Metrohm 765 Dosimat - Manual (Page 18)

2.2. Modes
765 Dosimat
14
The formulae for calculation of the volume to be dispensed "add V" are shown in the
following table, with
cnt content in the selected unit
M molar mass of substance to be weighed out
f factor
dens density of the solvent
s weight of substance
Unit Formula for
add V =
Amount-of-substance
concentration mol/L
mmol/L
f·s·10 3
cnt·M
f·s·10 6
cnt·M
Mass concentration g/L
mg/L
f·s·10 3
cnt
f·s·10 6
cnt
Mass fraction %
ppm
f·s(10 2 -cnt)
cnt·dens
f·s(10 6 -cnt)
cnt dens
Molality mol/kg
mmol/kg
s·10 3
cnt·M·dens
s·10 6
cnt·M·dens
Application of factor f
Factor f for ionic standards
With ionic standards, the mass fraction of a single ion A is usually specified. On the other
hand, the solution is prepared from A
n
B
m
, e.g. a standard of 10 ppm Pb 2+ prepared from
Pb(NO
3
)
2
. The factor f is calculated from the formula:
n*M(A) m*M(B)
f = ———— or f = ————
M(A
n
B
m
) M(A
n
B
m
)
M(A): molar mass of ion A
M(B): molar mass of ion B
M(A
n
B
m
): molar mass of substance A
n
B
m