Measurement of endogenous leucine enkephalin in canine thalamus by high-performance liquid chromatography and field desorption mass spectrometry

A combination of high-performance liquid chromatography and field desorption mass spectrometry is used to quantify endogenous amounts of leucine enkephalin in canine thalamus tissue. Reversed-phase high-performance liquid chromatography effects rapid high resolution of brain neuropeptides using a triethylamine formate buffer. An internal standard, 2Ala-leucine-enkephalin, is used. Field desorption mass spectra of neuropeptides generally display only protonated molecular ions. (M + H)+ ion currents of endogenous leucine enkephalin and internal standard were integrated by field desorption mass spectral-selected ion monitoring techniques. The ratio of the two integrated ion currents was used to calculate endogenous amount of leu-enkephalin in thalamus tissue extracts. Leucine enkephalin was determined in this structurally unambiguous fashion in canine thalamus tissue at 50 ng/g thalamus tissue, or the 50 part per billion level.