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 method for analyzing organoselenium and organic acid metabolites using laser desorption from graphite surfaces coupled to vacuum ultraviolet single photon ionization mass spectrometry (LD/SPI MS) is described. The 1-10-fmol sensitivity and linear dynamic range allows quantitative detection of selenomethionine, trimethylselenonium ion, methylselenogalactosamine, and 1beta-methylseleno-N-acetyl-D-galactosamine in complex biological samples such as human urine. In addition, common urinary metabolites such as tartronic, glutaric, orotic, uric, suberic, and hydroxyhippuric acids, are readily detected. Screening and quantitative detection of these organoselenium and organic acid metabolites is achieved within minutes. The results are also consistent with those obtained using high-performance liquid chromatography tandem mass spectrometry techniques. The study demonstrates the viability of matrix-free LD/SPI MS for molecular characterization and quantitative analysis of biological metabolites in the m/z 10-500 range that are present in complex biological fluids.
Silica and polymer PEEK 1 capillaries were used to modify an oscillating capillary nebulizer (OCN) in order to make it sturdier and more durable for routine analyses, and also to improve response sensitivity. The performance of four modified OCNs was compared to that of the original OCN design and also to a Meinhard High Efficient Nebulizer (HEN), using an identical single-pass cylindrical spray chamber for all the nebulizers. The effects of spray chamber design, droplet size and turbulence on analyte transport efficiency of low molecular weight organoselenium compounds were also investigated. Three organoselenium standards: (1) selenocystamine; (2) selenomethionine; and (3) trimethylselenonium iodide were used as test compounds with inductively coupled plasma-mass spectrometry (FI/ICP-MS). Droplet size distributions and Sauter mean diameters of aerosols were measured by laser Fraunhofer diffraction. An OCN fabricated with PEEK 1 gas capillary, with either a thicker capillary wall or a larger inner diameter liquid capillary tube, performed better than the original OCN design. The optimal improvement of analytical signal of 3-4 times, corresponding to a 2.5-3.0 times improvement in analyte transport efficiency was found, compared to the original OCN design and also to a standard Meinhard HEN. Contrary to literature reports, we observed that moderate increases in mean droplet sizes resulted in improved analyte transport efficiencies and higher signal intensities for the volatile compounds tested. However, nebulizers producing aerosols with Sauter mean diameters, D [3,2] , greater than approximately 9.5 mm gave lower transport efficiencies and reduced signal intensities. Although greater turbulence in the gas flow inside a single-pass spray chamber predictably decreased net analyte transport efficiencies, the overall loss of aerosol was unexpectedly 3-5 times greater for small droplets (v3 mm) than for larger droplets (w3 mm, v9 mm). Experimental Chemicals and reagentsAll solvents were of HPLC grade. Nitric acid, acetic acid and trifluoroacetic acid (TFA) were trace metal grade (Fisher
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.