The citrate levels in the bone start to decrease after death. Therefore, it may be possible to estimate the post-mortem interval if the citrate content decreases at regular and predictable intervals. To verify this, it was used twelve fresh porcine tibiae and femora, fifteen recently buried porcine bones, two samples of human bones curated from the anatomical teaching collection from Bournemouth University, UK (never been buried) and fifteen samples of archaeological human bones from Saint Augustine the Less, Bristol, UK. The results obtained in this study align together with the data available in the literature, with higher citrate content in the fresh porcine bones and lower in the archaeological samples, however, a statistical significance was not found. Moreover, the formula used to estimate the time since death largely overestimated the known PMI. Further research should be done with a larger sample and a new formula to estimate the post-mortem interval is required.