Infrared microspectroscopy mapping studies of packaging materials: experiment design and data profiling considerations

Over the past decade, infrared microspectroscopy mapping has been applied t o a wide variety of sample types [H.J. Humecki (Ed.), Practical Guide to In frared Microspectroscopy, Marcel Dekker, New York, 1995.], including polyme rs [J.A. Reffner, in: P.E. Russell (Ed.), Microbeam Analysis, San Francisco Press, San Francisco, 1989, p. 167.], wheat kernels [D.L. Wetzel, J.A. Ref fner, Cereal Foods World 38 (1) (1993) 9.], painted manuscripts [M.R. Derri ck, Mater. Res. Sec. Symp. Proc. 352 (1995) 97.], and carcinoma tissue sect ions [P. Lasch, D. Naumann, in: P. Carmona (Ed.), Spectroscopy of Biologica l Molecules: Modem Trends, Kluwer Academic Publishers, Netherlands, 1997, p . 441.]. However, little has been mentioned regarding proper mapping condit ions and data treatment. Proper experiment design (sample preparation, map definition) and data treatments (viewing formats, profile creation) are ess ential for success, especially if the sample contains features that are sma ller than the diffraction limit (10 mu m at 1000 cm(-1)). The data obtained from line maps is especially susceptible to misinterpretation if not handl ed properly. For example, diffraction is a well-known property that every i nfrared microspectroscopist is aware of, yet its effect on mapping experime nts, especially when it comes to creating profiles is not documented and is often neglected. This paper will discuss how mapping experiments and profi les can be successfully used to extract useful and valid data from line map s. Examples will be discussed of two challenging line map samples: finding a thin adhesive layer, and the reverse-engineering of a complex multi-layer laminate. (C) 2000 Elsevier Science B.V. All rights reserved.