Abstract:A variety of derivatized fullerenes have been studied by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Of particular emphasis has been the evaluation of a recently introduced solvent-free sample/target preparation method. Solvent-free MALDI is particularly valuable in overcoming adverse solvent-related effects, such as insolubility and/or degradation of the sample. The method was applied to fullerene derivatives susceptible to decomposition under insufficiently "soft" MALDI conditions.… Show more
“…Therefore, a matrix material was needed that promoted rather than suppressed lithium ion adduction to the FAs. 7,7,8,8-Tetracyanoquinodimethan (TCNQ) has previously been used as a matrix material for the MALDI analysis of such compounds as polycyclic aromatic hydrocarbons [14,15,18], dendrimers [14], synthetic polymers [19,20], carbon pitches [21], and fullerenes [14,22]; molecular ion species are often produced using significantly lower laser power [14,20]. Because TCNQ is aprotic and very electron deficient, we reasoned that it would be an ideal candidate to transfer a Li ϩ ion from a lithium salt to FAs.…”
In numerous studies charge remote fragmentation (CRF) has been shown to be a powerful technique for determination of primary structure by allowing location of double bonds, various functional groups, and branching in a variety of compound types directly by mass spectrometry. Instrumentation and ionization methods traditionally used for CRF, however, are becoming rare, in large part because ESI and MALDI have to a significant extent replaced them. Here we demonstrate that by selecting a matrix that promotes rather than suppresses ionization of fatty acids (FA) by lithium ion adduction, and using a TOF-TOF mass spectrometer for high-energy collisional activation, CRF ions are produced that allow location of double-bond and branching positions. Further, we show that by using solvent-free MALDI sample preparation methods, thus eliminating the inherent segregation of the hydrophobic fatty acid from the hydrophilic LiCl that can occur during the evaporation of solvent, the desired [FAϪHϩ2Li] ϩ ions are greatly enhanced. Because FAs can be vaporized using laser desorption, matrix assistance in desorption of the fatty acid may occur, but is not necessary. However, the matrix plays a crucial role in enhancing or suppressing ionization. For example, matrix materials with acid (e.g., 2,5-dihydroxybenzoic acid) or hydroxy groups (e.g., dithranol) compete with the FA for Li ϩ and because of the high ratio of matrix to analyte, FA lithium adduction is minimized. However, highly electron-deficient matrix materials (e.g., TCNQ) readily donate Li ϩ to FAs because of the instability associated with being positively charged. (J Am Soc Mass
“…Therefore, a matrix material was needed that promoted rather than suppressed lithium ion adduction to the FAs. 7,7,8,8-Tetracyanoquinodimethan (TCNQ) has previously been used as a matrix material for the MALDI analysis of such compounds as polycyclic aromatic hydrocarbons [14,15,18], dendrimers [14], synthetic polymers [19,20], carbon pitches [21], and fullerenes [14,22]; molecular ion species are often produced using significantly lower laser power [14,20]. Because TCNQ is aprotic and very electron deficient, we reasoned that it would be an ideal candidate to transfer a Li ϩ ion from a lithium salt to FAs.…”
In numerous studies charge remote fragmentation (CRF) has been shown to be a powerful technique for determination of primary structure by allowing location of double bonds, various functional groups, and branching in a variety of compound types directly by mass spectrometry. Instrumentation and ionization methods traditionally used for CRF, however, are becoming rare, in large part because ESI and MALDI have to a significant extent replaced them. Here we demonstrate that by selecting a matrix that promotes rather than suppresses ionization of fatty acids (FA) by lithium ion adduction, and using a TOF-TOF mass spectrometer for high-energy collisional activation, CRF ions are produced that allow location of double-bond and branching positions. Further, we show that by using solvent-free MALDI sample preparation methods, thus eliminating the inherent segregation of the hydrophobic fatty acid from the hydrophilic LiCl that can occur during the evaporation of solvent, the desired [FAϪHϩ2Li] ϩ ions are greatly enhanced. Because FAs can be vaporized using laser desorption, matrix assistance in desorption of the fatty acid may occur, but is not necessary. However, the matrix plays a crucial role in enhancing or suppressing ionization. For example, matrix materials with acid (e.g., 2,5-dihydroxybenzoic acid) or hydroxy groups (e.g., dithranol) compete with the FA for Li ϩ and because of the high ratio of matrix to analyte, FA lithium adduction is minimized. However, highly electron-deficient matrix materials (e.g., TCNQ) readily donate Li ϩ to FAs because of the instability associated with being positively charged. (J Am Soc Mass
“…For example, the ability to apply lower laser power33 reduces undesired fragmentation of labile compounds 27, 34. A number of laboratories are engaged in understanding fundamentals and solving new challenges using solvent‐free MALDI 70–79…”
Section: Total Solvent‐free Analysis By Msmentioning
Progress in research is hindered by analytical limitations, especially in biological areas in which sensitivity and dynamic range are critical to success. Inherent difficulties of characterization associated with complexity arising from heterogeneity of various materials including topologies (isomeric composition) and insolubility also limit progress. For this reason, we are developing methods for total solvent-free analysis by mass spectrometry consisting of solvent-free ionization followed by solvent-free gas-phase separation. We also recently constructed a novel matrix-assisted laser desorption ionization (MALDI) source that provides a simple, practical and sensitive way of producing highly charged ions by laserspray ionization (LSI) or singly charged ions commonly observed with MALDI by choice of matrix or matrix preparation. This is the first ionization source with such freedom -an extremely powerful analytical 'switch'. Multiply charged LSI ions allow molecules exceeding the mass-to-charge range of the instrument to be observed and permit for the first time electron transfer dissociation fragment ion analysis.
“…25 In addition to elucidating the electron transfer mechanism using the DCTB matrix, 26,27 we have successfully employed DCTB to a variety of fullerene-related MALDI studies. 28–32 Figure 1.Structures of the fullerene derivatives under investigation with abbreviated names and nominal masses.…”
Inspired by reports on the use of pencil lead as a matrix-assisted laser desorption/ionization matrix, paving the way towards matrix-free matrix-assisted laser desorption/ionization, the present investigation evaluates its usage with organic fullerene derivatives. Currently, this class of compounds is best analysed using the electron transfer matrix trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene] malononitrile (DCTB), which was employed as the standard here. The suitability of pencil lead was additionally compared to direct (i.e. no matrix) laser desorption/ionization-mass spectrometry. The use of (DCTB) was identified as the by far gentler method, producing spectra with abundant molecular ion signals and much reduced fragmentation. Analytically, pencil lead was found to be ineffective as a matrix, however, appears to be an extremely easy and inexpensive method for producing sodium and potassium adducts.
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