Thin amorphous layers of poly(ethylene terephthalate-ethylene isophthalate) (PETI) containing variable concentration of an antioxidant additive (Irgafos 168) were deposited by spin casting from solution onto silicon wafers. ToF-secondary ion mass spectrometry (SIMS) results showed that a very low bulk percentages (similar to1 wt.%) of additive led to an almost uniform covering of the polymer surface, indicating a strong surface segregation (blooming effect). Multivariate statistical methods (PCA) allowed us to quantify the additive surface concentration in the lower concentration range (less than or equal to0.3 wt.%). ToF-SIMS imaging confirmed the uniform surface covering and, for higher concentration (5.5 additive wt.%), showed the formation of additive crystals on the top of the additive covered PETI surface. (C) 2002 Elsevier Science B.V. All rights reserved.