Mass spectrometry data acquisition

Xie, H., Gilar, M. and Gebler, J. C. Characterization of protein impurities and site-specific modifications using peptide mapping with liquid chromatography and data independent acquisition mass spectrometry. Anal. Chem. 81 5699-5708, 2009. 

Multidimensional or hyphenated instmments employ two or more analytical instmmental techniques, either sequentially, or in parallel. Hence, one can have multidimensional separations, eg, hplc/gc, identifications, ms/ms, or separations/identifications, such as gc/ms (see CHROMATOGRAPHY Mass spectrometry). The purpose of interfacing two or more analytical instmments is to increase the analytical information while reducing data acquisition time. For example, in tandem-mass spectrometry (ms/ms) (17,18), the first mass spectrometer appHes soft ionization to separate the mixture of choice into molecular ions the second mass spectrometer obtains the mass spectmm of each ion. 

LC/MS/MS. LC/MS/MS is used for separation and quantitation of the metabolites. Using multiple reaction monitoring (MRM) in the negative ion electrospray ionization (ESI) mode, LC/MS/MS gives superior specificity and sensitivity to conventional liquid chromatography/mass spectrometry (LC/MS) techniques. The improved specificity eliminates interferences typically found in LC/MS or liquid chro-matography/ultraviolet (LC/UV) analyses. Data acquisition is accomplished with a data system that provides complete instmment control of the mass spectrometer. 

Various analytical methods have made quantum leaps in the last decade, not least on account of superior computing facilities which have revolutionised both data acquisition and data evaluation. Major developments have centred around mass spectrometry (as an ensemble of techniques), which now has become a staple tool in polymer/additive analysis, as illustrated in Chapters 6 and 7 and Section 8.5. The impact of mass spectrometry on polymer/additive analysis in 1990 was quite insignificant [100], but meanwhile this situation has changed completely. Initially, mass spectrometrists have driven the application of MS to polymer/additive analysis. With the recent, user-friendly mass spectrometers, additive specialists may do the job and run LC-PB-MS or LC-API-MS. The constant drive in industry to increase speed will undoubtedly continuously stimulate industrial analytical scientists to improve their mass-spectrometric methods. 

MS/MS Duty Cycle Typical MS/MS analysis is a serial process, relying on the selection of precursors (peptides) in MS mode, followed by high-energy fragmentation in MS/MS. This process is termed data dependent acquisition (DDA). The duty cycle for the completion of MS and MS/MS cycles (the time necessary for MS/MS spectrum acquisition) is of primary importance. When the separation performance is viewed from the mass spectrometry perspective, the peak capacity can be characterized by the number of MS/MS scans, yielding successful... 

Ricci, M. P., Merritt, D. A., Freeman, K. H. and Hayes, J. M. (1994) Acquisition and processing of data for isotope ratio monitoring mass spectrometry. Organic Geochemistry 21, 561 571. 

Pyrolysis-Gas Chromatography-Mass Spectrometry. In the experiments, about 2 mg of sample was pyrolyzed at 900°C in flowing helium using a Chemical Data System (CDS) Platinum Coil Pyrolysis Probe controlled by a CDS Model 122 Pyroprobe in normal mode. Products were separated on a 12 meter fused capillary column with a cross-linked poly (dimethylsilicone) stationary phase. The GC column was temperature programmed from -50 to 300°C. Individual compounds were identified with a Hewlett Packard (HP) Model 5995C low resolution quadruple GC/MS System. Data acquisition and reduction were performed on the HP 100 E-series computer running revision E RTE-6/VM software. 

Traditional methodologies for structural identification of trace level impurities in drng substances/products usually involve fractionation of each impurities using a scaled-np analytical chromatographic method, followed by off-line spectroscopic analysis. Coupling of HPLC separation and electrospray mass spectrometry allows on-line acquisition of full scan mass spectra and generation of tandem mass spectrometric data. LC/ESI MS has revolntionized trace analysis for qnalitative and quantitative studies in pharmaceutical analysis. 

Legionella pneumophila produces a siderophore named legiobactin, which shows no catecholate or hydroxamate reactions (206). Enzymatic studies suggest a citrate structure in agreement with the data obtained by mass spectrometry (molecular mass ca. 350 Da) and NMR (three carbonyl and ten aliphatic C atoms). It is not clear yet as to whether legiobactin is essential for the iron acquisition in the aqueous habitat of the bacterium or during lung infection (2, 65). 

With the introduction of computerized data systems for data acquisition, reduction, and storage during the 1960s, the efficiency of mass spectrometric analysis grew rapidly and continues to grow to this day. The use of computers for data reduction and analysis helped gas chro-matography/mass spectrometry (GC/MS) become a practical and powerful tool for qualita-... 

R.A. Beyer, Molecular Beam Sampling Mass Spectrometry of High Heating Rate Pyrolysis. Description of Data Acquisition System and Pyrolysis of HMX in a Polyurethane Binder ,... 

O Connor, D., and Mortishire-Smith, R. (2006). High-throughput bioanalysis with simultaneous acquisition of metabolic route data using ultra performance liquid chromatography coupled with time-of-flight mass spectrometry. Anal. Bioanal. Chem. 385 114-121. 

After separation of the sample and acquisition of spectroscopic data, the sample can be collected in a fraction collector. This allows further investigation, especially by mass spectrometry, if the MS spectra were not already collected on-line. 

They are still the workhorses of coupled mass spectrometric applications, as they are relatively simple to run and service, relatively inexpensive (for a mass spectrometer), and provide unit mass resolution and scanning speeds up to approximately 10,000 amu/s. This even allows for simultaneous scan/ selected ion monitoring (SIM) operation, in which one part of the data acquisition time is used to scan an entire spectrum, whereas the other part is used to record the intensities of selected ions, thus providing both qualitative information and sensitive quantitation. They are thus suitable for many GC-MS and liquid chromatography-mass spectrometry (LC-MS) applications. In contrast to GC-MS with electron impact (El) ionization, however, LC-MS provides only limited structural information as a consequence of the soft ionization techniques commonly used with LC-MS instruments [electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)]. Because of this limitation, other types of mass spectrometers are increasingly gaining in importance for LC-MS. 

Flash pyrolysis-gas chromatography-mass spectrometry. Flash pyrolysis-GC-MS analyses were performed as described in detail previously (48), although another mass spectrometer (VG-70S) was used. Electron impact mass spectra were obtained at 70 eV with a cycle time of 1.7 s and a mass range m/z 50-800 at a resolution of 1000. Data acquisition was started 1 min. after pyrolysis. 

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