API/TOF

PE Corp http //WWW.pecorporation.com http //www.appliedbiosystems.com Symbiot workstation Voyager STR MALDI-TOF MS, the Voyager DE-PRO or the Mariner API-TOF LC-MS Protein Solution 1, SQL-LiMS, ProteinKeeper (under development)and Protein Prospector... 

MS analysis MS analysis was carried out on an API-TOF Mariner spectrometer. The samples were dissolved in methanol to which either 1% HCOOH for positive-ion experiments or 0.5% NH4OH for negative-ion experiments was added. 

FIGURE 7.13 Schematics of (a) the API-TOF mass spectrometer with an ion mirror and (b) the ion-storage modulator. (Reprinted with permission from reference 25). 

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... 

Figure 1.14. MRM chromatograms of SCH 29851 (383.0. 337.0) and SCH 34117 (311.1 259.1) obtained using Sciex API 3000 (triple-stage quadrupole) and Sciex QSTAR pulsar (Q-TOF). Comparison of MRM chromatograms of SCH 29851 and SCH 34117 obtained at the LOQ (1 ng/mL) using the API 3000 mass spectrometer with those from the Q-TOF mass spectrometer indicated that the S/N ratio is at least 10-20 times better on the API 3000 mass spectrometer. However, the MRM chromatograms from the API 3000 mass spectrometer do not provide the option to further examine the MS/MS spectra whereas the full-scan MS/MS spectra from a Q-TOF based quantitative bioanalysis assay allows one to easily eliminate any questions about false-positive data. (Rephnted with permission from Yang et a ., 2001b.)...

TOF analysers are directly compatible with pulsed ionization techniques such as plasma or laser desorption because they provide short, precisely defined ionization times and a small ionization region. However, to take advantage of TOF analysers, it is interesting to combine such powerful analysers with continuous ionization techniques. These ionization techniques can be compatible with TOF analysers but require some adaptations to pulse the source or to transform a continuous ion beam into a pulsed process. For instance, the coupling of an ESI (or any other API) source with a TOF mass spectrometer is difficult, because ESI yields a continuous ion beam, whereas the TOF system works on a pulsed process. 

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. 

The TOF mass analyser requires high-frequency (kHz) pulsed ion introduction (Ch. 2.4.3). For optimum mass resolution, orthogonal acceleration is preferred. Boyle et al. [109] first reported an API ion source for a linear TOF analyser via the on-axis ESI source from Analytica of Branford. Later, orthogonal acceleration and a reflectron TOF analyser was applied [110]. Similar systems were subsequently described by others. 

FIGURE 11.1 A generalized flow scheme that indicates the fundamental elements of LC-MS-based bioanalysis. Abbreviations LLE = liquid-liquid extraction SPE = solid-phase extraction RAM = restricted-access media TEC = turbulent flow liquid chromatography API = atmospheric-pressure ionization APCI = atmospheric-pressure chemical ionization ESI = electrospray ionization SQMS = single-quadrupole mass spectrometry TQMS = triple-quadrupole mass spectrometry TOF = time-of-flight Q-TOF = quadrupole TOF. (Reprinted from Ackermann et al. [4], with permission from John Wiley Sons, Inc.)... 

Another area of recent interest is the interfacing of API techniques with TOF mass spectrometers. TOF/MS instruments combine ease of operation, relatively low cost, excellent ion transmission, and virtually unlimited mass range. The only significant disadvantage with respect to other mass spectrometers is the limited mass resolution. A tremendous effort in development and performance opti-... 

All mass spectrometric data were acquired on an LCT orthogonal TOF mass spectrometer (Micromass Ltd, Manchester, UK) fitted with a prototype version of a novel four-way multiplex API interface. Each liquid stream was sampled for 0.1 s with 0.1 s used to move to the adjacent sampling position. Mass spectra were acquired from 200 to 1000 daltons with a cycle time of 10 Hz. The instrument was operated under MassLynx software V3.3. The overall system layout is presented in Fig. 10 and the design of the multiplex head is shown in detail in Fig. 11. 

Amershant Pharmacia Biotech http //www.apbiotech.com Under development Ettan design LC-MS system (API-MS) ETTAN design MALDI-TOF ImageMaster 2D Elite and Database. Partnership with Cimarron Software Inc. 

Once ions have been formed, either outside the mass spectrometer using API methods or within the vacuum system by El, Cl, or MALDI, the ions must be separated according to their m/z ratios. There are several types of mass analyzer with significantly different modes of operation, but all separate ions according to their miz ratios, so that these ratios and their intensities can be recorded by the detector. Current mass analyzers include quadrupole (Q), quadrupole ion traps (QIT, LIT), Fourier transformed based (FT), time-of-flight (TOF), and to a much lesser extent, magnetic field (B). 

The need to generate pulses of ions has consequences, depending on whether the ion source produces pulses or a continuous stream of ions. In MALDI sources, ions leave in packets upon each laser pulse. The repetition of the pulses is on the millisecond scale, thus MALDI is well suited to the microsecond operation of TOF analyzers. Each set of ions will clear the flight tube prior to the introduction of the next packet of ions. In contrast, ESI and other API sources produce ions continn-ously. The need to form ion packets has been accommodated by the development of orthogonal TOE analyzers (discussed below). 

Ions are generated continuously in API sources, thus, the individual packets of ions required in TOF analysis must be excised from the ion beam and accelerated orthogonally into the analyzer using a pulsed pusher voltage. 

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