Serial dilution / calibration curve

What is the first step?

Label a series of tubes for each dilution (e.g. 10⁻¹, 10⁻², 10⁻³) and add a fixed volume of distilled water (e.g. 9 cm³) to each.

What is the second step?

Using a pipette, add a measured volume of the original solution (e.g. 1 cm³) to the first tube and mix thoroughly to ensure an even distribution.

What is the third step?

Then transfer the same volume (1 cm³) from this tube into the next tube and mix again. Repeat this process down the series, ensuring the solution is mixed at each stage and a fresh pipette tip is used to avoid contamination.

What is the last step?

Each step reduces the concentration by the same factor (e.g. tenfold), producing a range of known concentrations suitable for further investigation

How do you use a calibration curve to find the concentration?

Prepare a range of known concentration and absorbance using a colorimeter. Plot a graph of concentration on the x-axis against the measured value on the y-axis and draw a line of best fit to create the calibration curve. Then measure the same variable for the unknown sample, locate this value on the y-axis, and draw a line across to the curve and then down to the x-axis to find the corresponding concentration.

How do colorimeters improve conclusions?

Quantitative, no bias