Evaluation of the influence of the formalin fixation time on the elemental content of tissues measured with X-ray fluorescence

One of the most widely used methods for tissue preservation and fixative during transportation is the conservation in formalin during variable amounts of time. In this study, we have evaluated the influence of formalin fixation time in the elemental composition of human tissue samples using Energy Dispersive X-Ray Fluorescence (EDXRF). Ten sets of human tissue samples (from colon, ileum, stomach, and spleen) were exposed to different formalin fixation times, between 2 and 24 days, and for each tissue, the elemental content throughout time was compared to the elemental content of the snap-frozen sample of the same tissue that was not exposed to formalin. Additionally, in order to further evaluate the transference of elements, the formalin solution was also analysed using EDXRF. Our results showed a clear decrease of Cl and K in the tissues, transferred to the formalin solution. Conversely, there is an uptake of P in the tissue, likely due to the buffered formalin solution. The consistent alterations seen in the studied elements across all the ten different tissues allow us to hypothesize that in the future, there will be different thresholds for their use as diagnostic tools in unfixed (intraoperative exams) as well as formalin fixed paraffin embedded tissues.