How to measure ppm of copper
The absolute approach:

Note: colloidal copper is small flecks of copper mixed with purified water. Typically colloidal copper is sold in dilute quanitities (like 100 ppm).  

Measure and record the density of the colloidal copper solution (in grams per liter). Measure and record the weight of an empty flask. Put a sample of the colloidal copper solution in the flask. Measure and record the total weight of the sample (and flask). Subtract the weight of the flask from the total weight of the sample and record the total weight of the sample (only). Boil off the aqueous portion of the sample. Weigh and record the total weight the container of dried copper. Subtract the weight of the flask from the total weight of the container of dried copper and record the weight the dried copper. 

Use the following conversions to determine the ppm of copper: 1 ppm = 1 mg per liter; and sample weight/density = liters of sample. 

Example:


sample density = 1000g/L
(total) sample weight = 250g
(dry) copper weight = 25mg




250g/(1000g/L) = 0.25L

25mg/0.25L = 100 ppm.