Determination of amino acids by capillary electrophoresis-electrospray ionization-mass spectrometry: an evaluation of different protein hydrolysis procedures.

In this work, a CE equipment, online hyphenated to an IT MS analyzer by a linear sheath liquid interface promoting ESI, was used to develop a method for quantitative determination of amino acids. Under appropriate conditions (BGE composition, 0.8% HCOOH, 20% CH3OH; sheath liquid composition, 0.8% HCOOH, 60% methanol; V ESI, +4.50 kV), analytical curves of all amino acids from 3 to 80 mg/L were recorded presenting acceptable linearity (r >0.99). LODs in the range of 16-172 micromol/L were obtained. BSA, a model protein, was submitted to different hydrolysis procedures (classical acid and basic, and catalyzed by the H+ form of a cation exchanger resin) and its amino acid profiles determined. In general, the resin-mediated hydrolysis yields were overall similar or better than those obtained by classical acid or basic hydrolysis. The resulting experimental-to-theoretical BSA concentration ratios served as correction factors for the quantitation of amino acids in Brazil nut resin generated hydrolysates.