title: Optimisation of derivatisation procedures for the determination of delta13C values of amino acids by gas chromatography/combustion/isotope ratio mass spectrometry.
abstract: Compound-specific stable carbon isotope analysis of amino acids by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) is a highly selective and sensitive method for probing the biosynthetic/diagenetic pathways, pool size and turnover rates of proteins, previously intractable to bulk isotope analyses. However, amino acids are polyfunctional, non-volatile compounds which require derivatisation prior to GC analysis. While a wide range of derivatives exist for the GC analysis of amino acids only a handful have been utilised for their GC/C/IRMS analysis. Significantly, none of those derivatives currently employed appear completely satisfactory and a thorough assessment of their relative utility is lacking. Seven derivatives (three previously reported and four novel) for obtaining delta(13)C values of amino acids via GC/C/IRMS analysis were compared. More specifically, standard mixtures of 15 protein amino acids were converted into N-acetylmethyl (NACME) esters, N-acetyl n-propyl (NANP) esters, N-acetyl i-propyl (NAIP) esters, N-trifluoroacetyl-i-propyl (TFA-IP) esters, N-pivaloyl methyl (NPME) esters, N-pivaloyl n-propyl (NPNP) esters and N-pivaloyl i-propyl (NPIP) esters. Each derivative was assessed with respect to its applicability to carbon isotope determinations of all the common alpha-amino acids, reaction yield, chromatographic resolution, stability, analyte-to-derivative carbon ratio, kinetic isotope effects and errors associated with their carbon isotope determinations. The NACME derivative was concluded to be the preferred derivative mainly due to the highest analyte-to-derivative carbon ratio being achieved, resulting in the lowest analytical errors for amino acid delta(13)C value determinations, ranging from +/-0.6 per thousand for phenylalanine, leucine and isoleucine to +/-1.1 per thousand for serine and glycine.
authors.affiliation: Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
authors.forename: Lorna T
authors.initials: LT
authors.lastname: Corr
authors.forename: Robert
authors.initials: R
authors.lastname: Berstan
authors.forename: Richard P
authors.initials: RP
authors.lastname: Evershed
mesh_terms: D000465:Algorithms; D000596:Amino Acids / Q000032:analysis* / Q000737:chemistry*; D002250:Carbon Radioisotopes / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D006358:Hot Temperature; D011786:Quality Control; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D000596:Amino Acids; D002250:Carbon Radioisotopes