Carbon dioxide measured label

Blanck H, Admrraal W, eleven REMJ, Guasch H, van den Hoop MAGT, Ivorra N, Nystrom B, Paulsson M, Petterson RP, Sabater S, Tubbing GMJ (2003) Variability in zinc tolerance, measured as incorporation of radio-labeled carbon dioxide and thymidine, in periphyton communities sampled from 15 European river stretches. Arch Environ Contam Toxicol 44 17... 

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

Williams [176] has studied the rate of oxidation of C-labelled glucose in seawater by persulfate. After the oxidation, carbon dioxide was blown off and residual activity was measured. For glucose concentrations of 2000, 200, and 20 xg/l, residual radioactivities (as percentage of total original radioactivity) were 0.04, 0.05, and 0.025, respectively, showing that biochemical compounds are extensively oxidised by persulfate. With the exception of change of temperature, modifications of conditions had little or no effect. Oxidation for 2.5 h at 100 °C was the most efficient. 

The greater the rate of production of carbon dioxide by the body, the greater the rate of fall of the 0/ H ratio, which is measured in a sample of urine collected every day. From the difference in the slope of the decline of the two labels, the rate of CO2 production is calculated (Figure 2.3). 

The most fundamental work on polyethylene degradation is being done by A. C. Albertsson in Sweden(27,28,29,30,31) using elegant science with labelled polymers to measure the rate and quantity of carbon dioxide evolution from buried high and low density polyethylene films. Degradation occurs at about... 

Rauch, S.L., Jenike, M.A., Alpert, N.M., Baer, L., Breiter, H.C., Savage, C.R., and Fischman, A.J. (1994) Regional cerebral blood flow measured during symptom provocation in obsessive-compulsive disorder using oxygen 15-labeled carbon dioxide and positron emission tomography. Arch Gen Psychiatry 51 62-70. 

SFC provides complementary quantitative data to the structural information afforded by mass spectrometry. Thermally label materials such as isocyanates can be easily analyzed with minimal sample preparation. Supercritical carbon dioxide is nontoxic and can be obtained in high purity as measured by FID. The easy coupling of SFE with SFC makes the selective isolation and quantification of targeted analytes possible. Furthermore, we are in an age of increased environmental awareness. Solvent disposal is discouraged and has become very expensive. The waste disposal costs associated with supercritical carbon dioxide are negligible when compared to the solvent disposal costs generated by traditional Soxhlet methods. 

The Fick s law diffusion coefficient of a permeating molecule is a measure of the frequency with which the molecule moves and the size of each movement. Therefore, the magnitude of the diffusion coefficient is governed by the restraining forces of the medium on the diffusing species. Isotopically labeled carbon in a diamond lattice has a very small diffusion coefficient. The carbon atoms of diamond move infrequently, and each movement is very small—only 1 to 2 A. On the other hand, isotopically labeled carbon dioxide in a gas has an extremely large diffusion coefficient. The gas molecules are in constant motion and each jump is of the order of 1000 A or more. Table 2.1 lists some representative values of diffusion coefficients in different media. 

Calazel, C. M., Young, V., Evans, W., and Roberts, S. (J993). Effect of fasting and feeding on measurement of carbon dioxide production using doubly labeled water. ]. Appl. Physiol. 74, 1824-J829. 

Direct measurements of active centre concentrations have been made by terminating the polymerization with some reagent such as iodine [86], carbon dioxide [115] or an alcohol [116], labelled with an isotope which introduces radioactivity into the polymer e.g. 

One simple test is to measure the level of radioactivity from the sample. Synthetic vanillin is not radioactive. However, natural vanilla, like all natural products, is. This is, of course, because atmospheric carbon dioxide contains some radioactive 14C formed by exposure to cosmic radiation in the upper atmosphere. Plants then incorporate this into their photosynthetic pathway and produce metabolites which exhibit a low level of radioactivity. Synthetic vanillin is prepared from coal tar, which is not radioactive since the 14C has long-since decayed. However, unscrupulous dealers know this and can synthesize radio-labelled or hot vanillin and dose it into synthetic material so that the level of radioactivity matches that of a natural sample. Another method of checking for naturalness must, therefore, be found. When plant enzymes synthesize molecules, they, like all catalysts, are suscep-... 

The effects of concentration on the degradation of 2,4-D in soil have been studied using (14C)labeled herbicide with the release of (14C)carbon dioxide being used as a measure of the rate of breakdown of the 2,4-D. In some of these studies, the loss of 2,4-D was considered to be.biphasic with a slow initial evolution of (14C)carbon dioxide beipg followed by a more rapid release (12-14). In contrast, other studies have shown the evolution of (14C)carbon dioxide from (14C)2,4-D treated systems to be uniform with time (13, 15, 16). A similar phenomenon has been reported for the breakdown of (14C)MCPA in soil (17). In all the above experiments no attempts were made to specifically analyze for (14C)2,4-D or (14CJMCPA actually remaining, and it has been cautioned (2, 5) that evolution of (14C)carbon dioxide is not a true measure of the decomposition rate of (14C)phenoxyalkanoic acids in soils. 

Knowles and co-workers observed (V/K) at C-1 of glyoxalate by analyzing the isotopic composition of the malate produced in the reaction at early and late stages (23). In order to measure this ratio accurately they developed a procedure to convert C-2 of malate to carbon dioxide. Through a series of enzymic reactions, C-2 was converted to the carbonyl carbon of the acetyl group of acetyl-carnitine (through the reaction sequence malate — pyruvate — acetyl-CoA - acetylcarnitine). The labeled carbon then was carried flirough another cycle back to malate, but in this case the label was in the carboxylate carbon at C-4 (acetyl-carnitine acetyl-CoA 4-[ 3C]malate). Malic enzyme converts this to pyruvate and labeled carbon dioxide, whose isotopic ratio is determined by mass spectrometry. 

The most sensitive method for measuring carbon dioxide production by histidine decarboxylase is that in which histidine labelled with carbon-14 in the carboxyl group is used as substrate. The C02 evolved is trapped in a suitable absorbent medium, and its radioactivity is then determined directly in a scintillation spectrometer. Several variations of this procedure have been described - - - - , and these compare favourably in speed and sensitivity with alternative isotopic methods in which the production of radioactive histamine from ring- C-labelled histidine is measured (see following section). 

Further development of the method has made it possible to apply it to the analysis of labelled compounds [130]. The conversion to hydrogen and carbon dioxide and separate determination of the activity of these chromatographic zones with the aid of flow-through counters have substantial advantages over the conventional method for measuring the activity of different compounds (1) an important factor is the operational stability of the flow-through counter (2) measurements can be made at room temperature, so that sophisticated equipment is not necessary (3) it is possible to determine simultaneously the activity with reference to C and H in doubly labelled molecules. 

PET can be used to measure quantitatively the chemical composition of tissues of the body by using appropriately selected compounds labeled with positron-emitting radioisotopes that rapidly distribute between the blood and the tissue of interest. The measurement is based on the determination of the tissue-to-blood partition coeflBcient of the tracer at equilibrium. Knowledge of the tissue-to-blood partition coeflBcient plus the concentration of the compoimd of interest in the vascular compartment permits the calculation of the actual tissue concentration. This concept has been tested by measuring brain carbon dioxide content using C-labeled carbon dioxide as a tracer (31). These measurements were... 

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