Analysis of Organoselenium Compounds in Human Urine Using Active Carbon and Chemically Modified Silica Sol−Gel Surface-Assisted Laser Desorption/Ionization High-Resolution Time-of-Flight Mass Spectrometry

Abstract

Laser desorption/ionization time-of-flight mass spectra of three thermally labile low molecular weight organoselenium compounds (selenomethionine, selenoethionine, trimethylselenonium iodide) in human urine matrix have been obtained by using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). Four active layers, active carbon, silica sol-gel, and silica sol-gel impregnated with crown ether and with active carbon, were deposited on three different support substrates: (i) microscope slide coverslips; (ii) Al foil; and (iii) Cu tapes. Primarily protonated molecular ions and alkali metal adducts were observed in the mass spectra. A mixed-silica sol-gel and active carbon substrate active layer gave the best signal response for all compounds. Sol-gel substrates offered very clean backgrounds compared to the pure active carbon layers; however, the mass spectral signal intensities acquired were substantially lower for the sol-gel surfaces than those of the pure active carbon under the same conditions. Cu tape and Al foil support materials gave strong mass spectra of molecular ions and alkali metal molecular ion adducts, with lower Na and K adducts found with the Cu tape than with Al foil. Glass coverslips gave no response under all experimental conditions examined. Aerosol deposition was used to prepare SALDI substrates to avoid the localized "sweet spot" phenomenon encountered in conventional SALDI substrate preparation. Various nebulizers were examined and found to be effective in producing SALDI films with controlled and reproducible thicknesses. We were able to obtain exact mass identification of all three selenium species by high-resolution TOF-MS. To the best of our knowledge, this is the first time low molecular weight organoselenium compounds have been identified by SALDI-high-resolution TOF-MS.

A novel laser desorption/ionization method using through hole porous alumina membranes

“…To date a number of ionization techniques that belong to SALDI have been proposed,1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, ...…”

“…nanoparticles as typical, in treatable forms such as suspension liquids in order to ensure that the photon energies of the laser can act to desorp and ionize analytes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45. Indeed, the soft ionization laser method such as the original form of MALDI also belongs to this category 1.…”

Surface-assisted laser desorption/ionization mass spectrometry

“…In an early example of SALDI-MS using a silicabased film, Chen and coworkers used graphite drawn by a soft carbon pencil on silica to analyze small molecules dissolved in a sucrose, glucose and methanol solution [30]. Building on these results, Hoang and coworkers doped active carbon into a silica sol-gel for the characterization of several organoselenium compounds [48]. In an interesting combination of MALDI and SALDI, Lin and coworkers have doped silica with standard MALDI matrices, such as 2,5-dihydroxybenzoic acid (DHB) and 3,4-diaminobenzoic acid (DABA) for MS analyses [31][32][33][34] The silica-encapsulated organic matrix molecules absorb and transfer energy to analytes spotted on their surfaces, without being significantly ionized when the concentration of matrix is less than 10,000 parts per million [34].…”

On-Plate Desalting and SALDI-MS Analysis of Peptides with Hydrophobic Silicate Nanofilms on a Gold Substrate

“…Graphite21, carbon nanomaterials22, silicon nanoparticles23, silica24, metal oxide particles25, 26 and metal nanoparticles27–29 have been used as SALDI substrates where some of the nanomaterials have served as selective probes for analyte pre-concentration with their unique surface properties30, 31. But aggregation of nanomaterials on MALDI-plate often results in erratic LDI efficiency32 and there has been concern over co-desorption of nanomaterials in LDI that may contaminate the mass spectrometer29, 33.…”