Ortho-nitrophenol production can be measured with a spectrophotometer because ortho-nitrophenol has a distinct color that absorbs light at a specific wavelength, typically around 420 nm. This colorimetric property allows quantification by measuring the absorbance of the yellow color produced, which is directly proportional to the concentration of ortho-nitrophenol in the solution.

Key Characteristic for Measurement

• Color and Absorbance : Ortho-nitrophenol forms a yellow compound during production or hydrolysis reactions. At alkaline pH, it forms the ortho-nitrophenolate ion, which has an intensified yellow color with a strong absorbance peak near 420 nm. This makes it suitable for spectrophotometric analysis by measuring light absorbance at this wavelength.
• This absorbance allows construction of a standard curve relating absorbance values to ortho-nitrophenol concentration, enabling quantitative determination of its production in enzymatic or chemical reactions.

Thus, the characteristic enabling its measurement by spectrophotometry is its color due to light absorption at a characteristic wavelength.