High-temperature Catalytic Oxidation Technique Research Articles

Dissolved organic carbon in rainwater: Glassware decontamination and sample preservation and volatile organic carbon

The efficiency of different methods for the decontamination of glassware used for the analysis of dissolved organic carbon (DOC) was tested using reported procedures as well as new ones proposed in this work. A Fenton solution bath (1.0 mmol L −1 Fe 2+ and 100 mmol L −1 H 2O 2) for 1 h or for 30 min employing UV irradiation showed to combine simplicity, low cost and high efficiency. Using the optimized cleaning procedure, the DOC for stored UV-irradiated ultra-pure water reached concentrations below the limit of detection (0.19 μmol C L −1). Filtered (0.7 μm) rain samples maintained the DOC integrity for at least 7 days when stored at 4 °C. The volatile organic carbon (VOC) fraction in the rain samples collected at two sites in São Paulo state (Brazil) ranged from 0% to 56% of their total DOC content. Although these high-VOC concentrations may be derived from the large use of ethanol fuel in Brazil, our results showed that when using the high-temperature catalytic oxidation technique, it is essential to measure DOC rather than non-purgeble organic carbon to estimate organic carbon, since rainwater composition can be quite variable, both geographically and temporally.

Determination of dissolved organic carbon in seawater using high temperature catalytic oxidation techniques

The high temperature catalytic oxidation (HTCO)–discrete injection method for liquid samples is currently the preferred analytical technique for the determination of dissolved organic carbon (DOC) in natural water samples. This approach yields equivalent or greater amounts of DOC than wet chemical oxidation methods, is suitable for routine analyses and is stable for shipboard determinations. However, a limited understanding of evaluation criteria for instrument performance presents a number of analytical challenges. This article discusses current practical problems encountered in the (i) collection and handling, (ii) preservation, (iii) decarbonation and (iv) analysis of seawater samples and reviews recent improvements in HTCO systems. Particular reference is made to the issue of certified reference materials and the oxidation efficiency of the technique.

Application of the wet oxidation method for dissolved organic carbon analysis in the Southern Ocean

Results of dissolved organic carbon (DOC) measurements by wet photochemical oxidation method are presented for series of seawater samples collected from September–November 1995 in the Indian sector of Southern Ocean. DOC concentrations in Antarctic Surface Water (AASW) were 57 ± 9 μM C, and were about 48 ± 10 and 46 ± 6 μM C in Circumpolar Deep Water (CDW) and in Antarctic Bottom Water (AABW), respectively. We also measured total organic carbon (TOC) by using the High Temperature Catalytic Oxidation technique and particulate organic carbon (POC) in AASW by using a CHN analyzer. In AASW, TOC and POC concentrations were 49 ± 3 (xM and 4 ± 2 μM C, respectively, whereas TOC concentrations averaged 42 ± 3 in CDW and 37 ± 1 in AABW. The labile pool was estimated at 12 μM C.

Wet-oxidation and automated colorimetry for simultaneous determination of organic carbon, nitrogen and phosphorus dissolved in seawater

Abstract We developed a simple and reliable method which allows simultaneous determination of organic forms of carbon (DOC), nitrogen (DON) and phosphorus (DOP) dissolved in seawater. Conversion of dissolved organic matter (DOM) to inorganic products (carbon dioxide, nitrate+nitrite and soluble reactive phosphate) is performed by a persulfate wet-oxidation in low alkaline condition. After oxidation, the concentration of the inorganic products dissolved in the sample was measured automatically by colorimetry using a 3-channel Technicon AutoAnalyzer system. A number of pure organic compounds were tested in the concentration range encountered in coastal and open ocean, indicating a high efficiency of the digestion procedure. The recovery range is similar to that obtained by other wet-oxidation procedures and by high-temperature catalytic oxidation techniques. Direct comparisons with usual methods used for separate determination of DOC, DON and DOP indicated a high efficiency of the procedure. Reproducibility tests demonstrated a very good precision (around 5%) for lagoonal and coastal waters, while precision was sometimes around 10–25% in oligotrophic oceanic waters, especially for DOP where values approached limits of detection for measuring phosphate. This method is highly suitable for routine analysis and especially appropriate for shipboard work.

Dissolved carbon in pore waters from the carbonate barrier reef of Tahiti (French Polynesia) and its basalt basement

This paper deals with dissolved inorganic carbon (DIC) and organic carbon (DOC) in pore waters from a 150 m deep hole drilled through the carbonate barrier reef of Tahiti and its underlying basalt basement. Alkalinity-pH measurements were used to calculate the DIC species concentration, and DOC was analysed according to the high temperature catalytic oxidation technique. Salinity was used as a conservative tracer to help identify water origin and mixing within the hole. Water mixing, calcium carbonate dissolution and mineralization of organic carbon combined to form three distinct groups of pore water. In the deeper basalt layers, pore water with alkalinity of 1.4 meq kg−1 pH of 7.6 and p(CO2) of 1.2 mAtm was undersaturated with respect to both aragonite and calcite. In the intermediate carbonate layer, pore water with alkalinity of more than 2.0 meq kg−1, pH of 7.70 and p(CO2) of 1.4 mAtm was supersaturated with respect to both aragonite and calcite. The transition zone between those two groups extended between 80 and 100 m depth. The shift from aragonite undersaturation to supersaturation was mainly attributed to the mixing of undersaturated pore waters from the basalt basement with supersaturated pore waters from the overlaying limestone. In the top of the reef, inputs from a brackish water lens further increased p(CO2) up to 5.6 times the atmospheric P(CO2).

A High‐Temperature Catalytic Oxidation Technique for Determining Total Dissolved Nitrogen

AbstractA high‐temperature catalytic oxidation method for determination of total dissolved N has been developed and tested on soil solution and throughfall. Unlike methods generally used for total dissolved N, this method is rapid, quantitative, and does not require use of strong acids or bases. The technique couples a commercially available chemiluminescent N detector with the combustion furnace of a commercially available C analyzer. An aqueous sample is combusted in an ultra pure oxygen environment at 680°C, converting all forms of N to nitric oxide, which then reacts with ozone. The product, metastable NO2, is measured chemiluminescently by the N detector. The method is appropriate for samples collected in studies of forest soil solution and throughfall, having a method detection limit of 0.03 mg L−1 total N, and a range from 0.03 to 10.0 mg L−1. Tests of several organic and inorganic N‐containing compounds showed recoveries >90% for concentrations up to 5.0 mg N L−1. Urea was the only compound tested with recoveries <90%. Numerous field samples were analyzed and compared with results obtained using persulfate oxidation and high‐temperature oxidation (uncatalyzed oxidation at 1100°C). Results from this high‐temperature catalytic oxidation method compare well with persulfate oxidation and high‐temperature oxidation.

Results and observations from the measurement of DOC and DON in seawater using a high-temperature catalytic oxidation technique

Operating temperatures for the high-temperature catalytic oxidation of dissolved organic matter (DOM) in seawater were evaluated for optimization of total dissolved nitrogen analysis. In addition, the possibility of NO2 being produced upon combustion, a gas not seen by the detector used here, was explored. Finally, some concentrations of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in coastal waters are reported. NO was most efficiently passed through the combustion furnace at temperatures 40°C or more above the 680°C temperature recommended earlier for DOM analysis. NO2 was apparently not an important product of combustion, as an NO2 calibration gas was efficiently converted to NO in the furnace and because the addition of a ferrous sulfate NO2 converter did not result in significant increases in the detector response. DOC and DON concentrations were determined in seawater collected from three coastal sites—Santa Monica Basin and Monterey Bay in California and the Bering Sea inner shelf. The highest near-surface concentration of DOC reported here (123μM at 20 m) was found in Monterey Bay, and the lowest value (72 μM at 20m) was found in the Bering Sea. The highest DON concentration found in the surface 50 m was 6.0 μM in Santa Monica Basin.

Comparison of TOC concentrations by persulphate-UV and high-temperature catalytic oxidation techniques in the Marmara and Black Seas

Total organic carbon (TOC) concentrations were determined in the Marmara Sea and both oxic and anoxic waters of the Black Sea, using the Shimadzu high-temperature catalytic oxidation technique and the Technicon persulphate-UV oxidation method. The TOC values in the deep waters of the Marmara Sea ranged between 60 and 73 μ MC by the Shimadzu technique and from 40 to 50 μMC by the Technicon method. The TOC values obtained by both methods in the deep anoxic waters of the Black Sea varied between 105 and 130 μM. These values differ significantly from those in the literature, indicating that available TOC data are not accurate enough for reliable estimation of the carbon budget of the Black Sea. Storage of the anoxic water samples accompanied by freezing, acidifying or poisoning with HgCl2 did not increase TOC recovery.

Some practical aspects of measuring DOC — sampling artifacts and analytical problems with marine samples

Abstract Efforts to reproduce the high-temperature catalytic oxidation technique for the determination of dissolved organic carbon (DOC) in marine samples are described and details of the construction of a home-made DOC analyzer are presented. Calibration of this instrument is compared with that of a commercial analzyer. Various problems relating to the determination of the instrument blank, instrument calibration, sample collection, preservation and processing are presented. Several hypotheses explaining the observed analytical artifacts are proposed and possible implications of these artifacts are discussed.