title: Atmospheric pressure laser desorption/ionization using a 6-7 µm-band mid-infrared tunable laser and liquid water matrix.
abstract: Due to the characteristic absorption peaks in the IR region, various molecules can be used as a matrix for infrared matrix-assisted laser desorption/ionization (IR-MALDI). Especially in the 6-7 µm-band IR region, solvents used as the mobile phase for liquid chromatography have absorption peaks that correspond to their functional groups, such as O-H, C=O, and CH3. Additionally, atmospheric pressure (AP) IR-MALDI, which is applicable to liquid-state samples, is a promising technique to directly analyze untreated samples. Herein we perform AP-IR-MALDI mass spectrometry of a peptide, angiotensin II, using a mid-IR tunable laser with a tunable wavelength range of 5.50-10.00 µm and several different matrices. The wavelength dependences of the ion signal intensity of [M + H](+) of the peptide are measured using a conventional solid matrix, α-cyano-4-hydroxycinnamic acid (CHCA) and a liquid matrix composed of CHCA and 3-aminoquinoline. Other than the O-H stretching and bending vibration modes, the characteristic absorption peaks are useful for AP-IR-MALDI. Peptide ions are also observed from an aqueous solution of the peptide without an additional matrix, and the highest peak intensity of [M + H](+) is at 6.00 µm, which is somewhat shorter than the absorption peak wavelength of liquid water corresponding to the O-H bending vibration mode. Moreover, long-lasting and stable ion signals are obtained from the aqueous solution. AP-IR-MALDI using a 6-7 µm-band IR tunable laser and solvents as the matrix may provide a novel on-line interface between liquid chromatography and mass spectrometry.
authors.affiliation: Graduate School of Engineering, Osaka University, Suita, Osaka, Japan.
authors.forename: Ryuji
authors.initials: R
authors.lastname: Hiraguchi
authors.forename: Hisanao
authors.initials: H
authors.lastname: Hazama
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Masuda
authors.forename: Kunio
authors.initials: K
authors.lastname: Awazu
mesh_terms: D000634:Aminoquinolines / Q000737:chemistry; D000804:Angiotensin II / Q000032:analysis / Q000737:chemistry; D001274:Atmospheric Pressure; D003373:Coumaric Acids / Q000737:chemistry; D004867:Equipment Design; D006801:Humans; D007834:Lasers; D010455:Peptides / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation* / Q000379:methods; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry
chemical_list: D000634:Aminoquinolines; D003373:Coumaric Acids; D010455:Peptides; D012997:Solvents; D014867:Water; D000804:Angiotensin II; C007175:alpha-cyano-4-hydroxycinnamate
keywords: atmospheric pressure ionization; liquid matrix; mid-infrared; molecular vibration mode; tunable laser