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How do spectrophotometers help biochemists measure substances in samples?

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Diagram showing how epinephrine binding to a beta-adrenergic receptor on a cell membrane activates a G-protein, which then stimulates adenylyl cyclase to convert ATP into cyclic AMP (cAMP), leading to physiological effects such as increased heart rate, blood vessel dilation, and glycogen breakdown. — Biochemistry In biochemistry, researchers study the chemical substances and processes that occur in living organisms and cells. In particular, various processes by which cells gain energy, such as epinephrine-stimulated cAMP synthesis, have been deduced through the study of biochemistry.

Spectrophotometers allow biochemists to measure the concentration and identity of substances by analyzing how they absorb radiant energy across the electromagnetic spectrum.12

The process relies on the Beer-Lambert law, which states that the amount of radiation absorbed by a substance is directly proportional to its concentration and the path length of the sample cell. By measuring the decrease in intensity of a light beam after it passes through a sample, biochemists can accurately calculate the concentration of an analyte.132

Key methods include:
* Quantitative Analysis: Ultraviolet-visible spectrophotometry is frequently used to measure concentration. If a substance does not absorb light strongly, biochemists may add a chemical reagent to create a complex that absorbs light effectively, a process known as spectrochemical analysis.4
* Qualitative Analysis: By scanning different wavelengths, researchers generate a spectrum. Because substances absorb radiation at specific wavelengths based on their chemical structure, these patterns help identify the components within a sample.2
* Titrations: Spectrophotometric titrations track absorption changes during a reaction to determine the end point and calculate analyte concentration.4