title: Determination of phenylalanine isotope ratio enrichment by liquid chromatography/time- of-flight mass spectrometry.
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.
authors.affiliation: Analytical Instrument Division, JEOL USA, Inc., 11 Dearborn Road, Peabody, MA 01960, USA. zwu@jeol.com
authors.forename: Zhanpin
authors.initials: Z
authors.lastname: Wu
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Zhang
authors.forename: Robert B
authors.initials: RB
authors.lastname: Cody
authors.forename: Robert R
authors.initials: RR
authors.lastname: Wolfe
mesh_terms: D000818:Animals; D002247:Carbon Isotopes; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003903:Deuterium / Q000032:analysis; D007553:Isotope Labeling; D010649:Phenylalanine / Q000032:analysis* / Q000493:pharmacokinetics; D011817:Rabbits; D012867:Skin / Q000737:chemistry / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D002247:Carbon Isotopes; D010649:Phenylalanine; D003903:Deuterium