Wet chemical oxidation

Wet chemical oxidation methods, using oxidants such as persulfate, are widely used in oceanographic and limnologic work [46,47]. The main drawbacks of these methods are their manual and cumbersome techniques and incomplete oxidation of some organic compounds [48]. 

The merits and limitations of wet chemical oxidation, high-temperature combustion, and photo-oxidation methods for seawater analysis were summarised by Gershey et al. [58]. 

Smith, G. Fredrick, The Wet-Chemical Oxidation of Organic Compositions, Employing Perchloric Acid, G. F. Smith Chemical Co., Columbus, Ohio, 1965. 

Chemical oxygen demand (COD) is another wet chemical oxidation method. The chemical basis is the reaction of dichromate in concentrated sulfuric acid matrix according to Eq. (10.3). COD values are given mg liter1 02. 

Burkhardt, M.R., R.W. Brenton, J.A. Kammer, V.K. Jha, P.G. O Mara-Lopez, and M.T. Woodworth. 1999. Improved method for the determination of non-purgeable suspended organic carbon in natural water by silver filter filtration, wet chemical oxidation, and infrared spectrometry. Water Resour. Res. 35 329-334. 

McKenna, J.H. and P.H. Doering. 1995. Measurement of dissolved organic carbon by wet chemical oxidation with persulfate Influence of chloride concentration and reagent volume. Mar. Chem. 48 109-114. 

Masiello and Druffel (1998) measured the abundance and radiocarbon content of BC (isolated by wet chemical oxidation) in sediment cores from two deep Pacific Ocean sites. They found BC comprises 12-31% of the total sedimentary OC, and was between 2,400 yr and 13,000 yr older than non-BC sedimentary OC (Figure 5). For sediment intervals deposited prior to the Industrial era (i.e., free of BC inputs from fossil fuel utilization), the authors argue that the older ages for BC must be due to storage in an intermediate reservoir before deposition. Possible intermediate pools are oceanic DOC and terrestrial soils. They conclude that if DOC is the intermediate reservoir, then BC comprises 4-22% of the DOC pool. If soils are the intermediate reservoir, then the importance of riverine OC has been underestimated. 

GD-carbon dioxide detection BAWIS 10- -2x10 moir Wet chemical oxidation... 

Analytical techniques, which have been employed for the measurement of DOC in seawater, are (1) wet chemical oxidation (WCO), (2) ultraviolet (UV) oxidation, (3) dry combustion, and (4) high-temperature catalytic oxidation (HTCO). 

Total organic carbon (TOC) analysis is based on the principle that carbon in an aqueous sample is converted to carbon dioxide by catalytic combustion or wet chemical oxidation. The carbon dioxide formed is measured directly by an infrared detector or converted to methane and measured by a flame ionization detector. The amount of carbon dioxide or methane is directly proportional to the concentration of carbonaceous material in the sample. Inorganic carbon is removed by acidification of the sample prior to analysis. 

After an additional deposition of smooth and thin metallic gold film and coating it with an alkyl thiol self-assembled monolayer (SAM), we were able to decrease this hysteresis to values of around 10°. By using thin and rough metallic films like wet chemically oxidized titanium oxide tmd a lluoralkylsilane SAM, the hysteresis values could be reduced to only 4°. 

As described by the Wenzel wetting model, the increase of surface roughness should lead to a certain increase of contact angle (CA) values. To verify this statement, we investigated three different kinds of commonly used thin films known to be very different in grain size and, therefore, in surface roughness. Figure 3 shows the comparison of a 50 nm Au film, an 800 nm native oxidized titanium film (TiO") and an 800 nm wet chemically oxidized titanium film (TiO ) on a polished silicon substrate. 

Surface Treatment. Most film surfaces require surface treatment for use in subsequent steps of coating, printing, lamination, or metallization. This treatment results in the chemical modification of the polymer at the surface. The most widely employed surface modification is oxidation of the polymer to create a polar smface (43). Processes that are widely employed are corona and flame treatment. Wet chemical oxidative treatments are seldom used and are restricted to low speed operations. A new surface oxidation technique has been recently developed which uses an atmospheric plasma generated in a hollow cathode with helium or helium gas blends (44). 

By combining the cold-vapor technique with HPLC, a very sensitive method for the determination of Hg spedes at the sub-ng level becomes possible [322]. When applying cold-vapor AAS to the detection of mercury subsequent to the separation of the species by HPLC, which also enables thermally labile compounds to be separated, the organomercury compounds have to be destroyed to allow for the AAS determination. They can be destroyed by wet chemical oxidation with H2S04-Ct207 or by photochemical oxidation. It is then possible to perform spe-ciation of mercury in gas condensates easily, where the species can be separated by reversed phase HPLC [323]. 

Photo-oxidation instead of wet-chemical oxidation is often considered an attractive method because of the very low blanks. However, irradiation with UV light does not seem to ensure complete recovery of mercury from organically assodated and related species. Reduced signals have even been observed following extended irradiation times (Gerwinski et al., 19%) which might indicate the formation of compounds with decomposition products from which Hg cannot be liberated by reduction with Sn. Therefore, to determine true total mercury concentrations, UV irradiation must be followed by wet-chemical oxidation. For samples with DOC concentrations of > 25 mg/L, an initial preoxidation by UV-irradiation was found necessary to ensure total oxidation of DOC and accurate determination of Hgx by the bromine monochloride method (Olson et al, 1997). 

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