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A simple, rapid and cost-effective laboratory method was developed for labelling soil-feeding earthworms simultaneously with 15N and 13C. The method circumvents the production of labelled plant material and can be adapted to devise pulse-labelling or long-term labelling protocols. Soil was amended with 15NH4+ and incubated for 7 days. Then, U-13C-glucose was added and endogeic earthworms, Aporrectodea caliginosa (Oligochaeta: Lumbricidae), were provided individually with 4 g of this pre-incubated soil. The labelling period was 4 days. The labelling efficiency (percentage of tracer retained in earthworm tissues) was estimated to be 15.8% for 15N and 10.3% for 13C. The loss of 15N and 13C label from tissue and mucus was traced for 21 days post-labelling. Label loss from mucus was best described by a two-term exponential function, whereas the label loss in body tissue followed a single-term exponential function. Half-life estimates for the 15N and 13C tracers in body tissue were 16 and 37 days, respectively.

13C-2 labeled phenyl ethynyl triflone undergoes regiospecific CH alkynylation upon reaction with cyclohexane. The 13C label is found to be exclusively adjacent to the phenyl group in the product phenyl cyclohexyl acetylene, consistent with cyclohexyl radical addition at the α-position. Control studies show preferential phenyl migration from a vinylidine carbene, thus excluding the presence of such an intermediate.

Determination of glycolic acid by stable isotope dilution was applied to the measurement of the glycolic acid pool size in tomato and maize leaves during photorespiration. Detached leaves were maintained in the presence of 18O2; [13C]glycolate was added to the foliar extract as an internal standard and the mixture of biological glycolate and [13C]glycolate was analyzed by combined gas chromatography-mass spectrometry. The level of foliar glycolate pool was measured via the 13C label, and 18O incorporation was determined.