Calibration curve

A graph relating known analyte amounts to instrument responses. It is used to estimate unknown concentrations from measured responses.

Analytical standard: A material with a known composition or analyte amount used to calibrate or validate an analytical measurement. Known analyte amounts in standards anchor the curve.
Analyte: The chemical substance or component whose amount or concentration is being measured. The curve is built to quantify this target in unknown samples.
Spectrophotometry: An analytical technique that measures how much light a sample absorbs at selected wavelengths. Absorbance measurements are often converted to concentration with a calibration curve.
External calibration: A calibration approach that measures standards separately from the unknown samples. It is the usual curve-based approach when standards and samples behave comparably.
Instrument response: The measurable output produced by an instrument when it interacts with a sample. The response is plotted against known analyte amounts.
Concentration: The amount of a substance in a defined volume or mass of mixture. Calibration standards specify the analyte levels represented on the curve.
High-performance liquid chromatography: A separation technique that pumps a liquid sample through a column under high pressure. Peak response can be calibrated against known analyte amounts for quantification.
Internal standard: A known substance added in a fixed amount to samples and standards to compensate for measurement variation. Its signal can correct fluctuations that an external curve alone misses.
Linear regression: A statistical method that models a variable as a linear function of one or more predictors. It estimates the line used to convert response into concentration.
Absorbance: A measure of how much light a sample absorbs at a specified wavelength. In spectrophotometry, absorbance commonly supplies the instrument response.

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