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 delta13C 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 per thousand (n = 
6). In addition delta13C 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.