DETERMINATION OF DELTA-C-13 VALUES OF VALINE IN PROTEIN HYDROLYSATE BY GAS-CHROMATOGRAPHY COMBUSTION ISOTOPE RATIO MASS-SPECTROMETRY

A gas chromatographic-combustion isotope ratio mass spectrometric (GC- C-IRMS) method for the determination of [1-C-13]valine enrichments in protein hydrolysates is described. Using a quick derivatization method , delta(13)C values of the N-methoxycarbonyl methyl ester of valine ca n be determined from baseline separated GC peaks. Evaluation studies w ith respect to precision, accuracy, linearity, reduction capacity of t he CuO combustion furnace and isotope dilution as a result of derivati zation, showed that our GC-C-IRMS system allows robust measurement of enrichments of [1-C-13]valine in the range 0 to 1.5 MPE (S.D.+/- 0.01 MPE, n = 3). Therefore this method is suited to determine fractional s ynthetic rates (FSRs) of proteins as low as one-tenth of the FSR of hu man albumin, in studies using a primed, continuous (6 h) infusion with [1-C-13]valine plasma enrichments of approximately 15 MPE and an hour ly sampling schedule. (C) 1998 Elsevier Science BSI. All rights reserv ed.