So I did an experiment today using ATR-IR spectroscopy, thus I didn't know what the exact pathlength was (I should have just used traditional FT-IR!). Anyhow, I know that Beer's Law states that:(adsbygoogle = window.adsbygoogle || []).push({});

A(Absorbance)= a(wavelength) * b (pathlength) * c (concentration)

I know absorbance and wavelength, and am trying to find the concentration of my sample. However, I have no idea what the pathlength was since I used ATR. I looked up a formula online for penetration depth (which may be interchangeable with pathlength, not really sure), and it read:

dp= λ / 2(π)(n1) sqrt(sin^2θ - (n2/n1)^2)

I'm just confused as how to find the incident angle, ATR crystal refractive index and sample refractive index?

Any help would be much appreciated! thanks.

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# How to use Beer-Lampert law without knowing pathlength?

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