Isolation of underivatized amino acids by ion-pair high performance liquid chromatography for precise measurement of nitrogen isotopic composition of amino acids: Development of comprehensive LC × GC/C/IRMS method

- Development of comprehensive liquid chromatography × gas chromatography/combustion/isotope ratio mass spectrometry (LC × GC/C/IRMS).
- High precision measurement of nitrogen isotopic composition of amino acids.
- High recovery during chromatographic separation without isotopic fractionation.
- Applicable to chemical, biological, and geological samples without matrix effects.