Gravimetric analysis is an unique technique by means of which either an element or a compound is obtained in its purest form through isolation and subsequent weighing. In order to achieve this, the element or compound is first and foremost separated from a specific portion of the pharmaceutical substance being determined and consequently the weight of the constituent in the given sample is calculated on the basis of the weight of the product.
However, in actual gravimetric analysis, the final weight of the product is usually accomplished by adopting anyone of the following standard methods, namely :
(a) Solvent extraction,
(b) Ignition or volatalization, and
(c) Precipitation from solution.
Gravimetric techniques are broadly based upon the quantitative precipitation of the respective cation or anion from a given solution in two different ways :
(i) as an insoluble compound that yields a residue having a specific composition after ignition, and
(ii) as an insoluble compound having a known composition.
There are four vital steps that are essentially required for a successful gravimetric method, namely :
(a) Identify an insoluble form with a definite composition,
(b) Separate the analyte exclusively from another constituents which may cause interference,
(c) Wash the precipitate free of coprecipitants and impurities as far as possible, and
(d) Convert the precipitate ultimately to a reasonably measurable form.