Evidence of acid–base interactions between amines and model indoor surfaces by ATR-FTIR spectroscopy

Molecular associations of pyridine with cellulose and gypsum, surrogates for common indoor surface materials, were studied using an attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectrophotometric method. The purpose of this study was to gain insight into the molecular interactions of amines with well-characterized materials that affect their partitioning between indoor air and surfaces. The experimental results suggest the presence of at least two sorptive states for volatile and semivolatile amines, attributed to the chemisorbed species and to a more labile surface state (i.e., physisorbed pyridine). Both exhibited spectroscopic signatures corresponding to aromatic C–H stretching modes (2950–3100 cm−1) in the studied spectral region. Chemisorbed pyridine could be identified by the presence of additional IR signals in the N–H and O–H stretching region of the spectrum (2900–3600 cm−1). During desorption under a stream of N2, surface enrichment in the chemisorbed species was evidenced by a slower reduction of the absorbance of the broad band at 2900–3600 cm−1 in relation to the total pyridine absorbance change. This spectroscopic evidence for acid–base interactions between amines and surfaces is consistent with the desorption behavior observed in previous work for nicotine from model surfaces.