Ultrahigh-resolution mass spectrometry

High and in particular ultrahigh-resolution in combination with a soft ionization method such as ESI, MALDI, or FD presents another way to achieve the separation of the molecular species contained in a mixture. Given a sufficient level of resolution, isobaric ions are displayed separately in the range of their common nominal mass value (Chap. 3.3.2, 3.4). 

Classically, high-resolution work is the domain of double-focusing magnetic sector instruments. More recently, TOP and to a certain degree triple quadrupole instruments are also capable of resolutions up to about 20,000. However, the rapid development of FT-ICR instruments has established those as the systems of choice if ultrahigh-resolution ( 100,000) and highest mass accuracy (1 ppm) are required (Chap. 4.6). 

The potential of ultrahigh-resolution mass spectrometry for the analysis of complex chemical mixtures is particularly illustrated by FT-ICR-MS which definitely sets a new standard. For example, ultrahigh-resolution was applied to separate several thousand components in crude oil, [85,86] fuels, [87,88] or explosion residues. [89] 

Example ESI selectively ionizes the basic compounds, i.e., only a small fraction of the entire chemical composition, in a sample of South American cmde oil. Nevertheless, the positive-ion ESI-FT-ICR mass spectrum exhibits more than 11,100 resolved peaks, of which 75 % may be assigned to a unique elemental composition (CcHhOoNnSJ. Such a separation in mass is possible because the average mass resolution in the m/z 225-1000 broadband spectrum is approximately 350,000 (Fig. 12.12). This demonstrates the current upper limit for the number of chemically distinct components resolved and identified in a single step. [86] 

Williams, J.D. Burinsky, D.J. Mass Spec-trometric Analysis of Complex Mixtures Then and Now the Impact of Linking Liquid Chromatography and Mass Spectrometry. Int. J. Mass Spectrom. 2001, 212, 111-133. 

Example In a sample of South American crude oil positive-ion ESI selectively delivers ions of the basic compounds, i.e., only a small fraction of the en- 

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Sleighter, R. L., and Hatcher, P. G. (2007). The application of electrospray ionisation coupled to ultrahigh resolution mass spectrometry for the molecular characterization of natural organic matter. I. Mass Spectrom. 42, 559-574. 

We have recently determined the structural parameters and composition of some asphaltene samples obtained from the Synthoil and Exxon Donor Solvent (EDS) liquefaction processes. The particular EDS sample used was sufficiently volatile for analysis by ultrahigh resolution mass spectrometry, so we could obtain very detailed data on its composition in terms of the distribution of individual carbon-number homologs. Information from this approach, integrated with data from NMR, IR, molecular weight determinations, elemental analyses, and separations furnished us with a novel and detailed insight into the nature of these asphaltenes. The excellent agreement observed between composites calculated from the detailed MS data, where available, and the averages determined by NMR, IR, and elemental analyses reinforces the credibility of the approaches used and allows extrapolations to heavier samples that are not amenable to detailed MS characterization. 

Kujawinski, E.B., Longnecker, K., Blough, N.V., Del Vecchio, R., Finlay, L., Kitner, J.B., and Giovannoni (2009). Identification of possible markers in marine dissolved organic matter using ultrahigh resolution mass spectrometry. Geochim. Cosmochim Acta, 73, 4384 399. 

Sleighter, R.L., Liu, Z., Xue, J., and Hatcher, P.G. (2010). Multivariate statistical approaches for the characterization of dissolved organic matter analyzed by ultrahigh resolution mass spectrometry. Environ. Sci. Technol, 44,7576-7582. 

Solouki, T. Emmet, M.R. Guan, S. Marshall, A.G. Detection, Number, and Sequence Location of Sulfur-Containing Amino Acids and Disulfide Bridges in Peptides by Ultrahigh-Resolution MALDI-FTICR Mass Spectrometry. Anal. Chem. 1997,69, 1163-1168. 

In 1974, Comarisov and Marshall60 developed Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). This technique allows mass spectrometric measurements at ultrahigh mass resolution (R = 100000-1000000), which is higher than that of any other type of mass spectrometer and has the highest mass accuracy at attomole detection limits. FTICR-MS is applied today together with soft ionization techniques, such as nano ESI (electrospray ionization) or MALDI (matrix assisted laser/desorption ionization) sources. 

Fourier transform ICR mass spectrometers together with any type of ion source, such as nanoESI, MALDI (or also an inductively coupled plasma ion source) permit mass spectrometric measurements to be performed at ultrahigh mass resolution (R = m/hm = 105—106) with a very low detection limit and the highest possible mass accuracy (Am = 10 3—10 4 Da). In addition, a high mass range is possible and FTICR-MS can be applied for MS/MS experiments.48 A comparison of different separation systems used in inorganic mass spectrometry is presented in Table 3.1. 

Stenson, A. C., Landing, W. M., Marshall, A. G., and Cooper, W. T. (2003). Exact masses and chemical formulas of individual Suwannee River fulvic acids from ultrahigh resolution electrospray ionisation fourier transform ion cyclotron resonance mass spectrometry. Anal. Chem. 75,1275-1284. 

Technological advances of ion-trap mass spectrometers are the ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and the recently released technique, the Orbitrap Fourier transform mass spectrometry (Hu et al., 2005), which enable the determination of molecular formulae with a high mass resolution and mass accuracy in mixtures. Today these ion-trap mass spectrometers are most frequently coupled with atmospheric pressure ionization (API) techniques such as electrospray ionization (ESI) (e.g., Fievre et al., 1997 Qian et al., 2001 Kujawinski et al., 2002 Llewelyn et al., 2002 Stenson et al., 2002,2003 Fard et al., 2003) or matrix-assisted laser desorption/ionization (MALDI) (e.g., Solouki et al.,... 

Fu, J., Klein, G. C., Smith, D. F., Kim, S., Rodgers, R. R, Hendrickson, C. L., and Marshall, A. G. (2006a). Comprehensive compositional analysis of hydrotreated and untreated nitrogen-concentrated fractions from syncrude oil by electron ionization, field desorption ionization, and electrospray ionization ultrahigh-resolution FT-ICR mass spectrometry. Energy Fuels 20,1235-1241. 

Solouki, T., Emmett, M. R., Guan, S., and Marshall, A. G. (1997). Detection, number, and sequence location of sulfur-containing amino acids and disulfide bridges in peptides by ultrahigh-resolution MALDI FTICR mass spectrometry. Anal. Chem. 69,1163-1168. 

The analytically important features of Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometry (1) have recently been reviewed (2-9) ultrahigh mass resolution (>1,000,000 at m/z. < 200) with accurate mass measurement even 1n gas chromatography/mass spectrometry experiments sensitive detection of low-volatility samples due to 1,000-fold lower source pressure than in other mass spectrometers versatile Ion sources (electron impact (El), self-chemical ionization (self-Cl), laser desorption (LD), secondary ionization (e.g., Cs+-bombardment), fast atom bombardment (FAB), and plasma desorption (e.g., 252cf fission) trapped-ion capability for study of ion-molecule reaction connectivities, kinetics, equilibria, and energetics and mass spectrometry/mass spectrometry (MS/MS) with a single mass analyzer and dual collision chamber. 

Shi, S.D.H., Hendrickson, C.L. and Marshall, A.G. (1998) Counting individual sulfur atoms in a protein by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry experimental resolution of isotopic fine structure in proteins. Proc. Natl. 

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