Differential X-Ray Diffraction by Wavelength Variation: A Preliminary Investigation

Abstract

In powder diffraction experiments involving mixtures of compounds, identification of each individual phase is complicated by the presence of other phases. The interpretation of such complex patterns is often very difficult, and much effort has gone into computational search-match algorithms which attempt to identify individual phases (Nichols, 1966; Johnson, 1977; Frevel, 1976). The success achieved by these programs and by manual search-match methods accounts for the fact that X-ray diffractionists have, in the past, not actively searched for other techniques that could be used to simplify such complex problems. In a recent work (Nichols & Johnson, 1980), a comparison was made of the search-match methodologies employed by several similar technologies (mass spectroscopy, fingerprint identification, X-ray diffraction etc.). A significant observation was made that only in the X-ray method was there so much emphasis on analysis of phases in their “as received” condition. In the other cases, emphasis was placed on the separation of phases before obtaining the spectra. A classical example is the GC-MS instrument which employs a gas chromatograph to separate phases before the mass spectrographic analysis is carried out on what are, by that time, essentially pure phases.