Micro-Xray-fluorescence measurements have a wide array of applications in fields like biology, cultural heritage, geology, for the investigation of the three-dimensional elemental distribution of elements. Still quantitative interpretations of such measurements are difficult due to the complex nature of the problem. The energy dependent transmission properties of polycapillary optics, as well as the structure of the sample play important roles in the quantification procedure. In this talk we will present important steps towards a full quantification procedure for CMXRF setups using polycapillary optics using the example of a monochromatic CMXRF setup for the lab. The measured transmission properties of the polycapillaries are compared to Monte-Carlo calculations [1]. The software package voxTrace, a voxel-based Monte-Carlo raytracing code for the quantitative interpretation of CMXRF measurements, will be presented. voxTrace is a C ++- software package for tracing rays through a sample described by a set of voxels , with interfaces for the freely available software packages shadow3 [2] and polycap [1], for the modelling of X-ray sources and polycapillary optics. Each voxel is modelled using its spatial dimensions and material composition i.e., weight concentrations and densities. voxTrace considers X-ray fluorescence, the auger-effect, absorption, scattering, and higher order effects by tracing photons through the sample “deciding” the nature of the interaction via the comparison of random numbers with spectroscopic X-ray data, using the xraylib library [3]. Taking the weight concentration of each voxel as a variation parameter, global optimization algorithms can be used to fit the calculated signal to the measured one. This constitutes a full model of a CMXRF setup and makes quantitative interpretations possible. Furthermore, this mode of calculation makes the reconstruction of the sample for step sizes smaller than the focal volume very easy, as the overlap of two neighboring positions of the confocal volume is considered. As only very few of the photons generated by the source, reach the detector, this is a problem of high computational effort. Calculations conducted on the Vienna Scientific Cluster (VSC) are presented. [1] Tack, Pieter & Schoonjans, Tom & Bauters, Stephen & Vincze, Laszlo. (2020). An X-ray ray tracing simulation code for mono- and polycapillaries: Description, advances and application. Spectrochimica Acta Part B: Atomic Spectroscopy. 173. 105974. 10.1016/j.sab.2020.105974. [2] M. Sanchez Del Rio, N. Canestrari, F. Jiang, and F. Cerrina, “SHADOW3: A new version of the synchrotron X-ray optics modelling package,” J. Synchrotron Radiat., vol. 18, no. 5, pp. 708–716, 2011, doi: 10.1107/S0909049511026306. [3] T. Schoonjans et al., “The xraylib library for X-ray-matter interactions. Recent developments,” Spectrochim. Acta - Part B At. Spectrosc., vol. 66, no. 11–12, pp. 776–784, 2011, doi: 10.1016/j.sab.2011.09.011.