Sample Contamination from Grinding and Sieving Determined by Emission Spectrometry

The trace element contaminations, introduced by grinding or sieving samples of Specpure silica and calcium carbonate in various devices in common usage, have been measured using emission spectrometry. The tungsten carbide vial introduced large amounts of Co and Ti. The alumina mortar introduced Al, Cr, Fe, Ga, and Zr. The alumina-ceramic vial introduced Al, Cu, Fe, Ga, Li, Ti, B, Ba, Co, Mn, Zn, and Zr. The boron carbide mortar (except for B), the agate mortar, and the Lucite grinding vials introduced little or no contamination, as did sifting with nylon sieves. Stainless steel or brass sieves introduced appreciable levels of Co, Cu, Fe, Mn, Ni, Pb, Sn, and Zn. The contamination Cu, Pb, and Zn from sieving with the brass was greatest in the smaller size fraction. Pregrinding an aliquot of the sample is recommended. Greater reductions in contamination from the grinding material were noted by pregrinding with soft fine CaCO3 than with SiO2. Cross contamination from previously ground samples was demonstrated to be a major source of contamination. Grinding with the hard, more abrasive SiO2 removed more of the cross contaminants than did the CaCO3.