The oxygen-containing functional groups, introduced by common purification procedures, on single-walled carbon nanotubes (SWNTs) made by both the HiPco and laser-ablation (Rice Tubes) techniques are studied by Fourier Transform Infrared (FTIR) spectroscopy from 90 to 1400 K under vacuum. The fate of the functional groups under heating and the physically trapped CO2 generated from the decomposition of these functional groups are investigated. Vacuum heating to similar to 1300 K removes most of the oxygen-containing functionalities in the purified samples. The similarities in the infrared spectra of the Rice Tubes after a 1400 K treatment with spectra for the as-received and air/HCl treated HiPco nanotubes suggests the observation of intrinsic SWNT IR bands. Vacuum heating of nitric acid treated HiPco samples leads to the formation of a new feature, tentatively assigned to cyclic anhydride groups, in the 1850 cm(-1) region. The cyclic anhydride groups decompose and ultimately disappear after thermal annealing to 600 K. Above 700 K, the quantity of CO2 trapped in HNO3 treated HiPco SWNTs decreases and trapped CO2 is completely released from the nanotubes after 1100 K even though oxygen-containing functionalities are still present on the sample. The Rice Tubes made by the laser ablation technique retain the physically trapped CO2 even after heating to 1400 K.