Correlation of compositional change with visualization enhancement results and morphology evolution of blood based on thermal performance analysis

The morphology evolution and compositional change of blood during heating are crucial for understanding the results of visualization enhancement when using chemical reagents. Given the complexity of blood composition, human and two other mammalian blood samples were initially centrifuged and prepared as dried whole blood, dried erythrocytes, and dried plasma for further TG-IR analysis. The results indicated that the decomposition process of blood could be divided into four distinct stages: 35-190 °C, 190-430 °C, 430-610 °C, and 610-800 °C. In the second stage, lipids and proteins underwent thermal decomposition, resulting in an approximately 50 % mass loss of blood with the release of NH₃ and CO₂, and obvious bulges presented with a black metallic appearance due to the rapid release of gases. The bloodstains could be visualized by the luminol test after heating at 310 °C for 5 min. Also, a positive reaction could be obtained by using tetramethylbenzidine (TMB) after heating at 400 °C for 5 min. In the third stage, the mass loss was further reduced by approximately 40 %. The streaks or block-like fractures appeared on the surface, with the metallic luster largely disappearing. Negative visualization results were obtained from bloodstains after heating at 480 °C for 5 min, suggesting that the hemoglobin was completely decomposed. The thermal decomposition process was gradually decreased when heating above 610 °C and completed around 880 °C, with minimal fibrous residues left. The compositional changes of blood during heating were correlated with morphology evolution and visualization enhancement, providing the evidence for blood detection in fire scenes.