LC-FTICR

Lee, S.W., Berger, S.J., Martinovic, S., Pasa-Tolic, L., Anderson, G.A., Shen, Y., Zhao, R., Smith, R.D. (2002). Direct mass spectrometric analysis of intact proteins of the yeast large ribosomal subunit using capillary LC/FTICR. Proc. Natl. Acad. Sci. USA 99, 5942-5947. 

Schrader, S., and Klein, H.-W. (2004). Liquid chromatography/Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR MS) An early overview. Anal. Bioanal. Chem. 379,1013-1024. 

Figure 6.14 Representative LC/UV and LC/FTICR-MS chromatograms obtained from a six component mixture. The solid circles represent temporal location of mass spectra with an acquisition time of 1 s. (Reprinted with permission from Speir et al., 2000. Copyright 2000 John Wiley Sons.)...

LC-FTICR MS liquid chromatography fourier transform ion cyclotron resonance mass... 

PTM in a consistent and reproducible manner. Clearly other technologies such as the LC/MS/MS and the LC-FTICR are far more sensitive and better in defining the composition of these biomarkers. 

In this chapter we focus primarily on calibration of LC-MS where the mass spectrometer is operating at unit resolution, resolution that is sufficient to separate two peaks one mass unit apart. This kind of low-resolution mass filter covers almost 90 percent of the instruments commonly used for qualitative and/or quantitative analysis of small molecules. Batch-to-batch qualification testing of the instrument is also described. For the calibration of high-resolution mass spectrometers such as magnetic sector, TOF, or FTICR coupled with liquid chromatography, readers are referred to specific publications. 

The LTQ-Orbitrap has resolution and mass accuracy performance close to that of the LTQ-FTICR. As shown in Table 5.3 (column 4), LTQ-Orbitrap accurate mass measurements, using external calibration, for a set of 30 pharmaceutical compounds resulted in less than 2.3 ppm error. The data were acquired with a 4-min, 1-mL/min-flow-rate, positive-mode LC-ESI-MS method where all measurements were performed within 5h from mass calibration. Mass accuracies below 2-3 ppm, and often below 1 ppm, can be routinely achieved in both the positive- and negative-ion mode (Table 5.3, columns 4 and 5). The long-term mass stability of the LTQ-Orbitrap is not as consistent as observed for the LTQ-FTICR-MS, and the Orbitrap requires more frequent mass calibration however, mass calibration is a routine procedure that can be accomplished within 5-10 min. Figure 5.7 displays a 70-h (external calibration) mass accuracy plot for three negative ions collected with a LTQ-Orbitrap where the observed accuracy is 2.5 ppm or better with little mass drift for each ion. Overall, for routine accurate mass measurements on the Orbitrap, once-a-week calibration (for the desired polarity) is required however, considering the ease of the process, more frequent external calibration is not a burden. 

The full-scan BPC obtained from LTQ-FTICR LC-MS data does not display diclofenac or its monohydroxyl metabolite (Ml) that were spiked into rat bile sample due to the significant interference from ions of endogenous components in the bile (Fig. 6.9a). In contrast, MDF analysis of the LC-MS data file completely removed these interfering ions, resulting in a BPC that clearly exhibits only the drug and Ml (Fig. 6.9b). The same bile sample was analyzed with NLS and PIS using a triple-quadmpole instrument. Diclofenac lost a neutral fragment (46 Da) to form a major ion at m/z 250 under CID conditions (Fig. 6.8a). 

Figure 6.9. Detection of diclofenac metabolite in rat bile by three LC-MS screening methods (a) full-scan BPC from LTQ-FTICR (b) MDF-treated full-scan BPC from LTQ-FTICR (c) ion current of NLS of 46 Da (d) ion cunent of PIS of m/z 250 (e) ion current of PIS of m/z 266.

Another example is the analyses of the clozapine metabolites M2 (the N-desmethyl product) and M3 (N-oxide) in rat urine. The metabolite peaks of M2 and M3 were hardly observable in the full-scan TIC obtained by LC-LTQ-FTICR (Fig. 6.10a). After removing the majority of endogenous components and chemical noise by MDF, M2, M3, and clozapine became the predominant peaks in the full-scan TIC (Fig. 6.1 Oh). Precursor ion scan analysis of the same spiked... 

Selected topics in Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry instrumentation are discussed in depth, and numerous analytical application examples are given. In particular, optimization ofthe single-cell FTMS design and some of its analytical applications, like pulsed-valve Cl and CID, static SIMS, and ion clustering reactions are described. Magnet requirements and the software used in advanced FTICR mass spectrometers are considered. Implementation and advantages of an external differentially-pumped ion source for LD, GC/MS, liquid SIMS, FAB and LC/MS are discussed in detail, and an attempt is made to anticipate future developments in FTMS instrumentation. 

FTICR, magnetic sector, and time-of-flight (TOF) mass spectrometers are also capable of acquiring accurate mass measurements on molecular and fragment ions from both GC/MS and LC/MS experiments on trace level impurities. Applications of FTICR LC/MS... 

At the time of this writing, new so-called hybrid LC/MS systems are available, which combine quadruples (Q) with TOF, quadruples with FTICR, and ion traps with FTICR. These instruments are capable of... 

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