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Chemistry · Glossary

What is Calibration line?

Definition 29.12 School Chemistry — Grades 1 to 12 · Chapter 29 — Colour and Absorbance

A calibration line is the graph of the absorbance of a series of standard solutions of one species, measured at the same wavelength in the same cell, against their concentration. When the Beer–Lambert law holds, it is a straight line through the origin.

Calibration line of the blue dye: five standards (points) and the line through the origin, of slope 0.164\, L/ mg. An unknown reading A = 0.590 has a concentration of 0.590 / 0.164 = 3.6\, mg/ L.
Calibration line of the blue dye: five standards (points) and the line through the origin, of slope 0.164 L/mg0.164\,\mathrm{L}/\mathrm{mg}. An unknown reading A=0.590A = 0.590 has a concentration of 0.590/0.164=3.6 mg/L0.590 / 0.164 = 3.6\,\mathrm{mg}/\mathrm{L}.

Examples

Example 29.14 (The five standards)

A stock solution of the blue dye at 100 mg/L100\,\mathrm{mg}/\mathrm{L} is diluted to give 100.0 mL100.0\,\mathrm{mL} of each standard: for 2.0 mg/L2.0\,\mathrm{mg}/\mathrm{L}, the dilution factor is 50, so 2.0 mL2.0\,\mathrm{mL} of stock are made up to 100.0 mL100.0\,\mathrm{mL}. The five standards, from 1 to 5 mg/L5\,\mathrm{mg}/\mathrm{L}, read 0.168, 0.325, 0.494, 0.652 and 0.823: within a few thousandths of 0.164×C0.164 \times C, the line of the figure.

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