dried for half an hour. Then 1-2g of dry Na-bicarbonate is
added to it + HCI until the color of the water again turns red, then it is airdried again for 20 min. After this, into the sample a new portion of bicarbonate and HCl is added, heated to boiling, and boiled for 1 min to extract the
CO, again. Only then is there hope that the 14C02 background will drop to
-20cpm per 100ml. To check the 14C02 background in the filtrate thus
processed, 50ml of it is placed in the flask c of the apparatus for CO2 distillation shown in Fig. 2.3. The absorber e should be filled with 5 ml of 5% solution of phenethylamine of hyamine in the methoxyethanol or in toluene. The
0.1 N KOH solution of in methanol also could be used. After regulating a slow
flow of COrfree air through the apparatus, to flask 1 are added: 1 ml 0.5%
Na2C03 solution +2ml 5% H 2S04, The water in flask 1 is heated and then
boiled for 3 min. Then the stream of air is accelerated. The distillation of CO2
takes about 10 min. The alkaline solution is then washed from absorber 2 with
2-4 ml of methanol or methoxyethanol into the scintillation vial and its
radioactivity is assayed after addition of the scintillation cocktail. It should not
be more than 20-30cpm per 100mi of the original filtrate subsample. After
such a control of the 14COz-background, the radioactivity in both filtrates
(from light and dark incubations), is neutralized with COz-free KOH solution,
and its volume (V) is determined. Now the filtrate is ready for estimation of
the 14C-radioactivity of its organic matter. Depending upon the kind of water,
two different approaches can be used. In freshwater a definite volume of
sample can be concentrated by evaporation or drying under vacuum. Some
20-ml portions of sample can be dried directly in the scintillation vial at 70-80
0c. Then the scintillation cocktail is added and the radioactivity is counted.
To measure the radioactivity of organic matter in seawater samples, it
should be subjected to the wet combustion procedure and transformed to
14C02. The latter is concentrated on the filter as BaC03 sediment and its
radioactivity is then estimated. For this purpose 50-ml subsamples of filtrate
are distributed into several parallel bottles or cylinders of some 60-ml capacity, into which are then added: Ig dry Na-persulfate + 100mg dry sodium permanganate + 2g dry KOH and some 10mg AgS04. The bottles are capped with
glass caps or balls and autoclaved for 1 h at 1.5 atm. In the field or on ship this
can be done in the pressure cooker. After cooling, their content is transferred
into flask c of the apparatus for CO2 distillation (Fig. 2.3). The absorber (Fig.
2.3e) is filled with 5-10 ml of 0.05 N KOH solution free of CO2• A slow flow of
COz-free air is established through the apparatus and 5 ml of freshly prepared
20% solution of Na-persulfate + lOm150% H 2S04 are added to the flask (Fig.
2.3c), which is then heated and boiled for 5min, followed by 10min of further
CO2 distillation by enhanced flow of air via the apparatus. Then the alkaline
solution is washed out from the absorber into a small flask with boiled hot distilled water, and 1 ml of 10% BaCtz solution is added into it. Some 10min later,
the BaC03 sediment thus formed is filtered through the membrane filters and
the radioactivity of BaC03 sediments is measured (Rt, Rd)' Instead of KOH
solution, 5% hyamine in methanol or in methoxyethanol (or in toluene) can
The Radiocarbon Method to Estimate Primary Production
in the flask is air-dried for half an hour. Then 1-2g of dry Na-bicarbonate is
added to it + HCI until the color of the water again turns red, then it is airdried again for 20 min. After this, into the sample a new portion of bicarbonate and HCl is added, heated to boiling, and boiled for 1 min to extract the
CO, again. Only then is there hope that the 14C02 background will drop to
-20cpm per 100ml. To check the 14C02 background in the filtrate thus
processed, 50ml of it is placed in the flask c of the apparatus for CO2 distillation shown in Fig. 2.3. The absorber e should be filled with 5 ml of 5% solution of phenethylamine of hyamine in the methoxyethanol or in toluene. The
0.1 N KOH solution of in methanol also could be used. After regulating a slow
flow of COrfree air through the apparatus, to flask 1 are added: 1 ml 0.5%
Na2C03 solution +2ml 5% H 2S04, The water in flask 1 is heated and then
boiled for 3 min. Then the stream of air is accelerated. The distillation of CO2
takes about 10 min. The alkaline solution is then washed from absorber 2 with
2-4 ml of methanol or methoxyethanol into the scintillation vial and its
radioactivity is assayed after addition of the scintillation cocktail. It should not
be more than 20-30cpm per 100mi of the original filtrate subsample. After
such a control of the 14COz-background, the radioactivity in both filtrates
(from light and dark incubations), is neutralized with COz-free KOH solution,
and its volume (V) is determined. Now the filtrate is ready for estimation of
the 14C-radioactivity of its organic matter. Depending upon the kind of water,
two different approaches can be used. In freshwater a definite volume of
sample can be concentrated by evaporation or drying under vacuum. Some
20-ml portions of sample can be dried directly in the scintillation vial at 70-80
0c. Then the scintillation cocktail is added and the radioactivity is counted.
To measure the radioactivity of organic matter in seawater samples, it
should be subjected to the wet combustion procedure and transformed to
14C02. The latter is concentrated on the filter as BaC03 sediment and its
radioactivity is then estimated. For this purpose 50-ml subsamples of filtrate
are distributed into several parallel bottles or cylinders of some 60-ml capacity, into which are then added: Ig dry Na-persulfate + 100mg dry sodium permanganate + 2g dry KOH and some 10mg AgS04. The bottles are capped with
glass caps or balls and autoclaved for 1 h at 1.5 atm. In the field or on ship this
can be done in the pressure cooker. After cooling, their content is transferred
into flask c of the apparatus for CO2 distillation (Fig. 2.3). The absorber (Fig.
2.3e) is filled with 5-10 ml of 0.05 N KOH solution free of CO2• A slow flow of
COz-free air is established through the apparatus and 5 ml of freshly prepared
20% solution of Na-persulfate + lOm150% H 2S04 are added to the flask (Fig.
2.3c), which is then heated and boiled for 5min, followed by 10min of further
CO2 distillation by enhanced flow of air via the apparatus. Then the alkaline
solution is washed out from the absorber into a small flask with boiled hot distilled water, and 1 ml of 10% BaCtz solution is added into it. Some 10min later,
the BaC03 sediment thus formed is filtered through the membrane filters and
the radioactivity of BaC03 sediments is measured (Rt, Rd)' Instead of KOH
solution, 5% hyamine in methanol or in methoxyethanol (or in toluene) can