Masataka WAKAYAMA - Simultaneous analysis of amino acids and carboxylic acids by capillary electrophoresis-mass spectrometry using an acidic electrolyte and uncoated fused-silica capillary

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      Anal.   Chem. 82:   9967-9976


      A simple, low-cost capillary electrophoresis−mass spectrometry   (CE−MS) method is demonstrated for the simultaneous analysis of   amino acids and small carboxylic acids (glycerate, lactate,   fumarate, succinate, malate, tartrate, citrate,   iso-citrate, cis-aconitate, and shikimate). All   CE−MS experiments were performed using a single uncoated   fused-silica capillary and with a single separation electrolyte,   formic acid. For CE polarity, the CE inlet was set as the anode,   and the MS side was set as the cathode. By using high-speed   sheath gas flow, the apparent mobilities of all compounds were   sped up; thus, the migration times of the carboxylic acids were   reduced. In positive ion mode ESI−MS detection, small carboxylic   acids were detected faintly as m/z = [M +   18]+ or [M + 23]+, after protonated   molecule detection (m/z = [M + 1]+)   of the amino acids. In negative ion mode, all of these small   carboxylic acids were detected clearly as deprotonated molecules   (m/z = [M − 1]), after detection of   the amino acids. By changing the polarity of the MS during CE   separation, both amino acids and small carboxylic acids were   detectable in a single electrophoresis analysis run. With this   method, the diurnal metabolic changes of pineapple leaves were   observed as reflecting Crassulacean acid metabolism.

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