Analysis of underivatized amino acid mixtures using high performance liquid chromatography/dual oscillating nebulizer atmospheric pressure microwave induced plasma ionization-mass spectrometry

A dual oscillating capillary nebulizer (OCN) in conjunction with an atmosph eric pressure microwave induced plasma ionization (AP-MIPI) source was appl ied to the analysis of underivatized amino acid mixtures. It was found that , compared to the single OCN, the dual OCN enhanced the sensitivity of dete ction several fold. Enhanced sensitivity was compound dependent. For small molecules, such as amino acids, it was 2-5 times more sensitive, while for larger molecules such as peptides it was more than an order of magnitude. T he increase in sensitivity was attributed to the enhanced nebulization of t he new torch. By using water/ acetonitrile containing 0.1% nonafluoropentan oic acid as the high performance liquid chromatography (HPLC) mobile phase and a C18 column, all common amino acids were separated and detected. A com parison between the results obtained using microwave induced plasma, atmosp heric pressure chemical ionization (APCI), and electrospray ionization (ESI ) at flow rates compatible with micro LC (10-100 muL/min) showed a higher s ensitivity of detection with the AP-MIPI technique for the analysis of unde rivatized amino acids. (C) 2001 American Society for Mass Spectrometry.