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A survey of the literature is made for the XPS analysis of food products (mainly spray-dried powders, which reveal a considerable surface enrichment in lipids) and of microorganisms and related systems (extracellular polymer substances and biofilms). This survey is used as a background for discussions and recommendations regarding methodology. Sample preparation methods reviewed are freeze drying, analysis of frozen hydrated specimens and adsorption of surface-active biocompounds on model substrates. Peak decomposition is a way to increase the wealth of information provided by the XPS spectra. It should be performed after a check that sample charge stabilization is satisfactory. Moreover, ensuring the precision needed to make comparisons within sets of samples may involve a trade-off between imposing constraints and generating information. The examination of correlations between spectral data in the light of chemical guidelines is useful to validate or improve peak decomposition and component assignment, and may also upgrade the chemical information regarding speciation. Further upgrading may be achieved by expressing marker XPS data in terms of concentrations of compounds of interest. Different methods of computation are discussed, providing a composition in terms of ingredients, classes of biochemical compounds, or various organic and inorganic compounds. As an alternative or complement to this deterministic approach, multivariate analysis of suitable spectral windows provides spectral components, which may be used for comparing samples, and which may have a direct chemical relevance or be used to identify features of interest.

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The chemistry of thorium phosphate reported in the literature has been found to be erroneous. It was reconsidered in terms of careful chemical preparations and specific analytical methods. Special attention has been paid to the atom ratio value referred to r = thorium/phosphorus, which was experimentally fixed in order to obtain the correct composition of the final compound. A new compound with the chemical formula Th4(PO4)4P2O7, derived from the crystal structure determination, has been obtained. The unit cell parameters were obtained from powder and single-crystal X-ray diffraction data. It is orthorhombic (space group Pcam, Z = 2) with the cell dimensions a = 12.8646(9) Å, b = 10.4374(8) Å, c = 7.0676(5) Å, and V = 949.00(9) Å3. The atomic positions were derived from Patterson and Fourier methods and the structure was refined to an R value of 0.039. The structure consists of layers parallel to (010) containing both PO4 and P2O7 groups. These layers alternate with planes of Th atoms. The coordination sphere of the two independent heavy atoms is formed by eight O atoms from five PO4 and one P2O7 groups. The formula of thorium phosphate Th4(PO4)4P2O7 is in good agreement with the elementary composition derived from electron microprobe analysis, which gave a ratio r = 2/3. Any other value of r (1/2 < r < 3/4) induces the formation of polyphase systems:  Th4P6O23 and ThO2 for r > 2/3; Th4P6O23 and ThP2O7 for r < 2/3. The characterization of thorium phosphate diphosphate by means of infrared spectroscopy confirmed the presence of diphosphate groups in the compound.