Acidification does not alter the stable isotope composition of bone collagen

Abstract

In this study, we compared the elemental and isotopic composition of modern and ancient bone samples pre-treated using different demineralization agents with acidic and neutral pH. The purpose of our research was to examine if demineralization using a mineral acid such as hydrochloric acid (HCl) significantly alters the δ ¹⁵N and δ ¹³C values of bone collagen. Evidence from the elemental and amino acid composition of the samples were incorporated alongside isotopic compositions to provide a holistic view of the effect of demineralization agents on the composition of bone collagen. The stable isotope compositions of collagen extracts were also compared against equivalent whole bone samples to assess whether whole bone has a stable isotope composition that is comparable to collagen demineralized with a neutral agent. Our results demonstrate that bone demineralization using either ethylenediaminetetraacetic acid (EDTA) or HCl yields collagen extracts with stable isotope compositions that are not significantly different, indicating that mineral acid does not alter δ ¹⁵N and δ ¹³C values of bone collagen. The results comparing whole bone and extracted collagen stable isotope compositions indicate that whole bone cannot be used as an effective replacement for bone collagen due to the significantly different stable isotope compositions between these sample materials. In ecological and archaeological studies performing stable isotope analysis on bone, sample pre-treatment to isolate collagen is a necessity to obtain the most reliable and reproducible isotopic measurements.