A calibration curve is a general method used in analytical chemistry to determine the concentration of a substance in an unknown sample by comparing it to a set of standard samples of known concentration. It is a plot of how the instrumental response, or analytical signal, changes with the concentration of the analyte. Calibration curves are used to understand the instrumental response to an analyte and predict the concentration in an unknown sample. The curve is created by first preparing a set of standard solutions with known concentrations of the analyte. The instrument response is measured for each, and plotted vs. concentration of the standard solution. The linear portion of this plot can then be used to predict the concentration of a sample of the analyte, by correlating its response to concentration.

Calibration curves are useful in many fields of analytical chemistry, biochemistry, and pharmaceutical chemistry. They are commonly used with spectroscopy, chromatography, and electrochemistry measurements. Calibration curves can be used to understand the concentration of an environmental pollutant in a soil sample, determine the concentration of a neurotransmitter in a sample of brain fluid, vitamin in pharmaceutical samples, or caffeine in food. Calibration curves are also used in food technology to determine various substances, such as caffeine in coffee or soft drinks.

In summary, the purpose of a calibration curve is to determine the concentration of an unknown sample by comparing it to a set of standard samples of known concentration. Calibration curves are useful in many fields of analytical chemistry, biochemistry, and pharmaceutical chemistry, and are commonly used with spectroscopy, chromatography, and electrochemistry measurements.