Fourier transform coupling limit

Laser desorption methods (such as LD-ITMS) are indicated as cost-saving real-time techniques for the near future. In a single laser shot, the LDI technique coupled with Fourier-transform mass spectrometry (FTMS) can provide detailed chemical information on the polymeric molecular structure, and is a tool for direct determination of additives and contaminants in polymers. This offers new analytical capabilities to solve problems in research, development, engineering, production, technical support, competitor product analysis, and defect analysis. Laser desorption techniques are limited to surface analysis and do not allow quantitation, but exhibit superior analyte selectivity. 

Even though these approaches are powerful methods for determining functional sites on proteins, they are limited if not coupled with some form of structural determination. As Figure 2 illustrates, molecular biology and synthetic peptide/antibody approaches are not only interdependent, they are tied in with structural determination. Structural determination methods can take many forms, from the classic x-ray crystallography and NMR for three-dimensional determination, to two-dimensional methods such as circular dichroism and Fourier Transformed Infrared Spectroscopy, to predictive methods and modeling. A structural analysis is crucial to the interpretation of experimental results obtained from mutational and synthetic peptide/antibody techniques. 

Fourier transform ICR mass spectrometers together with any type of ion source, such as nanoESI, MALDI (or also an inductively coupled plasma ion source) permit mass spectrometric measurements to be performed at ultrahigh mass resolution (R = m/hm = 105—106) with a very low detection limit and the highest possible mass accuracy (Am = 10 3—10 4 Da). In addition, a high mass range is possible and FTICR-MS can be applied for MS/MS experiments.48 A comparison of different separation systems used in inorganic mass spectrometry is presented in Table 3.1. 

We have presented a new technique for the investigation of intramolecular couplings in the electronic ground state 50. The new technique of CIS is based on the special population dynamics induced by the coherent excitation of a three-level system with two narrow-band Fourier-transform-limited laser pulses. It allows the investigation of high-lying intermolecular vibrational states in the electronic ground state of van der Waals complexes. These... 

No discussion has been devoted to the recent use of Fourier transform spectrometers rather than dispersion instruments. The ease with which the spectral data can be manipulated and background subtracted make the FT methods particularly useful for studies of surface species, particularly during catalytic reaction. Recently there has been a surge of interest in the coupling of computer subtraction techniques to conventional grating instruments. For many IR surface studies, where only limited frequency range is required, this... 

In recent years the application of electrospray ionization (ESI) mass spectrometry, quadrupole time-of-flight (QqTOF) mass spectrometry, and Fourier transform ion cyclotron resonance (FT-ICR) are used for further structural characterization of DOM (Kujawinski et al., 2002 Kim et al., 2003 Stenson et al., 2003 Koch et al., 2005 Tremblay et al., 2007 Reemtsma et al., 2008). MS/MS capabilities provide the screening for selected ions, and FT-ICR allows exact molecular formula determination for selected peaks. In addition, SEC can be coupled to ESI and FTICR-MS to study different DOM fractions. Homologous series of structures can be revealed, and many pairs of peaks differ by the exact masses of -H2, -O, or -CH2. Several thousand molecular formulas in the mass range of up to more than 600 Da can be identified and reproduced in element ratio plots (O/C versus H/C plots). Limitations of ESI used by SEC-MS are shown by These and Reemtsma (2003). 

Fourier transform infrared microscopy is the primary infrared technique for structural identification of materials at microquantities. The method is non-destructive and non-invasive. When using a proper transmittance sampling technique and a proper detector, the limit of detection can be as low as the picogram level. In the pharmaceutical industry, FTIR microscopy is used to analyze bulk drugs, excipients, and particulate contaminants. " Recent studies have shown that by coupling FTIR microscopy with GC, HPLC, SFC, or GPC systems, the detection limit of the method is substantially improved. ... 

Inductively coupled plasma Fourier transform (ICP-FT) can be useful for correcting unexpected spectral interference. However, such a technique has limited applications and development is only in its infancy. 

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