Ultraviolet regions INDEX

Samples of the 1,4-dihydrobenzoic acid, after both the first and the second distillations, are transparent in the ultraviolet region between 220 mu and 300 m/i, indicating the absence of benzoic acid or conjugated dihydrobenzoic acids. The refractive index cited in Reference 3 is in error. 

As cyclamate was banned in a number of countries before HPLC techniques were fully developed, there have not been many methods published for its analysis using modem procedures. The substance offers a challenge to the analyst as it does not have a useful chromophore in the ultraviolet region and its detection by a change in refractive index would be difficult at the levels used in soft drinks (a maximum of 400 ppm). 

The calculation of the dispersion interactions of the solute molecule with the surrounding medium according to Equation (17) is a feasible project, (see Reference 26 for the case of a pure liquid), although it requires somewhat more information on the polarizability than presently available. Refractive index data in the visible and ultraviolet regions are sufficient for the purpose of calculation of dispersion interactions (see References 25 and 26). In the procedure of spherical cavity and spherical averaging the calculated differences in dispersion energy between various conformations of the solute molecule result from variations in cavity size. 

The spectral dispersion dn/dx is a function of prism material and wavelength X. Figure 4.13 shows dispersion curves n(x) for some materials commonly used for prisms. Since the refractive index increases rapidly in the vicinity of absorption lines (see Fig.2.16), glass has a larger dispersion in the visible and near ultraviolet regions than quartz which, on the other hand, can be used advantageously in the uv down to 180 nm. In the vacuum-ultraviolet range CaF, MgF, or LiF prisms are sufficiently transparent. 

The most commonly-used detectors are those based on spectrophotometry in the region 184-400nm, visible ultraviolet spectroscopy in the region 185-900nm, post-column derivativisation with fluorescence detection (see below), conductivity and those based on the relatively new technique of multiple wavelength ultraviolet detectors using a diode array system detector (described below). Other types of detectors available are those based on electrochemical principles, refractive index, differential viscosity and mass detection. 

The wavelengths of main peaks are listed for acid, alkaline, and neutral solution in the index of Ultraviolet Absorption Maxima (p. 1128). Infra-Red Absorption. The wavenumbers of the six major peaks in the range 2000 to 650 an (5 to 15 Lim), in descending order of ampHtude, are recorded in the monographs in Pm 2. In many cases ftie infi-a-red spectrum is also reproduced. When selecting the six principal peaks, those which are in ftie region where Nujol absorbs (1490 to 1320 cmr, 6.7 to 7.6 um) have been omitted. Corrections for cahbration errors have been applied where these are known. The six principal peaks, in ascending order of ftie main peak, are listed in the index of Infra-red Peaks (p.1141). 

ID. Optical Methods of Analysis. Optical methods of analysis of reaction systems are very convenient where they can be applied. The optical properties which characterize the system may be the absorption at one or more particular wavelengths (in the ultraviolet, visible infrared, or microwave region), the refractive index of the mixture, the optical rotation of one or more species, the light-scattering properties of large molecules, or the fluorescent emission of one or more of the substances present. 

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