LC-Orbitrap

DETERMINATION OF ILLICIT DRUGS IN THE WATER CYCLE BY LC-ORBITRAP MS... 

With recent instrumental development, such as fast LC, fast GC and two-dimensional gas chromatography (GCxGC) and advanced tandem hybrid MS detection systems (i.e., QqTOF, QqLIT, Orbitrap) the analysis of complex mixtures... 

MS11 capabilities. However, ions may then subsequently be detected at unit resolution using an electron multiplier or, alternatively, focused in a C-Trap (Figure 5.2) and then transferred and detected at high resolution using the Orbitrap. In our experience with the LTQ-Orbitrap, ions may be measured with a resolution of approximately 60,000 with online LC/MS in the full scan mode. 

Advances in high resolution mass analyzers (TOF, FT-ICR, orbitrap) have greatly improved the detection and identification of metabolites based on accurate mass measurements. In single MS mode accurate mass determination is mainly used to differentiate between isobaric ions. Combined with LC-MS, it allows the detection of predicted metabolites by performing extracted ion current profiles... 

A similar approach using accurate mass measurements and predictive fragmentation sofiware was also applied for the examination of the human microsomal metabolism of nefazodone using a linear ion trap-orbitrap hybrid mass spectrometer. Based on a single LC-MS run, using data-dependant acquisition, 15 metabolites of nefazodone could be identified in MS and MS/MS with a mass accuracy better than 3 ppm. 

Figure 4.1 Separation of H3 9-17 trimethylated subsequentlydigested with trypsin. The resulting at l<9 from H3 9-17 monoacetylated. Histone peptides were analyzed by LC-MS/MSemploying H3 isolated from Drosophila melanogaster was LTQ-Orbitrap (Thermo Scientific) as detector, acylated with deuterated acetic anhydride and (a) Chromatogram of the analysis. The y axis...

The Orbitrap-based systems have emerged as the newest option for LC-HRMS. When configured as hybrid linear trap-Grbitrap (LTQ-Orbitrap), the systems are conceptually similar to Q-TOF in that mass analyzer 1 is nominally a unit mass analyzer, and mass analyzer 2 is capable of high resolution. These systems are capable of either LC-HRMS or LC-MS/HRMS operation. A new variant on the commercial Orbitrap, the Exactive, is expected to be released in late 2008. This system, which consists only of the single mass analyzer, has shown promising results in early assessment of quantitation by LC-HRMS (Bateman et al., 2008). 

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 sensitivity of the LTQ-Orbitrap is demonstrated using a mixture of synthetic standards of buspirone metabolites spiked into a rat plasma extract. The samples were analyzed with a standard 4.6-mm HPLC column. LC-MS/MS chromatograms for the five-component mixture obtained using the Orbitrap and the LTQ mass spectrometers are compared in Figs 5.8a and h. Also shown are MS/MS (m/z 402) spectra of the oxa-buspirone metabolite (R, = 7.4 min) at 10 pg on column in the Orbitrap (Fig. 5.8c) and LTQ (Fig. 5.8e). As discussed above, the MS/MS fragmentation spectra, obtained in the Orbitrap (Figs 5.8c and d), are very similar to those from the LTQ (Fig. 5.8e), and even at such low concentrations excellent mass accuracies are maintained. 

Synthetic standards of five hydroxylated buspirone metabolites were spiked into rat plasma and analyzed on a 4.6 x 150-mm YMC-ODS AQ S3 column at a flow rate of 1 mL/min LC-MS chromatograms at 10 pg on column for (a) Orbitrap and... 

Figure 5.8. Synthetic standards of five hydroxylated buspirone metabolites spiked into rat plasma and analyzed on a 4.6 x 150-mm YMC-ODS AQ S3 column at a flow rate of 1 mL/min LC-MS chromatograms obtained following injection of 10 pg of each metabolite on column (a) Orbitrap and (b) linear ion trap. MS/MS (m/z 402) spectra of oxa-buspirone metabolite (Rt = 7.4min) (c) Orbitrap at 10pg on column, (d) Orbitrap at 100pg on column, and (e) linear ion trap at 10 pg on column.

Chen, G., Khusid, A., Daaro, I., Irish, P., and Pramanik, B. N. (2007). Structural identification of trace level enol tautomer impurity by on-line hydrogen/deuterium exchange HR-LC/MS in a LTQ-Orbitrap hybrid mass spectrometer. J. Mass Spectrom. 42 967-970. 

Chen, G. et al., Structural characterization of in vitro rat liver microsomal metabolites of antihistamine desloratadine using LTQ-Orbitrap hybrid mass spectrometer in combination with online hydrogen/deuterium exchange HR-LC/MS, J. Mass Spectrom., 44(2), 203, 2009. 

Varoglu, M. et al., Simultaneous quantitative and qualitative measurements of in vitro microsomal metabolism assays by Orbitrap LC-MS methods, Proceeding of 56th ASMS Conference on Mass Spectrometry and Allied Topics. Denver, CO, June 1-5, 2008. 

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