Determination of heavy metals in TiO2 with isotope dilution mass spectrometry

An isotope dilution mass spectrometric (IDMS) method has been developed for the determination of trace impurities (Fe, Cu, Cr, Ni, Cd, Pb, Tl, and U) in TiO₂; this is of special interest for the quality control of this pigment substance. The measurement of the isotope ratios was carried out using a compact thermal ionization quadrupole mass spectrometer by producing positive thermal ions. For the dissolution of the sample, microwave digestion with HF was applied. Different separation techniques (ion exchange chromatography, extraction, electrolytic deposition) were used for the trace/matrix separation and the element specific isolation of the different trace elements to be determined. The detection limits obtained were (in ng/g): Fe=90, Cu=11, Ni=8, Cd=7, Pb=26, Tl=0.6, U=0.2. Because IDMS usually results in accurate analytical results, this method can best be used for calibration of other analytical methods, or for the certification of corresponding standard reference materials.