Determining enrichments of tracers of glucose by mass spectrometry

A method for determining, in a sample, enrichments of a first and at least one second stable-labeled tracer of at least one target substance including glucose, the first tracer and the second tracer being generated by isotopic or bioisosteric substitution in the target substance, the method comprising:

• ionizing the first tracer, the second tracer and the target substance of the sample;
• measuring intensities of ions deriving from the target substance, of ions deriving from the first tracer and of ions deriving from the second tracer using a high-resolution mass analyzer;
• calculating an enrichment of the first tracer from a first ratio of the intensity of the ions deriving from the first tracer to the intensity of the ions deriving from the target substance employing a first calibration curve being independent of enrichments of each of the at least one second tracer,
• wherein the high-resolution mass analyzer is operated so as to resolve an ion peak deriving from a tracer and having a width Δ(m/z) at half maximum peak height equal to or smaller than 1×10−2.