Nephelometers

Aircraft can take vertical temperature soundings and can measure air pollutant and tracer concentrations and turbulence intensity. Airborne lidar can measure plume heights, and integrating nephelometers can determine particle size distributions. 

Nephelometer an instrument that measures the amount of light scattered. 

Nephelometer A device used to determine the suspended particulate size and concentration by the scattering of light. 

Trubtmgs-grad, m. degree of turbidity, -mes-ser, m. turbidimeter nephelometer opac-imeter. -punkt, m. turbidity point, -stoff, m. substance causing turbidity. 

Instruments that measure scattered light, such as the Photo-Nephelometer (Coleman Instruments, Oak Brook, IL), are used to evaluate and set clarity standards for parenteral preparations. It is not possible to establish an overall standard value for all products (e.g., 30 ne-phelos) because the value itself is relative and influenced by many factors, including concentration, aging, stopper extracts, and the solubility characteristics of the raw materials. Nephelometer readings are insensitive to contamination by large (visible) particulates. 

Most of the instruments, commonly used in an analytical laboratory, such as UV-Spectrophoto-meter, IR-Spectrophotometer, single—pan electric balance, pH-meter, turbidimeter and nephelometer, polarimeter, refractometer and the like must be calibrated duly, before use so as to eliminate any possible errors. In the same manner all apparatus, namely pipettes, burettes, volumetric flasks, thermometers, weights etc., must be calibrated duly, and the necessary corrections incorporated to the original measurements. 

In general, nephelometric measurements essentially require an instrument with a photocell placed in position so that it may receive selectively the scattered light rather than the transmitted light. As this principle and geometry also hold good specifically to fluorimeters and, therefore, these can be employed as nephelometers by selecting proper filters. 

In actual practice, the so called visual nephelometer (comparator type) have been more or less superseded by the photoelectric instruments Nevertheless, a Duboscq Colorimeter with a slight modification may be used conveniently for nephelometric analysis, for instance ... 

The most important characteristic feature of a nephelometer is the reflector that has been specifically designed so as to collect the light which has undergone scattering by the particles present in a turbid or cloudy solution. A typical nephelometer is illustrated in Figure 20.3, below ... 

Permit each flask to stand for 2-3 minutes and read out the turbidity in the nephelometer,... 

Insert the Blank solution in the nephelometer and adjust to zero reading of the scale by the aid of zero-control-knob,... 

Repeat the measurements with the remaining standard sulphate solution and plot the nephelometer reading Vs the S042- ion content per ml,... 

Place the blank solution into the matched test-tube of the nephelometer and adjust the reading to zero. 

Desocibe in details the assay of the following drug substances by using a nephelometer ... 

To test the applicability of statistical techniques for determination of the species contributions to the scattering coefficient, a one-year study was conducted in 1979 at China Lake, California. Filter samples of aerosol particles smaller than 2 ym aerodynamic diameter were analyzed for total fine mass, major chemical species, and the time average particle absorption coefficient, bg. At the same time and location, bgp was measured with a sensitive nephelometer. A total of 61 samples were analyzed. Multiple regression analysis was applied to the average particle scattering coefficient and mass concentrations for each filter sample to estimate aj and each species contribution to light scattering, bgn-j. Supplementary measurements of the chemical-size distribution were used for theoretical estimates of each b pj as a test of the effectiveness of the statistical approach. 

Aerosol sampling instruments were housed in an air conditioned monitoring trailer operated by NWC. The particle light scattering coefficient, bg, was continuously measured with modified MRI Model 1561 integrating nephelometer. The nephelometer automatically zeroed daily and was calibrated quarterly. 

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