What instrument converts electrophoretic separation into quantitative data?

• A. Densitometer
• B. Mass spectrometer
• C. UV-Vis spectrophotometer
• D. Fluorometer

Answer: (A)

Quantifying how much material is in each separated band is done through densitometry. A densitometer analyzes the gel or blot image, measuring the optical density or pixel intensity of each band and translating that brightness into numerical values that reflect relative amounts, often after background subtraction and comparison to standards. This makes it the standard tool for turning electrophoretic separation into quantitative data. A mass spectrometer identifies and quantifies molecules by mass-to-charge ratio, not by band intensity on a gel. A UV-Vis spectrophotometer measures absorbance of a solution rather than discrete gel bands, and a fluorometer relies on fluorescence signals, which require labeled samples and specific detection that isn’t the general approach for standard gel quantitation.