Non-Metals
101
sulphuric acid (94 %) or sulphuric: acetic acid (l : 4), or the azomethine hydrogen ion
association complex (415 nm) formed at pH 5.2, were used for borate measurement.
4.3.2
Sulphide and Elementary Sulphur
Valkov and Zhabina [284] reduced elemental sulphur in marine sediments to hydrogen sulphide using metallic chromium. The liberated hydrogen sulphide was absorbed in cadmium solution and estimated iodimetrically.
Chen et al. [285] extracted elemental sulphur from marine sediments with aromatic
solvents and determined S4' S6' and S8 in the extract by gas chromatography.
Morse and Cornwell [286] investigated methods for determining acidvolatile sulphides and pyrites in marine sediments from several typical depositional environments which were permanently or seasonally anoxic. Extractants gave similar results
under different acid conditions, with the exception of stannous chloride in hot
hydrochloric acid. The use of scanning electron microscopy combined with simultaneous elemental analysis showed that identifiable iron sulphides were almost always
pyrite.
4.3.3
Organic Carbon
Mills and Quinn [287] used persulphate oxidation at 130°C with subsequent measurement of carbon dioxide produced by a non-dispersive infrared detector to determine
organic carbon in high carbonate oceanic sediments and estuarine sediments. Sediment samples were predried for 4 h at 110°C to remove moisture and, if carbonate
was present, were pretreated with hydrochloric acid and phosphoric acid to decompose carbonates, then washed and dried. The results of organic carbon determinations
in some marine sediments by this method, and by high temperature combustion
using the Carlo Erba elemental analyser, shows that there appears to be no significant
bias between the methods. The average relative standard deviation obtained by the
persulphate method is 11.4 %, which is higher than the value of 5.1 % obtained by
high temperature oxidation. The overall precision of the persulphate method was
6.4%.
Weliky et al. [288] have developed a procedure for determination of both organic
and inorganic carbon in a single sample of marine deposit, thus avoiding errors
occurring in the method most commonly used. Carbonate carbon is determined from
the carbon dioxide evolved by treatment of the sample with phosphoric acid, and the
residue is then treated with a concentrated solution of dichromate and sulphuric acid
to release carbon dioxide from the organic matter.
101
sulphuric acid (94 %) or sulphuric: acetic acid (l : 4), or the azomethine hydrogen ion
association complex (415 nm) formed at pH 5.2, were used for borate measurement.
4.3.2
Sulphide and Elementary Sulphur
Valkov and Zhabina [284] reduced elemental sulphur in marine sediments to hydrogen sulphide using metallic chromium. The liberated hydrogen sulphide was absorbed in cadmium solution and estimated iodimetrically.
Chen et al. [285] extracted elemental sulphur from marine sediments with aromatic
solvents and determined S4' S6' and S8 in the extract by gas chromatography.
Morse and Cornwell [286] investigated methods for determining acidvolatile sulphides and pyrites in marine sediments from several typical depositional environments which were permanently or seasonally anoxic. Extractants gave similar results
under different acid conditions, with the exception of stannous chloride in hot
hydrochloric acid. The use of scanning electron microscopy combined with simultaneous elemental analysis showed that identifiable iron sulphides were almost always
pyrite.
4.3.3
Organic Carbon
Mills and Quinn [287] used persulphate oxidation at 130°C with subsequent measurement of carbon dioxide produced by a non-dispersive infrared detector to determine
organic carbon in high carbonate oceanic sediments and estuarine sediments. Sediment samples were predried for 4 h at 110°C to remove moisture and, if carbonate
was present, were pretreated with hydrochloric acid and phosphoric acid to decompose carbonates, then washed and dried. The results of organic carbon determinations
in some marine sediments by this method, and by high temperature combustion
using the Carlo Erba elemental analyser, shows that there appears to be no significant
bias between the methods. The average relative standard deviation obtained by the
persulphate method is 11.4 %, which is higher than the value of 5.1 % obtained by
high temperature oxidation. The overall precision of the persulphate method was
6.4%.
Weliky et al. [288] have developed a procedure for determination of both organic
and inorganic carbon in a single sample of marine deposit, thus avoiding errors
occurring in the method most commonly used. Carbonate carbon is determined from
the carbon dioxide evolved by treatment of the sample with phosphoric acid, and the
residue is then treated with a concentrated solution of dichromate and sulphuric acid
to release carbon dioxide from the organic matter.