Total carbon, measurement methods

Carbon-13 nmr. Carbon-13 [14762-74-4] nmr (1,2,11) has been available routinely since the invention of the pulsed ft/nmr spectrometer in the early 1970s. The difficulties of studying carbon by nmr methods is that the most abundant isotope, has a spin, /, of 0, and thus cannot be observed by nmr. However, has 7 = 1/2 and spin properties similar to H. The natural abundance of is only 1.1% of the total carbon the magnetogyric ratio of is 0.25 that of H. Together, these effects make the nucleus ca 1/5700 times as sensitive as H. The interpretation of experiments involves measurements of chemical shifts, integrations, andy-coupling information however, these last two are harder to determine accurately and are less important to identification of connectivity than in H nmr. 

The n-d-M correlation is an ASTM (D-3238) method that uses refractive index (n), density (d), average molecular weight (MW), and sulfur (S) to estimate the percentage of total carbon distribution in the aromatic ring structure (% C ), naphthenic ring structure (Cj,), and paraffin chains (% Cp). Both refractive index and density are either measured or estimated at 20°C (68°F). Appendix 4 shows formulas used to calculate carbon distribution. Note that the n-d-M method calculates, for example, the percent of carbon in the aromatic ring... 

With the exception of instrumental dry combustion methods [32], the techniques referred to above for the analysis of organic (and total) carbon in sediments are time consuming (e.g. 2-3h). An instrumental technique described by Van Hall and Stenger [33] makes use of a non-dispersive infrared detector and measures the carbon dioxide resulting from the combustion of the carbonaceous compounds. Total and inorganic carbon can be differentiated by the use of different combustion columns and temperatures. 

The range of applicability of equation 11.122 depends on the limits of detection of in the sample. The current maximum age attained by direct radioactivity counting is about 4 X 10" a. To measure residual radioactivity, the total carbon in the sample is usually converted to CO2 and counted in the gas phase, either as purified CO2 or after further conversion to C2H2 or CH4. To enhance the amount of counted carbon, with the same detection limit (about 0.1 dpm/g), counters attain volumes of several liters and operate at several bars. More recent methods of direct detection (selective laser excitation Van de Graaif or cyclotron acceleration) has practically doubled the range of determinable ages (Muller, 1979). 

Aerosol carbon concentrations have been measured at two sites in the Los Angeles basin. Samples were analyzed for total carbon content and for elemental carbon content by the Gamma Ray Analysis of Light Elements technique and by several optical methods. Elemental carbon was shown to constitute a substantial fraction of total carbonaceous aerosol mass in the wintertime in Los Angeles. 

These samples were studied by chemical and microscopic methods. Chemical data include moisture, ash, volatile matter, total carbon, and hydrogen. Microscopic data include reflectance measurements on samples from both cores and maceral analyses of core DDH-B. 

In both TOC and dissolved organic carbon (DOC) determinations, OC in the water sample is oxidized to produce carbon dioxide (C02), which is then measured by a detection system. Inorganic carbon (IC) is removed prior to the analysis by acidifying the sample. Alternatively, TOC can be determined indirectly through the measurement of total carbon (TC) and IC. TOC in the indirect method is calculated as the difference between the two. 

Measurements of the total carbon content (TC) of water, which consists of 1C and TOC (TC = IC-i-TOC), are usually based on the catalytic combustion of the water sample in the presence of oxygen to yield the TC value. Alternatively, the determination of TOC is possible by a photochemical method, i.e. the VUV-initiated oxidation of organic matter in the low pg L concentration range with formation of CO2 (Huber and Frimmel, 1991). The CO2 resulting from both procedures is analyzed quantitatively in a nondispersive infrared analyzer (NDIR). 

However, unless combined with a specific analytical method, the total radioactivity measurements potentially reflect the presence of the parent substance as well as possible metabolite(s) and possible metabolized carbon, which have been incorporated in the fish tissue in organic molecules. BCF values determined by use of radiolabelled test substances are therefore normally overestimated. 

Together with details of sample preparation and storage, an appropriate analytical method of known accuracy, precision, and sensitivity must be available for the quantification of the substance in the test solution and in the biological material. If these are lacking it is impossible to determine a true BCF. The use of radiolabelled test substance can facilitate the analysis of water and fish samples. However, unless combined with a specific analytical method, the total radioactivity measurements potentially reflect the presence of parent substance, possible metabolite(s), and possible metabolized carbon, which have been incorporated in the fish tissue in organic molecules. For the determination of a true BCF it is essential to clearly discriminate the parent substance from possible metabolites. If radiolabelled materials are used in the test, it is possible to analyse for total radio label (i.e. parent and metabolites) or the samples may be purified so that the parent compound can be analysed separately. 

Total carbon dioxide is used here to describe the quantity that is measured most often in automated analyzers by acidification of a serum or plasma sample and measurement of the carbon dioxide released by the process, or by alkaliniza-tion and measurement of total bicarbonate. Under certain conditions of collection and specimen handling, total carbon dioxide values determined in this manner may be almost identical with values for the calculated concentration of total carbon dioxide obtained in blood gas analysis (see later section in this chapter on blood gas methods). The patho-... 

With the sample preparation method described earlier, the optimal amount of total carbon for AMS analysis is around l.Omg. When the total carbon level is far below that level, a precise amount of suitable carrier carbon is added. Petroleum-based tributyrin is often used as the carrier because it is a nonvolatile liquid, contains depleted levels of 14C and 3H, and its measurement is highly reproducible [18]. 

With the previous combustion method, analysis is performed when carbon compounds are combusted in an oxygen-rich environment, resulting in the complete conversion of carbon to carbon dioxide. This procedure is not applicable to water samples with a very low concentration in elemental carbon as used for semiconductor manufacturing processes or required in pharmaceutical industries. For these cases the organic contaminants are measured by the total carbon... 

Appropriate analytical methods must be used to measure these three fractions of the total carbon content. 

In some instances the method for carbon determination has to be modified, e.g., the determination of trace amounts of what is referred to as dissolved organic carbon in water after inorganic carbon has been removed. This type of carbon determination involves wet oxidation activated by silver ions in a solution of potassium persulphate in sulphuric acid. The oxidation of organic compounds gives carbon dioxide, which is adsorbed by molecular sieves. The molecular sieves are then heated in a flow of helium to desorb the carbon dioxide, the amount of which is measured by a TCD. The lowest concentration of organic carbon that can be measured in water is 0.2—2ppm [55]. The application of chromatographic elemental analysis to the determination of the total carbon content in water has been described [56]. 

In this study, the authors tried to determine the stoichiometry of Zr-carbonate complexes using a combination of cryoscopic measurements and potentiometric titrations. Both methods point to the formation of Zr(C03)4 in high ionic strength KNO3 solutions with 0.4 M total carbonate and up to 0.1 M ZrOCl2. Our recalculations confirmed this interpretation although alternative species could be invoked to explain the cryoscopic and potentiometric data, only Zr(C03)4 is consistent with both sets of results. 

TOC Total organic carbon (TOC) is analyzed in accordance with those procedures specified by the manufacturer (model DC-190, Rosemount Analytical, Inc., Dohrmann Division) as well as those in the ASTM Standard Method 505A Organic Carbon (Total) Combustion-Infrared Method [308,309].The analyzer determines TOC by calculating the difference between the measured total carbon (TC) and inorganic carbon (IC) content of a sample. 

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. 

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