Photometer, dispersive

These can provide more spectral information than photometers or conventional dispersive spectrophotometers but are much more expensive and generally less sensitive (Figure 4.34(a) and p. 355). 

Different types of IR instruments are available dispersive grating spectrophotometers, FT instruments, and nondispersive photometers. Until the 1980s, and the... 

The easiest way to calibrate a light scattering photometer is to use a suitable standard as a reference. Although polymer solutions and dispersions of colloidal silica have been used for this purpose, commercial photometers are equipped with opal glass reference standards. 

Light-Scattering Photometer. In one type, suspended particles are determined (counted). Another type is used to determine the molecular weight of macromolecules dispersed in solution. The former type operates on the basis of a nephelometer the latter is of much higher precision and uses monochromatic light. 

There are two groups of UV analyzer designs photometers and spectrophotometers. Photometers are nondispersive analyzers in which the source radiates over its full UV spectrum, and discrete wavelengths are separated by narrow (2-10 nm) band-pass filters. Most process analyzers are nondispersive. Spectrophotometers are dispersive analyzers in which a prism is used to separate the spectral components of the UV spectrum. Most laboratory analyzers are dispersive. 

UVIVisible Photometers and Dispersive Spectrophotometers These detectors respond to UV/visible absorbing species in the range 190 to 700 nm and their response is linear with concentration, obeying the Beer-Lambert law (p. 355). They are not appreciably flow or temperature sensitive, have a wide linear range and good but variable sensitivity. 

Drop stabilization methods rely on the immediate stabilization of drops by encapsulation with thin polymer films or surfactants [219-221] a photomicrographic method has been employed usually after encapsulation of drops. However this method cannot always be used due to incompatibility of the encapsulating materials with some systems. The method also has the disadvantage of the influence of the chemical treatment on drop size. A special sampling apparatus has been developed to withdraw a sample of dispersed phase from the mixing vessel to stabilize drops with a surfactant and to force the dispersed sample through a capillary with a photometer assembly to measure both droplet size and concentration [222]. 

Curl and co-workers (R15, R16, V2) forced the stabilized dispersion through a capillary, where a specially designed photometer assembly (shown in Fig. 4) measured both the drop size distribution and the dye concentration of the drops. Sedimentation techniques have also been used for measuring the drop size distribution (BI3, Gil, Kl, S4). 

Curl and co-workers (R15, R16, VI1) have measured coalescence frequencies in a continuous flow vessel by introducing two dispersed-phase feed streams containing different concentrations of dye. Samples removed from the vessel are analyzed by a specially designed photometer that measures the bivariate drop volume-dye concentration distribution in the dispersion (see Fig. 4). The appropriate equation for obtaining oa in this... 

Three types of infrared instruments are found in modem laboratories dispersive spectrometers (or spectrophotometers), Fourier-transform (FTIR) spectrometers, and fdter photometers. The first two are used for obtaining complete spectra for quali-... 

Rhodamine B was added to the tank inflow, and the resulting effluent concentration was recorded as a function of time in a double-beam (Zeiss) spectral photometer. These measurements were evaluated statistically in order to describe the hydraulic characteristics of the tanks. Effluent concentrations of the tracer, dosed as a delta impulse, observed for different (hydraulic) surface loading (q = 0.28, 0.58, and 1.0 m/h) were evaluated in terms of a characteristic (dimensionless) number, the dispersion number (4), and shown in Figure 3. 

Note that a quadrupole mass speciromeicr is more analogous to an optical variable-band filter photometer than to an optical spectrometer in which a grating si-mullaneously disperses a spectrum of clcctromagnclic radiation. For this reason, the device is sontetimes referred to as a mass filter rather than a mass analyzer. 

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