A combined chemical imaging approach using (MC) LA-ICP-MS and NIR-HSI to evaluate the diagenetic status of bone material for Sr isotope analysis

This paper presents a combination of elemental and isotopic spatial distribution imaging with near-infrared hyperspectral imaging (NIR-HSI) to evaluate the diagenetic status of skeletal remains. The aim is to assess how areas with biogenic n(⁸⁷Sr)/n(⁸⁶Sr) isotope-amount ratios may be identified in bone material, an important recorder complementary to teeth. Elemental (C, P, Ca, Sr) and isotopic (n(⁸⁷Sr)/n(⁸⁶Sr)) imaging were accomplished via laser ablation (LA) coupled in a split stream to a quadrupole inductively coupled plasma mass spectrometer (ICP-QMS) and a multicollector inductively coupled plasma mass spectrometer (MC ICP-MS) (abbreviation for the combined method LASS ICP-QMS/MC ICP-MS). Biogenic areas on the bone cross section, which remained unaltered by diagenetic processes, were localized using chemical indicators (I(C)/I(Ca) and I(C) × 10/I(P) intensity ratios) and NIR-HSI at a wavelength of 1410 nm to identify preserved collagen. The n(⁸⁷Sr)/n(⁸⁶Sr) isotope signature analyzed in these areas was in agreement with the biogenic bulk signal revealed by solubility profiling used as an independent method for validation. Elevated C intensities in the outer rim of the bone, caused by either precipitated secondary minerals or adsorbed humic materials, could be identified as indication for diagenetic alteration. These areas also show a different n(⁸⁷Sr)/n(⁸⁶Sr) isotopic composition. Therefore, the combination of NIR-HSI and LASS ICP-QMS/MC ICP-MS allows for the determination of preserved biogenic n(⁸⁷Sr)/n(⁸⁶Sr) isotope-amount ratios, if the original biogenic material has not been entirely replaced by diagenetic material. [Figure not available: see fulltext.].