y = mx + b → concentration from absorbance.
A calibration curve plots instrument response (absorbance, peak area, signal intensity) versus known concentrations of standards. The resulting linear equation y = mx + b allows determination of unknown concentrations by substituting the measured response. The slope m represents sensitivity — higher slopes mean the method can detect smaller concentration differences. The y-intercept b should ideally be zero but often isn't due to matrix effects or blank signal. R² should be >0.99 for a good calibration. Standards should bracket the expected concentration range. At least 5 data points are recommended for reliable regression. External calibration uses separate standards; internal standard calibration adds a known compound to correct for matrix effects and instrument variability.