Evaluating Volatilization Gravimetry

Evaluating Volatilization Gravimetry

The scale of operation, accuracy, and precision of gravimetric volatilization methods are similar to that described for precipitation gravime- try. The sensitivity for a direct analysis is fixed by the analyte’s chemical form following combustion or volatilization. For an indirect analysis, however, sensi- tivity can be improved by carefully choosing the conditions for combustion or volatilization so that the change in mass is as large as possible. For example, the thermogram in Figure 8.9 shows that an indirect analysis for CaC₂O₄ H₂O based on the weight of the residue following ignition at 1000 °C will be more sensitive than if the ignition was done 300 °C. Selectivity does not present a problem for direct volatilization gravimetric methods in which the analyte is a gaseous product retained in an absorbent trap. A direct analysis based on the residue’s weight following combustion or volatilization is possible when the residue only contains the analyte of interest. As noted earlier, indirect analyses are only feasible when the residue’s change in mass results from the loss of a sin- gle volatile product containing the analyte.

Volatilization gravimetric methods are time- and labor-intensive. Equipment needs are few except when combustion gases must be trapped or for a thermogravi- metric analysis, which requires specialized equipment.