A robust phase-lock of a quantum-cascade-laser to a near-infrared frequency-comb allows absorption spectra of a CO(2) gas sample to be acquired at different pressures with extreme repeatability and accuracy by tuning the repetition-rate of the comb, thus ensuring an absolute frequency scale on the acquired spectra. The method proves useful to retrieve traceable spectroscopic parameters such as line-center frequencies, line intensity factors, pressure shift, and pressure broadening coefficients, with unprecedented quality from the metrological point of view. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3671081]