Analysis of amino acid 13C abundance from human and faunal bone collagen using liquid chromatography/isotope ratio mass spectrometry

Abstract

The scope of compound‐specific stable isotope analysis has recently been increased with the development of the LC IsoLink which interfaces high‐performance liquid chromatography (HPLC) and isotope ratio mass spectrometry (IRMS) to provide online LC/IRMS. This enables isotopic measurement of non‐volatile compounds previously not amenable to compound‐specific analysis or requiring substantial modification for gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), which results in reduced precision. Amino acids are an example of such compounds. We present a new chromatographic method for the HPLC separation of underivatized amino acids using an acidic, aqueous mobile phase in conjunction with a mixed‐mode stationary phase that can be interfaced with the LC IsoLink for compound‐specific δ¹³C analysis. The method utilizes a reversed‐phase Primesep‐A column with embedded, ionizable, functional groups providing the capability for ion‐exchange and hydrophobic interactions. Baseline separation of 15 amino acids and their carbon isotope values are reported with an average standard deviation of 0.18‰ (n = 6). In addition δ¹³C values of 18 amino acids are determined from modern protein and archaeological bone collagen hydrolysates, demonstrating the potential of this method for compound‐specific applications in a number of fields including metabolic, ecological and palaeodietary studies. Copyright © 2006 John Wiley & Sons, Ltd.