Rapid scanning spectrometer

Experimental limitations initially limited the types of molecular systems that could be studied by TRIR spectroscopy. The main obstacles were the lack of readily tunable intense IR sources and sensitive fast IR detectors. Early TRIR work focused on gas phase studies because long pathlengths and/or multipass cells could be used without interference from solvent IR bands. Pimentel and co-workers first developed a rapid scan dispersive IR spectrometer (using a carbon arc broadband IR source) with time and spectral resolution on the order of 10 ps and 1 cm , respectively, and reported the gas phase IR spectra of a number of fundamental organic intermediates (e.g., CH3, CD3, and Cp2). Subsequent gas phase approaches with improved time and spectral resolution took advantage of pulsed IR sources. 

Since modern FTIR spectrometers can operate in a rapid scan mode with approximately 50 ms time resolution, TRIR experiments in the millisecond time regime are readily available. Recent advances in ultra-rapid scanning FTIR spectroscopy have improved the obtainable time resolution to 5 ms. Alternatively, experiments can be performed at time resolutions on the order of 1-10 ms with the planar array IR technique, which utilizes a spectrograph for wavelength dispersion and an IR focal plane detector for simultaneous detection of multiple wavelengths. ... 

Rapid scanning mass spectrometers providing unit resolution are routinely used as chroaatographic detectors. Ion separation is accomplished using either a magnetic sector, quadrupole filter or ion trap device. Ions can also be separated by time-of-flight or ion cyclotron resonance mass analyzers but these devices are not widely used with chromatograidiic inlets and will not be discussed here [20]. 

Snively, C.M., Katzenberger, S., Oskarsdottir, G. et al. (1999) Fourier-transform infrared imaging using a rapid-scan spectrometer. Opt. Lett., 24, 1841. 

A modern variation on the rapid scan spectrometer, which is under development, uses a laser-generated plasma as a high intensity broad-band IR source (65). This method has been used to probe the vc—o absorption of W(CO)6. Another technique TRISP (time-resolved IR spectral photography), which involves up-conversion of IR radiation to the visible, has also been used to probe transients (66). This method has the enormous advantage that efficient phototubes and photodiodes can be used as detectors. However, it is a technically challenging procedure with limitations on the frequency range which depend on the optical material used as an up-converter. 

Both Porter s original flash photolysis apparatus and Pimentel s rapid scan spectrometer recorded the whole spectral region in a time which was short compared to the decay of the transient species. Kinetic information was obtained by repeatedly firing the photolytic flash lamp and making each spectroscopic measurement at a different time delay after each flash. The decay rate could then be extracted from this series of delayed spectra. Such a process clearly has limitations, particularly for IR measurements, where the decay must be slow compared to the scan rate of the spectrum. 

In order to observe a short-lived species it may be necessary to employ a rapid-scanning spectrometer, such as a diode-array instrument (Sms for a 240nm-800nm spectrum). In addition, the absorbances of electrogenerated species can be very small and signal-averaging or phase-sensitive detection may be necessary to achieve the required signal-to-noise ratio (cf. EMIRS and FTIR). 

Figure 8.3 Schematic diagram of a quadrupole mass spectrometer. It consists of two pairs of parallel metal rods carrying a DC plus an oscillating voltage, in such a way that only a particular mass-to-charge ratio will pass down the center of the rods for a given setting. The mass spectrum can be rapidly scanned by varying the potentials on the rods. Adapted from Beynon and Brenton (1982), Figs. 4.6 and 4.7, by permission of University of Wales Press.

Cordero, M.M. Cornish, T.J. Cotter, R.J. Lys, LA. Sequencing Peptides Without Scanning the Reflectron Post-Source Decay With a Curved-Field Reflectron TOF Spectrometer. Rapid Commun. Mass Spectrom. 1995, 9, 1356-1361. 

For visual observation of the cell interior through the sapphire windows a lamp mounted behind one end is used. A mirror and stereo microscope at the other end facilitate the observation. The microscope is equipped with a normal camera or a video camera. Normally the phenomena within the cell are continuously observed and controlled with video camera and colour monitor. A video recorder serves for documentation, for inspection of short time processes and for the production of standing flame pictures for size and shape determination. Instead of the microscope a Jarrell-Ash diode array rapid scan spectrometer can be attached to the cell to obtain flame spectra in the visible and UV-regions. 

Studies by Crawford Rotenberg (Ref 4) who used a rapid-scan spectrometer in conjunction with a strand burning apparatus to examine NG-NC low temperature decomposition and flames. During the decomposition of commercial double-base propellants, the gas products were NO, N20, C02 CO. When these propellants were burned under 100-150 psi nitrogen pressure at a linear velocity of 100 cm/sec, C02 CO absorption bands appeared even at 2 cm away from the burning surface. Nitric oxide was barely detectable and N20 was completely absent... 

Other desirable features of a monochromator are stability and multi-element capabUity. Initially, direct reading spectrometers, based on a polychromator, were used for simultaneous multi-element analysis, although these were expensive, bulky and generally limited to specific elements. The development of rapid-scanning monochromators under... 

If we have a single-beam spectrometer, we may separately record spectra Bm(x), Um(x), and Z>M(x) and apply Eq. (45) later in the computer. With special rapid-scanning spectrometers this approach may be practical, but... 

There are several ways to measure Tx and T2. If Tx is greater than, say, 10 sec, one can place the sample in the B0 field of the spectrometer and immediately make a series of rapid scans of a resonance line, keeping Bx small. The absorption signal is proportional to n, so the approach of n to neq can be followed, and Tx obtained from (8.100). If T2 is less than, say, sec, one can obtain T2 directly from the measured line width. However, if T2 is greater than j sec, then the true line width is quite narrow, and in fact is narrower than the width produced by inhomogeneities in the applied field 0. For Tx and T2 not in the above ranges, one uses various pulse techniques to measure them (Becker, Section 9.7). 

The earliest estimate of kB was by Johnston.224 On the basis of work he had performed on the N205 system,313 he computed a lower limit for k5 of 1010 Af-1 sec-1 at room temperature. Hisatsune, Crawford, and Ogg,202 using a rapid-scanning infrared spectrometer, studied the decomposition of N205 in the presence of NO. Relevant to the NO + N03 reaction is their determination of k6 and k6k5/k-6, where kg and k 6 are forward- and reverse-rate constants for the reaction... 

The transparency of the electrode also enables spectra to be recorded of electrogenerated species as well as of any species produced as a result of a homogeneous chemical reaction. Such spectra have been recorded with rapid scanning spectrometers that are capable of recording as many as 100 or more spectra per second in the UV-visible range [22]. Spectra can be useful for structural identification of intermediate components in the reaction sequence and for... 

The procedures for irradiation, collection, and analysis of the volatile compounds have all been described (1, 2, 3, 5, 7, 9, 11). A cryogenically programmed gas chromatograph coupled to a rapid scanning mass spectrometer provided for the analysis of the volatile components isolated from several irradiated meats and lipid substances (6). These studies have now been extended to include other component substances in order to acquire still further understanding of the source of the irradiation-induced volatile compounds from among the various meat constituents. 

Hager, J. W., and Yves Le Blanc, J. C. (2003). Product ion scanning using a Q-q-Q linear ion trap (QTR.AP) mass spectrometer. Rapid Commun. Mass Spectrom. 17 1056-1064. 

Mutlib, A., Lam, W., Atherton, J., Chen, H., Galatsis, P., and Stolle, W. (2005). Application of stable isotope labeled glutathione and rapid scanning mass spectrometers in detecting and characterizing reactive metabolites. Rapid Commun. Mass Spectrom. 19 3482-3492. 

Transient absorption spectroscopy, wherein one measures the electronic absorption spectrum of a molecule in an excited state, is still in its infancy, but the growing availability of ultra-high-speed, rapid-scan spectrometers augurs well for this area of spectroscopy. Thus one may, in the future, routinely probe excited state absorption spectra as well as ground state absorption spectra. The former can be expected to be as valuable in obtaining information about the excited state as is the latter for the ground state. 

Protein Adsorption. The development of medical implant polymers has stimulated interest in the use of ATR techniques for monitoring the kinetics of adsorption of proteins involved in thrombogenesis onto polymer surfaces. Such studies employ optical accessories in which an aqueous protein solution (93) or even ex - vivo whole blood (94-%) can be flowed over the surface of the internal reflection element (IRE), which may be coated with a thin layer of the experimental polymer. Modem FT-IR spectrometers are rapid - scanning devices, and hence spectra of the protein layer adsorbed onto the IRE can be computed from a series of inteiferograms recorded continuously in time, yielding ah effective time resolution of as little as 0.8 s early in the kinetic runs. Such capability is important because of the rapid changes in the composition of the adsorbed protein layers which can occur in the first several minutes (97). 

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