6.2 Calculable Quantitation Methods
261
weighed prior to and after electrolysis, the weight difference corresponding
to the mass of analyte initially present in the sample.
(c) Volatilization of the analyte by heating of the sample. There are two different
approaches to this gravimetric mode. One is based on the difference in
sample mass before and after heating; in this way, sample moisture can be
determined by using an automatic device which acts as the sample holder
and is fitted to a commercially available balance. The other approach relies
on the selective sorption (retention) of the analyte following volatilization.
Such is the case with the gravimetric determination of carbonate by sorption of carbon dioxide released upon addition of a strong acid to the sample.
The CO2, held in a closed vessel, is retained by a trap containing sodium
hydroxide and a desiccator:
The weight difference of the trap prior to and after volatilization corresponds to the mass of CO2 released from the sample.
The so-called gravimetric factor is the materialization of the stoichiometric
relationship between the analyte and the weighed form, and is the traceability
link established by chemical standards (atomic weights). The factor can be
defined in two complementary ways, namely:
(a) the ratio of the formula weight of the analyte - depending on the way the
results are to be expressed - to the molecular weight of the species being
weighed; and
(b) a dimensionless number Fg by which the gravimetric weighing (Wg) must be
multiplied in order to obtain the analyte weight (Wa ):
Box 6.8 illustrates the gravimetric factor concept with typical examples.
__ Box 6.8
Gravimetric Factor
Let us complete the definition of gravimetric factor given in the text with selected examples.
The gravimetric factor is the result of a rule of three that establishes stoichiometric
(traceability) and experimental relations. Thus, in the determination of dissolved Ag + by
precipitation with CI (the reagent) to obtain an AgCl precipitate (which is also the weighed
form), one has:
TRACEABILITY ~ Atomic weight of Ag (1 : 1) ~ Moleculor weight of AgO
EXPERIMENTAL ~ Analyte weight (W a ) ~ Gravimetric weighing (Wg)
Atomic weight of Ag
W a =
. W. = F . W.
Molecular weight of Agel 9 9 9
261
weighed prior to and after electrolysis, the weight difference corresponding
to the mass of analyte initially present in the sample.
(c) Volatilization of the analyte by heating of the sample. There are two different
approaches to this gravimetric mode. One is based on the difference in
sample mass before and after heating; in this way, sample moisture can be
determined by using an automatic device which acts as the sample holder
and is fitted to a commercially available balance. The other approach relies
on the selective sorption (retention) of the analyte following volatilization.
Such is the case with the gravimetric determination of carbonate by sorption of carbon dioxide released upon addition of a strong acid to the sample.
The CO2, held in a closed vessel, is retained by a trap containing sodium
hydroxide and a desiccator:
The weight difference of the trap prior to and after volatilization corresponds to the mass of CO2 released from the sample.
The so-called gravimetric factor is the materialization of the stoichiometric
relationship between the analyte and the weighed form, and is the traceability
link established by chemical standards (atomic weights). The factor can be
defined in two complementary ways, namely:
(a) the ratio of the formula weight of the analyte - depending on the way the
results are to be expressed - to the molecular weight of the species being
weighed; and
(b) a dimensionless number Fg by which the gravimetric weighing (Wg) must be
multiplied in order to obtain the analyte weight (Wa ):
Box 6.8 illustrates the gravimetric factor concept with typical examples.
__ Box 6.8
Gravimetric Factor
Let us complete the definition of gravimetric factor given in the text with selected examples.
The gravimetric factor is the result of a rule of three that establishes stoichiometric
(traceability) and experimental relations. Thus, in the determination of dissolved Ag + by
precipitation with CI (the reagent) to obtain an AgCl precipitate (which is also the weighed
form), one has:
TRACEABILITY ~ Atomic weight of Ag (1 : 1) ~ Moleculor weight of AgO
EXPERIMENTAL ~ Analyte weight (W a ) ~ Gravimetric weighing (Wg)
Atomic weight of Ag
W a =
. W. = F . W.
Molecular weight of Agel 9 9 9