Most elements in nature exist as isotopes, differing by the number of neutrons. Isotopes can be divided into two types, radioisotopes and stable isotopes. Radioisotopes (also called radioactive isotope) contain an unstable combination of neutrons and protons that emit radiation. In contrast, stable isotopes are non-radioactive forms of atoms and do not emit radiation. The utilization of stable isotopes has steadily increased with the development of highly sensitive detection methods and increasing health concerns regarding the use of radiolabeled compounds. Radioisotopes and stable isotopes are interchangeable for some applications, but stable isotopes are used in a much wider range of applications. Applications of stable isotopes range from exploitation as natural tracers in geology, ecology, archaeology, climatology, and plant biology through use as supplied tracers in metabolic flux analyses to widespread use in proteomics, structural biology, and pharmacology and drug development and design. Stable isotope-labeled compounds can be produced by chemical synthesis or by metabolic enrichment in organisms. In chemical synthesis, a compound is labeled by replacing one or more specific atoms with an isotope through chemical reaction. Nature itself produces stable isotope-labeled compounds by metabolic binding, but the extent of stable isotopic labeling by natural substrates is low. High enrichment of isotopic labeling is achieved by artificially increasing the stable isotopic environment of organisms using highly enriched substrates. From enriched organisms, desired metabolites can be harvested and processed. Isotope-labeled compounds maintain the physicochemical properties of the target molecule while being easily detectable. In environmental studies and regulatory testing, stable isotope-labeled compounds are used to monitor the movement of chemicals in ecosystems, identify pollution sources in the environment, and understand bioaccumulation and degradation processes. In drug development, isotope labeled precursors have been routinely used for pharmacokinetic, bioavailability and toxicity studies due to their sensitive detectability.
Various stable isotopes of the same element differ only in atomic masses, and some of them also differ in nuclear spin, thus routine detection methods of isotopes must be sensitive to molecular features that depend on the weight of the atoms or their nuclear spin. Stable isotope-labeled compounds can be characterized and detected by mass spectrometry methods (MS), and through different frequencies of their molecular vibrations by means of vibrational spectroscopy. The different nuclear spins of some stable isotopes can be exploited by various methods of nuclear magnetic resonance (NMR). Stable isotope-labeled compounds are usually identified and quantified using MS- and NMR-based analytical methods in combination with separation methods such as gas chromatography, and high-pressure liquid chromatography. MS and NMR bulk analytical method are standard tools for stable isotope detection methods to trace fluxes of nutrients and explore metabolic pathways in organisms. Amerigo Scientific provides biochemical and organic compounds labeled with highly enriched, stable isotopes of carbon, hydrogen, nitrogen, and oxygen for research and industrial applications.
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