To determine the purity of the nanotubes TGA gives a quantitative analysis of the level of concentration of up to 98% nanotubes and if necessary we can reprocess the tubes to achieve the proper purity level and metal content < .2%. by weight*
We also use SEM and TEM to view and evaluated the material.
Typically, SEM is used to evaluate the raw, as produce, nanotubes and TEM is used to evaluate the purified nanotubes.
Not every batch is tested due to cost and test equipment availability, but tests are ordered when processes are changed.

*(Care must be taken when weighting the ash/metal content of the Nanotube in the TGA, the metal catalyst Nickel tends to form NiO  in the TGA.  This can offset the actual weight of the metal through the addition of the oxygen.)