Absorbance?

[Andiio]

How is absorbance defined? (all the finer details )

To put it in 'informal' terms, would absorbance simply be the amount of EMR (Electromagnetic radiation) absorbed or is it the intensity of EMR detected?

What units is absorbance measured in as well, if any? Is it a ratio?

Thanks!

[Zien]

If I0 = original beam (incident beam) intensity
and It = transmitted beam intensity

Therefore, the transmittance (T) = It / I0

Absorbance (A) = log 1/T

Absorbance doesn't have any units because they cancel when calculating the value of T.

Hope this helps. :p

[Andiio]

Weird, I read somewhere (probably a simplified version without logs and such) that absorbance = initial radiation intensity - final radiation intensity
But I also read somewhere that Abs = -log(T)

What do you mean by log 1/T? O_O that'd just = 0 wouldn't it?

Thanks!

[Aurelian]

But I also read somewhere that Abs = -log(T)

What do you mean by log 1/T? O_O that'd just = 0 wouldn't it?

log1/T = logT^-1=-logT

Same thing =)

[pi]

What do you mean by log 1/T? O_O that'd just = 0 wouldn't it?

EDIT: beaten

[Andiio]

Woops I read that as (log 1)/T haha, my bad.

[Andiio]

Just a Q about UV-Vis - is one lamp used or are two lamps used as a light/radiation source in a simple UV-Vis analysis? I thought you could just utilise a source of white light? (not talking about double beam spec)

[Mao]

, where T0 is the amount of light at the source.

Thus absorbance is the log of the ratio of transmittance. It is unitless, and it also has an arbitrary zero due to the log scale. At least two absorbances must be measured to use absorbance for any calculations (generally, this is the sample + blank), this is because of the arbitrary zero.