Determination of Free H2S and Labile Sulfides in Bottom Sediments
293
(see Sect. 5.6.2.2) with no addition of acid. When distillation ends, all clamps
are closed. The contents of the absorber is discharged down into the flask containing 20 ml of water into which is added 5 ml of 0.04 N 12 + 5 mil: 5 HCl solutions. Then the absorber is rinsed with the same solution from the flask and
with water. A blank flask is made using the same 8-10ml of Zn acetate-KOH
mixture. Both tiasks are titrated with O.02N thlOsulfate. The content of tree
.
.
( ).
l i d
11
(N - N.) x 320
H 2S III the sedIment sample Ks IS ca cu ate as fo ows: Ks = 0
I
Vs
mg S dm- 3 wet sediment where No and N; are ml of 0.02 N thiosulfate used for
the blank and the sample titrations, and Vs is the volume of sediment taken
for the distillation procedure, cm 3 • In order to control the completeness of H 2S
distillation from the sediment, 1 ml of 1 % freshly made NazS9H20 solution,
neutralized to pH 8.5 (fading red color of the phenolphtalein indicator added),
is injected into the distillation vessel of the apparatus containing the remains
of a similarly treated sediment sample with extracted HzS. This is closed with
a rubber stopper and its contents mixed and attached to the apparatus. Then
the above distillation procedure is repeated. The results of titration are compared with those received after titration of the flask with the iodine-HCl
mixture into which 1 ml of NazS9HzO solution has also been injected directly.
Instead of iodometric titration, the more sensitive colorimetric method by
Cline may also be used. For this, the contents of the absorber at the end of
distillation is washed out with 0.05 N HCl into the calibrated cylinder. Its contents is mixed and its volume recorded. Then a 5-1O-ml aliquot is transferred
into a 50-ml cylinder with a glass stopper, which is then filled with distilled
water up to the mark and the HzS is fixed with appropriate reagents (Parsons
et al. 1984).
To estimate the total stock of acid-volatile labile sulfides (AVS) represented in the bottom sediments mainly by hydrotroilite (FeS9HzO), CaS, and
free hydrosulfide and sulfide ions (free H 2S), the samples are fixed at the place
of sampling. A sample ~250cm3 is taken from the grab or corer first into a
300-ml plastic beaker, into which is added 3-5 ml of Zn mixture prepared 1: 1
by mixing 20% Zn-acetate and 10% Na2C03 solutions. The contents of the
beaker is then carefully mixed with the aid of a plastic spoon. The sediment
samples thus fixed are placed into a plastic 100-ml bottle and closed without
air bubbles. They may be preserved in the refrigerator before processing for
2 months.
The distillation of HzS from acidified sediment subsamples is accomplished exactly as described above (see Chap. 5) with the absorber filled with
10ml of 1: 1: 1 mixture of the solutions 2% CdClz, 3% Zn-acetate, and 5%
Na2C03. Instead of this mixture, used for the iodometric end, 1-2% permanganate solution may also be used for the gravimetric end. If the iodometric
end is preferred, the flask is prepared containing 40ml of water +5 ml of 1: 3
HCl + 10 ml of ~ 0.2 N of Iz solution. After distillation of H 2S from the acidified
sediment subsample is finished and all clamps are closed, the content of
293
(see Sect. 5.6.2.2) with no addition of acid. When distillation ends, all clamps
are closed. The contents of the absorber is discharged down into the flask containing 20 ml of water into which is added 5 ml of 0.04 N 12 + 5 mil: 5 HCl solutions. Then the absorber is rinsed with the same solution from the flask and
with water. A blank flask is made using the same 8-10ml of Zn acetate-KOH
mixture. Both tiasks are titrated with O.02N thlOsulfate. The content of tree
.
.
( ).
l i d
11
(N - N.) x 320
H 2S III the sedIment sample Ks IS ca cu ate as fo ows: Ks = 0
I
Vs
mg S dm- 3 wet sediment where No and N; are ml of 0.02 N thiosulfate used for
the blank and the sample titrations, and Vs is the volume of sediment taken
for the distillation procedure, cm 3 • In order to control the completeness of H 2S
distillation from the sediment, 1 ml of 1 % freshly made NazS9H20 solution,
neutralized to pH 8.5 (fading red color of the phenolphtalein indicator added),
is injected into the distillation vessel of the apparatus containing the remains
of a similarly treated sediment sample with extracted HzS. This is closed with
a rubber stopper and its contents mixed and attached to the apparatus. Then
the above distillation procedure is repeated. The results of titration are compared with those received after titration of the flask with the iodine-HCl
mixture into which 1 ml of NazS9HzO solution has also been injected directly.
Instead of iodometric titration, the more sensitive colorimetric method by
Cline may also be used. For this, the contents of the absorber at the end of
distillation is washed out with 0.05 N HCl into the calibrated cylinder. Its contents is mixed and its volume recorded. Then a 5-1O-ml aliquot is transferred
into a 50-ml cylinder with a glass stopper, which is then filled with distilled
water up to the mark and the HzS is fixed with appropriate reagents (Parsons
et al. 1984).
To estimate the total stock of acid-volatile labile sulfides (AVS) represented in the bottom sediments mainly by hydrotroilite (FeS9HzO), CaS, and
free hydrosulfide and sulfide ions (free H 2S), the samples are fixed at the place
of sampling. A sample ~250cm3 is taken from the grab or corer first into a
300-ml plastic beaker, into which is added 3-5 ml of Zn mixture prepared 1: 1
by mixing 20% Zn-acetate and 10% Na2C03 solutions. The contents of the
beaker is then carefully mixed with the aid of a plastic spoon. The sediment
samples thus fixed are placed into a plastic 100-ml bottle and closed without
air bubbles. They may be preserved in the refrigerator before processing for
2 months.
The distillation of HzS from acidified sediment subsamples is accomplished exactly as described above (see Chap. 5) with the absorber filled with
10ml of 1: 1: 1 mixture of the solutions 2% CdClz, 3% Zn-acetate, and 5%
Na2C03. Instead of this mixture, used for the iodometric end, 1-2% permanganate solution may also be used for the gravimetric end. If the iodometric
end is preferred, the flask is prepared containing 40ml of water +5 ml of 1: 3
HCl + 10 ml of ~ 0.2 N of Iz solution. After distillation of H 2S from the acidified
sediment subsample is finished and all clamps are closed, the content of