HIGH-SENSITIVITY TRACER DETECTION USING HIGH-PRECISION GAS-CHROMATOGRAPHY COMBUSTION ISOTOPE RATIO MASS-SPECTROMETRY AND HIGHLY ENRICHED [U-C-13]-LABELED PRECURSORS

The use of highly enriched, uniformly labeled fatty acid ([U-C-13]) with analysis by high-precision gas chromatography-combustion isotope ratio mass spectrometry (GCC-IRMS) has been evaluated as a metabolic tracer technique. C-13/C-12 ratios are routinely determined to precisions (SD) of < 0.00001 (delta(PDB) < 1 parts per thousand) for > 10 ng of fatty acid, and < 0.001 (delta(PDB) < 100 parts per thousand) for samples of 30 pg of fatty acid, the latter corresponding to a 100-fmol sample. Baseline fatty acid C-13/C-12 In human plasma fractions is shown 10 fluctuate not more than 0.00004 (delta(PDB) 4 parts per thousand) over 10 h. C-13/C-12 enrichments greater than 0.001 (delta(PDB) 100 parts per thousand) are obtained in a fatty acid plasma fraction subsequent to a 10-mg dose of 42% C-13-labeled stearic acid to a 78-kg adult. Blokinetics are discerned over an C-13/C-12 enrichment range of less than 0.0002 (almost-equal-to 13 parts per thousand in delta(PDB) units) in plasma. A means for correction of isotope ratio contamination due to carbon-containing derivatives is presented. High-precision GCC-IRMS used in concert with highly enriched tracers is shown to possess advantages versus organic GC/MS for stable isotopic tracer detection and is superior to radiotracer methods in terms of dose sizes and analysis efficiency.