Studying Sulfur Cycling with the Aid of 35S
235
instantly added to it to prevent oxidation of labeled sulfide during the following procedure. For example, approximately 1 ml of 5% NazS9H20 solution
should be added per batch containing 0.3 m Ci of labeled sulfide. Then the contents of the batch is extracted from the container by a Pasteur pipette attached
to the syringe and transferred into the small test tube containing 10ml of
0.05N NaOH.
The following step is the evaluation of the quality of 35S_ sulfide in the
batch by estimation of the presence of the above-listed products of sulfide oxidation. In order to do this, 0.5ml of the carrier solution containing NazS9HzO
- 10%, NaS203 - 35%, NaZS04 -10% is added to 100ml of water. Then 50111
of the above diluted batch solution is injected into it. After mixing, 5 ml of this
dilution is transferred into 25 ml of water. The first two steps of the analytical
procedure: the estimation of radioactivity in the molecular sulfur (SO) and in
the HzS are as described below for the simplified version of processing the
experimental samples. To estimate the radioactivity present in thiosulfate and
sulfate, the filtrate is collected into the flask containing 2ml of 5% KMn04 +
1 ml of 112 HCl + 1 ml 10% BaCh after the separation of ZnS precipitate. The
mixture is boiled for 2-3 min to oxidize thiosulfate to sulfate. The BaS04 precipitate thus formed is filtered and radio assayed after being resuspended in an
Instagel scintillation cocktail with a glass stick.
Simultaneously, the summary radioactivity (Rt) in the same 5-ml portion
of diluted batch solution is measured. This portion is injected directly into
20ml of water containing 2ml of 5% KMn04 + 1 ml of HCl + 1 mllO% BaClz.
The rest of the procedure is as described above. If the joint radioactivity of
oxidized sulfur (including SO) appears to be less than 10% of the total radioactivity of sulfur compounds (Rt ), the given batch solution of Na~sS is suitable
for preparation of the working solution. If not, it could be easily cleaned by
passing it via the gas phase as H2 35 S, just as the 14C-carbonate batches for the
preparation of working solution (see Sect. 2.3.2.3) are cleaned; but because
the amount of the substance to be cleaned (NazS) in the batch even after the
addition of the carrier remains rather small, and because the substance to be
cleaned is unstable, being subjected to oxidation during contact with oxygen,
the procedure of H 2S distillation should be performed in the miniaturized
version of apparatus shown in Fig. 5.9. This apparatus should be approximately
half the normal size specially for this purpose.
The procedure has the following format. The batch solution diluted up to
lOml with the carrier added is placed into the reaction tube a of the apparatus. b 3-4ml of 0.5N NaOH is added to the absorber. The apparatus first is
blown for several minutes with nitrogen. Then the temperate flow through the
apparatus is established. Then 1 % H 2S04 is added to the tube with labeled
sulfide in 5-ml portions and the HzS formed is distilled for approximately
15 min. After this procedure has ended, all clamps are closed. The contents of
the absorber is drained via the tube with the capillary end placed into the glass
balloon (Fig. 5.7) containing 100ml of deoxygenated distilled water by boiling
235
instantly added to it to prevent oxidation of labeled sulfide during the following procedure. For example, approximately 1 ml of 5% NazS9H20 solution
should be added per batch containing 0.3 m Ci of labeled sulfide. Then the contents of the batch is extracted from the container by a Pasteur pipette attached
to the syringe and transferred into the small test tube containing 10ml of
0.05N NaOH.
The following step is the evaluation of the quality of 35S_ sulfide in the
batch by estimation of the presence of the above-listed products of sulfide oxidation. In order to do this, 0.5ml of the carrier solution containing NazS9HzO
- 10%, NaS203 - 35%, NaZS04 -10% is added to 100ml of water. Then 50111
of the above diluted batch solution is injected into it. After mixing, 5 ml of this
dilution is transferred into 25 ml of water. The first two steps of the analytical
procedure: the estimation of radioactivity in the molecular sulfur (SO) and in
the HzS are as described below for the simplified version of processing the
experimental samples. To estimate the radioactivity present in thiosulfate and
sulfate, the filtrate is collected into the flask containing 2ml of 5% KMn04 +
1 ml of 112 HCl + 1 ml 10% BaCh after the separation of ZnS precipitate. The
mixture is boiled for 2-3 min to oxidize thiosulfate to sulfate. The BaS04 precipitate thus formed is filtered and radio assayed after being resuspended in an
Instagel scintillation cocktail with a glass stick.
Simultaneously, the summary radioactivity (Rt) in the same 5-ml portion
of diluted batch solution is measured. This portion is injected directly into
20ml of water containing 2ml of 5% KMn04 + 1 ml of HCl + 1 mllO% BaClz.
The rest of the procedure is as described above. If the joint radioactivity of
oxidized sulfur (including SO) appears to be less than 10% of the total radioactivity of sulfur compounds (Rt ), the given batch solution of Na~sS is suitable
for preparation of the working solution. If not, it could be easily cleaned by
passing it via the gas phase as H2 35 S, just as the 14C-carbonate batches for the
preparation of working solution (see Sect. 2.3.2.3) are cleaned; but because
the amount of the substance to be cleaned (NazS) in the batch even after the
addition of the carrier remains rather small, and because the substance to be
cleaned is unstable, being subjected to oxidation during contact with oxygen,
the procedure of H 2S distillation should be performed in the miniaturized
version of apparatus shown in Fig. 5.9. This apparatus should be approximately
half the normal size specially for this purpose.
The procedure has the following format. The batch solution diluted up to
lOml with the carrier added is placed into the reaction tube a of the apparatus. b 3-4ml of 0.5N NaOH is added to the absorber. The apparatus first is
blown for several minutes with nitrogen. Then the temperate flow through the
apparatus is established. Then 1 % H 2S04 is added to the tube with labeled
sulfide in 5-ml portions and the HzS formed is distilled for approximately
15 min. After this procedure has ended, all clamps are closed. The contents of
the absorber is drained via the tube with the capillary end placed into the glass
balloon (Fig. 5.7) containing 100ml of deoxygenated distilled water by boiling