Turbidity instruments

Many field scientists, however, despite the range of commercially available turbidity instrumentation, still recognize a need for low cost, rugged, and reliable systems. This is especially so when a network of instruments is required for permanent installation to define a turbidity field, for simultaneous manual turbidity measurements by a research team, or for specialist applications such as in subglacial environments. This has led many researchers to custom-build their own instruments. 

Turbidimetric analysis determinations by, 729 general discussion on, 726 instruments for, 727 Turbidity method for D. of silver, 347 Tyndall effect 419, 726... 

Heller and Tabibian (13) noted that errors, due to laterally scattered light and the corona effect, as large as to cause a 30 reduction in measured turbidity, may result if instruments which are perfectly suitable for ordinary absorption measurements are used for turbidity measurements without proper modifications. To evaluate the performance of our turbidity detector, particle suspensions of various concentrations of several polystyrene latex standards were prepared. Their extinction coefficients were measured using both a bench-top UV spectrophotometer (Beckman, Model 25) and the online detector (Pharmacia). 

Since the scattering due to dust is negligible relative to the very large scattering from colloidal suspensions, procedure (b) is inherently attractive. Using the definition of turbidity t and the interrelation between r and R90, the calibration constant of the instrument is given by... 

Hence c(g/ml) is the concentration of colloidal suspension G90 is the reading on the LS photometer at 6 = 90°, 2 is the path length, which equals the cell diameter when using a cylindrical cell t is the turbidity obtained from measurements of optical density. Table 4 gives the results of calibrating a Sofica instrument with colloidal... 

The principles of absorptiometry have been applied to the measurement of turbidity. Suspensions of particles scatter incident radiation and, while there is no absorption of radiation by the analyte, the reduction in the transmitted radiation can be used as a measure of the degree of turbidity. Because absorption is not involved, there is no requirement for monochrornation but the fact that the extent of light scattering increases as the wavelength of the incident radiation decreases explains the fact that some instruments do incorporate a simple monochrornation system. 

The instrument used in the turbidity measurement was Hatch Model 2100 A Turbidimeter. A Hotech Shaker Bath, Model 901 (Hotech Instruments Corp.) was used in mixing the oil and surfactant solution. The nonionic surfactants, Newcol 1102, 1103 and 1105 were produced by Sino-Japan Chemical Co., Ltd. The active ingredient is dodecanol ethoxylate. Sodium dodecyl sulfate (SDS, No. L. 5750, Sigma Chemical Co. 95% active, containing 65% Cj 2>... 

In the SDS solutions containing 0.1-0.4 M NaCl, the turbidity increase is mainly due to micellar solubilization. The solubilization rate (di/dt) of the solutions seems to be in this order 0.1M> 0.2M> 0.3M> 0.4M NaCl. The final solubilization of the solutions is also in the same order. The size of the pure SDS micelles in solutions containing NaCl has been shown to increase with the NaCl concentration (Table II). Our instrument is not sensitive enough to distinguish the size between these small micelles at different NaCl concentrations. In the solubilization of oleic acid in 0.5% SDS solutions, the maximum seems to occur when the NaCl concentration is around 0.1 M. 

Carrasco, A. and Siebert, K. J. (1999). Human visual perception of haze and relationships with instrumental measurements of turbidity. Thresholds, magnitude estimation and sensory descriptive analysis of haze in model systems. Food Qual. Pref. 10, 421 436. 

Gales, P. W. (2000). A comparison of visual turbidity with turbidity measured by commercially available instruments. J. Am. Soc. Brew. Chem. 58,101-107. 

In the turbidostat, P and F are kept equal but the dilution rate D is automatically adjusted to a preset cell concentration in the product by continuously measuring its turbidity. Compared to chemostat, turbidostat operation can be more stable in the region near the washout point, but requires more expensive instruments and automatic control systems. 

Lex, D Turbidity Measurement, iu Process/lndustrial Instruments Controls Handbook, D.M. Considine, Editor, 4th Edition, McGraw-Hill, New York, NY,... 

The Parr turbidimeter is an extinction type instrument, which consists of a cylinder to contain the turbid suspension, a lamp filament of fixed intensity at the base, and an adjustable plunger through which visual observation is made. Measurement is made of the depth of turbid medium necessary to extinguish the image of the lamp filament Standard suspensions are used to prepare a calibration curve, which is a plot of depdi vj. concentration. 

For membrane proteins in membrane fragments, the intrinsic turbidity offers special problems, which should be addressed by instrumental modifications. A useful discussion of the problems involved can be found in Swords and Wallace (1993). 

These measure turbidity, usually by sensing light scattered at 90° to the direction of the incident light beam. This type of turbidimeter is frequently termed a nephelo-meter or nephelometric turbidimeter. A typical arrangement is shown in Fig. 6.46. The nephelometer is commonly used for detecting solid particles present in water (e.g. waste water) or in air (e.g. smoke). The instrument requires periodic cleaning due to fouling of the optical system. 

The methods that do not contain steps to ensure the establishment of equilibrium can be considered nonequilibrium methods. In the past few years, several methods commonly used for solubility measurements in the early discovery setting have been reported (Curatolo, 1996 Lipinski et al., 1997 Pan et al., 2001). These methods typically begin with dimethylsulfoxide (DMSO) solutions or with amorphous material. Turbidity and ultraviolet detection are commonly used because they easily can be designed into high-throughput instrumentation. 

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