5.15 : Gravimetry: Overview

Gravimetric analysis is a quantitative method where the analyte is isolated and weighed directly or after conversion into a substance of known composition. Gravimetric analysis can be classified as precipitation, electrogravimetry, volatilization, and particulate gravimetry, based on the method used to isolate the analyte.

In precipitation gravimetry, the analyte is converted into a precipitate and weighed. For example, the silver content in a sample can be estimated by precipitating and weighing silver chloride. In electrogravimetry, the analyte undergoes a redox reaction in an electrolytic cell, following which a solid film of the analyte is deposited over an electrode. Cu²⁺ and Pb²⁺ are ions that can be estimated by electrogravimetry. Volatilization gravimetry can be applied to a volatile analyte or an analyte that undergoes thermal/chemical decomposition to release a volatile component. The volatile species can be trapped and the mass determined by weighing the trapped species in an adsorbent trap. Alternatively, the loss of mass from the sample can be determined.

In particulate gravimetric analysis, particulate analytes are removed by filtration or extraction, and their mass is determined. This type of method is frequently employed in air and water quality monitoring systems.