# 8.S: Gravimetric Methods (Summary)

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In a gravimetric analysis, a measurement of mass or a change in mass provides quantitative information about the analyte. The most common form of gravimetry uses a precipitation reaction to generate a product whose mass is proportional to the amount of analyte. In many cases the precipitate includes the analyte; however, an indirect analysis in which the analyte causes the precipitation of another compound also is possible. Precipitation gravimetric procedures must be carefully controlled to produce precipitates that are easy to filter, free from impurities, and of known stoichiometry.

In volatilization gravimetry, thermal or chemical energy decomposes the sample containing the analyte. The mass of residue remaining after decomposition, the mass of volatile products collected with a suitable trap, or a change in mass due to the loss of volatile material are all gravimetric measurements.

When the analyte is already present in a particulate form that is easy to separate from its matrix, then a particulate gravimetric analysis may be feasible. Examples include the determination of dissolved solids and the determination of fat in foods.

## 8.5.1 Key Terms

 coagulation conservation of mass coprecipitate definitive technique digestion direct analysis electrogravimetry gravimetry homogeneous precipitation ignition inclusion indirect analysis occlusion particulate gravimetry peptization precipitant precipitation gravimetry quartz crystal microbalance relative supersaturation reprecipitation supernatant surface adsorbate thermogram thermogravimetry volatilization gravimetry

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