Spectrometer resonator

In most modern spectrometers resonance is observed as a function of RF energy at a constant magnetic field. A short pulse of RF radiation is applied to the sample and excites simultaneously all of the nuclei of a particular type, for example, 1H. The emitted signal is measured as the thermal population of the spin states is re-established this is known as the free induction decay (FID). An FT of the FID produces a frequency domain spectrum. 

Si-NMR spectra were recorded on a Bruker VJM-250 (liquid) or a Bruker CXP-300 Fourier transform magic-angle-spinning (FT MAS) solid state spectrometer. Resonances are relative to tetramethyl-silane (TMS). Dynamics of the silicate solutions were studied by selective excitation techniques by using DANTE-type (131 pulse sequences. 

Sureau F et al (1990) An ultraviolet micro-Raman spectrometer— resonance Raman-spectroscopy within single living cells. Appl Spectrosc 44(6) 1047-1051... 

In some experiments the cell, being connected to a gas flow system via long capillaries, was taken out from the low-temperature spectrometer resonator, placed in a high-temperature furnace, calcined in a gas stream, placed back in the resonator, cooled in-situ under gas flow and the ESR spectra were taken at 120"K. 

H NMR measurements were performed at 20°C using a Maran NMR spectrometer (Resonance Instruments, UK) operating at resonance frequency of 23 MHz. The second moment of the FIDs was calculated using Microsoft Excel Solver. 

R. K. Julian, M. Nappi, C. Weil, and R. G. Cooks, Multiparticle simulation of ion motion in the ion trap mass spectrometer resonant and direct current pulse excitation, 7. Am. Soc. Mass Spectrom. 6, 57-70 (1995). 

N.J., USA) as a lyophylized powder and used without further purification. 1% NMR spectra were recorded on a Bruker HFX-90 hlgh-resolution spectrometer ( % resonance frequency 9.12 MHz). (The Instrument was equipped with a Bruker Fast Fourier transform unit, a Nlcolet 1o8o data hemdling system, a Bruker B-SV 2 proton decoupler, and a.Bruker deuterium lock system.) The probe was kept at 43 - 2°c with a flow of temperature controlled air (Bruker temperature control unit B-ST 1oo/7oo). Field frequency lock was obtained from D2O In a 2 mm capillary Inserted into the I0- or 15-mm sample tube. 27.36 MHz I NMR spectra of the rlbonuclease-nucleotlde complexes were recorded on a Bruker WH-27o spectrometer In the Fourier transform mode. The chemical shift data cure given In ppm relative to the external stemdard (4 M solution of 95%-enriched I5NH4NO3 In 2 M HNO3). 

F. Sureau, L. Chinsky, C. Amirand, J.P. BalUni, M. Duquesne, A. Laigle, P.Y. Turpin, P. Wgny, An ultraviolet micro-Raman spectrometer resonance Raman spectroscopy within single living cells. Appl. Spectrosc. 44, 1047-1051 (1990)... 

Figure 13 shows a plot of Ti versus Tc for various spectrometer frequencies. At short (rapid tumbling of small molecules, left side of the curve), mV 1 and 1/Ti is linearly related to l/r This is sometimes referred to as the extreme narrowing region of molecular motion. In the extreme narrowing region, Ti is independent of field strength (i.e., the spectrometer resonance frequency) and = 7. ... 

In an electron spin resonance spectrometer, transitions between the two states are brought about by the application of the quantum of energy hv which is equal to g H. The resonance condition is defined when hv = g H and this is achieved experimentally by varying H keeping the frequency (v) constant. Esr spectroscopy is used extensively in chemistry in the identification and elucidation of structures of radicals. 

This spectrum is called a Raman spectrum and corresponds to the vibrational or rotational changes in the molecule. The selection rules for Raman activity are different from those for i.r. activity and the two types of spectroscopy are complementary in the study of molecular structure. Modern Raman spectrometers use lasers for excitation. In the resonance Raman effect excitation at a frequency corresponding to electronic absorption causes great enhancement of the Raman spectrum. 

To find explosives Gas analyzers, chromatography instruments, drift-spectrometers, neutron defectosopes, nuclear-magnetic and nuclear-quadrupole resonant instruments... 

The most widely used type of trap for the study of ion-molecule reactivity is the ion-cyclotron-resonance (ICR) [99] mass spectrometer and its successor, the Fourier-transfomi mass spectrometer (FTMS) [100, 101]. Figure A3.5.8 shows the cubic trapping cell used in many FTMS instmments [101]. Ions are created in or injected into a cubic cell in a vacuum of 10 Pa or lower. A magnetic field, B, confines the motion in the x-y... 

The chapter is divided into sections, one for each general class of mass spectrometer magnetic sector, quadnipole, time-of-flight and ion cyclotron resonance. The experiments perfonned by each are quite often unique and so have been discussed separately under each heading. 

B1.7.6 FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETERS... 

Figure Bl.7.18. (a) Schematic diagram of the trapping cell in an ion cyclotron resonance mass spectrometer excitation plates (E) detector plates (D) trapping plates (T). (b) The magnetron motion due to tire crossing of the magnetic and electric trapping fields is superimposed on the circular cyclotron motion aj taken up by the ions in the magnetic field. Excitation of the cyclotron frequency results in an image current being detected by the detector electrodes which can be Fourier transfonned into a secular frequency related to the m/z ratio of the trapped ion(s).

In the other types of mass spectrometer discussed in this chapter, ions are detected by having them hit a detector such as an electron multiplier. In early ICR instruments, the same approach was taken, but FT-ICR uses a very different teclmique. If an RF potential is applied to the excitation plates of the trapping cell (figure B 1.7.18(b)) equal to the cyclotron frequency of a particular ion m/z ratio, resonant excitation of the ion trajectories takes place (without changing the cyclotron frequency). The result is ion trajectories of higher... 

The absolute measurement of areas is not usually usefiil, because tlie sensitivity of the spectrometer depends on factors such as temperature, pulse length, amplifier settings and the exact tuning of the coil used to detect resonance. Peak intensities are also less usefiil, because linewidths vary, and because the resonance from a given chemical type of atom will often be split into a pattern called a multiplet. However, the relative overall areas of the peaks or multiplets still obey the simple rule given above, if appropriate conditions are met. Most samples have several chemically distinct types of (for example) hydrogen atoms within the molecules under study, so that a simple inspection of the number of peaks/multiplets and of their relative areas can help to identify the molecules, even in cases where no usefid infonnation is available from shifts or couplings. 

The original method employed was to scan eitiier the frequency of the exciting oscillator or to scan the applied magnetic field until resonant absorption occiined. Flowever, compared to simultaneous excitation of a wide range of frequencies by a short RF pulse, the scanned approach is a very time-inefficient way of recording the spectrum. Flence, with the advent of computers that could be dedicated to spectrometers and efficient Fourier transfomi (FT) algoritluns, pulsed FT NMR became the nomial mode of operation. 

The heart of an NMR spectrometer is the probe, which is essentially a tuned resonant circuit with the sample contained within the main inductance (the NMR coil) of that circuit. Usually a parallel tuned circuit is used with a resonant frequency of coq = The resonant frequency is obviously the most important probe... 

A refinement of the ENDOR experiment is electron-nnclear-nnclear triple resonance, now commonly denoted TRIPLE. In TRIPLE experiments one monitors the effect of a simnltaneons excitation of two nnclear spm transitions on the level of the EPR absorption. Two versions, known as special TRIPLE (ST) and general TRIPLE (GT), are rontinely perfonned on connnercially available spectrometers. 

Figure Cl.3.1. Schematic diagram of a molecular beam electric resonance spectrometer. (Taken from [60].)...

FIGURE 13 5 Diagram of a nuclear magnetic resonance spectrometer (Reprinted with permis Sion from S H Pine J B Hendrickson D J Cram and G S Hammond Organic Chemistry 4th ed McGraw Hill New York 1980 p 136)... 

Other types of mass spectrometer may use point, array, or both types of collector. The time-of-flight (TOF) instrument uses a special multichannel plate collector an ion trap can record ion arrivals either sequentially in time or all at once a Fourier-transform ion cyclotron resonance (FTICR) instrument can record ion arrivals in either time or frequency domains which are interconvertible (by the Fourier-transform technique). 

Other types of mass spectrometer can use point, array, or both types of ion detection. Ion trap mass spectrometers can detect ions sequentially or simultaneously and in some cases, as with ion cyclotron resonance (ICR), may not use a formal electron multiplier type of ion collector at all the ions can be detected by their different electric field frequencies in flight. 

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