Determination of (13C) urea enrichment by gas chromatography/mass spectrometry and gas chromatography/isotope ratio mass spectrometry.
We present gas chromatographic/mass spectrometric and gas chromatographic/isotope ratio mass spectrometric assays of the 13C enrichment of plasma urea converted to its dimethylaminomethylene derivative. The limits of sensitivity of the two techniques are 0.2% and 0.02%, respectively. The techniques were tested in rats and humans infused with (13C)urea or (3-13C)lactate. (13C)Urea enrichment during the infusion of (3-13 C)lactate in humans was not detectable by gas chromatography/mass spectrometry but was easily measured by gas chromatography/isotope ratio mass spectrometry. These assays should be useful for clinical investigations, in which the incorporation of a (13C)gluconeogenic substrate into glucose must be corrected for the incorporation of 13CO2 derived from the oxidation of the substrate. This correction involves measuring the low-level 13C enrichment of urea.
Beylot
M
M
INSERM U. 197, Faculté A. Carrel, Lyon, France.
David
F
F
Khalfallah
Y
Y
Normand
S
S
Large
V
V
Brunengraber
H
H
D000328:Adult; D000818:Animals; D002247:Carbon Isotopes; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007773:Lactates / Q000493:pharmacokinetics; D019344:Lactic Acid; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D014508:Urea / Q000737:chemistry*
D002247:Carbon Isotopes; D007773:Lactates; D019344:Lactic Acid; D014508:Urea