Quadrupole QqTOF

The instrumental analysis for the identification of UV filters degradation products formed during the fungal treatment process was performed by means of HPLC coupled to tandem mass spectrometry using a hybrid quadrupole-time-of-flight mass spectrometer (HPLC-QqTOF-MS/MS). Chromatographic separation was achieved on a Hibar Purospher STAR HR R-18 ec. (50 mm x 2.0 mm, 5 pm, from Merck). In the optimized method, the mobile phase consisted of a mixture of HPLC grade water and acetonitrile, both with 0.15% formic acid. The injection volume was set to 10 pL and the mobile phase flow-rate to 0.3 mL/min. 

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. 

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... 

In tandem MS mode, because the product ions are recorded with the same TOF mass analyzers as in full scan mode, the same high resolution and mass accuracy is obtained. Isolation of the precursor ion can be performed either at unit mass resolution or at 2-3 m/z units for multiply charged ions. Accurate mass measurements of the elemental composition of product ions greatly facilitate spectra interpretation and the main applications are peptide analysis and metabolite identification using electrospray iomzation [68]. In TOF mass analyzers accurate mass determination can be affected by various parameters such as (i) ion intensities, (ii) room temperature or (iii) detector dead time. Interestingly, the mass spectrum can be recalibrated post-acquisition using the mass of a known ion (lock mass). The lock mass can be a cluster ion in full scan mode or the residual precursor ion in the product ion mode. For LC-MS analysis a dual spray (LockSpray) source has been described, which allows the continuous introduction of a reference analyte into the mass spectrometer for improved accurate mass measurements [69]. The versatile precursor ion scan, another specific feature of the triple quadrupole, is maintained in the QqTOF instrument. However, in pre-... 

The majority of H/D studies that have been reported employ quadrupole ion trap (QIT) instruments due to their ease of use, excellent sensitivity, ability to perform MS/MS experiments, compact size, and low cost. Other reports discuss the use of instruments with higher mass-resolving power such as the hybrid QqTOF instruments [47]. A few groups have utilized FT-ICR mass spectrometry, which offers ultra-high mass-resolving power and improved mass accuracy [48, 49]. 

In recent years the application of electrospray ionization (ESI) mass spectrometry, quadrupole time-of-flight (QqTOF) mass spectrometry, and Fourier transform ion cyclotron resonance (FT-ICR) are used for further structural characterization of DOM (Kujawinski et al., 2002 Kim et al., 2003 Stenson et al., 2003 Koch et al., 2005 Tremblay et al., 2007 Reemtsma et al., 2008). MS/MS capabilities provide the screening for selected ions, and FT-ICR allows exact molecular formula determination for selected peaks. In addition, SEC can be coupled to ESI and FTICR-MS to study different DOM fractions. Homologous series of structures can be revealed, and many pairs of peaks differ by the exact masses of -H2, -O, or -CH2. Several thousand molecular formulas in the mass range of up to more than 600 Da can be identified and reproduced in element ratio plots (O/C versus H/C plots). Limitations of ESI used by SEC-MS are shown by These and Reemtsma (2003). 

As shown in Figure 2.68, the most common of these instruments include a quadrupole analyser Q1 and a quadrupolar collision cell q2, followed by an oa-TOF. They thus have the QqTOF configuration. This instrument can be described as a triple quadrupole where the last quadrupole is replaced by an oa-TOF, or as the addition of a quadrupole analyser and a collision cell to a TOF analyser. In some commercial instruments, the q2 quadrupole is replaced by an hexapole, but the principle remains the same. 

Time-of-fiight instruments are configured as either a stand-alone TOF mass analyzer (TOF MS) or as a hybrid quadrupole time-of-fiight (QqTOF) mass spectrometer the latter consists of a quadmpole front-end and an orthogonal acceleration TOF back-end for MS/MS experiments (Fig. 6.10). The orthogonal design minimizes the ions initial velocity spread as they are accelerated into the TOF by a pulsed potential. A QqTOF can be operated as a TOF mass analyzer (QqTOF MS, full-scan) or a quadmpole TOF tandem mass spectrometer (QqTOF MS/MS, product ion scan). Compared to a TOF MS, the... 

Figure 6.10 Hybrid quadrupole trme-of-flight (QqTOF) mass analyzer. (Schematic diagram provided courtesy of Agilent Technologies.)...

QTOF systems (also called QqTOF) are versatile configurations. The quadrupole may be used in either a wide or narrow band pass mode to determine which ions are passed into the collision region (q) and then into the time-of-flight analyzer (Figure 2.36). Full-scan MS data are obtained in the basic mode when the quadrupole... 

MS/MS with QqQ suffers from relatively poor sensitivity and limited resolution. The replacement of the last quadrupole section (Q3) of a triple quadrupole by a TOF analyzer to form a hybrid quadrupole—time-of-flight instrument (QqTOF) (Fig. 8.17) represents a powerful combination of mass range, resolution, and sensitivity (Chernushevich et al., 2001 Morris et al., 1996). In single MS mode the quadrupole serves as RF ion guide and the mass analysis is performed in the TOF. 

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. 

Both quadrupole and sector analyzers have also been combined with time-of-flight (TOE) analyzers, to give BE-TOF and QqTOF configurations. In the... 

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