Phase corrections setting

At the end of the 2D experiment, we will have acquired a set of N FIDs composed of quadrature data points, with N /2 points from channel A and points from channel B, acquired with sequential (alternate) sampling. How the data are processed is critical for a successful outcome. The data processing involves (a) dc (direct current) correction (performed automatically by the instrument software), (b) apodization (window multiplication) of the <2 time-domain data, (c) Fourier transformation and phase correction, (d) window multiplication of the t domain data and phase correction (unless it is a magnitude or a power-mode spectrum, in which case phase correction is not required), (e) complex Fourier transformation in Fu (f) coaddition of real and imaginary data (if phase-sensitive representation is required) to give a magnitude (M) or a power-mode (P) spectrum. Additional steps may be tilting, symmetrization, and calculation of projections. A schematic representation of the steps involved is presented in Fig. 3.5. 

The next step after apodization of the t time-domain data is Fourier transformation and phase correction. As a result of the Fourier transformations of the t2 time domain, a number of different spectra are generated. Each spectrum corresponds to the behavior of the nuclear spins during the corresponding evolution period, with one spectrum resulting from each t value. A set of spectra is thus obtained, with the rows of the matrix now containing Areal and A imaginary data points. These real and imagi-... 

For 2D data which need no phase correction the PHmod parameter in FI, available in the General parameter setup dialog box opened via the Process pull-down menu, must be set to me if a magnitude, or to ps if a power spectrum should be calculated. Use the Help tool for more informations. 

Attention With spectra measured on spectrometers equipped with digital filters (DMX, DRX spectrometers), the automatically performed phase correction (DMX Phase Corr.) will be applied twice when the newly created FID is Fourier transformed again. This will introduce the baseline roll characteristic for the data of these type of spectrometers. A first order phase correction must then be performed manually by setting the PHCl value close to -22000 for the data available in the NMR data base. 

Correction, Window Function (Exponential LB = 1.0 Hz) and FT. In the frequency domain select Phase Correction (6th Order), Peak Picking (positive Peaks only X Range whole Spectrum) of the whole region. Save Spectrum (set Processing Number Increment = 1) and Plot Spectrum (set the plot parameters according to your preferences). Execute the automatic processing and if you are satisfied with the result, store this job for processing 1D C raw data as C.JOB. 

Shaped pulses are created from text files that have a line-by-line description of the amplitude and phase of each of the component rectangular pulses. These files are created by software that calculates from a mathematical shape and a frequency shift (to create the phase ramp). There are hundreds of shapes available, with names like Wurst , Sneeze , Iburp , and so on, specialized for all sorts of applications (inversion, excitation, broadband, selective, decoupling, peak suppression, band selective, etc.). The software sets the maximum RF power level of the shape at the top of the curve, so that the area under the curve will correspond to the approximately correct pulse rotation desired (90°, 180°, etc.). When an experiment is started, this list is loaded into the memory of the waveform generator (Varian) or amplitude setting unit (Bruker), and when a shaped pulse is called for in the pulse sequence, the amplitudes and phases are set in real time as the individual rectangular pulses are executed. 

Besides, let us note the automatic observance (certainly with correctly set initial data) and, hence, needlessness of the formalized descriptions in equilibrium modeling of such important regularities of macroscopic system behavior as the Gibbs phase rule, the Le Chatelier-Brown principle, mass action laws, the Henry law, the Raoult law, etc. 

The foregoing discussion has presumed that the < ( s are known. If the is an ideal gas, then each < , is unity. If the phase is an ideal solution, becomes it and can at least be estimated. For real gases, each is a f of the y, s, the quantities being calculated. Thus an iterative procedure is ind The calculations are initiated with each < f set equal to unity. Solution equations then provides a preliminary set of yf s. For low pressures or, temperatures this result is usually adequate. Where it is not satisfacto equation of state is used together with the calculated y, s to give a new and nearly correct set of t s for use in Eq. (15.40). Then a new set of y, s is dete The process is repeated until successive iterations produce no significant in the yf s. All calculations are well suited to computer solution, includ calculation of the < , s by equations such as Eq. (11.48) or (14.47). 

Considering the models in Table I, it follows that the response of model III-T will be more close to reality due to (i) the correct way the transfer phenomena in and between phases is set up, and (ii) radial gradients are taken into account. Therefore, the responses of the different models will be compared to that one. It is obvious that the different models can be derived from model III-T under certain assumptions. If the mass and heat transfer interfacial resistances are negligible, model I-T will be obtained and its response will be correct under these conditions. If the radial heat transfer is lumped into the fluid phase, model II-T will be obtained. This introduces an error in the set up of the heat balances, and the deviations of type II models responses will become larger when the radial heat flux across the solid phase becomes more important. On the other hand, the one-dimensional models are obtained from the integration on a cross section of the respective two-dimensional versions. In order to adequately compare the different models, the transfer parameters of the simplified models must be calculated from the basic transfer... 

Fig. 3. An example of the automatic phase correction method as described by Witjes and co-workers In (a) are five representative spectra for a small expanded region in a H NMR spectra data set containing 15 total spectra. Note the small differences in phase shift between the spectra, most notable in the central spectrum. In (b) the same NMR spectra are shown following three iterations of the phase and frequency correction. The (c) first five initial loadings (P for the NMR data set reveal that the first loading (Pi) is a good descriptor of the desired spectral line shape, while higher loadings (P2 and P3) contain the majority of the information concerning phase shifts and frequency shifts between spectra in the data set.

By choosing 0corr such that (0corr + tJ = 0 ( 0COrr = - real part of the spectrum will have the required absorption lineshape. In practice, the value of the phase correction is set "by eye" until the spectrum "looks phased". NMR processing software also allows for an additional phase correction which depends on frequency such a correction is needed to compensate for, amongst other things, imperfections in radiofrequency pulses. 

Load the configuration file ch3234c.cfg. Run the simulation and process the data as in part a. Using the Numerical option correct the zero-order phase (Process I Phase Correction, phcO -40 and phc1 0). Ensure that the cursor is set on top of the peak at 3.75 ppm click the First Order button and adjust the phase of the off-resonance signals for the correct absorptive lineshape.-... 

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