Subattomole Amino Acid Analysis by Laser-Induced Fluorescence: The Sheath Flow Cuvette Meets Capillary Zone Electrophoresis

Subattomole analysis of fluorescein isothiocyanate (FITC) derivatives of amino acids is produced by combining capillary zone electrophoresis for high-efficiency separation with laser-induced fluorescence for high sensitivity detection. To optimize the separation process, several buffer systems were investigated. A pH 10 carbonate buffer provided good separation of 14 FITC amino acids. Concentration detection limits range from 5 × 10-12 M for alanine to 9 × 10-11 M for lysine, injected onto the column; ∼9 × 10-21 mol of alanine is contained within the ∼1-nL injection volume at the detection limit. The alanine detection limit corresponds to less than 6000 molecules injected onto the column and represents a four order of magnitude improvement in the state of the art for fluorescent detection of amino acids and a six order of magnitude improvement in the state of the art for the detection limit for isothiocyanate derivatives of amino acids.