After a rigorous cleaning process, recycled food-grade poly(ethylene terephthalate) (PET), can be mixed with virgin PET resin in different concentrations and used for packaging of soft drinks. Therefore, it is important to have an experimental method to distinguish the presence of recycled polymer in a batch and to check its "true quality." One of the issues to be verified is the presence of inorganic contaminants due to the recycling process. X-ray fluorescence technique is one alternative for this kind of analysis. The results obtained in this work show that bottle-grade PET samples (PET-btg) are made either via direct esterification or by a transesterification process. Samples that were subjected to thermo-mechanical processings (superclean processing, PET-btg blends processed in our laboratory and soft drink PET packaging) present Fe K alpha emission lines with higher intensities than those presented by virgin bottle-grade PET. After applying principal component analysis, it can be concluded that Fe is an intrinsic contaminant after the recycling process, furnishing a way to indicate class separations of PET-btg. A calibration and validation partial least squares model was constructed to predict the weight percent of post-consumption bottle-grade PET in commercial PET samples. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2993-3000, 2010