GI-XRF is a non-destructive analytical method by which nanolayers can be characterized in terms of elemental composition, thickness and density by fitting theoretical curves to measured, angle dependent fluorescence signals. When Measuring X-Ray fluorescence of low Z elements it is important, due to low energies and intensities, to reduce absorption as much as possible. Therefore it is needed to perform analysis under vacuum using a detector equipped with an ultra-thin-window (UTW). In order to show the usability of the low Z TXRF spectrometer of Atominstitut, TU Wien for characterization of low Z nanolayers by GI-XRF, multiple samples were measured including three Ti monolayers and one stack of organic layers containing F with a nominal thickness of 2, 10, 20 and 60nm respectively. Quantification was performed by fitting theoretical curves to the measured X-Ray fluorescence signals, of elements present in layers and substrate, by variation of parameters via differential evolution algorithm with JGIXA software [1]. Measurements were performed with the low Z TXRF Spectrometer of Atominstitut, TU Wien which provides ideal conditions for detection of light elements. Excitation was provided by a 1300W Cr-tube. ML monochromator, a 20mm2 SDD detector with an UTW and a sample stage are housed within a vacuum chamber. Motorized rotation of the sample stage allows for the performance of GI-XRF measurements with this setup. It was shown that nanolayers containing Ti and F can be successfully quantified by using GI- XRF measurements of their low Z components in combination with JGIXA software, the results will be presented. [1] D. Ingerle, G. Pepponi, F. Meirer, P. Wobrauschek, C.Streli, Spectrochimica Acta Part B vol. 118, 2016, 20.