Nephelometric techniques

For the determination of PAM, UV adsorbance at 189 nm was measured for various PAM concentrations. The nephelometric technique of Attia and Rubio (8 ) as modified by Pradip (9 ) was used to check the calibration curve obtained by the UV method. 

The flow nephelometric technique is a very fast and reliable method for studying the interaction between tannins and proteins (Figure 16.7) [84]. The possibility of changing the flow and changing the gradient of the different substrates involved is very convenient and versatile and the technique can be applied to complex samples such as different phenolic extracts and beverages (red and white wines, fruit juices, beers). 

Research work performed in the end of the last century by Haslam and co-workers showed that carbohydrates inhibit the protein-tannin interactions in solution (Luck et al. 1994 Ozawa et al. 1987). More recently, similar findings have been reported by de Freitas and co-workers using nephelometric techniques (Fig. 9D.12) for different carbohydrates and protein-tannin systems (Carvalho et al. 2006a, b de Freitas et al. 2003 Mateus et al 2004a). 

Immunochemical methods using specific albumin antiserum. Radial immunodiffusion, electroimmunodiffusion and nephelometric techniques can all be used. 

A technique for the measurement of light scattered by a suspension of particles. The amount of light scattered is proportional to the number and size of the particles. Thus the light is measured at an angle to the direction of the incident light (cf. turbidi-metry, when transmitted light is measured). Nephelometric techniques are used for the measurement of lipoproteins and proteins (the latter by their reaction with a specific antibody to form immune complexes). 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

Typically, quantitative protein determination is done on the one hand by colorimetric or nephelometric methods, on the other hand for more difficult analytical problems by more sophisticated techniques such as high performance liquid chromatography (HPLC), gel-electrophoresis and immunoassay. However, these methods are tedious, time-consuming and expensive. 

A number of pharmaceutical substances are assayed either turbidimetrically or nephelometrically. The assay methods of these two techniques shall be discussed briefly below with the help of appropriate examples ... 

Similar problems occur for the nephelometric and turbidimetric methods, where the sizes of the IgG-Lp(a) complexes depend upon that of apo(a) itself (L2, W4). Furthermore, problems due to interferences from elevated plasma triglyceride are commonly encountered in the precipitation techniques (C3). As Lp(a) can be redistributed among the Lp(a) fraction and the triglyceride-rich lipoproteins, especially in patients after a fatty meal (B11), these methods are not appropriate for monitoring Lp(a) levels and distribution in plasma. 

The majority of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimctric and nephelometric detection means. 

Spectrophotometric techniques based on the dispersion of radiation, for example, the nephelometric determination of sulfate. 

A number of immunochemical techniques have been used to quantify analytes of clinical interest. They include radial diffusion (RID) and electroimmunoassays, turbidimetric and nephelometric assays, and labeled immunochemical assays. 

Most immunochemical methods are applicable to the measurement of any of the proteins in this chapter (see Chapter 9). Because of their speed and ease, nephelometric and tur-bidimetric methods are most widely used for most serum proteins. These techniques are performed either by measuring the amount of Ag-Ab complex formation (equhibrium methods) or by measuring the rate of complex formation (kinetic methods). The kinetic methods are slightly faster, with measurements completed within 20 s however, kinetic assays are somewhat less sensitive because low-affinity antibodies do not have time to react. In addition, many kinetic methods obtain the baseline reading after addition of antiserum, which can reduce the measured signal with high-affinity antibodies. A compromise is often used, with timed measurement before true equilibrium. 

Eor a dilute suspension containing roughly equal amounts of two particle sizes. Figure 20.11 shows the way turbidity changes with time at a distance, L, below the top of the liquid. Turbidity is usually expressed in terms of nephelometric turbidity units (NTu). This is in reference to a specific type of measurement technique. A nephelom-eter specifically measures the light reflected into the detector by the particles. 

The AgCl precipitate formed after the addition of silver nitrate reagent can be detected with nephelometric or turbidimetric techniques. In this way the chloride concentration can be measured in water samples using appropriate calibration curve [36-38]. To be able to measure in the low concentration range, the measurements are carried out in water-organic solvent mixtures such as water-methanol [39]. 

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