Slit width choice

Optimization in Flame AAS Source-related Parameters Effect of Lamp Current Effect of Lamp Warm Up Time Lamp Alignment Lamp Deterioration Choice of Lamp Atomizer-related Parameters Choice of Atomizer Effect of Fuel-to-oxidant Ratio Optimization of Burner Position Burner Design, Warm Up, and Cleanliness Gas Flow Stability Monochromator-related Parameters Choice of Slit Width Choice of Wavelength Optimization in Flame AFS Source-related Parameters Lamp Operating Parameters Lamp Alignment Atomizer-related Parameters Monochromator-related Parameters Optimization in Flame AES... 

Experimentally, several precautions must be taken if reliable Raman data are to be obtained from solution studies. Firstly, the instrumental slit-width should be appreciably smaller than the half-width of the band to be studied. This means that slits wider than 2 cm-1 are to be avoided. Secondly, photolytic decomposition of the sample and local boiling of the solvent have also to be avoided. Careful choice of laser frequencies, use of a low incident power and, if necessary, sample spinning are indicated. The need for a relatively high solute concentration usually means that there is little choice of solvent. Particularly for coloured samples the presence of a vestigal resonance Raman effect must be tested by measurements with a variety of... 

Iron also has a very complex spectrum and most other points that have been made in regard to manganese apply to this metal. The choice of the most sensitive among the many absorption lines again was made with the help of the photographic technique by Allan (A7). The strongest line is that at 2483.3 A at which sensitivity limits of 0.1 ppm have been obtained, but the line at 3720 A still permits the detection of iron at the 1 ppm level. Especially narrow slit width and high resolution monochromators are necessary for optimal results, because the resonance... 

A compromise must be reached in the choice of scan speed, slit width and response time, these factors being inter-related. Typical or starting values for the parameters in such an experiment might be 1-4 nm s", 2 nm spectral bandwidth and 0.1 s, respectively. 

Suspensions of biological materials are turbid. It is especially important in measurements of fluorescence to resolve fluorescence from scattered Ught. Since scattered light usually exceeds fluorescence by a substantial margin, careful choice of filters and slit widths is essential to record just fluorescence (2). It is important to be aware that substantial changes in turbidity, and hence in the absolute value of fluorescence or absorbance, occur when membrane vesicles are exposed to sudden changes in osmolarity or are exposed to permeant salts (3). In order to maximize the chances of capturing the emitted/transmitted photons, the cuvette is usually placed as close as possible to the detector. 

Finally, the choice of the common excitation wavelength for the sample and reference solutions, corresponding to isoabsorptive points, is of the highest importance for a high quality measurement of the quantum yield. This wavelength should be selected in a region where both absorption curves are not steep, in order to avoid errors related to small differences in the values of X (e.g., because of a slightly different calibration of the employed spectrophotometer and spectrofluo-rimeter) and of the slit widths. Commonly used reference standards for the determination of fluorescence quantum yields are listed in Table 5.3. Other similar tables can be found in [1, 6, 16, 17]. 

The choice of the slit size (width and height) depends on the shape and size of the spot. Usually, for a spot whose round shape is sharply defined, the slit width is set at 120% of the spot diameter, when the spot is oval — at 120% of the spot length, and for a band — at 50-70% of its length [13]. 

The function Q(o-) is similar to the slit function which distorts lines in spectra collected on dispersion instruments. Q(instrument line shape and can be varied by changing the maximim optical retardation L or by changing the form of a(8). Figure 3 shows several choices for the apodization function and the resulting instrument line shape for each. It can be seen that the width of the instrument line shape is proportional to 1/L. Thus, the larger the optical retardation, the narrower the spectral lines become. For the case where a(8) = 1 for all 8 between 0 and L, the narrowest lines are achieved, but the side-lobes or "ringing" are most severe. When many absorption or emission lines in a spectrim are convolved with this instrument line shape, the spectrum can become difficult to interpret. Therefore, a compromise is usually reached between an apodization function a(8) which produces narrow spectral lines and one which reduces the side-lobes. 

Sheet is usually defined as being thicker than film, or thicker than 1 to 4 mm ( 0.003-0.010 in). Sheet thickness can be at least 2 mm (0.5 in.), and widths can be up to 30 m (10 ft). Basically, hot melt from a slit die is directed to a combination of an air knife with two cooling rolls, or, a more popular choice, to a three-cooling-roll stand (Fig. 3-28), which cools, calibrates, and produces a smooth sheet. To aid the chill rolls, end sections of the die are operated at a higher heat than the center (Fig. 3-12c). Cooling rolls require this type of heat control from their ends to the center. 

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