Carbon dioxide direct titration

Various workers have discussed the determination of total alkalinity and carbonate [ 10-12], and the carbonate bicarbonate ratio [ 12] in seawater. A typical method utilises an autoanalyser. Total alkalinity (T milliequivelents per litre) is found by adding a known (excess) amount of hydrochloric acid and back titrating with sodium hydroxide solution a pH meter records directly and after differentiation is used to indicate the end-point. Total carbon dioxide (C milliequivelents per litre of HCO3 per litre) is determined by mixing the sample with dilute sulfuric acid and segmenting it with carbon dioxide-free air, so that the carbon dioxide in the sample is expelled into the air segments. The air... 

After an investigation of several years with the same type of algae and approximately the same intensity of monochromatic light as used by Warburg we are forced to conclude that the photosynthetic process is considerably less efficient than the 0.2 or 0.3 which is now accepted.63 With the monochromator already described and with direct, microchemical analysis of the gas or by titration for oxygen we find a quantum yield of about 0.05 changing somewhat with the conditions. Under our conditions ten to twenty quanta instead of the classical four seem to be necessary to convert one molecule of carbon dioxide into plant material. 

Note Solutions of alkali hydroxides absorb carbon dioxide when exposed to air. Connect the buret used for titrations with barium hydroxide solution directly to the storage bottle, and provide the bottle with a soda-lime tube so that air entering must pass through this tube, which will absorb carbon dioxide. Frequently restandardize standard solutions of barium hydroxide. 

The second direct method depends on the ability of aqueous potassium chloride, adjusted to pH 4 with carbon dioxide, to selectively elute hydrogen ions from sulfonic acid groups in pulps that first have been converted to their hydrogen form with 0.1 M hydrochloric acid (Cappelen and Schoon 1966). Carbon dioxide is removed from the eluent by sparging with nitrogen and the remaining acid is titrated with 0.1 M sodium hydroxide. Again, a correction factor for interference from carboxylic acids is required. This factor, as before, is based on the protons eluted from bleached pulps by the eluent. As the results depend on the concentration of potassium chloride used, the letter is adjusted so that the sulfonate content corresponds to the sulfur content of pulps assumed to contain only acidic sulfur. 

The evolution of carbon dioxide by the action of 12% hydrochloric acid on purified cotton fiber to the extent of 0.026 to 0.056% has led to the conclusion that carboxyl groups are fundamental constituents of the cellulose molecule. From these values the average chain length of the cellulose molecule can be calculated to be 496 to 1068 anhydro-n-glucose units. These values are essentially in agreement with the results obtained by direct titration of the carboxyl groups with dilute caustic and by various base-combining procedures. ... 

Carbon dioxide reacts with primary amines to form a carbamic acid (Pine et al., 1980). Carbamic acids are unstable the very act of dissolving the carbamic acid in a solvent for titration or for conducting NMR studies, for example, converts the acid back to amine plus CO2 (Elsbernd, 1988). Heating the acid to about 50-100°C can force the reaction in the reverse direction, and if the CO2 that is generated is removed, the amine can be recovered. Although the conversion of carbamic acid back to amine plus CO2 occurs quite readily (Pine et al., 1980) the reversion is not instantaneous (Gallagher and Krukonis, 1987). What can also occur during the reverse reaction is reaction between any unconverted carbamic acid and the amine that has just reformed to form a urea. 

The measurement of total organic carbon (TOC) is the best means of assessing the organic content of a water sample [20]. Organic carbon is oxidized to carbon dioxide (CO,) by heat and oxygen, ultraviolet irradiation, chemical oxidants, or by various combinations of these. The CO, may be measured directly by a non-dispersive infrared analyser or it may be reduced to methane and measured by a flame ionization detector in a gas chromatograph or in a TOC analyser thus equipped. The CO2 may also be titrated chemically. 

It must be pointed out that this method of testing and calculation is only to be regarded as giving general information. It is, however, important to add that if large discrepancies occur between the levels of hydrogen carbonate ions measured by direct titration and by subtracting the free CO2 from the total carbon dioxide, this is in all probability attributable to the presence of other titratable substances. 

Because many of the solvents used are aggressive, volatile, and obnoxious, nonaqueous titrations are normally carried out in a closed environment, which also minimizes the ingress of moisture (Figure 8). It is essential to ensure that all apparatus used is dry and, especially for titrations in basic solvents, a stream of nitrogen is used to prevent access of carbon dioxide to the solution being titrated. The titrant is stored in a reservoir connected directly to the burette. 

The formaldehyde formed in a periodate reaction is determined gravimet-rically with Dimedon, or colorimetrically with chromotropic acid, after the excess oxidant is destroyed with ethylene glycol, stannous chloride, sodium arsenite, or sodium bisulfite 221), The formic acid is generally titrated directly. Titration to pH 6.0 will measure all the formic acid present. Titration to higher alkalinities will usually measure any formic acid bound as an ester 222) but also other acidic products the end-point may be indefinite. Sucrose will give 80 to 90 % of the theoretical formic acid, and maltose and lactose similarly low values. Both formaldehyde and formic acid are attacked only extremely slowly by periodate, but light apparently accelerates an oxidation to carbon dioxide and water 223),... 

Ammonium bicarbonate, NH4HCO3, Mol. Wt. 79 06, is weighed for determination by difference from a weighing bottle into excess of N acid the solution may be titrated back direct to methyl orange, or, preferably, after boiling off the carbon dioxide, titrated back with N alkali to methyl red. 1 ml N - 0-07906 g. 

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