I agree that this device wouldn't work for that assay, but the opacity of the pills isn't a factor: the optical bench is too small and the illumination will be too low to do anything worthwhile.

What about: handedness of the molecules, variations in density (the surface of pills tends to be compressed)?

You're right that chirality is important and this thing isn't able to probe that. As to what I'll broadly call "sample prep", you're right again to point out how that is a critical consideration. So you're double right. Operating in NIR does give deeper penetration, which is one of the reasons to consider NIR spectroscopy in an application; I'd guess that this thing operates somewhere in the 700–900nm range, but I admittedly don't know what kind of interrogation volume that gives for a pill.

So, I'm wrong to casually dismiss opacity of the target. That stems from a bias due to a background in instrumentation (meaning, I start my thinking there). I think I'm still right though to think that instrumentation is a bigger problem than sample prep for this device, which I didn't do a good job in stating earlier.

Fair enough. And I should have done a (much) better job at indicating why I thought this instrument would not be suitable.