<jats:p>It is known from crystallographic investigations that there are two distinct Pt–S modifications, PtS and PtS2 [see R. Collins, R. Kaner, P. Russo, A. Wold, and D. Avignant, Inorg. Chem. 18, 727 (1979); A. Finley, D. Schleich, J. Ackerman, S. Soled, and A. Wold, Mater. Res. Bull. 9, 1655 (1974); S. Soled, A. Wold, and O. Gorochov, ibid. 11, 927 (1976); L. Thomasson, Z. Phys. Chem. Bd. 2, 349; and L. Thomasson, ibid. 4, 277]. They are not commercially available in high grade purity. In the present study the production of pure PtS reference materials and its characterization by x-ray photoelectron spectroscopy is presented. The PtS2 investigation is shown in a second submission. The PtS samples were produced by annealing stoichiometric mixtures of elemental platinum (DEGUSSA, grade 99.9%) and sulfur (Riedle de Haen, grade 99.5%). Both powders were blended homogeneously and pressed into pellets. The pellets were annealed for 3 weeks in an evacuated quartz tube (800 °C, 10-4 Pa) and cooled in defined steps to room temperature over 8 days. The materials were investigated by x-ray diffraction. The diffraction spectrum of PtS agrees with JCPDS 18-972. This demonstrates the crystalline purity of the reference material. The samples were also characterized by transmission electron microscopy (TEM). The PtS sample consists of isometric particles with sizes between 1 and 3 μm. Selected area diffraction (SAD) and energy dispersive x-ray spectroscopy (EDXS) give no indication of impurities in the samples.</jats:p>