PPM Meter
The concentration of a colloidal metal or colloidal mineral in a liquid is indicated by ppm, which is equal to parts per million, which in turn is equal to the number of milligrams per liter (mg / l). The only good method to measure the concentration is through ICP (Inductive Coupled Plasma). You will find a good explanation of this measuring principle in the Report from Hogeschool Zuyd on colloidal gold.