Gravimetric analysis Electro

In electro-gravimetric analysis the element to be determined is deposited electroly tically upon a suitable electrode. Filtration is not required, and provided the experimental conditions are carefully controlled, the co-deposition of two metals can often be avoided. Although this procedure has to a large extent been superseded by potentiometric methods based upon the use of ion-selective electrodes (see Chapter 15), the method, when applicable has many advantages. The theory of the process is briefly discussed below in order to understand how and when it may be applied for a more detailed treatment see Refs 1-9. 

SOME TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS... 

In the common method of electro-gravimetric analysis, a potential slightly in excess of the decomposition potential of the electrolyte under investigation is applied, and the electrolysis allowed to proceed without further attention, except perhaps occasionally to increase the applied potential to keep the current at approximately the same value. This procedure, termed constant-current electrolysis, is (as explained in Section 12.4) of limited value for the separation of mixtures of metallic ions. The separation of the components of a mixture where the decomposition potentials are not widely separated may be effected by the application of controlled cathode potential electrolysis. An auxiliary standard electrode (which may be a saturated calomel electrode with the tip of the salt bridge very close to the cathode or working electrode) is inserted in the... 

N. Subramanian and P. B, Janardhanan "Controlled Potential Electro-gravimetric Analysis" J. Madras Univ, 25B, No. 3, 341-52 (1955). 

Analytical chemistry is that branch of science that deals with the determination of the composition of matter, its elements, ions, radicals and compounds, by chemical or physical methods. It is, therefore, one of the bases on which the whole structure of chemistry is erected. The methods employed are very numerous and include the following chromatography, electro-analysis, elementary analysis, gas analysis, gas chromatography, gravimetric analysis, colorimetry, mass analysis, micro-analysis, polarography, potentiometry, qualitative and quantitative analysis, spectral analysis, thermal analysis, spot analysis and many others. 

Nickel also is deterrnined by a volumetric method employing ethylenediaminetetraacetic acid as a titrant. Inductively coupled plasma (ICP) is preferred to determine very low nickel values (see Trace AND RESIDUE ANALYSIS). The classical gravimetric method employing dimethylglyoxime to precipitate nickel as a red complex is used as a precise analytical technique (122). A colorimetric method employing dimethylglyoxime also is available. The classical method of electro deposition is a commonly employed technique to separate nickel in the presence of other metals, notably copper (qv). It is also used to estabhsh caUbration criteria for the spectrophotometric methods. X-ray diffraction often is used to identify nickel in crystalline form. 

---