Simultaneous Analysis of Amino Acids and Carboxylic Acids by Capillary Electrophoresis−Mass Spectrometry Using an Acidic Electrolyte and Uncoated Fused-Silica Capillary

摘要

A simple, low-cost capillary electrophoresis-mass spectrometryn(CE-MS) method is demonstrated for the simultaneousnanalysis of amino acids and small carboxylicnacids (glycerate, lactate, fumarate, succinate, malate,ntartrate, citrate, iso-citrate, cis-aconitate, and shikimate).nAll CE-MS experiments were performed using a singlenuncoated fused-silica capillary and with a single separationnelectrolyte, formic acid. For CE polarity, the CE inletnwas set as the anode, and the MS side was set as thencathode. By using high-speed sheath gas flow, the apparentnmobilities of all compounds were sped up; thus, thenmigration times of the carboxylic acids were reduced. Innpositive ion mode ESI-MS detection, small carboxylicnacids were detected faintly as m/z ) [M + 18]+ or [M +n23]+, after protonated molecule detection (m/z ) [Mn+ 1]+) of the amino acids. In negative ion mode, all ofnthese small carboxylic acids were detected clearly asndeprotonated molecules (m/z ) [M - 1]-), afterndetection of the amino acids. By changing the polaritynof the MS during CE separation, both amino acids andnsmall carboxylic acids were detectable in a singlenelectrophoresis analysis run. With this method, thendiurnal metabolic changes of pineapple leaves werenobserved as reflecting Crassulacean acid metabolism.