Analysis of Nitrocresols and Related Compounds by Gas Chromatography/Matrix-Isolation Infrared Spectrometry

Abstract

The capabilities of gas chromatography/matrix-isolation infrared (GC/MIIR) spectrometry for characterizing nitrocresols in air sample extracts were evaluated. The IR spectra of selected nitrocresols were recorded in an argon matrix, in a xenon matrix, in the vapor phase, and in dilute CCl4 solution. The MIIR spectra of the nitrocresols that do not undergo intramolecular hydrogen bonding exhibited split OH stretching bands. Several factors that might cause band splitting, including aggregation, solute–matrix interactions, and the isolation of conformers, were investigated. The presence of aggregates was indicated by a broad band assigned to intermolecular hydrogen bonding in the MIIR spectra of 3-and 4-nitrocresol isomers deposited in an argon matrix at a matrix-to-solute ratio ≤ 283:1. The split OH absorption bands persisted, however, when there was no evidence of aggregate formation. The complexity of the split OH stretching bands was also influenced by steric factors and by the choice of matrix gas. This result suggests that isolation of rotational isomers and solute-matrix interactions also contribute to the band splitting. The presence of the split OH absorption bands did not preclude the use of the GC/MIIR technique to identify several nitrocresols produced from the photooxidation of toluene and NO x.