Tracer categorization

In normal RIA-procedures the labelled drug or metabolite not only serves as the tracer for recovery but also for RIA quantification. However, the isotope dilution method categorically makes a clear separation of the drug and its metabolites. Consequently, a non-specific antiserum is employed to actually quantify the total amount of both unlabelled and labelled substance present. 

Within the framework of this equation, tracers may be broadly categorized as... 

Embellishing the categorization made in Section 6.08.2, transient tracers can be defined as substances whose concentration distributions are changing on interannual timescales and in a noncyclical nature. Thus, dissolved oxygen or argon in the seasonal layer would be excluded... 

The first two unenclosed iron-enrichment studies were carried out in 1993 and 1995 in the Equatorial Pacific. In both, nanomolar concentrations of iron were induced in the surface layer by release of iron sulfate, the patches being labeled by SFg addition. The SEg(initial addition of iron, the tracer component was then used as a guide to keep track of the affected patch of ocean. Sampling could be reliably categorized as in or out the patch, even after all the measurable iron had disappeared from solution. In the second study, the main experiment included reseeding the patch with iron, but not tracer, twice after the initial release. Important secondary aims of the tracer component of the experiments have been the study of mixing rates both horizontally in the mixed layer, and vertically across the thermocline. 

Isotopic dilution and tracer techniques represent different methodologies, but they overlap to a degree that obviates any clear-cut categorization. Both are techniques for quantitative analysis. In an isotopic dilution experiment one adds a known amount of an isotopomer (sometimes called the spike ) of a known compound (usually containing a rare isotope) and measures the abundance of ions derived from it relative to those from the analyte (which is usually the more common isotopomer). If, for example, one wished to quantitate phenol (CgHjOH) in a mixture, one might add a known quantity of pentadeuterated phenol (CeDsOH) as a spike and measure the m/z 94 m/z 99 intensity ratio by mass spectrometry. 

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