Turbidimetric systems

To limit further the impact of problematic algal growth on the optics, field turbidimetric systems can be equipped with a pulsed light source, antifouling chemicals or films, and/or wiper blades for convenient (sometimes automated) cleaning of optical surfaces. Alternatively, a dual-beam (twin-gap) instrument to compensate for these effects can be deployed. 

A sequential injection turbidimetric system able to cany out the determination of sulfate in natural and residual water, without previous treatment, was presented by Morais et al. [17]. The authors concluded that using SIA method, the overlapping and the dispersion of the plugs were minimized. 

Phase diagrams of a polyacrylate-phosphonate system with temperature and calcium ion concentration can be established with turbidimetric measurements [1830]. Conductometric titrations also are suitable to characterize the phase behavior of scale inhibitors [514] (Table 7-2). 

The classical microbial assay approaches to measuring antibiotic residues, diffusion, turbidimetric and acid production were described and the advantages and limitations reviewed. Other systems so discussed and reviewed were the affinity or receptor methods and the immunological approach using ELISA or EMIT assay techniques. The classical systems, in general, could measure antibiotic residues at the fractional ppm to the ppb levels. The potentials of the receptor and immunological assay system were discussed. 

An application in power production, particularly in coal-fired power plants, is the analysis of flue gas scrubbers which remove excess SO2 following coal combustion. Tests run by SAMBESRL at the EPA s Research Triangle Park facility (8,9) have demonstrated the effectiveness of IC in determining sulfite and sulfate in flue gas desulfurization systems. Table III gives results of direct IC analysis of scrubber liquors compared with turbidimetric and titration methods. 

Polyacrylonitrile was ground under a constant pressure of one atm with vinyl chloride and with butadiene to give graft and block copolymers as well as minor amounts of homopolymer in the first system (27). The products were characterized by chemical and infrared analysis, viscometric and turbidimetric measurements, and solubility. The results are reported in Table 4. 

Next, we used an in-house library design software (see details in Chapter 15) to enumerate the virtual libraries and then calculated various physical properties. Products were removed from consideration if MW is > 300, number of rotatable bonds > 3, and ClogP > 3. For solubility, two in-house model calculations were applied as filters turbidimetric >10 mg/mL and thermodynamic solubility >100 xM. The resulting cherry-picked library was then reviewed by NMR spectroscopists to remove compounds with possible artifacts, likely to be insoluble, or likely to be false positive. These included some conjugated systems and compounds with likelihood of indistinct NMR spectra. 

Like crystallization, US also successfully assists the formation of extremely finely divided and uniform particles, which can be termed sonoprecipitation. This effect, which has not yet been used in analytical chemistry and might facilitate sample preparation in nephelometric or turbidimetric methods, has been widely exploited by the pharmaceutical industry to prepare liquid dispersions of drugs for oral or subcutaneous administration where extremely small particle sizes ensure stable suspensions of the drug and faster assimilation into the body. On a laboratory scale, US-assisted precipitation of magnesium carbonate in a model system has been studied [65]. 

Zollars [52] described an on-line turbidity system for the estimation of particle size distribution, refractive index and solids concentration. In a review and simulation of turbidimetric methods of on-line analysis Brandolin and Garcia-Rubio [53] state that this method is suitable only for... 

A short report demonstrated the absence of a reliable correlation between kiUing kinetics and normal laboratory tests for pristinamycin susceptibility testing of some pneumococci (42). Eight selected multiresistant clinical isolates and two reference pristinamycin-resistant Streptococcus pneumoniae strains were studied. Disk diffusion susceptibility and MICs were determined by the agar dilution method, and all clinical isolates appeared to be susceptible to pristinamycin, whereas the two reference strains were not. In contrast, time-kill experiments identified a limited bactericidal effect of pristinamycin in three clinical and both reference strains. These three strains had been classified as pristinamycin-resistant by the Vitek-II system, which uses a kinetic turbidimetric measurement of bacterial growth. Epidemiological information is hindered by the use of highly selected strains for the study. 

Turbidimetric measurements are easily performed on photometers or spectrophotometers and require little optimization. The principal concern of turbidimetric measurements is signal-to-noise ratio. Photometric systems with electro-optical noise in the range of 0.0002 absorbance unit or less are useful for turbidity measurements. ... 

Nephelometric and turbidimetric methods (see Chapter 3) are performed on most current automated analytical systems, although most nephelometric assays are performed on dedicated instruments. RID requires no instrumentation other than pipettes, although some type of illuminated plate reader is advantageous. RIA requires radiation scintillation counters and an automated pipetting station. 

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