Purest Colloids (Mesosilver) uses their own labs - but I trust their results (other than the fact that Utopia-Silver 's Advanced Colloidal Silver has improved significantly since it was tested). I have also seen independent lab results for Advanced Colloidal Silver , which is very much a true Colloidal Silver (about 85% of the silver is ultra small particle colloidal silver). Most recently Advanced Colloidal Silver has had their PPM increased to 30 PPM.
Full disclosure: The owner of Utopia-Silver is a lifelong friend of mine. I worked in an office directly above his "Star Wars" production room and also got to see and listen to a great number of testimonials, including testimonials from people who had tried overly hyped ionic silver products that called their products colloidal silver Isn't it amusing to see how many ionic silver makers claim that their product is somehow uniquely superior to all others> It is to me! But not as amusing and downright irksome as the bogus claims of "atomic silver" and ultra high PPM silver makers (mainly one maker in particular).