Concentration methods

The magnitude of a method s relative error depends on how accurately the signal is measured, how accurately the value of k in equations 3.1 or 3.2 is known, and the ease of handling the sample without loss or contamination. In general, total analysis methods produce results of high accuracy, and concentration methods range from high to low accuracy. A more detailed discussion of accuracy is presented in Chapter 4. 

Concentration methods frequently have both lower and upper limits for the amount of analyte that can be determined. The lower limit is dictated by the smallest concentration of analyte producing a useful signal and typically is in the parts per million or parts per billion concentration range. Upper concentration limits exist when the sensitivity of the analysis decreases at higher concentrations. 

Alternatively, equations 3.11 or 3.12 can be solved for the amounts of both the analyte and the interferent. To do so, however, we must obtain two independent values for Sjneas- Using a concentration method as an example, gives two equations... 

Eor a typical concentration method, however, the procedure might state... 

A certain concentration method works best when the analyte s concentration is approximately 10 ppb. 

Although the size separation/classification methods are adequate in some cases to produce a final saleable mineral product, in a vast majority of cases these produce Httle separation of valuable minerals from gangue. Minerals can be separated from one another based on both physical and chemical properties (Fig. 8). Physical properties utilized in concentration include specific gravity, magnetic susceptibility, electrical conductivity, color, surface reflectance, and radioactivity level. Among the chemical properties, those of particle surfaces have been exploited in physico-chemical concentration methods such as flotation and flocculation. The main objective of concentration is to separate the valuable minerals into a small, concentrated mass which can be treated further to produce final mineral products. In some cases, these methods also produce a saleable product, especially in the case of industrial minerals. 

Another concentration method involves passing an inert gas such as N2 or CO2 through the reaction medium (12). As the gas passes through, it becomes humidified and carries captured water with it. Most of the energy required for the gas humidification comes from the heat of reaction. An advantage is that expensive drying equipment is not needed. Also, the sulfuric acid mist formed in typical concentrators is minimized. Du Pont uses a similar process in its nitrobenzene production faciUty. 

The second example is the SE-HPLC analysis of recombinant hGH. In this example, SE-HPLC is used for both a purity and a protein concentration method for bulk and formulated finished products. This method selectively separates both low molecular weight excipient materials and high molecular weight dimer and aggregate forms of hGH from monomeric hGH, as shown... 

Solutions to complex ionic equilibrium problems may be obtained by a graphical log concentration method first used by Sillen (1959) and more recently described by Butler (1964) and Morel (1983). These types of problems are described further in Chapter 16 as they relate to natural systems. Computer-based numerical methods are also used to solve these problems (Morel, 1983). 

Rasmussen RA, Harsch DE, Sweany PH, et al. 1977. Determination of atmospheric halocarbons by a temperature-programmed gas chromatographic freezeout concentration method. J Air Pollut Control Assoc 27 579-581. 

Specific extraction methods are used to prepare the analyte for immunoassay by freeing the analyte fromboth specific and nonspecific interferences. Supercritical fluid extraction has been used to decrease the amount of solvent waste generated. Solid-phase extraction has gained popularity, and many different supports are available. One promising extraction and concentration method is immunoaffinity chromatography, which will be addressed later. 

Separation processes, as could be seen from Figure 2.1, position themselves at the back end of the sequence in operations in the mineral processing flowsheet. The front-end operations has been found virtually to terminate with the liberation or the size-reduction processes involving crushing and grinding. It is important to limit the amount of size reduction to that at which adequate liberation is accomplished. The term adequacy is related to the cost involved in comminution and to performance of the concentration methods that follows. The concentration is obtained by separation processes which rely on differences in the properties of the particles, the physical and physico-chemical characteristics of minerals. In this context, it will only be relevant to refer to Table 2.5 which presents a summary of the processes along with the properties of the minerals that are exploited. 

When ores are mineralized in such a way that discrete grains of valuable minerals are contained in a matrix of gangue minerals, physical concentration methods such as flotation, gravity separation, and magnetic separation can yield valuable mineral concentrates with recoveries in the range of 80 to 95% of the value in the ore. However, there are important ore types in which the nature of mineralization is not amenable to physical concentration, and so primary processing by chemical means is necessary. 

The original procedure from which the Formalinethyl acetate centrifugal sedimentation technique was adapted was the Formalin-ether concentration method of Ritchie. Hie Formalin-ethyl acetate procedure avoids problems with the flammability and storage of ether. This procedure can be performed on specimens which have been fixed in Formalin for a time or on specimens with Formalin added during the processing. The procedure can also be performed on material fixed in MIF. 

Cation Pre-concentration method Analytical finish Detection limit Reference... 

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