Hydrogen peroxide in seawater

Petasne, R. G. M.S. Thesis ( Cycling of Hydrogen Peroxide in Seawater ), University of Miami, 1987. 

K. Fujiwara, T. Ushiroda, K. Takeda, Y. Kumamato, H. Tsubota (1993). Diurnal and seasonal distribution of hydrogen peroxide in seawater of the Seto Inland Sea. Geochem. J., 27,103-115. 

The measurement of significzmt concentrations of hydrogen peroxide in seawater (Van Baalen and Marler, 1966) and the demonstration of its photochemical production (Zika, 1978) in seawater support the occurrence of such processes. If hydrogen peroxide generation is ubiquitous over the oceans then through its spontaneous degradation pathways it represents an important secondary reaction process. 

Sakamoto [243] determined picomolar levels of cobalt in seawater by flow injection analysis with chemiluminescence detection. In this method flow injection analysis was used to automate the determination of cobalt in seawater by the cobalt-enhanced chemiluminescence oxidation of gallic acid in alkaline hydrogen peroxide. A preconcentration/separation step in the flow injection analysis manifold with an in-line column of immobilised 8-hydroxyquinoline was included to separate the cobalt from alkaline-earth ions. One sample analysis takes 8 min, including the 4-min sample load period. The detection limit is approximately 8 pM. The average standard deviation of replicate analyses at sea of 80 samples was 5%. The method was tested and inter calibrated on samples collected off the California coast. 

Moore [355] used the solvent extraction procedure of Danielson et al. [119] to determine iron in frozen seawater. To a 200 ml aliquot of sample was added lml of a solution containing sodium diethyldithiocarbamate (1% w/v) and ammonium pyrrolidine dithiocarbamate (1 % w/v) at pH to 4. The solution was extracted three times with 5 ml volumes of 1,1,2 trichloro-1,2,2 trifluoroethane, and the organic phase evaporated to dryness in a silica vial and treated with 0.1 ml Ultrex hydrogen peroxide (30%) to initiate the decomposition of organic matter present. After an hour or more, 0.5 ml 0.1 M hydrochloric acid was added and the solution irradiated with a 1000 W Hanovia medium pressure mercury vapour discharge tube at a distance of 4 cm for 18 minutes. The iron in the concentrate was then compared with standards in 0.1 M hydrochloric acid using a Perkin-Elmer Model 403 Spectrophotometer fitted with a Perkin-Elmer graphite furnace (HGA 2200). 

Kawabuchi and Kuroda have concentrated molybdenum by anion exchange from seawater containing acid and thiocyanate [497] or hydrogen peroxide [497,498], and determined it spectrophotometrically. Korkisch et al. [499] concentrated molybdenum from natural waters on Dowex 1-X8 in the presence of thiocyanate and ascorbic acid. 

In another procedure [522] the sample of seawater (0.5-3 litres) is filtered through a membrane-filter (pore size 0.7 xm) which is then wet-ashed. The nickel is separated from the resulting solution by extraction as the dimethylglyoxime complex and is then determined by its catalysis of the reaction of Tiron and diphenylcarbazone with hydrogen peroxide, with spectrophotometric measurement at 413 nm. Cobalt is first separated as the 2-nitroso-1-naphthol complex, and is determined by its catalysis of the oxidation of alizarin by hydrogen peroxide at pH 12.4. Sensitivities are 0.8 xg/l (nickel) and 0.04 xg/l (cobalt). 

Korkisch and Koch [106,107] determined low concentrations of uranium in seawater by extraction and ion exchange in a solvent system containing trioctyl phosphine oxide. Uranium is extracted from the sample solution (adjusted to be 1 M in hydrochloric acid and to contain 0.5% of ascorbic acid) with 0.1 M trioctylphos-phine oxide in ethyl ether. The extract is treated with sufficient 2-methoxyethanol and 12 M hydrochloric acid to make the solvent composition 2-methoxyethanol-0.1 M ethereal trioctylphosphine acid-12 M hydrochloric acid (9 10 1) this solution is applied to a column of Dowex 1-X8 resin (Cl" form). Excess of trioctylphosphine oxide is removed by washing the column with the same solvent mixture. Molybdenum is removed by elution with 2-methoxyethanol-30% aqueous hydrogen peroxide-12 M hydrochloric... 

A continuous flow system utilising the oxidation of formaldehyde and gallic acid with alkaline hydrogen peroxide to produce a chemiluminescence was studied by Slawinska and Slawinski [ 137]. While the major peak of the chemiluminescence spectrum occurred at 635 nm, the photomultiplier used summed all of the available light between 560 and 850 nm. The intensity of the chemiluminescence was linearly proportional to formaldehyde concentration from 10 7 to 10 2 M, producing a detection limit of 1 xg/l. This method should be sensitive enough for use in seawater. 

Oxidation of DMS to DMSO and DMSO. DMS is chemically and biochemically oxidized to dimethylsulfoxide (DMSO). Mechanisms for the in situ oxidation of DMS to DMSO in seawater have received little attention, even though this may be an important sink for DMS. Hydrogen peroxide occurs in surface oceanic waters (22) and is produced by marine algae (98). It may participate in a chemical oxidation of DMS, since peroxide oxidizes sulfides to sulfoxides (991. Photochemical oxidation of DMS to DMSO occurs in the atmosphere and DMSO is found in rain from marine regions (681. DMS is also photo-oxygenated in aqueous solution to DMSO if a photosensitizer is present natural compounds in coastal seawater catalyzed photo-oxidation at rates which may be similar to those at which DMS escapes from seawater into the atmosphere (1001. 

The oceans at this time can be thought of as the solution resulting from an acid leach of basaltic rocks, and because the neutralization of the volatile acid gases was not restricted primarily to land areas as it is today, much of this alteration may have occurred by submarine processes. The atmosphere at the time was oxygen deficient anaerobic depositional environments with internal CO2 pressures of about 10-2-5 atmospheres were prevalent, and the atmosphere itself may have had a CO2 pressure near lO-25 atmospheres. If so, the pH of early ocean water was lower than that of modern seawater, the calcium concentration was higher, and early global ocean water was probably saturated with respect to amorphous silica (—120 ppm). Hydrogen peroxide may have been an important oxidant and formaldehyde, an important reductant in rain water at this time (Holland et al., 1986). Table 10.5 is one estimate of seawater composition at this time. 

Hydrogen sulfide can be oxidized in less than an hour in seawater. This removal can be through oxidation by oxygen or iodate. There is a possibility of oxidation, by hydrogen peroxide, but it is probably a minor pathway (Radfordknoery and Cutter, 1994). Photo-oxidation is also possible (Pos et ai, 1998), along with oxidation by Fe(III) oxide particles. This latter process is dependent on the way in which the particle forms and on pH with a maximum near 6.5. The Fe(III) oxide route gives mostly elemental sulfur as a product, which may have implications for pyrite formation (Yao and Millero, 1996). 

Plutonium Purification. The same purification approach is used for plutonium separated from sediments or seawater. In case reduction may have occurred, the plutonium is oxidized to the quadrivalent state with either hydrogen peroxide or sodium nitrite and adsorbed on an anion exchange resin from 8M nitric acid as the nitrate complex. Americium, curium, transcurium elements, and lanthanides pass through this column unadsorbed and are collected for subsequent radiochemical purification. Thorium is also adsorbed on this column and is eluted with 12M hydrochloric acid. Plutonium is then eluted from the column with 12M hydrochloric acid containing ammonium iodide to reduce plutonium to the non-adsorbed tervalent state. For seawater samples, adequate cleanup from natural-series isotopes is obtained with this single column step so the plutonium fraction is electroplated on a stainless steel plate and stored for a-spectrometry measurement. Further purification, especially from thorium, is usually needed for sediment samples. Two additional column cycles of this type using fresh resin are usually required to reduce the thorium content of the separated plutonium fraction to insignificant levels. 

J.W. Moffet, R.G. Zika (1987). Reaction kinetics of hydrogen peroxide with copper and iron in seawater. Environ. Sci. Technol., 21, 804-810. 

Several possible mechanisms are available for UV-induced photoreactions of iron complexes. First, direct photoreactions involving ligand-to-metal charge transfer are likely to be one of the most important mechanisms for photoreaction [117,198,224]. Second, iron complexes can be reduced by photochemically-produced superoxide [207-209]. Superoxide ions are formed via the photoreduction of molecular oxygen by CDOM and it is one of the most concentrated radicals in seawater and is the precursor to hydrogen peroxide [Chapter 8]. Superoxide-induced reduction of Fe(iii) is an important mechanism in certain lakes [207]. However, the fact that Fe(ii) photoproduction can be more rapid in oxygen-free water than in air-saturated water in acidic estuaries [59] or model systems with well-defined organic acid complexes of Fe(iii) [117] indicates that direct photolysis of Fe(iii) is likely to be a dominant mechanism for Fe(ii) photoproduction in many aquatic systems. 

Figure 1 Schematic summary of the sources and removal pathways of ROS in natural waters including singlet oxygen ( 02), superoxide (02 ), hydrogen peroxide (H Oj) and the hydroxyl radical ( OH). The main ROS are indicated by squares. Notation FW, freshwater SW, seawater Me"+ or Me " +, metal in the n-l- or (n-l)-l- oxidation state NO, the nitrate or nitrite anion and , unknown pathway.

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