OaTOF

Requires high-cost magnetic sector instruments or oaToF-MS... 

ToFs can also be used in combination with other mass analysers. Both hybrid sector and quadrupole systems are available. oaToF-MS has been interfaced to a quadrupole mass filter and hexapole gas collision cell, such as to allow recording of mass spectra and product ion spectra with good mass resolution (ca. 10000), high sensitivity, high mass range (ca. 10 000 Da) and high mass accuracy (<5ppm) [177,178]. QqToFMS may be fitted with API sources with flow-rates from nL... 

Applications With the current use of soft ionisation techniques in LC-MS, i.e. ESI and APCI, the application of MS/MS is almost obligatory for confirmatory purposes. However, an alternative mass-spectrometric strategy may be based on the use of oaToF-MS, which enables accurate mass determination at 5 ppm. This allows calculation of the elemental composition of an unknown analyte. In combination with retention time data, UV spectra and the isotope pattern in the mass spectrum, this should permit straightforward identification of unknown analytes. Hogenboom et al. [132] used such an approach for identification and confirmation of analytes by means of on-line SPE-LC-ESI-oaToFMS. Off-line SPE-LC-APCI-MS has been used to determine fluorescence whitening agents (FWAs) in surface waters of a Catalan industrialised area [138]. Similarly, Alonso et al. [139] used off-line SPE-LC-DAD-ISP-MS for the analysis of industrial textile waters. SPE functions here mainly as a preconcentration device. 

Up to here, the discussion has focused on MALDI-TOF equipment, because MALDI is a pulsed ionization method. MALDI initiated tremendous improvements of TOF analyzers which makes it attractive to combine such compact but powerful analyzers with any other non-pulsed ionization method desirable. The major breakthrough came from the design of the orthogonal acceleration TOF analyzer (oaTOF), i.e., a TOF analyzer into which pulses of ions are extracted or-... 

Geometries composing of an oaTOF as MS2 bear the advantage that advanced TOFs offer accurate mass measurements close the the accuracy of magnetic sector instruments. Currently, QqTOF systems can be regarded as the commercially most successful hybrid. While the linear quadrupole serves as MSI in MS/MS experiments, it is operated in RF-only mode when tandem MS is not intended, because... 

The next higher level of performance can be achieved by replacing the oaTOF MS2 with an FT-ICR analyzer while employing a linear ion trap (Thermo Electron LTQ-FT) or a quadmpole as MSI (Bruker Daltonik APEX-Q). 

Hsu, C.S. Green, M. Fragment-Free Accurate Mass Measurement of Complex Mixture Components by Gas Chroma-tography/Field lonization-oaTOF-MS an Unprecedented Capability for Mixture Analysis. Rapid Commun. Mass Spectrom. 2001,15, 236-239. 

Morris, H.R. Paxton, T. Dell, A. Langhome, J. Berg, M. Bordoli, R.S. Hoyes, J. Bateman, R.H. High Sensitivity CID Tandem MS on a Novel Quad-rapole-oaTOF Mass Spectrometer. Rapid Commun. Mass Spectrom. 1996, 10, 889-896. 

Hopfgartner, G. Chemushevich, I.V. Covey, T. Plomley, J.B. Bonner, R. Exact Mass Measurement of Product Ions for the Structural Elucidation of Drug Metabolites With a Tandem Quad-rupole oaTOF Mass Spectrometer. J. Am. Soc. Mass Spectrom. 1999, 10, 1305-1314. 

Fig. 5.16. Tip of a direct exposure probe of a (JC-oaTOF mass spectrometer for El, Cl, FI). By courtesy of Waters Corporation, MS Technologies, Manchester, UK.

Magnetic sector instruments (Chap. 4.3) were used first to demonstrate the beneficial effects of resolution on ESI spectra of biomolecules. [96,103,104] Fourier transform ion cyclotron resonance (FT-ICR, Chap. 4.6) instruments followed. [105-107] The more recently developed orthogonal acceleration of time-of-flight (oaTOF, Chap. 4.2 and 4.7) analyzers also present an effective means to resolve all or at least most peaks. [108-110]... 

While the principles of time-of-flight (TOF) mass spectrometry were well established for many years, significant breakthroughs in TOF technology and application were made in the 1990 s [57-58], This can be attributed to the emergence of MALDI as an ionization technique. TOF is considered as the ideal mass analyser for MALDI. This stimulated developments and research in TOF analysers, which in turn led to the rediscovery of the orthogonal-acceleration TOF (oaTOF). 

These modifications result in a mass resolution in excess of 10,000 (FWHM) for modem TOF-MS systems, resulting in mass accuracies of better than 5 ppm in the combination of API-oaTOF-MS, i.e., accurate-mass determination within 5 ttiDa or better for a compound up to 1000 Da. 

H. R. Morris, T. Paxton, A. Dell, J. Langhome, M. Berg, R.S. Bordoli, J. Hoyes, R.H. Bateman, High-sensitivity CTD-MS-MS on a novel Q-oaTOF-MS, Rapid Commun. Mass Spectrom., 10 (1996) 889. 

A. C. Hogenboom, W. M. A. Niessen, U. A. Th. Brinkman, Characterization of photodegradation products of alachlor in water by on-line SPE—LC combined with MS-MS and oaTOF-MS, Rapid Conunun. Mass Spectrom., 14 (2000) 1914. 

Rainville, P.D., Stumpf, C.L., Shockcor, J.P., Plumb, R.S. and Nicholson, J.K. (2007) Novel application of reversed-phase UPLC-oaTOF-MS for bpid analysis in complex biological mixtures A new tool for lipidomics. J. Proteome Res. 6, 552-558. 

Trends in MALDI-ToFMS research are search for new matrices, solvent-free sample preparation, advances in analyser design (oaToF-MS, Q-ToFMS, QITMS, QIT-ToF, ToF-ToF), and (on-line) coupling to other (pre)separation techniques. 

The question remains whether the mass of the electron (5.48 x 10" u) has really to been taken into account. This issue was of almost pure academic interest as long as mass spectrometry was limited to mass accuracies of several 10 u. As FT-ICR, orbitrap, and even recent oaTOF instruments deliver mass accuracies in the order of < 10 u, one should routinely include the electron mass in calculations [12,13]. Here, neglecting the electron mass would cause a systematic error of the size of m, which is unacceptable when mass measurement accuracies in the order of < 10 u are to be achieved. 

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