A non-derivatized method for simultaneous quantitation of proteinogenic, urea-cycle, and acetylated amino acids by liquid chromatography–high-resolution mass spectrometry
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The quantification of amino acids as freely dissolved compounds or from hydrolyzed peptides and proteins is a common endeavor in biomedical and environmental sciences. In order to avoid the drawbacks of derivatization and application challenges of tandem mass spectrometry, we present here a robust 13-min liquid chromatography coupled with a full-scan mass spectrometry method to achieve rapid detection and quantification of 30 amino acids without derivatization. We combined hydrophilic interaction liquid chromatography with heated electrospray ionization and high-resolution mass spectrometry operated with polarity switching to analyze the 20 proteinogenic amino acids, ornithine, citrulline, homoserine, cystine, and six acetylated amino acids. We obtained high mass accuracy and good precision of the targeted amino acids. Limits of detection ranged from 0.017 to 1.3 µM. Noteworthy for environmental samples, we found comparable ionization efficiency and quantitative detection for the majority of the analytes prepared with pure water versus a high-salt solution. We applied the method to profile carbon source-dependent secretions of amino acids by Pseudomonas protegens Pf-5, a well-known plant-beneficial bacterium.
KeywordsPolarity switching Non-targeted analysis Acetylated amino acids Urea-cycle amino acids High-resolution mass spectrometry
Postdoctoral supports for A.R.K. and K.B-H. were provided, respectively, by a National Science Foundation CAREER Grant (award # 1653092) and a research fellowship from Cornell University, both awarded to L. A. We thank Rebecca A. Wilkes (Aristilde Research Group, Cornell University) for preparing the bacterial cultures.
Compliance with ethical standards
Conflicts of Interest
The authors declare no conflicts of interest.
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