Photometers light scattering

Calibration is required to convert measurements of scattered light intensity from arbitrary to absolute values, an essential step in the calculation of molecular weight. Fortunately, because the calibration constant of most photometers remains stable for long periods of time, the calibration procedure need be carried out only infrequently. Should it need to be calibrated, the procedure described in ASTM D4001-93 or that of the instrument vendor should be followed. 

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As a result of these considerations, the primary difference between a spectrophotometer and a light-scattering photometer is the fact that the photodetector is mounted on an arm which pivots at the sample so that intensity measurements can be made at various angles. 

Figure 10.9 Light-scattering photometers, (a) Schematic top view showing movable photodetector. (Reprinted from Ref. 2, p. 176.) (b) Cutaway photograph of commercial light-scattering instrument, the Brice-Phoenix Universal Scattering Photometer. (Photo courtesy of the Virtis Co., Gardiner, New York.)...

Detectors Model 410 differential refractive index (Waters Corporation) Model 100 differential viscometer (Viscotek Corporation) Dawn-F multiangle laser light-scattering photometer (Wyatt Technology)... 

Molecular-weight-sensitive detectors, such as a laser light-scattering photometer... 

Podzimek, S., The use of GPC coupled with a multiangle laser light-scattering photometer for the characterization of polymers. On the determination of molecular weight, size, and branching, /. Appl. Polym. Sci., 54, 91, 1994. 

For determination of Molecular weight by scattering of light photometers/light scattering photometers... 

Fig Sketch of the essential components of a light scattering photometer. 

In this method, at every concentration, scattering should be measured at a number of different angles and therefore light scattering photometer should have a provision for continuous variation of scattering angle. 

SEC System, Data Processing, and Chromatography Procedures. The SEC/LALLS system contained a Model IlOA pump (Altex), Model 7125 injector (Rheodyne), KMX-6 Low-Angle Laser Light Scattering Photometer (LDC/Milton Roy), and a Model 98.00... 

Probably the most accurate approach is to directly connect, or couple, the SEC to a device, such as a light-scattering photometer, which directly measures the molecular weight for each elution fraction. Here both molecular weight and MWD are accurately determined. 

Bartholdi, M., G. C. Salzman, R. D. Hiebert, and M. Kerker, 1980. Differential light scattering photometer for rapid analysis of single particles in flow, Appl. Opt., 19, 1573-1581. 

Light scattering photometer, with absolute calibration carried out in advance plus appropriate neutral filters, and data collection system... 

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. 

Except for the movable photomultiplier tube, a light scattering photometer is very nearly identical to an ordinary spectrophotometer, which measures the ratio of the intensity of transmitted light to the intensity of incident light /,//0. The absorbance per unit optical path cabs is defined in terms of this quantity as... 

Equation (67) shows clearly that i should be measured as a function of both concentration and angle of observation in order to take full advantage of the Debye theory. The light scattering photometer described in Section 5.4 is designed with this capability, so this requirement introduces no new experimental difficulties. The data collected then consist of an array of i/I0 values (i needs no subscript since it now applies to small and large particles) measured... 

DLS- 700S light scattering photometer at 633nm, calibrated with benzene. The optical clarification was performed with teflon filters. The specific refractive index increment (dn/dc) was obtained with Chromatix KMX-16 reffactometer at the same wavelength, calibrated with NaCl solution. 

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. 

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