Intensity and resolution

Curved analyzing crystals, because of their focusing action, give greater intensity than flat crystals. 

As we saw in Fig. 6-10, resolution depends both on A20, the dispersion, or separation, of line centers, and on B, the line breadth at half-maximum intensity. The resolution will be adequate if A26 is equal to or greater than 2B. By differentiating the Bragg law, we obtain 

When the minimum value of A26, namely 2B, is inserted, this becomes 

For a typical slit with / = 10 cm and s = 0.025 cm, a = 0.3°. But further divergence is produced by the mosaic structure of the analyzing crystal this divergence is related to the extent of disorientation of the mosaic blocks, and has a value of about 0.2° for the crystals normally used. The line width B is the sum of these two effects and is typically of the order of 0.5°. The line width can be decreased by increasing the degree of collimation, but the intensity will also be decreased. Conversely, if the problem at hand does not require fine resolution, a more open collimator is used in order to increase intensity. Normally, the collimation is designed to produce a line width of about 0.5°, which will provide adequate resolution for most work. 

When a curved reflecting crystal (Fig. 15-5) is used, the line width depends mainly on the width of the source slit 5 and the precision with which the crystal is ground and bent. The line width is normally about the same as that obtained with a flat crystal, namely, about 0.5°. 

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The addition of a liquid matrix, usually glycerol, improves the reproducibility of the mass spectra because inhomogeneities caused by analyte and matrix co-crystallisation are avoided. In some cases, it also enhances signal intensity and resolution. However, analytes can also be desorbed from dry surfaces [7 9]. 

A further low-intensity peak, known as the Raman band, is also observed in spectra (see Fig. B3.6.1). This is a low-intensity band of scattered radiation whose distance from the excitation band is a measure of the vibrational energy of the H-0 bond in solvent water. At A,ex = 280 nm, the Raman band for water occurs at 311 nm in general, it occurs at l/ (1/X.ex) - (3.6 x 10-4), where A,ex is the excitation wavelength in nm. The intensity and resolution of the Raman band provide a useful empirical check on the performance of the spectrofluorometer. A decrease in the signal-to-noise ratio usually indicates a deterioration of the lamp. 

Depending on the intensity and resolution requirement of the FISH spot, one can try binning twice. (Hint The sample will look brighter at the expense of a reduced special resolution). For more details on this topic, please visit the Microscopy Resource Center ... 

It is important to determine the optimum filter for any particular application. Too much smoothing and the signal itself is reduced in intensity and resolution. Too little smoothing, and noise remains. The optimum smoothing function depends on peak-widths (in datapoints) as well as noise characteristics. 

After the sample is inserted into the probe in the magnet, it must be locked and shimmed, and the probe must be tuned. To achieve the best signal intensity and resolution, the magnetic field must be as homogeneous as possible. Spectrometers use the... 

The pile fast chopper systems so far have contributed most of the available information on slow neutron resonances. They have advantages of a steady source, a very small minimum slit size (< i cm ) that permits measurements using separated isotopes, with relatively high intensity and resolution. 

The most common way to perform method development is to infuse the analyte and allow software to optimize all tuning parameters that will give the best intensity and resolution. However, even though most vendors offer the ability to automatically tune many different compounds simultaneously, this process could take a long time, which is not ideal for drug discovery applications. An alternative is to use a low concentration, 250 tig/mL of analyte with a generic LC method and application of a full data dependent mass spectrometer scan (Toll et al., 2005 Saunders et al., 2009). First, a full Qi or Q3 scan verifies that the mass of the parent compound is detected, followed by dependent scans... 

Excited states and, to a lesser extent, the ground state may be sensitive to changes in environmental parameters such as temperature, pressure, viscosity and polarity. This manifests itself in a number of quantifiable parameters, such as (i) spectral shifts (ii) change in the emission quanmm yield (iii) change in the nature of the emissive state (iv) change in non-radiative and radiative decay rates (v) variations in the intensity and resolution of vibronic fine structure and (vi) the emergence of excimer or exciplex emission. These response mechanisms can be used to design sensor platforms to monitor both microscopic and macroscopic environmental parameters. 

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