The measurement of the hydrogen desorption properties of sodium alanate (NaAlH4) powder compacts presents a particular challenge due to various material changes. Therefore, a parallel measurement method for both spectral and gravimetrical data acquisition has been developed. The optical tracking of such chemical reactions with gaseous exhalation requires a special apparatus, since hydrogen absorption/desorption alters the granularity and volume of the sample. The technique combines a commercial Fourier transform infrared spectrometer with a self-developed heatable attenuated total reflection (ATR) cuvette that maintains the indispensable close contact between the ATR medium and sample. In particular, strongly absorbing or scattering samples can be characterized with respect to their transmission changes and their mass loss, due to the evanescent field's penetration depth of a few micrometers into the bulk of the sample. In this work, the first and second desorption step of 2 mol. % CeCl3- and TiCl3-doped NaAlH4 compacts has been investigated. It was shown that the technique is able to monitor the hydrogen content in an alanate compact by means of the purely optically measured signal. In addition, a detailed analysis of the individual phase transformations was carried out. While the first reaction from the tetragonal to the monoclinic phase (NaAlH4=>Na3AlH6) showed a conversion nearly linear in time, the following reaction from the monoclinic to the hydride phase (Na3AlH6=>NaH) showed a nonlinear desorption process. The phase changes were accompanied by discontinuous intensity changes of certain absorption bands, as well as by nonconstant changes over time. Therefore, the second-phase conversion could be divided into two regions with different desorption behaviors. The optical and gravimetric measurements were supported by x-ray diffraction measurements to verify the composition of the materials after hydrogen desorption. For the technical application of this method, e.g., for use as a level sensor, these special optical features are essential and must be taken into account.