title: Analysis of (1-13C)leucine and (13C)KIC in plasma by capillary gas chromatography/mass spectrometry in protein turnover studies.
abstract: The methods used for the determination of the concentration and isotope enrichment of (1-13C)leucine and its metabolite (13C) alpha-ketoisocaproic acid (KIC) in plasma for the study of whole-body protein turnover are described. Leucine was analysed as its N-heptafluorobutyryl isobutyl ester and KIC as its quinoxalinol-TMS derivative, both by chemical ionization selected ion monitoring gas chromatography/mass spectrometry (GC/MS). The sensitivity of the leucine assay was improved 30 times by monitoring the negative ions under the conditions described. The coefficient of variation for enrichment and concentration measurements were 0.5% and 2%, respectively, with a minimum detectable enrichment of 0.1 at% excess for both assays.
authors.forename: G C
authors.initials: GC
authors.lastname: Ford
authors.forename: K N
authors.initials: KN
authors.lastname: Cheng
authors.forename: D
authors.initials: D
authors.lastname: Halliday
mesh_terms: D002208:Caproates / Q000097:blood*; D002247:Carbon Isotopes; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D007651:Keto Acids / Q000097:blood*; D007930:Leucine / Q000097:blood*; D011506:Proteins / Q000378:metabolism*
chemical_list: D002208:Caproates; D002247:Carbon Isotopes; D007651:Keto Acids; D011506:Proteins; C013082:alpha-ketoisocaproic acid; D007930:Leucine