Carbon black prepared by combustion of hexane has been studied by Fourier transform infrared (FTIR) spectroscopy, with the use of transmission, attenuated total reflectance, diffuse reflectance, and photoacoustic detection methods. When compared, the results indicate the presence of oxidative functional groups on the carbon black lattice. The results obtained by photoacoustic detection differ substantially from those obtained by other methods. The explanation offered is that the photoacoustic method produces a spectrum which is defined only by the optical characteristics of the interferometer head. A ratio of the photoacoustic spectrum (PAS) to the standard TGS detector single beam spectrum results in the observation of the spectroscopic sensitivity profile of the TGS detector. For these low acoustic modulation frequencies, carbon black is observed to display no surface functionality by FTIR/PAS detection. This distinguishes FTIR/PAS as an analytical tool for this particular chemical system. -- AATA