PPM Formula
Very low concentration measurement
Definition
ppm = (mass_solute / mass_solution) × 10^6
For aqueous solutions, ppm ≈ mg/L when density ≈ 1 g/mL.
Example
Given: 5.0 mg solute in 2.0 L water.
Assuming ρ ≈ 1 g/mL, 2.0 L ≈ 2000 g solution.
ppm = (5.0 mg / 2000 g) × 10^6 = (0.005 g / 2000 g) × 10^6 ≈ 2.5 ppm
Answer: ≈ 2.5 ppm
Notes
- For gases, ppm often refers to volume ratio.
- Check density if solution is not water; mg/L may not equal ppm.