Slit, monochromator

Because infrared spectrophotometry is detector noise limited, a profitable trade-off is possible between signal-to-noise ratio and resolution. Such a trade-off may be useful when deconvolution is used to recover resolution lost by opening monochromator slits to increase acquisition rates. In any system where degrading the resolution improves the signal-to-noise ratio nonlinearly, a potentially useful trade-off is possible. 

What are the advantages and disadvantages of decreasing monochromator slit width ... 

Fluorescence excitation and emission spectra of the two sodium D lines in an air-acetylene flame, (a) In the excitation spectrum, the laser was scanned, (to) In the emission spectrum, the monochromator was scanned. The monochromator slit width was the same for both spectra. [From s. J. Weeks, H. Haraguchl, and J. D. Wlnefordner, Improvement of Detection Limits in Laser-Excited Atomic Fluorescence Flame Spectrometry," Anal. Chem. 1976t 50,360.]... 

If the monochromator slit is too wide, more than one line may be transmitted to the detector. In this case the calibration graph will show greater curvature than would be the result if only the desired line were transmitted to the detector. 

In some assays it is necessary to specify the minimum desirable resolution, since changes in the spectral bandwidth (or monochromator slit-width) can seriously affect the observed absorbance of sharp peaks. The British Pharmacopoeia (1980) requires that the spectral bandwidth employed should be such that further reduction does not lead to an increase in measured absorbance. This is particularly important for drugs that have aromatic or strongly-conjugated systems, e.g. diphenhydramine,... 

The fundamental parameters approach has been recently implemented in some of the current programs. It gives, to a certain extent, physical meaning to the parameters involved in pattern decomposition. This method attempts to model the contributions from various instrumental components (such as monochromators, slits) and geometry to the observed peak profile shapes. Since this is done considering the relevant physics involved from the generation, diffraction, and detection of PXRD, it leads to more physical meaning than the two methods described earlier. This method can be used not only to perform full pattern decomposition, but also effectively to do a standardless refinement of the sample effects such as crystallite size and microstrain. 

Fig. 18. Schematic diagram of the optical arrangement for single-crystal work. A, tungsten lamp B1 and B2, Polaroids C, focusing lens, D, light-collection lens E, capillary cell showing lens (1), solid phase (ice, s), liquid phase (solution, w), interface (i), and laser beam (b) F, filler tube G, monochromator slits and H, analyzer. Coordinate system is as indicated. Cold air flow is along the X direction. From Tomimatsu et al. (1976), reproduced with permission.

Why do quantitative and qualitative analyses often require different monochromator slit widths 25-5. Why is iodine sometimes introduced into a tungsten lamp ... 

In the spectrum of PVCA it seems that the 0-0 emission band is present only as an unresolved shoulder and that the remaining structural features of this spectrum are somewhat broadened compared with those of NEC. An attempt was made to achieve better resolution of the 0-0 band of PVCA using narrow monochromator slits and multiple scans of the emission band. In addition, spectra were recorded using variable delay times following excitation. These results are presented in Figure 2. 

The operation does not modify the original signal beyond reducing its amplitude, as an ideal monochromator slit also would, by restricting the amount of light that reaches the photodetector. Below we will take care of that signal attenuation. 

You have now simulated opening the monochromator slits (without changing the amount of light falling on the photodetector, because of the normalization you built in at step 17), and you will see the resulting distortion ofthe output signal, as illustrated in Fig. 7.5-3. 

Apparatus. Spectrofluorometer SPEX Fluorolog-2 (Edison, NJ, USA). Xenon lamp 450-W (OSRAM, Germany) and photomultiplier tube (R 928 Hamamatsu Co.) powered at 950 V as the detector. Excitation and emission monochromator slits, wavelength increment, and integration time were set at 1 mm, 1 nm and 1 second respectively. A pH meter (Model Orion 520A, USA) was used for pH adjustment. Basic procedure. Benserazide solution 2 mL (1.0 x 10 6 1.0 x 10 4mol/L) was added to 2 ml of Triton X-100 solution (4.0 10 4 mol/L) and 2 mL pH 4.0... 

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