What is a calibration curve and why is it used?

• A. A graph used to compare sample colors.
• B. A graph relating known concentrations to instrument responses to quantify unknown samples.
• C. A plot of gene expression over time.
• D. A chart listing sample IDs.

Answer: (B)

A calibration curve is a graph that shows how the instrument’s response changes with known concentrations, and it’s used to quantify unknown samples. By measuring signals from standards with known amounts, you establish a relationship (often a straight line within the instrument’s linear range) between concentration and signal. Then you measure an unknown sample’s signal and use the curve to read off its concentration, typically through interpolation or a fitted equation. This approach accounts for how the instrument behaves under the same conditions as your samples and allows you to convert a raw signal into an actual amount.

Other options describe tasks that don’t provide this link between signal and concentration—comparing colors, plotting gene expression over time, or listing sample IDs.