Phase-sensitive detection quadrature

The expressions for Sx and Sy are redundant. They are both detected in quadrature by the normal phase-sensitive detection scheme. Note that from /, where we gain the intensity factor of y,/ys = 4 for H/13C, the a magnetization precessing at fi — tt/ has intensity of 4, while from S this gives — 1, for an overall intensity of 3. For the /3 magnetization both components are negative to give a total of—5. 

Figure 3.8. Quadrature phase sensitive detection along with the phase cycling and signal routing used in CYCLOPS for eliminating quadrature artefacts.

All signals are collected simultaneously. The RF pulse delivered is generally on the order of watts while the NMR signal collected is on the order of microwatts. The FID signal in the time domain must be converted to a frequency domain spectrum by application of a Fourier transformation or other mathematical transformation. Commercial instruments generally use quadrature phase-sensitive detection to avoid spectrum artifacts... 

However, application of the above technique can be problematic when strong solution-phase absorption obscures weak bands of a surface species. To overcome this limitation, the phase rotation approach [263] can be used. Phase-sensitive detection such as with a lock-in amplifier (LIA) provides two signals the signal that is in phase IP) and the signal that is out of phase (the quadrature, Q) with the external perturbation [264]. These quantities can be represented at each... 

The FIDs and interferograms can be multiplied by appropriate mathematical functions before Fourier transformation in order to improve sensitivity, resolution, or line shape exactly as in ID NMR. The NMR data are usually obtained as two separate components 90° out of phase from each other in a mode called quadrature detection to yield two spectral components denoted real and imaginary. A suitable linear combination of these two components allows the generation of a spectrum with a pure absorption phase. In 2D NMR, this phase-sensitive detection sometimes results in line shapes and phases that do not allow a pure absorption spectrum to be obtained and then the compromise of a magnitude mode presentation is used. This comprises the square root of the sum of the squares of the real and imaginary components and is wholly positive. Usually, 2D NMR spectra are plotted as contour maps as though the 2D spectral peaks are a series of mountains viewed from above relative to the orthogonal ffli and 0)2 axes. 

Traficante, D. D. Phase-sensitive detection. Part II Quadrature phase detection. Concepts in Magnetic Resonance 2 181-195, 1990. 

The intensity of the fluorescent light was monitored by a photomultiplier and the time-dependent signal was isolated by an amplifier tuned to 462 kHz. The radiofrequency modulation of the fluorescent light was readily confirmed by this method, but the small percentage modulation of the incident light made phase-sensitive detection essential for detailed studies. This technique had the advantage that the amplitudes of the in-phase and quadrature components... 

Using phase-sensitive detection of the radio frequency-modulation of the cross-beam absorption signal both the in-phase and quadrature components of < M > may be studied separately. The in-phase component gives a signal proportional to... 

Fig.17.16. In-phase and quadrature components of the transverse magnetization, , obtained by phase-sensitive detection using the cross-beam technique in...

The coherent precession of spins in the x -y plane induces a current in the receiver coil. From the precessing motion of coherent spins, a signal oscillating at the Larmor frequency is recorded. The direct quadrature (or phase-sensitive) detection of most NMR spectrometers records the signal... 

Fourier transformation in (Fti), spectra are obtained with real (R) and imaginary (/) data points. For detection in the quadrature mode with simultaneous sampling, a complex Fourier transformation is performed, with a phase correction being applied in F. (c) A normal phase-sensitive transform P— RR and I- RI. (d) Complex FT is applied to pairs of columns, which produces four quadrants, of which only the RR quadrant is plotted. 

Quadrature detection A method for detecting NMR signals that employs two phase-sensitive detectors. One detector measures the jc-component of... 

The alternative method for obtaining quadrature phase detection with the use of a single phase-sensitive detector, developed initially by Redfield38 and used in some commercial spectrometers, has certain advantages in two-dimensional NMR. In this approach, the phase of the receiver is advanced by 90° after each measurement. The rationale can be better understood after we discuss digitization rates in Section 3.7. 

The spectra were acquired with 2048 t2 complex data points and 256 ri increments in the phase sensitive mode with quadrature detection using the method described by States et al. (25). Water resonance was supressed during the 1.5s relaxation period used in the NOESY, DQF-COSY and TOCSY experiments and the mixing period of the NOESY experiments by irradiating continuously at its resonance frequency. The amide exchange experiments were carried out by... 

Phase correction. Phase-sensitive acquisition of the FID with quadrature detection means that the pure absorption lineshape can be formed after FT but it may require some manipulation of the data to achieve this. If the real and the imaginary parts of the signal are Ar and A], the actual absorption spectrum A(w) can be formed as... 

Fig. 3. Basic pulse sequences for 2D- X,"T H correlations. Tbe same notation as in Hg. 1 is used. Minimum phase cycles for selection of correlation signals are given, more elaborate schemes for quadrature detection in FI and phase-sensitive spectra may be applied following standard rules. (a) HETCOR (without 180° pulses)/INEPT (with 180° pulses), the refocusing delays A are optional in both experiments setting the mixing pulses 8 to 45°/135° instead of 90° allows to determine coupling signs in ABX-type spectra. (b), HSQC. (c), HMQC the refocusing delay A2 is optional.

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