1 -labeled tracers

Figure Bl.14.8. Time course study of the arrival and accumulation of labelled sucrose in the stem of a castor bean seedling. The labelled tracer was chemically, selectively edited using CYCLCROP (cyclic cross polarization). The first image in the upper left comer was taken before the incubation of the seedlmg with enriched hexoses. The time given in each image represents the time elapsed between tire start of the incubation and the acquisition. The spectmm in the lower right comer of each image shows the total intensity...

The growth rate for tracers labeled with short-Hved isotopes such as P and was about 10—15% per year from 1990 through 1994. This trend reflects the increased use of these radiochemicals for research in molecular biology and genetics I-labeled tracers have also exhibited similar growth rates in this period. On the other hand, the market for C- and H-labeled chemicals essentiaHy leveled off The overaH growth rate for aH tracer chemicals was estimated at 5%/yr for 1990—1994. 

Isotopic-labeled tracers behave like the components in the fluid of interest. For example, tritium water behaves like water. If less similar chemicals are used as tracers, selective adsorption, chemical reaction, and liquid-liquid distribution must be considered. The tracer must be chosen so that the analytic method is sufficiently sensitive to detect the tracer in the desired amounts. 

Bollinger JN. 1970. Metabolic fate of mineral oil adjuvants using 14C-labeled tracers. I. Mineral Oil. J Pharm Sci 59 1084-1088. 

The tracer should be stable and conserved, so that it can be accounted for by a material balance relating the response to the input if the tracer decays (e.g., a radio-labeled tracer), its half-life should be such that tm (tracer) > 251 (fluid). 

V) The validity of RIA entirely depends upon the identical behaviour of standard and labelled substance unknown, and not on the identity of the labelled tracer and the unknown. Hence, the experimental conditions of incubation of standards and unknowns must be identical for any factors that might affect the extent of the immunochemical reaction, pH, ionic composition, protein content or any other substances of interest. However, these conditions may be tested conveniently and can be controlled effectively by preparing standards in hormone free plasma at the same dilution at which unknowns are assayed. 

Ding Y-S, Eowler JS (1996) 18F-Labeled tracers for positron emission tomography studies in the neurosciences. In Ojima 1, McCarthy J, Welch JT (eds) Biomedical frontiers of fluorine chemistry. ACS Symp Series 639. The American Chemical Society, Washington DC, chap 23, p 328... 

In addition Choi et al. utilized FlTC-labeled methamphetamine for competitive immunoassay of methamphetamine in urine (19). Instead of purified antibody or antibody fragment, antiserum was used. An aminobutyl derivative of metamphetamine was conjugated with proteins and used as an immunogen to produce antibodies for the assay. The free FITC-labeled tracer was well separated from the antibody-bound fraction, and the detection limit for the CE assay was lower than that for ELISA. 

A recent study found that cortical peripheral benzodiazepine receptors, as assessed with PET and [ C]PK11195, were increased by 30-40% in patients with AD when compared with healthy controls. This suggests active inflammatory processes in AD since PK11195 binds to activated microglia [72]. Several F-labeled tracers of the peripheral benzodiazepine receptor have been developed, and [i8p]PK14105 [73] and [i8p]FEDAA1106 [74] are the most well characterized. However, no reports have been published on the use of either of the two radiotracers in AD. The molecular structures of F-labeled tracers for the peripheral benzodiazepine receptor are shown in Fig. 5. 

F-Labeled radiopharmaceuticals have a special advantage for clinical and academic PET studies due to the relatively long half-life of F. The radiotracer can be used for several sequential PET studies of different patients, and it can also be shipped to remote PET centers that do not have a production of radiopharmaceuticals. p F]FDG is already an established tool in the diagnosis of patients with AD. A few F-labeled tracers for serotonin receptors and amyloid plaques have... 

Setchell KD, Faughnan MS, Avades T et al. Comparing the pharmacokinetics of daidzein and genistein with the use of C-labelled tracers in premenopausal women. Am. J. Clin. Nutr. 77,411-419, 2003. 

Theory for the self- and tracer-diffusion of a diblock copolymer in a weakly ordered lamellar phase was developed by Fredrickson and Milner (1990). They modelled the interactions between the matrix chains and a labelled tracer molecule as a static, sinusoidal, chemical potential field and considered the Brownian dynamics of the tracer for small-amplitude fields. For a macroscopically-oriented lamellar phase, they were able to account for the anisotropy of the tracer diffusion observed experimentally. The diffusion parallel and perpendicular to the lamellae was found to be sensitive to the mechanism assumed for the Brownian dynamics of the tracer. If the tracer has sufficiently low molecular weight to be unentangled with the matrix, then its motion can be described by a Rouse model, with an added term representing the periodic potential (Fredrickson and Bates 1996) (see Fig. 2.50). In this case, motion parallel to the lamellae does not change the potential on the chains, and Dy is unaffected by... 

The development of sensitive and accurate GLC-MS methodology permitted a preliminary study in man utilizing these techniques for the precise determination of A9-THC, 11-hydroxy-A9-thc and CBN in plasma. Previously we have made an extensive study (4) of the metabolism of A9-THC in man using radio-labeled tracers and thin layer chromatography. The procedures utilized (in addition to the undesirability of a radio-labeled tracer in man) suffer from two potential sources of error. 

The above novel radiofluorinated derivatives of benperidol have been synthesized to improve the selectivity for binding to D-2 receptors in the course of identifying a fluorine-18 labelled tracer. 

NMR can help to monitor energization, see, e.g. [121, 273], especially the levels of 31P-containing metabolites, e.g. [45, 366], enzyme kinetics, compartmentalized intracellular ion activities, the fate of 3H-, 2H-, 13C-, 15N-, or 19F-labeled tracers, e.g. [108,109], 02 tension, compartmentalized redox potential, membrane potential, cell number or cell volume, see [133], and even pH. Major drawbacks are the cost of the equipment, the low intrinsic sensitivity and the interpretation of spectra [430]. 

Carbon-11 has a very short half-life (just 20.4min) but the chance to substitute a carbon atom in any biological molecule by a positron-emitting nC is a very interesting possibility. This has led to a substantial development of nC-labeled tracers. The short half-life conditions everything and only PET centers equipped with a cyclotron can have a chnical program with nC tracers. The production of the radiopharmaceutical must in these cases be performed just before the imaging study and is usually not started until the patient is already on the PET scanner. 

At equilibrium the equal and opposite current densities Iq and /r are referred to as the exchange currents. They could be measured, in principle, by measuring the rate of exchange of suitably labeled tracer O or R as catalyzed by the surface. For a discussion of such exchange measurements see C. V. King, Ann, N,Y. Acad, Sci.f 58, 910 (1954). 

In a steady-state situation in which there is a constant rate of appearance of a substrate (e g, glucose) into i sma or extracellular fluid that is matched by an equal rate of tissue uptake, a constant infusion of an isotopicaHy-labeled tracer that is not distinguished metabolicalLy from the unlabeled tracee will cause... 

The ZLC method offers advantages of speed and simplicity and requires only a very small adsorbent sample thus making it useful for characterization of new materials. The basic experiment using an inert carrier (usually He) measures the limiting transport difiiisivity (Do) at low concentration. A variant of the technique using isotopically labeled tracers (TZLC) yields the tracer diffiisivity and counter diffusion in a binary system may also be studied by this method. To obtain reliable results a number of preliminary experiments are needed, e.g. varying sample quality, nature of the purge gas, the flow rate and, if possible, particle size to confirm intracrystalline diffusion control. 

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