To determine the concentration of a solution. Since the absorption of that solution is directly proportional to the concentration, the concentration of the solution can be determined.

It identifies substances that are in organic compounds by measuring the absorption of infrared radiation over a range of frequencies.

Frank Twyman has written:

'Prism and lens making'

'The practice of absorption spectrophotometry with Hilger instruments' -- subject(s): Absorption spectra, Spectrophotometer, Spectrophotometry, Spectrum analysis

'Wavelength tables for spectrum analysis'

NaOH is added to p-nitrophenol to change it into p-nitropenyl, which can give the maximum Absorption.

I've searched for couple of weeks but I couldn't find any thing

the only way is using atomic absorption spectroscopy