title: Chemically modified porous silicon for laser desorption/ionization mass spectrometry of ionic dyes.
abstract: Desorption/ionization on silicon (DIOS) mass spectra of model ionic dyes methylene blue (MB+Cl-) and methyl orange (Na+MO-) were studied using p+ type-derived porous silicon (PS) free layers. As-prepared PS (PS-H), the PS thermally oxidized at 300 degrees C (PS-OX), PS with chemically grafted cation-exchanging alkylsulfonic acid (PS-SO(3)H) and anion-exchanging propyl-octadecyldimethylammonium chloride (PS-ODMA+Cl-) groups was tested as ionization platforms. Two mechanisms of the methylene blue desorption/ionization were found: (1) the formation of [MB + H]+* ion due to the reduction/protonation of MB+, which is predominant for PS-H and PS-OX platforms and (2) direct thermal desorption of the MB+ cation, prevailing for PS-SO3H. The fragmentation of the cation is significantly suppressed in the latter case. The samples of PS-SO3H and PS-ODMA+ Cl- efficiently adsorb the dyes of the opposite charge from their solutions via the ion-exchange. Consequent DIOS MS studies allow to detect only low fragmented ions (MB+ and MO-, respectively), demonstrating the potential of the ion-exchange adsorption combined with DIOS MS for the analysis of ionic organic compounds in solutions.
authors: A. A. Chuiko Institute of Surface Chemistry, NAS of Ukraine, 17 General Naumov St., 03164 Kiev, Ukraine. ivshmigol@ukr.net
authors: I V
authors: IV
authors: Shmigol
authors: S A
authors: SA
authors: Alekseev
authors: O Yu
authors: OY
authors: Lavrynenko
authors: N S
authors: NS
authors: Vasylieva
authors: V N
authors: VN
authors: Zaitsev
authors: D
authors: D
authors: Barbier
authors: V A
authors: VA
authors: Pokrovsky
mesh_terms: D000327:Adsorption; D053000:Analytic Sample Preparation Methods; D001391:Azo Compounds / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D006358:Hot Temperature; D007202:Indicators and Reagents / Q000737:chemistry*; D007474:Ion Exchange; D008567:Membranes, Artificial; D008751:Methylene Blue / Q000737:chemistry*; D008832:Microchemistry / Q000295:instrumentation; D015394:Molecular Structure; D016062:Porosity; D012828:Silicones / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D001391:Azo Compounds; D004396:Coloring Agents; D007202:Indicators and Reagents; D008567:Membranes, Artificial; D012828:Silicones; C100258:methyl orange; D008751:Methylene Blue