Automatic gravimetric analysis

Figure 4.46. Automatic gravimetric analysis for a single-component system (18).

Figure 4.47. Automatic gravimetric analysis of a binary mixture (18).

Fig. 6.5 Automatic system for gravimetric analysis [26]. Reproduced with permission of Zjmark Corporation.

Traditional methods of elemental analysis depend on specific chemical reactions for given elements, either in solution using titrations (known as volumetric analysis) or precipitation of solids that can be weighed (gravimetric analysis). Although such methods are still used for specific and very accurate purposes, they have been replaced in routine work by automated instrumental methods. Combustion analysis is used to determine C, H, N, and sometimes S, by complete oxidation of the compound forming C02, H20, N2 and S02. The gases are separated and determined automatically... 

The statistical uncertainty arising from the analytical measurement is derived from the automatic data collection procedure noted before. The AGAS computer performs a standard error analysis and produces both a mean and the standard error of the mean associated with that value. A computer program is used to combine the uncertainties from the primary gravimetric process with the uncertainties produced from the standard deviation of the instrument s response for each of the gas mixtures. 

The use of internal standards makes it unnecessary to analyse all of the components of a mixture when evaluating process parameters, as it is sufficient to establish relative concentrations of the components and the standard. However, the introduction of a standard into the mbcture being analysed by gravimetric techniques leads to serious difficulties in laboratory analyses, especially in the analysis of gases clearly, such a solution is inapplicable to automatic production control. The standard may be a compound inert to a given reaction and incorporated in both the raw materials and the end products. Naturally, such compounds can be found only for a limited number of processes. For example, nitrogen contained in the air used for oxidation has been used as a standard for the oxidation of butane in a fluidized bed of a catalyst [163]. 

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