title: Analysis of histidine and urocanic acid isomers by reversed-phase high-performance liquid chromatography.
abstract: The qualitative separation performance of a C18, C8 and C4 reversed-phase column was investigated for the separation of histidine and its metabolites histamine, 1-methyihistamine and trans- and cis-urocanic acid. Trans- and cis-urocanic acid were baseline separated from their precursor histidine on all three columns using isocratic elution with a mobile phase composed of 0.01 M aqueous TEAP pH 3.0 and acetonitrile at a ratio of 98:2 (v/v). However, histidine was not separated from histamine and 1-methyihistamine. Selecting the C8 column and introducing 0.005 M of the ion pairing reagent 1-octanesulfonic acid sodium salt into the aqueous solution and acetonitrile at a ratio of 90:10 (v/v), significantly improved the separation. The separation was also followed by a change in the retention times and the order of elution. The sequence of elution was histidine, cis-urocanic acid, trans-urocanic acid, histamine and 1-methylhistamine with retention times of 5.58 +/- 0.07, 7.03 +/- 0.15, 7.92 +/- 0.18, 18.77 +/- 0.24 and 20.79 +/- 0.21 min (mean +/- SD; n=5). The separation on the C8 column in the presence of the ion-pairing reagent was further improved with gradient elution that resulted in a reduction in the retention times and elution volumes of histamine and 1-methylhistamine. The detection limits of histidine and trans-urocanic acid at a wavelength of 210 nm and an injection volume of 0.05 ml were 5 x 10(-8) mol l(-1) (n=3). The kinetic of the in-vitro conversion of trans- into the cis-isomer after UV irradiation was depending on the time of exposure and the energy of the light source. UVB light induced a significantly faster conversion than UVA light. TUCA and cUCA samples kept at -25 degrees C were stable for up to 50 weeks. Samples, eluted from human skin showed various concentrations of histidine and trans- and cis-urocanic acid with an average of 1.69 +/- 0.33 x 10(-5) mol l(-1), 1.17 +/- 0.43 x 10(-5) mol l(-1) and 1.67 +/- 0.33 x 10(-5) mol l(-1), respectively (n=8).
authors.affiliation: Klinik und Poliklinik für Dermatologie und Allergologie am Biederstein, Technische Universität München, Munich, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Hermann
authors.forename: D
authors.initials: D
authors.lastname: Abeck
mesh_terms: D000328:Adult; D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005260:Female; D006639:Histidine / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D007536:Isomerism; D007700:Kinetics; D008297:Male; D012680:Sensitivity and Specificity; D012867:Skin / Q000737:chemistry; D014466:Ultraviolet Rays; D014560:Urocanic Acid / Q000737:chemistry*
chemical_list: D006639:Histidine; D014560:Urocanic Acid