Orthogonal MALDI

Kovarik, P., Corr, J. J., and Covey, T. R. (2003). Application of orthogonal MALDI for quantitation of small molecules using a triple quadrupole mass spectrometer. In Proceedings of The 51st ASMS Conference on Mass Spectrometry and Allied Topics, Montreal, Canada. 

Figure 2.7 Orthogonal MALDI reflectron time-of-flight mass spectrometry.

A QStar Pulsar (Applied Biosystems, Foster City, CA, USA) hybrid QqTOF mass spectrometer equipped with an oMALDI (orthogonal MALDI) ion source and a nitrogen laser (337 nm) was used to generate high-quality MS and MS/ MS data. 

A significant body of work describing MALDI as a quantitative tool exists in the literature. " In recent years, more attention has been paid to optimizing MALDI instmmentation ° and matrices in order to maximize its utility as a quantitative tool. The development of orthogonal MALDI, which decoupled the laser ionization event from the mass analysis measurement, enabled the deployment of MALDI on mass analyzers other than TOR CoupUng MALDI to a triple quadrupole and the implementation of... 

Verentchikov, A. Smirnov, L Vestal, M. CoUisional cooling and ion formation processes in orthogonal MALDI at intermediate gas pressures. In Proceedings of the ASMS Conference on Mass Spectrometry and Allied Topics, 1999. 

Foret et al.98 collected fractions of model proteins and variants of human hemoglobins after fractionation by CIEF, and then analyzed them by matrix-assisted laser desorption-time-of-flight-mass spectrometry (MALDI-TOF-MS). As the authors point out, MS is an orthogonal method to CIEF because it separates according to molecular mass. 

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-... 

Laser desorption intrinsically is a pulsed ionization process, which is therefore ideally combined with time-of-flight (TOF) analyzers (Chap. 4.2). [16,49] Ever since the first MALDI experiments, MALDI and TOF have been forming a unit, and the majority of MALDI applications are MALDI-TOF measurements. Vice versa, it was the success of MALDI that pushed forth the tremendous delevopment of TOF mass analyzers. More recently, MALDI has also been adapted to orthogonal acceleration TOF analyzers. [147]... 

In general the commercial TOP instruments have two detectors one for the linear mode and one for the reflectron mode. The combination of MALDI with TOP is ideal because both techniques are pulsed techniques. However, it is also possible to arrange a continuous beam as generated by electrospray ionization. Por that purpose orthogonal acceleration was developed [65]. The ion beam is introduced perpendicularly to the TOP and packets are accelerated orthogonally (oa-TOP) at similar frequencies improving the sensitivity. While a packet of ions is analyzed, a new beam is formed in the orthogonal acceleration. 

The main goal of this chapter is to describe the synthesis details of complex, orthogonally protected peptide constructs. Thus, major emphasis is placed on the peptide chain assembly design and practice and the alterations from the solid-phase synthesis of simple, nonmodified peptides. The technology for peptide purification and quality control is not significantly different from that of other peptides, and these methods will be just briefly described. Many chapters of this book focus on the optimization of HPLC and MALDI-MS procedures for peptide separation and analysis and illustrate the expected and/or acceptable quality control parameters. 

Dendritic polymers feature homogeneous reaction conditions and enable the application of standard analytical techniques (TLC, IR, NMR, MALDI-TOF etc.) as well as the orthogonal use of insoluble reagents. One drawback of... 

Schematic diagram of a MALDI orthogonal acceleration TOF instrument.

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). 

Woods, A.S. et al., IR-MALDI-LDI combined with ion mobility orthogonal time-of-flightmass spectrometry, J. Preoteome Res., 5, 1484, 2006. 

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