Determination of phenylalanine isotope ratio enrichment by liquid chromatography/time-of-flight mass spectrometry

Eur. J. Mass Spectrom. 10, 619–623 (2004)
DOI: 10.1255/ejms.670

Determination of phenylalanine isotope ratio enrichment by liquid chromatography/time-of-flight mass spectrometry

Zhanpin Wu,^a* Xiao-Jun Zhang,^b Robert B. Cody^a and Robert R. Wolfe^b
^aAnalytical Instrument Division, JEOL USA, Inc., 11 Dearborn Road, Peabody, MA 01960, USA. E-mail: zwu@jeol.com
^bMetabolism Division, Department of Surgery, University of Texas Medical Branch at Galveston, Galveston, TX 77550, USA

ABSTRACT:

The application of time-of-flight mass spectrometry to isotope ratio measurements has been limited by the relatively low dynamic range of the time-to-digital converter detectors available on commercial LC/ToF-MS systems. Here we report the measurement of phenylalanine isotope ratio enrichment by using a new LC/ToF-MS system with wide dynamic range. Underivatized phenylalanine was injected onto a C₁₈ column directly with 0.1% formic acid/acetonitrile as the mobile phase. The optimal instrument parameters for the time-of-flight mass spectrometer were determined by tuning the instrument with a phenylalanine standard. The accuracy of the isotope enrichment measurement was determined by the injection of standard solutions with known isotope ratios ranging from 0.02% to 9.2%. A plot of the results against the theoretical values gave a linear curve with R² of 0.9999. The coefficient of variation for the isotope ratio measurement was below 2%. The method is simple, rapid, and accurate and presents an attractive alternative to traditional GC/MS applications.

Keywords: time-of-flight mass spectrometry, isotope ratio enrichments, amino acids

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