Chromatography Forum

According to Beers' law, the intensity of output light should be exponential relation to concentration. But if this is the case, when we integrate to get the peak area, it is not linear with injection amount. Is there any device in dector transfer the signal of light linear to concentration so that the peak area is linear to injection amount?

I do not understand exactly , your post. Take any solution of your compound injct 5,10,15,20 micro lit. and find areas for all peaks.Areas must be in linear with the injection amounts.

According to Beers' law, the intensity of output light should be exponential relation to concentration. But if this is the case, when we integrate to get the peak area, it is not linear with injection amount. Is there any device in dector transfer the signal of light linear to concentration so that the peak area is linear to injection amount?

Just give an another try to whatever you have been doing. You will get a linear relation between area vs concentration (Beer's law).

Regards,

Amaryl.

Try again you are on right track...Good luck!

The Beer-Lambert law states that the ratio (given as %, called transmittance, T) of transmitted light (I, or light intensity hitting the sensor) to incident light (Io, or light intensity hitting the sample) relates to the concentration of the light absorbing substance in the cell via a ln function:
-lnI/Io = -lnT = A = abc
where A is the absorbance put out by a photometer (HPLC detector),
a is the absorption coefficient or molar absorptivity, b is the distance the light travels through the solution, c is the concentration of light absorbing substance in this solution. Now, the relationship of c to A is of course linear, that´s all that one has to worry about, normally.
(This relationship can also be nonlinear if, as an example, the substance associates at higher concentrations).

if you are not getting a linear response for changed concentration then 4 things might be going on:
1. your injection volume is too low. (lower physical limitation of detector)
2. your injection volume is too high. (higher physical limit of detector)
3. your compound is doing something else another then just absorbing the light. maybe it has fluorescence, phosporous capacities?
4. your mobile phase is the one "reacting"

any other ideas, any one?

The injection volume is 10uL
I used 5 different concentrations: 0.11104g/L 0.22208g/L 0.37013g/L
0.5552g/L 1.1104g/L Biphenyl in MeOH.

I changed the uv detector sensitivity( from 0.01 to 0.1) all other setting remained the same. After that a more linear result was gotten (R2=0.97) Is it only the problem of UV detector setting>>??