Measuring Colloids with a TDS Conductivity Meter

Why is the ppm value on my TDS conductivity meter incorrect?

If the measurement was made with a TDS conductivity meter, you measured only the conductivity of the water.

A TDS conductivity meter is a simple device for measuring electrical resistance. Conductivity meters can display conductivity in µS/cm and also in ppm (mg/l), which makes them particularly suitable for measuring dissolved salts in solutions.

TDS conductivity meters mainly measure ions, or charged particles. A colloid, however, is always a mixture of charged and neutral particles. Conductivity also changes with the temperature of the liquid. Genuine colloids produced without chemicals generally show only very low ppm values.

A reliable measurement of a colloidal liquid or dispersion can only be obtained from specialised institutes. One correct method for determining concentration is ICP, or inductively coupled plasma.

ICP measurements require very expensive and specialised equipment and are therefore generally carried out by certified laboratories.

The concentration of colloids or ionic solutions such as colloidal silver or gold therefore cannot be verified with a ppm meter that measures conductivity only.

Unfortunately, there is no inexpensive method for measuring ppm in colloids.