Wavelength selection for

Prepare a benzene-toluene mixture by placing 0.05 mL of each liquid in a 25 mL graduated flask and making up to the mark with methanol. Take 1.5 mL of this solution, place in a lOmL graduated flask and dilute to the mark with methanol this solution contains benzene at the same concentration as solution 5, and toluene at the same concentration as solution 5. Measure the absorbances of this solution at the two wavelengths selected for the Beer s Law plots of both benzene and toluene. Then use the procedure detailed in Section 17.48 to evaluate the composition of the solution and compare the result with that calculated from the amounts of benzene and toluene taken. 

The presentation in this paper concentrates on the use of large-scale numerical simulation in unraveling these questions for models of two-dimensional directional solidification in an imposed temperature gradient. The simplest models for transport and interfacial physics in these processes are presented in Section 2 along with a summary of the analytical results for the onset of the cellular instability. The finite-element analyses used in the numerical calculations are described in Section 3. Steady-state and time-dependent results for shallow cell near the onset of the instability are presented in Section 4. The issue of the presence of a fundamental mechanism for wavelength selection for deep cells is discussed in Section 5 in the context of calculations with varying spatial wavelength. 

Note that this condition is extremely wavelength selecting. For a given angle of incidence between the input optical beam and the acoustic wave front, and a given value of the acoustic wavelength, only one value of A is permitted. 

FIGURE 5.68. Calibration spectra with the one wavelength selected for modeling component A (dashed vertical line) and the two wavelengths selected for modeling component B (solid vertical lines). 

Angel, S.M., and M.L. Myrick. 1990. Wavelength selection for fiber optic Raman spectroscopy. Applied Optics 29 1350-1352. 

Scalbert et al. (1989) described the chromatographic separation of cyanidin and delphinidin from methanolic extracts of oak heartwood using a C-18 Novapak column. The elution solvent was a mix of two solvents A and B that changed in composition from 0-100% B in a linear fashion over a period of 20 min. Solvent A was a mixture of 94 5 1 H20/methanol/H3P04, and solvent B was 99 1 methanol/H3P04, at a flow rate of 1 7mL/min. In this case a dual-channel spectrophotometer was used with two wavelengths selected for detection 280 and 530 nm. Under these conditions, and based on reference compounds, delphinidin eluted after 13.9 min and cyanidin after 14.8 min. 

High performance thin-layer chromatography (HPTLC) on silica gel plates was used for the separation >3-adrenoceptor blocking drugs. The detection limit for atenolol was 25.o ng, and the absorption wavelength selected for its determination was 2o5 nm.(8)... 

The mobile phase plays an important part in the fluorescence of a molecule. Unless chosen with care, the mobile phase can quench the fluorescence of the molecule of interest. Most of the non-halogen-containing solvents used in HPLC can be used with fluorescence detection. However, dissolved oxygen or other impurities in the eluent can cause quenching. The solvent polarity and the pH of the mobile phase can also affect the fluorescent process if they influence the charge status of the chromophore. For example, aniline fluoresces at pH 7 and at pH 12, but at pH 2, where it is cationic, it does not fluoresce. Table 3.5 shows wavelength selections for some common LC-fluorescence applications.30... 

Table 3.5 Wavelength Selections for Common LC-Ruorescence Applications3...

Variables 3 and 4 are found in the familiar relationship, i.e., that fluorescence in dilute solutions is directly proportional to the absorbance of the solute AX at the wavelength selected for excitation, times the quanta of light IoX available at the wavelength selected for excitation, times the fluorescence quantum efficiency X for the solute. Oftentimes the wavelengths available for maximum illumination in an excitation source do not... 

Components) of sunflower oil, the carrier solvent in oily injection formulations, were found to produce a negative Cotton effect below 334 nm which will interfere with that for testosterone phenylpropionate at its wavelength of maximum negative ellipticity, 330 nm. Consequently, the wavelength selected for the direct measurement of ellipticity of the steroids was 342.8 nm, the long wavelength of maximum negative ellipticity of the steroids, where the sunflower oil exhibits no CD. 

This characteristic of light absorption by dyes is important in the analysis of dye mixtures of the type found in spent dyebaths. For such dye mixtures, the absorbance can be measured at a number of wavelengths and the concentration of the dyes determined by simultaneous solution of a set of linear equations of the type shown above. The wavelengths selected for the analysis are generally those for which one of the dyes gives a maximum absorbance. 

Figure 8-13. Optimal wavelength selection for API and related impurities.

Quantitation was carried out by the simultaneous equation (Method 1) and the absorbance ratio (Method 2). The wavelengths selected for Method 1 were 257.10 and 288.66 nm of both drugs, respectively. In Method 2, two wavelengths 257.10 nm of paracetamol and 284.36 mn, the isobestic point, were selected. Both the methods were validated for linearity, accuracy, and precision. 

Chu, A.H. and Lopatin, W. (1986). Application of pattern-recognition techniques in wavelength selection for instrumentally read reagent strips. Clin. Chem. 32, 1666-1671. 

If the band of wavelengths selected for spectrophotometric measurements corresponds to a region of the absorption spectrum in which the molar absorptivity of the analyte is essentially constant, departures from Beer s law will be minimal. Many molecular bands in the UV/visible region fit this description. For these. Beer s law is obeyed, as demonstrated by Band A in Figure 24-17. Some absorption bands in the UV/visible region and many in the infrared region are very narrow, however, and departures from Beer s law are common, as illustrated for Band B in... 

Stray radiation Radiation of a wavelength other than the wavelength selected for optical measurement. 

Perhaps the most important feature of development chromatography is that the sample is separated by distance rather than time. This freedom from time constraints permits the utilisation of any of a variety of techniques to enhance the sensitivity of detection, such as reactions which increase light absorbance or fluorescence emission and wavelength selection for optimum response of each compound measured. The separation can be scanned as many times as desired, at a variety of wavelengths, and a complete UV visible or fluorescence spectrum can be easily plotted out for each component. Thus, the detection process in HPTLC is more flexible and variable than that for HPLC. Detection limits under optimum conditions are approximately the same for the two techniques. 

TABLE 7.1.7. Wavelengths Selected for Prediction of Some Constituents in Wheat, Canola, and Lentil using log VR and MLR... 

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