Which solutions are used for spectrophotometric calibration methods?

• A. p-nitrophenol and potassium dichromate
• B. Bovine serum albumin and glucose
• C. Sodium chloride and water
• D. Ethanol and water

Answer: (A)

Spectrophotometric calibration relies on standard solutions with well-established absorbance properties at known wavelengths, so the instrument’s wavelength accuracy and photometric response can be verified against predictable signals. Using p-nitrophenol and potassium dichromate fits this idea well. p-nitrophenol is a stable, color-producing compound with a well-characterized absorbance in the visible region (around 405 nm under basic conditions), giving a reliable reference point for calibrating measurements in the visible spectrum. Potassium dichromate, on the other hand, has a strong, well-documented absorption in the UV region, with known molar absorptivity, making it a classic standard for checking UV performance. Together, they span key parts of the spectrum and provide reproducible, known absorbance values that help ensure both the wavelength scale and the photometric response of the instrument are accurate.

Other options aren’t typically used as universal calibration standards. Bovine serum albumin and glucose are relevant to particular biochemical assays but do not provide the simple, stable, well-defined absorbance references needed for general spectrophotometric calibration. Sodium chloride and water lack distinct, reliable absorbance features in the visible range and are not used as calibration standards. Ethanol and water may have some UV absorbance, but they do not offer the stable, well-characterized references that standards like p-nitrophenol and potassium dichromate provide.