FTIR-Microscopic investigations of micro-phases and micro-phase-transitions in organic substances

Abstract

From visual inspection by light microscopy it is likely that structural modifications are coexisting in microdomains of e.g.a-oxofuran acetamide, salicylic acid hydrazide and benzotriazole-5-carbonic acid methyl ester. An isolation of these phases is, however, not easy and a direct analysisin situ requires a non-destructive method of molecular specific microanalysis. Using FTIR-microscopy the samples prepared as thin film by cooling from the molten stage on an Al-mirror could be characterized as heterogeneous (lateral resolution 20μm). The IR-spectra of the different microphases could be recorded for the first timein situ. Any conventional sample preparation technique (KBr-disk or dissolution) would destroy the important information about the microphase composition. A mere comparison of the micro-FTIR-spectra shows clearly the difference between the microphases. By using step scanning and image processing devices also invisible microphases can be detected (FTIR-microprobe). FTIR-microscopy can be successfully used to investigate temperatureinduced microphase transitions. Examples for D,L-norleucine, oxeladin citrate and 2-chloro-ethane-amine hydrochloride are given also.