MALDI-QqTOF

TOF analyzers are especially compatible with MALDI ion sources and hence are frequently coupled in aMALDI-TOF configuration. Nevertheless, many commercial mass spectrometers combine ESI with TOF with great success. For proteomics applications, the quadrupole TOF (QqTOF) hybrid instruments with their superior mass accuracy, mass range, and mass resolution are of much greater utility than simple TOF instruments.21,22 Moreover, TOF instruments feature high sensitivity because they can generate full scan data without the necessity for scanning that causes ion loss and decreased sensitivity. Linear mode TOF instruments cannot perform tandem mass spectrometry. This problem is addressed by hybrid instruments that incorporate analyzers with mass selective capability (e.g., QqTOF) in front of a TOF instrument. 

A variety of mass analyzers have been used in MSI experiments such as TOP, quadrupole ion trap (QIT), linear ion trap (LIT), QqQ, Fourier transform ion cyclotron resonance (FTICR), and Orbitrap. Also, various tandem configurations of these mass analyzers such as QqTOF, QqLIT, and TOF/TOF have been used. Due to the many possible interferenees from endogenous compounds or from the matrix, the use of tandem mass speetrometry (MS/MS or MS") or the ability to perform high-resolution and aeeurate mass measurements for the analysis of drugs by MALDI is essential. An overview of some of the established instrumentation and their respeetive eapabilities is presented below. 

Figure 6.2 MALDI-MS spectra of neutral oligosaccharides obtained by PNGase F digestion from lOOpg of glycoprotein, (a) IgGl (Herceptin), recorded on qQTOF instrument (b) Ovalbumin, recorded on...

Figure 6.13 MALDI-MS/MS spectra recorded obtained from (a) Healthy woodchuck with QqTOF mass spectrometer of glycans (b) Woodchuck with hepatocellular with [M + Na] precursor ions detected at carcinoma (c) Healthy mouse. Reprinted m/z 2206.7 (PHN-derivatized) in sera with kind permission from Ref [92].

Time of flight analyzers (TOFs) are important in two main areas, as high m/z analyzers for ions produced by MALDI and as analyzers of medium resolving power that can provide mass measurements for low mass ions to within a few ppm. They are available either in stand-alone single TOF arrangements, or hybrid tandem QqTOF or TOF-TOF arrangements. Use of any of these instruments for quantitation is really their secondary application, with the exception of GC/TOF instruments that were specifically designed for fast capillary GC. 

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. 

Load the MALDI plate into the MALDI chamber of a QStar Pulsar hybrid QqTOF mass spectrometer. 

---