Removal of inorganic carbon

For samples of approximately 10 mL in 16 mm diameter glass vials, 50 /iL of 2 mol/L acid are sufficient for acidification. The sample must then be bubbled for about 10 min to eliminate the inorganic carbon completely. The exact conditions depend on the volume of the sample, the shape of the tube or flask used and the size of bubbles. Each configuration needs some individual adjustment. 

Without an autosampler, the TOC 5000 is designed to allow bubbling in the same tube as is used for sampling. Only after sparging the sample is it taken up for injection. To save time, the purge gas can be directed so as to sparge the next sample, while the preceding sample is analysed. 

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Even if removal of inorganic carbon is complete, the analysis of the remaining carbon is difficult. At a concentration of 1 ppm, a normal value for surface water in the open ocean, a 1 ml sample will contain 1 ig carbon. If we are interested in differences between samples, we must strive for a precision of 5% or 0.05 xg C per ml sample. This requirement places severe constraints on the sensitivity and precision of instrumentation. 

The determination of dissolved organic carbon by oxidation methods in water comprises three analytical steps the removal of inorganic carbon from the sample, oxidation of the organic compounds to carbon dioxide, and the quantitative determination of the resulting carbon dioxide. The methods of oxidation can be classified into three major groups ... 

Hannaker and Buchanan [82] used a method based on wet oxidation with potassium persulfate [83] for the determination of dissolved organic content in concentrated brines following the removal of inorganic carbonates with phosphoric acid. The method involves wet oxidation with potassium persulfate at 130 °C followed by a hot copper oxidation and gravimetric measurement of the carbon dioxide produced. The technique overcomes difficulties of calibration curvature, catalytic clogging, and instrument fouling often encountered with instrumental methods. 

A pH of 3 was optimal for the complete removal of inorganic carbon and the most efficient oxidation of nitrogen-free organic compounds, while a pH of 2.5 was optimal for nitrogenous compounds (Fig. 11.1). 

Gershey et al. [58] have pointed out that persulfate and photo-oxidation procedures will determine only that portion of the volatile organics not lost during the removal of inorganic carbonate [30,79,92,181]. Loss of the volatile fraction may be reduced by use of a modified decarbonation procedure such as one based on diffusion [98]. Dry combustion techniques that use freeze-drying or evaporation will result in the complete loss of the volatile fraction [72,79, 92,93],... 

The exchange resins 6nd application in (i) the purification of water (cation-exchange resin to remove salts, followed by anion-exchange resin to remove free mineral acids and carbonic acid), (ii) removal of inorganic impurities from organic substances, (iii) in the partial separation of amino acids, and (iv) as catalysts in organic reactions (e.g., esterification. Section 111,102, and cyanoethylation. Section VI,22). 

In experiments where Mono Lake water was acidified to remove carbonate and bicarbonate ions and again adjusted to pH 10, more than 90 percent of the soluble plutonium moved to the sediment phase. When carbonate ion concentration was restored, the plutonium returned to solution—strong evidence of the importance of inorganic carbon to solubility in that system(13). Early studies with Lake Michigan water, which has low DOC, had also implicated bicarbonate and carbonate as stabilizing ligands for plutonium at pH 8(14). This latter research characterized the soluble species as mainly anionic in character. 

The removal of inorganic salts from reaction mixtures afforded by polymeric materials may be simply and effectively accomplished by dialysis,166 178 after decomposition of remaining periodate with ethylene glycol130 131 or butylene glycol. 161 170 Alternatively, the iodate and periodate ions may be removed as such, or after reduction to free iodine. The iodate and periodate ions have been effectively precipitated by means of sodium carbonate plus manganous sulfate,6 or by lead dithionate,191 barium chloride,24 192 193 strontium hydroxide194 202 or barium hydroxide,203 204 lead... 

Chemical precipitation has traditionally been a popular technique for the removal of heavy metals and other inorganics from wastewater streams. However, a wide variety of other techniques also exist. For example, ion-exchange, reverse osmosis, evaporation, freeze crystallization, electrodialysis, cementation, catalysis, distillation, and activated carbon have all been used for removal of inorganics. 

Chemical addition for the removal of inorganic compounds is a well-established technology. There are three common types of chemical addition systems that depend upon the low solubility of inorganics at a specific pH. These include the carbonate system, the hydroxide system, and the sulfide system. 

Removal of Inorganic Gases and VOCs ON Activated Carbons... 

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