Well, there isn't really a filter for dissolved substances, but there are other methods. To give you a really good answer, we need to know scale -- how much at once has to be processed, and what it is, so we can avoid conflicts. Also, how are you quantitating -- how do you know you have 50, and not 590 or 5, and how will you know when you have 1 ppm and not 2 or 1.61 ppm?