Tandem Mass Spectrometry with Hybrid Instruments

Tandem Mass Spectrometry with Hybrid Instruments 

Hybrid tandem mass spectrometers are constructed by coupling two different types of mass analyzers with the objective to accrue the benefits of the best performance features of each analyzer type. This arrangement enhances the capability 

Linear Ion Trap-oa-TOF Instrument A useful alternative design combines a quadrupole linear ion trap (LIT) with an oa-TOF mass analyzer [62]. This instrument consists of a short rf quadrupole ion guide, a quadrupole mass filter that operates in the rf-only mode, and an oa-TOF mass analyzer. The quadrupole mass filter is operated as an LIT to serve as an ion-accumulation and precursor-ion selection device. The mass-selected precursor is activated via a resonant excitation mode in the LIT, while the TOF instrument provides high-speed mass analysis of the resulting product ions. MS experiments have also been demonstrated with this hybrid system. A combination of QIT with an oa-TOF mass analyzer has also proven to be an effective tandem MS system [63,64]. The QIT performs tasks similar to those performed by an LIT in the LIT-oa-TOF design (i.e., its functions are ion accumulation, mass separation, and ion activation. 

Quadrupole-Fourier Transform Ion Cyclotron Resonance Instrument 

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Tandem Mass Spectrometry with Hybrid Instruments... 

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. 

The ESI and APCI are both soft ionization techniques, hence the spectra obtained using these methods are usually very simple and consist predominantly of the pseudomolecular ion. When more information is required, tandem mass spectrometry is a popular option. Several different types of tandem LC/MS systems can be found, with triple quadrupole and ion trap being the most popular choices. Hybrid systems including magnetic sector-quadmpole, magnetic sector-TOF, quadrupole-TOF (Q-TOF) and ion trap-TOF have been described. The most successful among these hybrids is the Q-TOF instrument. 

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