Characterization of low molecular weight hydrocarbon oligomers by laser desorption/ionization time‐of‐flight mass spectrometry using a solvent‐free sample preparation method

Laser desorption/ionization time-of-flight (LDI-TOF) mass spectrometry was applied for the direct analysis of cuticular waxes on intact plant tissues. Cuticular wax compounds were ionized by laser desorption in the presence of colloidal silver. Silver-adduct ions were detected on samples from Arabidopsis thaliana and from maize. Good spot-to-spot reproducibility indicated homogeneous coverage of the sample by the fine colloidal material. The results were consistent with GC-MS analyses of cuticular extracts, thus confirming the feasibility of direct analysis based on this protocol. Molecular masses of the adduct ions correspond well with the known composition of cuticular waxes. Moreover, LDI-TOF gave good estimates of the relative local abundances of a given compound. However, bias was found in cases where compounds with different ionization efficiencies were analyzed. (J Am Soc Mass Spectrom 2005, 16, 107-115)

Section: Colloidal Silver Additivementioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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In-situ probing of the biotic-abiotic boundary of plants by laser desorption/ionization time-of-flight mass spectrometry

Sluszny

Yeung

Nikolau

2005

“…A number of other sample preparation techniques have been introduced for polymer analysis to optimize the signal-to-noise ratio, especially for insoluble polymers [11][12][13][14][15][16]. Briefly, these methods involve mixing the analyte polymer, the matrix, and the cationizing agent together, in a suitable ratio, and grinding them with either a mortar and pestle or a ball mill.…”

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confidence: 99%

Hydrocarbon polymer analysis by external MALDI fourier transform and reflectron time of flight mass spectrometry

Jaber

Wilkins

2005

The traditional solvent-based matrix-assisted laser desorption ionization (MALDI) preparation method has been used to analyze nonpolar polymers of various molecular weights. High resolution silver cationized oligomers with masses of up to 12 KDa were measured using 9.4 tesla Fourier transform mass spectrometry (FTMS) with an external ionization source. It was observed that when time-of-flight mass spectrometry was used, the spectra of polyethylene polymers showed abundant low mass fragment ions. However, these fragments were absent from the FTMS spectra. (J Am Soc Mass

“…Chen and Li performed LD with two long chain alkanes (C 28 and C 36 ), in mixtures with a variety of metal powders, to obtain the metal-cationized species [10]. Pruns et al used silver trifluoroacetate addition to parafin samples for MALDI analysis [11]. Dutta and Harayama analyzed oil samples by laser mass spectrometry after depositing them on a sample prepared with silver nitrate.…”

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confidence: 99%

An in situ silver cationization method for hydrocarbon mass spectrometry

Grace

Abo-Riziq

deVries

2005

We have developed a novel cationization method for the analysis of long-chain hydrocarbons via UV laser desorption mass spectrometry. In this technique we electrospray a thin coating of AgNO 3 over a sample and perform UV laser desorption to produce Ag ϩ cationization of sample molecules. Use of this technique in our microscope/TOF-MS allows us to determine the spatial distribution of the species we detect in the sample. We demonstrate 8-spatial resolution, and submicron resolution is possible in principle. In mixed samples containing aromatic and aliphatic compounds, the aromatic compounds ionize directly and do not form adducts, and thus give single peaks as opposed to doublets from silver cations. This enables distinction between aromatic and aliphatic compounds that are in the same sample. S aturated straight-chain hydrocarbons pose a considerable challenge regarding their direct analysis by means of mass spectrometry. While electron impact spectra do show characteristic fragmentation patterns for such compounds, it is difficult, if not impossible, to determine parent molecular weights, especially for components within a mixture. The strong tendency of these compounds to undergo fragmentation upon ionization causes the parent ion to appear with only minimal intensity [1,2]. One can increase the relative intensity of the parent ion by lowering the electron energy, but this reduces the ionization efficiency and also necessitates cooling of the source [1]. In addition, branching of the carbon chain, or the presence of functional groups such as carbonyls, carboxylic acid groups, or hydroxyls further destabilizes the molecular ion to the point where it appears with even lower intensity than that of the corresponding alkane or not at all [1,2]. The relatively low vapor pressure of these compounds and their tendency to crack when heated makes them poor candidates for chemical ionization, and their low solubility or miscibility in commonly used matrices precludes the use of fast atom bombardment. Multiphoton ionization methods are unsuitable because of the relatively large energy gaps between the ground and first excited electronic states in these compounds. While single-photon ionization of such compounds is possible, provided one can generate intense enough beams in the vacuum ultraviolet, the molecules fragment unless they are introduced via a supersonic jet [3,4]. Here we present an alternative method, based on silver cationization, for ionizing such compounds, implemented such that it allows for analysis of unperturbed samples with micron spatial resolution.Grade and Cooks found that they could cationize several aromatic organic molecules through the formation of metal ion adducts by mixing metal salts into the matrix they used to perform SIMS [5]. Zackett et al. used laser desorption (LD) to generate silver cation adducts of sucrose by placing the sucrose on a silver foil support in the presence of ammonium chloride [6]. Cromwell et al. performed laser desorption of perfluorinated polyethers (PFPEs), and used ...