Abstract: A composition for chemical mechanical polishing a surface of a substrate having a plurality of ultra high purity sol gel processed colloidal silica particles for chemical mechanical polishing having alkali metals Li, Na, K, Rb, Cs, Fr and a combination thereof, at a total alkali concentration of about 300 ppb or less, with the proviso that the concentration of Na, if present, is less than 200 ppb; and a medium for suspending the particles is provided. Also, provided are methods of chemical mechanical polishing which included a step of contacting a substrate and a composition according to the present invention. The contacting is carried out at a temperature and for a period of time sufficient to planarize the substrate.