Safety and Precautions

Loss of label

Except in specific case where an exchange reaction is being studied, the isotopic marker should not be in a labile functional group that is easily exchanged under normal conditions, such as deuterium (2H) or tritium (3H) in place of an alcoholic, phenolic or acidic OH, or a 15O, 17O or 18O as a carbonyl oxygen in an aqueous environment, since the label will be readily washed out.

Although isotopic labeling is used extensively to study biochemical reactions, certain unanticipated bioreactions can lead to an unexpected loss of label. Problems such as in vivo dehalogenation can arise with substrates that contain isotopic halogens, as a result of enzymatic cleavage due to structural similarities to the thyroid hormones. The strong C-F bond makes the loss of isotopic fluorine rare, but bromine and particularly iodine can undergo dehalogenation in vivo. This can be especially problematic with long-lived iodide isotopes, which can subsequently experience significant and undesirable accumulation in both the thyroid and stomach tissues.

Storage

Compounds or reagents enriched with stable isotopes can be stored in the same manner as the unenriched materials. By definition, radiolabeled compounds and reagents emit radiation, and this can accelerate various decomposition processes. General guidelines to follow include: protection from light and storage under N2 or Ar; storage at low temperatures (<-80 C); storage as a solution (alcohols, especially ethanol, and acetonitrile are good solvents, water should be avoided); and when a compound is stored as a solid, it should be in crystalline form and not amorphous.3)

Disposal

Waste disposal procedures for materials that contain stable isotopes are generally not much different than those for handling the corresponding unenriched materials. The accompanying documentation commonly employed for handling laboratory waste often allows the user to note any special characteristics of the materials submitted, and the presence of the isotopes can be declared in this way.

The disposal of radioactive waste can pose a challenge, and must be handled separately by appropriately trained personnel. Radioactive waste materials should not by mixed with general laboratory waste. The disposal of mixed waste such as flammable or highly toxic radioactive waste (e.g., mercury or lead waste) can be extremely expensive, and in some cases, it is not even possible to find a vendor willing to handle the disposal.3) In all cases, the waste should be handled according to local regulations by properly certified companies.