Calibration curves and concentration explained

Use axes, an intercept and a dilution factor correctly.

A line from known samples

A calibration line connects a measured signal with known concentrations. Here A = 0.020 + 0.100 c, with c in mg/L. Signal A is dimensionless here. The data cover 0 to 5 mg/L.

Two separate steps

First subtract the intercept and divide by the slope. This gives the concentration of the measured sample. If it was diluted, multiply by the dilution factor afterwards. Outside the calibration range, further evidence is required.

Worked example

A sample diluted fivefold has A = 0.370.

c = (0.370 − 0.020) / 0.100 = 3.50 mg/L.
The original solution is five times as concentrated.

Originally: 5 × 3.50 = 17.5 mg/L.

Explore the model

EXPLORE THE CALIBRATION

A = 0.02 + 0.1 c

Measured signal A: 0.37

c = 3.5 mg/L

The same data in a table

c (mg/L)	A
0	0.02
1	0.12
2	0.22
3	0.32
4	0.42
5	0.52