CH4 and CO adsorption isotherms on microporous ice surfaces have been performed simultaneously by pressure measurements and infrared spectrometry in the 50-80 K temperature range in order to compare the two techniques: volumetric isotherms allow evaluation of the surface area of the ice and the net heat of adsorption by the BET model, while infrared spectrometry gives complementary information on the nature of the chemical or physical bonding interaction. Our results show that the two methods are well correlated and that their comparison provides valuable information on the different adsorption sites.