Digital resolution definition

Digital resolution The distance, in hertz, between successive data points determines the extent of peak definition by the data points. 

Before performing the FT, there are two things we can do to enhance the quality of the spectrum. First, the size of the data set can be artificially increased by adding zeroes to the end of the list of FID data. This process of zero filling has no effect on the peak positions, intensities, or linewidths of the spectrum, but it does increase the digital resolution (fewer hertz per data point) in the spectrum (Fig. 3.31). This can be useful to give better definition... 

Whilst the NMR response decays throughout the FID, the noise component remains essentially constant and will eventually dominate the tail of the FID. At this point there is little advantage in continuing acquisition since this only adds noise to the final spectrum. Provided the FID has fallen to zero when acquisition stops, one can artificially improve the digital resolution by appending zeros to the end of the FID. This process is known as zero-filling and it interpolates these added data points in the frequency-domain and so enhances the definition of resonance lineshapes (Fig. 3.15). 

An alternative method of analysis of NOESY data, which is usually sufficient for resolved peaks with a digital resolution much greater than the intrinsic line width and coupling constants, is to measure the maximum peak amplitude or to count the number of contours. NOESY cross peaks can then be classified as strong, medium or weak and can be translated into upper distance restraints of around 2.5, 3.5 and 5.0 A respectively. The lower distance constraint is usually the sum of the van der Waals radii (1.8 A for protons). This simple approach is reasonably insensitive to the effects of spin diffusion or non-uniform correlation times and can usually lead to definition of the global fold of the protein, provided a sufficiently large number of NOEs have been identified. 

Judeinstein et al have conducted direct measurement of through-space NMR interactions that provide definitive evidence for spatial proximity of different species. Dipole-dipole interactions can be measured in principle between any NMR active nuclei with heteronuclear correlation experiments in the liquid or solid state." The dipole-dipole interactions decay quickly with the internuclear distances (r ), and are difficult to evaluate for long-range distances and even more difficult when exchange, conformation, or motion phenomena are present. However, the measurement of the nuclear Overhauser method" based on the dipole-dipole-induced crossrelaxation, was proposed to successfully measure intermolecular interactions" and the formation of ion pairs." " In agreement with recent studies, the pulsed field gradient enhanced inverse HOESY (heteronuclear Overhauser enhancement spectroscopy) sequence is usually preferred because it is more sensitive for isotope pairs H- Li and also improves the digital resolution in the H crowded spectrum." ... 

It is very common to confuse the definition of optical sensor resolution with other optical system features. Different optical sensors are conceived to detect spatial differences in electromagnetic energy, as, for example, digital cameras (CCD and CMOS), tube detectors (vidicon and plumbicon), and pyroelectric and microbolometer detectors. Such optical sensors are able to resolve differences in the variations of the electromagnetic field. This ability depends... 

The display of line spectra on screen must be considered completely separately from the resolution of the analyser. By definition, a mass peak with unit mass resolution has a base width of one mass unit or 1000 mDa. On the other hand, the position of the top of the mass peak (centroid) can be calculated exactly. Data sometimes given with one or several digits of a mass unit lead to the false impression of a resolution higher than unit mass resolution. Components appearing at the same time at the ion source with signals of the same nominal mass, but slightly differing exact mass, which can naturally occur in GC-MS (as a result of co-eluates, the matrix, column bleed, etc.) cannot be separated at unit mass... 

---