Total reflection X-ray fluorescence spectrometry (TXRF) is a trace element sensitive technique down to the low ng/g level, mainly in the context of liquid samples. The standard method for quantification is to add an internal standard element (not present in the sample of interest, also avoiding potential line overlaps) to the sample with known concentration. The manufacturers of commercially available TXRF spectrometers will usually give sensitivities for the elements starting from sodium upwards (in respect to the periodic table of elements) as fixed constants. As consequence, predefined relative sensitivities, in respect to the selected internal standard element, are used in the quantification procedure. For one part of the so-called validation, suited certified reference materials (CRM) are used in order to compare the obtained results with the certified values. In the ideal case, for all found and quantified elements for such a CRM, the uncertainty ranges, accompanying the respective results, will embed the certified values. Many instances the user will make the observation that this will not hold true - certain elements’ results will deviate from this expectation, when using the sometimes only partially covered total uncertainty budget. A comprehensive study of the various contributions to the element specific total uncertainty budget for the named spectrometer (Atomika 8030C) will be presented and main contributors to it can be identified [1], [2], [3], [4]. [1] Practical guidelines for best practice on Total Reflection X-ray Fluorescence spectroscopy: Analysis of aqueous solutions, S Riaño, M Regadío, K Binnemans, T Vander Hoogerstraete, Spectrochimica Acta B 124, 2016, 109-115. [2] Measurement uncertainty in Total Reflection X-ray Fluorescence, G.H. Floor, I. Queralt, M. Hidalgo, E. Marguí, Spectrochimica Acta B 111, 2015, 30-37. [3] Uncertainty in the multi-elemental quantification by total-reflection X-ray fluorescence: theoretical and empirical approximation, R. Fernández-Ruiz, Anal. Chem. 80, 2008, 8372-8381. [4] Model estimated uncertainties in the calibration of a total reflection x-ray fluorescence spectrometer using single-element standards, O.K. Owoade, F.S. Olise, H.B. Olaniyi, D. Wegrzynek, X-Ray Spectrometry 35, 2006, 249-252.