  Mixed solid compounds are employed in a vast array of applications so an
accurate determination of their chemical compositions is of crucial importance.
All current characterization methods require specially-treated samples so the
availability of a more practical method with similar accuracy should alleviate
the quantification process. In this work, we show how the doping concentration
$\delta$ (or isotope concentration) of a mixed solid compound in powdered form,
where both parent compounds are diamagnetic, can be obtained from the
measurement of the mass magnetization. We exploit the additive nature of the
molar magnetic susceptibility $\chi_{Mol}$ and molar mass to construct two
equations with the same two unknowns in the $\chi_{Mol}$ vs. $\delta$ space to
simultaneously solve $\chi_{Mol}$ and $\delta$ of a mixed solid. Eight examples
are provided to show the wide applicability of this method:
NH$_{4(1-\delta)}$D$_{4\delta}$Br (where D = $^2$H),
NH$_4$I$_{1-\delta}$Br$_\delta$,
(NH$_4$H$_2$)$_{1-\delta}$(ND$_4$D$_2$)$_\delta$PO$_4$,
C$_{48}$H$_{22+6\delta}$Br$_{6(1-\delta)}$O$_{32}$Zr$_6$,
[creatine]$_{1-\delta}$[$_D$-glucose]$_\delta$, [$_L$-glutamic
acid]$_{1-\delta}$[$_L$-leucine]$_\delta$, [terephthalic
acid]$_{1-\delta}$[trimesic acid]$_\delta$ and
[p-terphenyl]$_{1-\delta}$[triphenylphosphine]$_\delta$. Experimental errors of
~1.2% were obtained for $\delta$ from average sample masses of 16.6 mg in
powdered form rendering the presented approach an attractive choice for
characterizing the ratios of mixed solids.
