Comprehensive spectroscopic and morphological analysis of the effects exerted by different acids on Pig bone: Forensic aspect

Demineralization of the chemically treated pig shoulder bone in hydrochloric, hydrofluoric, and acetic acid was monitored by ATR-FTIR, Raman, and LIBS spectroscopies and SEM-EDX technique. SEM-EDX analysis showed reduced calcium and phosphorus content after the treatment with acids and erosion of the overall morphology of the bone compared to the sample kept in water. Alterations in bone structure during the 14-day-long immersion in acid solutions indicated significant chemical changes in the obtained spectra. Fourier deconvolution applied in the amide I (1700–1600 cm⁻¹), phosphate (900–1200 cm⁻¹), and carbonate (500–650 cm⁻¹) region indicated the presence of different components in the bone sample, depending on the environment and acid concentration, providing information about the composition. Parameters such as mineral-to-matrix ratio, crystallinity index, and carbonate-to-phosphate ratio were calculated and compared using ATR-FTIR and Raman data. These parameters were also correlated with calcium ionic-to-atomic and phosphorous-to-carbon line intensities obtained from LIBS spectra. Calcium and phosphorus atomic contents obtained by SEM-EDX analysis were in agreement with LIBS data. The results suggested that an increase in acid concentration has primarily affected the phosphate band’s intensity and structure, as the phosphate content was more susceptible to demineralization. Hydrochloric acid was proven to be a more powerful demineralization agent than hydrofluoric and acetic acids. The results of this study could be further applied to the investigation of the bone remains at the crime scene, especially when their removal is attempted by immersion in acid solutions.