[en] Deuterium is monitored and quantitated in the presence of hydrogen in organic molecules with the helium microwave emission detector (MED). Various functional groups are tagged utilizing deuterated reagents which also serve to modify the components' chromatographic characteristics. Lithium aluminum deuteride (LAD) will reduce aldehydes, carboxylic acids, esters, amides and acid halides to non-exchangeable CD₂-tagged alcohols which can be further derivatized with multi-elemental reagents such as chlorodifluoroacetic anhydride. Other reagents include D₉-BSA (N, 0-bistrimethylsilylacetamide) for silylation, Deuter-8sup(TM) for esterifications, D₃-acetylchloride for acetylation and D₂-diazomethane for generalized N and O alkylations. Gas phase derivatization utilizes an on-line deuteration reactor in series with the GC injection port. The reactor contains catalysts such as nickel, platinum, or palladium coated on a suitable substrate in a deuterium atmosphere. This technique is used to tag olefins, alkanes, aromatics, nitriles and other functionalities subject to D-H exchange, reduction, isomeration, and a variety of cleavage reactions. The element-selective MED provides qualitative and quantitative information for a variety of compounds in which deuterium is incorporated. (author)