Capillary electrophoresis mass spectrometry with sheathless electrospray ionization for high sensitivity analysis of underivatized amino acids

A high durability sheathless electrospray ionization interface of CE ‐ MS is applied for the sensitive analysis of underivatized amino acids. The sheathless interface was realized using an ionophore membrane‐packed electro‐conduction channel. The interface functioned well with a volatile alkaline background electrolyte ( BGE ) and uncoated fused‐silica capillaries for CE ‐ MS analysis of underivatized amino acids. High electroosmotic flow with alkaline BGE facilitated high separation efficiency (>100 000 theoretical plates) and short analysis time (<15 min). Both the short‐term stability and long‐term durability are particularly suited for routine applications. Using electrokinetic injection and the multiple reaction monitoring ( MRM ) mode with a triple‐quadrupole analyzer, high sensitivity was achieved, which yielded detection limits of 0.05–0.81 μM. For the quantitation of underivatized amino acids, quantification precisions ( RSD s) for intra‐ and inter‐day analyses were less than 3%. Recoveries from serum were 96.3–101.8% for isotope dilution mass spectrometry ( IDMS ). When compared with HPLC ‐ IDMS for human serum samples, highly agreeable (96.9–102.0%) results were obtained with the proposed CE ‐ IDMS method.