Analytical Chemistry for RoHS/WEEE Compliance Testing
The first step to producing valid analytical results for electrical and electronic equipment samples is obtaining a representative aliquot for analysis. Samples can range from relatively simple materials (graphite, gold wire, silicon, etc.) to more complex examples of multi-component assemblies such as plastics, metal circuitry and solder.
A number of homogenization techniques are employed at ALS Environmental. These include ball mills, shatter box, mortar & pestle, Wiley mill, and manual particle size reduction with snips, clippers, etc. In addition to the standard use of various techniques, cryogenic techniques can be combined to aid the milling process.
The type of material(s) dictates the homogenization most appropriate for a particular sample. For example, carbon-filled silica is readily ground to a homogenous powder in a ball mill or shatter box. On the other hand, a metallic component is not amenable to milling. A manual approach is generally required to sufficiently reduce the particle size to allow representative sub-sampling and provide adequate surface area for efficient digestion and extraction. Generally speaking, brittle materials are processed through one of the mills or mortar & pestle. In cases where a component is pliable, it might be able to be made brittle for milling by freezing in liquid nitrogen, and then carried through the process accompanied by liquid nitrogen. As mentioned, metallic components present the most difficult challenge to homogenization because of their resistance to becoming brittle.