title: Determination of 13C and 15N enrichments of urea in plasma by gas chromatography-combustion isotope ratio mass spectrometry and gas chromatography-mass spectrometry using the 2-methoxypyrimidine derivative.
abstract: We describe a GC-MS and GC-c-IRMS method for the determination of labeled urea tracer enrichments in plasma as a result of combined 13C- and 15N(2)-urea infusion experiments in piglets. Urea was converted into 2-methoxypyrimidine, a stable derivative, suited for analyses by both GC-MS and GC-c-IRMS. Using calibration curves for the respective working ranges (13C-urea: 0-1% APE; 15N(2)-urea: 0-7% MPE) enrichments were established in single point measurements; for 15N(2)-urea as values+/-0.15% MPE (95% confidence interval); for 13C-urea as values+/-0.02% APE (95% confidence interval). 15N(1)-urea enrichments were determined by measurement of the same sample with GC-c-IRMS and GC-MS. Subtraction of the 13C specific GC-c-IRMS data from the nondiscriminating GC-MS data for the sum of 13C- and 15N(1)-urea resulted in 15N(1)-urea enrichments+/-0.15% MPE (95% confidence interval). Application of the method in a combined 13C-urea bolus and 15N(2)-urea primed constant infusion experiment in piglet was demonstrated.
authors.affiliation: VU University Medical Center, Department of Clinical Chemistry, Metabolic Laboratory, Amsterdam, The Netherlands. w.kulik@amc.uva.nl
authors.forename: W
authors.initials: W
authors.lastname: Kulik
authors.forename: M J S
authors.initials: MJ
authors.lastname: Oosterveld
authors.forename: R M
authors.initials: RM
authors.lastname: Kok
authors.forename: K
authors.initials: K
authors.lastname: de Meer
mesh_terms: D000818:Animals; D002138:Calibration; D002247:Carbon Isotopes; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D009587:Nitrogen Isotopes; D015203:Reproducibility of Results; D013552:Swine; D014508:Urea / Q000097:blood*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D014508:Urea