[shahed103]

 Please I need explanation

[ARGOS++]

Dear Shahed103;

It is only important for “Robustness” AND “mechanical Spectrometers”!
Advantage:  At Lambda_max the “ Sensitivity” (ΔAbsorbance/ΔConc.) is a Maximum!

Robustness:   In this sense: The result is less influenced by not stable Wavelength AND not constant preparation of the individual Sample (pH, Solvent mixture, etc.)

You may also read about: ε (Epsilon) and its dependences (influences) on the FAQ-Page on:

"Spectroscopy FAQ”

I hope to have been of help to you.

Good Luck!
                    ARGOS⁺⁺

P.S.:  For “Diode Array Spectrometers” (DAD, PDA) only the Robustness in Sample Preparation is important anymore and for ever!!
.