Determination of histidine and urocanic acid isomers in the human skin by high-performance capillary electrophoresis

Histidine was baseline separated from histamine, 1-methylhistamine and cis- and trans-urocanic acid using high-performance capillary electrophoresis (HPCE) on a fused-silica column (50 cm X 75 mum) with 0.05 M NaH2PO4 buffer, pH 5.0, and 12 kV. The detection Limit of histidine, trans- and cis-urocanic acid was 10(-6) M at a wavelength of 214 nm. The detection limit of the urocanic acid isomers was slightly enhanced to 5.10(-7) M at 267 nm. The transformation of the trans-urocanic acid standard in vitro into the cis-isomer was dependent on the time of exposure and the energy of the Light source. WE light induced a significantly faster conversion than WA light. The HPCE method was used for the characterization and measurement of histidine and urocanic acid in human skin eluates. The concentrations of histidine, trans- or cis-urocanic acid in ethanol washes from the skin of healthy, non-allergic volunteers were 2.22+/-0.40.10(-5), 0.96+/-0.26-10(-5) and 1.04+/-0.30.10(-5) M,respectively, (mean+/-SEM, n=8). The results obtained by HPCE correlated well with data obtained by HPLC. Correlation coefficients of r(2)=0.981, r(2)=0.814 and r(2)=0.956 were found for histidine, trans- and cis-urocanic acid, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.