Even if the accepted answer is well posed and clear, I would mention another method for dust measurements.
X-ray spectra can also help to infer the amount of dust, analyzing the absorption at low energy of the observed spectra.
Indeed, the neutral hydrogen column density $N_H$ and the extinction $A(V)$, which is caused by the dust, is found in our Galaxy to be (Guver & Ozel, 2009):
$N_H = 2.2\times 10^{21} A(V)\,$mag
From the extinction one can get the dust optical depth (see here), and from that the volumetric dust density.
A good example of how to obtain $N_H$ is given in the following plot (S. Ikeda et al. 2009, ApJ 692 608):

As it can be seen, the spectra is differently modified by different amounts of neutral hydrogen column density $N_H$. This, of course, can be related to different aboundances, to best-fit the spectra and find the metals amounts.
Also, this method is tightly related to the iron K$\alpha$ line at $6.4\,$keV, which is another measurement of the metals amount (Fabian et al. 2000):

To distinguish among different ionization states, high-resolution spectroscopy is very common.