title: Normal silica gel and reversed phase thin-layer chromatography coupled with UV spectroscopy and IR-MALDI-o-TOF-MS for the detection of tetracycline antibiotics.
abstract: Tetracyclines (TCs) form a group of bacteriostatic antibiotics with closely related structures and similar chemical and physicochemical properties. They are widely employed as therapeutics in human and veterinary medicine. Here, we introduce the combination of UV spectroscopic detection of high-performance thin-layer chromatography (HPTLC)-separated TCs with direct analysis on solid phase using infrared matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometry (IR-MALDI-o-TOF-MS). Normal silica gel phase- and water-wettable hybrid C(18) reversed phase layers (RP-18W) both allowed HPTLC separation and sensitive UV spectroscopic detection followed by MS analysis of distinct TCs bands using the liquid matrix glycerol. The novel approach of direct IR-MALDI-o-TOF-MS analysis resulted in the unequivocal identification of four structurally different TCs employed in this study, and linear calibration curves were produced for analyte amounts from 20 ng to 1 μg. MS analysis of TCs from RP-18W HPTLC plates was found to be superior when compared to the spectra acquired from the silica gel layer. Ionic analytes obtained from the RP-18W surface are mainly detected as protonated species of high abundance accompanied by a reduced formation of adducts as well as background ions arising from the matrix or the stationary phase. This results in decreased complexity of the spectra and enhanced sensitivity of the combinatorial method. An approximate detection limit of 5 ng of individual TCs in mixtures by combining RP-18W HPTLC with IR-MALDI-o-TOF-MS offers a novel timely and cost-efficient method for tracing TCs.
authors.affiliation: Institute for Hygiene, University of Münster, Robert-Koch-Str. 41, 48149 Münster, Germany. meisen@uni-muenster.de
authors.forename: Iris
authors.initials: I
authors.lastname: Meisen
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wisholzer
authors.forename: Jens
authors.initials: J
authors.lastname: Soltwisch
authors.forename: Klaus
authors.initials: K
authors.lastname: Dreisewerd
authors.forename: Michael
authors.initials: M
authors.lastname: Mormann
authors.forename: Johannes
authors.initials: J
authors.lastname: Müthing
authors.forename: Helge
authors.initials: H
authors.lastname: Karch
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Friedrich
mesh_terms: D000900:Anti-Bacterial Agents / Q000032:analysis*; D056148:Chromatography, Reverse-Phase / Q000379:methods*; D002855:Chromatography, Thin Layer / Q000379:methods*; D058428:Silica Gel / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation / Q000379:methods*; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D013754:Tetracyclines / Q000032:analysis*
chemical_list: D000900:Anti-Bacterial Agents; D013754:Tetracyclines; D058428:Silica Gel