重量測定: 概要

Gravimetric analysis is classified into four types based on analyte isolation method: precipitation, electrogravimetry, volatilization, and particulate gravimetry. In precipitation gravimetry, the analyte converts to a precipitate and is weighed. Electrogravimetry deposits ions on an electrode through redox reaction. Volatilization gravimetry traps volatile species released by decomposition. Particulate gravimetry removes suspended solids by filtration or extraction for weighing.

Precipitation gravimetry converts the analyte into a precipitate of known composition, then weighs it to determine the original analyte amount. For example, silver content is determined by converting it to silver chloride, which is then isolated and weighed. The mass of the precipitate directly relates to the analyte concentration through stoichiometric calculations.

Electrogravimetry isolates ions by depositing them as a solid film on an electrode through a redox reaction in an electrolytic cell. Ions such as Cu2+ and Pb2+ can be estimated using this method. The mass of the deposited solid film is then measured to determine the analyte concentration.

Volatilization gravimetry applies to analytes that undergo thermal or chemical decomposition to release volatile components. The volatile species is trapped in an adsorbent trap, and its mass is determined by weighing the trap. Alternatively, the loss of mass from the original sample can be measured directly to quantify the volatile analyte.

Particulate gravimetry removes suspended solids from the analyte matrix by filtration or extraction, then weighs them to determine concentration. This method is frequently employed in air and water quality monitoring systems to quantify particulate matter and contaminants in environmental samples.

Analyte conversion is essential because gravimetry requires isolating and weighing the analyte either directly or after converting it into a substance of known composition. This conversion ensures the measured mass can be accurately related back to the original analyte amount through stoichiometric relationships, enabling precise quantitative determination.

Precipitating agents convert dissolved analytes into solid precipitates that can be isolated and weighed. The choice of precipitating agent determines the composition and properties of the resulting precipitate. Using appropriate gravimetry inorganic and organic precipitating agents ensures accurate analyte isolation and reliable mass measurements.