Dependent scan

The major advantage of this instrument is that qualitative and quantitative analysis can be performed in the same LC-MS run. As an example in a data-dependent experiment, the selected reaction monitoring mode can be used as a survey scan and the enhanced product ion mode (EPI) as a dependent scan. The consequence is that for each quantified analyte a confirmatory MS/MS spectmm can be obtained. 

In this case the survey scan was set as a full scan and the dependent scan as a product ion scan. The problem with data dependent acquisition is to determine the selection criteria. In most cases the system picks up the most abundant ion in the full scan spectrum. An inclusion list with masses of potential metabolites or exclusion list of known interferences significantly improves the procedure. In the example shown in Fig. 1.39, a procedure called dynamic background subtraction (DBS) was applied. This procedure considers chromatographic peak shapes and monitors not the most abundant signal in the spectrum but the largest increase of an ion in a spectrum. The advantage is that once a signal of a peak has... 

Fig. 1.39 LC-MS data dependent analysis of vinpocetin in rat urine using dynamic background substraction (DBS) on a triple quadrupole linear ion trap. (A) Full scan MS (survey scan) trace. (B) Enhanced product ion scan (dependent scan). The major peak at 3.9 min corresponds to apovinpocetin, the minor one at 2.9 min to the hydroxylation product of apovinpocetin (m/z 339).

Selloni, A., Camevali, P., Tosatti, E., and Chen, C. D. (1985). Voltage-dependent scanning-tunneling microscopy of a crystal surface Graphite. Phys. Rev. B 31, 2602-2605. 

Triolo, A., Altamura, M., Dimoulas, T., Guidi, A., Lecci, A., and Tramontana, M. (2005). In vivo metabolite detection and identification in drug discovery via LC-MS/MS with data-dependent scanning and postacquisition data mining. J. Mass Spectrom. 40 1572-1582. 

The rapid structure identification of metabolites is a powerful complement to previously described quantitative approaches. The utility of an automated metabolite identification approach, using LC/MS/MS with an ion trap mass spectrometer has been demon-strated.f In this study, MS" analysis is automated to provide maximum structural information in combination with predictive strategies for biotransformation. Automated data-dependent scan functions are used to generate full scan, MS/MS, and MS" mass spectra of... 

There have been signihcant advances to harvest the power of the mass spectrometry-based analysis technique. The ability to perform real-time scanning experiments with real-hme automated dynamic feedback has become an essenhal component of qualitahve analysis, such as biotransformahon or proteomics applicahons. Most commercial mass spectrometry software packages provide the ability to perform data-dependent scanning procedures. Metabolic prohling and proteomics generate large quanhties of data that must be quickly and efficiently interpreted and hltered such that the data can be quickly reported in a way that will support rapid decisions. 

Data dependent scanning is a MS technique that utilizes algorithms to automatically make real-time decisions to control the acquisition mode of the mass spectrometer. The data system executes the next scan type based on previously collected data. -Eor example, an ESI mass spectrometer can be programmed to implement the following experiment. 

The application of an Orbitrap platform was also described for this purpose. In this case, one can use the excellent full scan sensitivity of the high-resolution accurate mass measurement in both the survey and data-dependent scan modes in order to identify the reactive intermediates and then provide data for their structure assignment [23], A labeled form of GSH 2 1 ratio of 5mM glutathione and I3( V5N Gly glutathione was used. The high mass accuracy in the survey scan can be used to detect the GSH adduct. The method was successfully applied for the detection and characterization of GSH conjugates of acetaminophen, tienilic acid, clozapine, ticlo-pidine, and mifepristone. 

Ma, L. et al., Rapid screening of glutathione-trapped reactive metabolites by linear ion trap mass spectrometry with isotope pattern-dependent scanning and postacquisition data mining, Chem. Res. Toxicol., 21 (7), 1477, 2008. 

LC/MS/MS Analysis The samples (75 pL) are loaded onto an Agilent Zorbax RX-C8 column (4.6 mm x 250 mm, 5 pm, Wilmington, DE). The flow rate is set at 1 mL/min with a 1 5 split to the mass spectrometer ion source and a waste container, respectively. The mobile phase consists of solvent A (5 mM ammonium acetate in water-acetonitrile-acetic acid, 95 5 0.05, v/v/v) and solvent B (5mM ammonium acetate in acetonitrile-water-acetic acid, 95 5 0.05, v/v/v). The HPLC runs are programmed by a linear increase from 0% to 80% of solvent B during a 30 min period. The mass spectra are recorded in full scan and data-dependent scans of MS" (n = 2, 3, or 4). The MS" spectra... 

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