Dataset: sulfide_peroxide
Deployment: TT045

ANALYSES
Oxygen and peroxide can be determined without deposition by applying a
negative potential scan from 0.0 V to -1.5 V using the linear sweep or
square wave voltammetry.  Oxygen and peroxide have peaks near -0.09 V
and -0.95 V, respectively (Meites, 1965).  After first scanning the
samples in linear sweep mode to determine the ratio of oxygen to
peroxide sulfide was determined by subsequent scans from -0.1 to -0.8 V
in the cathodic stripping square wave voltammetry (CSSWV) mode without
deposition.  The analyses was repeated with up to 120 second
deposition.  There is approximately one minute time lag between
measurement techniques.   Depths chosen at each station coincided with
levels of high iodide and/or high nitrite.  Sulfide was not measureable
at any of the stations for any of the depths sampled.  Depths chosen at
each station coincided with levels of high iodide and/or high nitrite.
The method detection limit for sulfide in seawater samples is 0.2 nM.
Measurements were undertaken to acertain that oxygen was present in the
samples.  Concentrations of oxygen and peroxide were not quantitated.

EQUIPMENT Electrochemical measurements were made in 10 mL glass
polarographic cells.  EG & G Princeton Applied Research model 384 B
polarographic analyzers equipped with 303A hanging mercury drop working
electrode (HDME) stands were used throughout.  Potentials were measured
vs. a saturated calomel reference electrode (SCE). A platinum counter
electrode was used for current measurements in a standard three
electrode voltammetric arrangement.  A blanket of nitrogen gas is
maintained over the sample so oxygen will not dissolve into the sample
from the laboratory atmosphere.

REFERENCES:

Farrenkopf, A.M., G.W. Luther, III, V.W. Truesdale and C.H. van der
Weijden (in press) Sub-surface iodide maxima: Evidence for biologically
catalyzed redox cycling in Arabian Sea OMZ during the SW intermonsoon.
Deep-Sea Research.
 
Luther, G.W., III (1991) Sulfur and iodine speciation in the water
column of the Black Sea, in Black Sea Oceanography, E. Izdar and J. W.
Murray, Editors.  Kluwer Publishers:  Netherlands. p. 187-204.

Meites (1965) Polarographic Techniques 2nd Edition.  Inter Science
Publications: New York, 752 pp.

Theberge, S.M., III G.W. Luther and A.M. Farrenkopf (in press)  On the
existence of free and metal complexed sulfide in the Arabian Sea and
it's Oxygen Minimum Zone. Deep-Sea Research.