The concentration of a colloidal metal or colloidal mineral in a liquid is indicated by ppm which is equivalent to parts per million which in turn is equal to the number of milligrams per liter (mg / l).
The only good method for measuring the concentration is by ICP (Inductively Coupled Plasma). In the Report of the Hogeschool Zuyd on colloidal gold you will find a good explanation of this measurement principle.
ICP measurements are performed with rather expensive (tens of thousands) and specialist equipment and therefore we outsourced these measurements to certified laboratories.
Many people use a ppm meter, which one can buy tens of pounds. These meters measure conductivity. The conductivity of the liquid increases when the concentration of the particles increases.
A common mistake is not taking into account that ionic silver is much more conductive than colloidal silver because the ions of the ionic silver have a charge.
With the same concentration of ionic silver and colloidal the conductivity meter will indicate a much greater concentration in ionic silver.
This phenomenon explains why in many products, only a fraction of silver is present to what it indicates on the package.
It’s simply an error of measurement.
Another point of attention of a conductivity measurement is the temperature of the liquid. The conductivity of a liquid is in fact dependent on temperature. Therefore the temperature must always be corrected.
So one can actually conclude that it is impossible to measure the concentration of colloidal silver with a ppm meter which uses the conductivity.Unfortunately this happens a lot for where one gets a totally wrong impression of quality.