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A comparison of minimally-invasive sampling techniques for ZooMS analysis of bone artifacts: MALDI-TOF mass spectra

Citation

Evans, Zara; Paskulin, Lindsey; Rahemtulla, Farid; Speller, Camilla (2022), A comparison of minimally-invasive sampling techniques for ZooMS analysis of bone artifacts: MALDI-TOF mass spectra, Dryad, Dataset, https://doi.org/10.5061/dryad.zkh1893d3

Abstract

Bone and antler are important raw materials for tool manufacture in many cultures, past and present. The modification of osseous features which take place during artifact manufacture frequently makes it difficult to identify either the bone element or the host animal, which can limit our understanding of the cultural, economic, and/or symbolic factors which influence raw material acquisition and use. While biomolecular approaches can provide taxonomic identifications of bone or antler artifacts, these methods are frequently destructive, raising concerns about invasive sampling of culturally-important artifacts or belongings. Collagen peptide mass fingerprinting (Zooarchaeology by Mass Spectrometry or ZooMS) can provide robust taxonomic identifications of bone and antler artifacts. While the ZooMS method commonly involves destructive subsampling, minimally-invasive sampling techniques based on the triboelectric effect have also been proposed. In this paper, we compare three previously proposed minimally-invasive sampling methods (forced bag, eraser, and polishing film) on an assemblage of 15 bone artifacts from the pre-contact site EjTa-4, a large midden complex located on Calvert Island, British Columbia, Canada. We compare the results of the minimally-invasive methods to 10 fragmentary remains sampled using the conventional destructive ZooMS method. We assess the reliability and effectiveness of these methods by comparing MALDI-TOF spectral quality, the number of diagnostic and high molecular weight peaks as well as the taxonomic resolution reached after identification. We find that coarse fiber-optic polishing films are the most effective of the minimally-invasive techniques compared in this study, and that the spectral quality produced by this minimally-invasive method was not significantly different from the conventional destructive method. Our results suggest that this minimally-invasive sampling technique for ZooMS can be successfully applied to culturally significant artifacts, providing comparable taxonomic identifications to the conventional, destructive ZooMS method.

Methods

Fifteen bone artifacts were sampled for ZooMS using three different minimally-invasive techniques: forced bag, eraser, and coarse polishing film. Sampling was conducted following modified versions of the outlined procedures in Fiddyment et al. (2015) for the eraser method (E), in McGrath et al. (2019) for forced bag method (B), and in Kirby et al. (2020) for polishing disc method (P). Sampling and extraction blanks were included for all three methods. Additionally, 10 bone fragments from Calvert Island were analyzed using the destructive acid (0.6 M HCl) demineralisation method (Buckley et al., 2009; as modified in McGrath et al., 2019). Six bone objects were tested using two different types of ultra-fine polishing film: coarse (fiber optic polishing film disc with aluminum oxide grit size of 30µm) (P1) and fine (aluminum oxide grit size 6µm) (P2).

 Following individual sampling procedures, all samples were gelatinized in AmBic at 65℃ for one hour; 50µL of the resulting supernatant was removed, and the remaining pellet was stored in the freezer. Samples were incubated overnight (12–18 hours) at 37℃ with 0.4 µg of trypsin. The trypsin was deactivated using 1 µL of 5% TFA solution. Collagen in the samples was purified and desalted using Pierce C18S Tips. Each purified sample was spotted in triplicate, along with calibration standards, onto a 384-spot Bruker MALDI ground steel target plate using 1 µL of sample and 1 µL of α-cyano-hydroxycinnamic acid matrix. The samples were run on a Bruker ultraflex III MALDI TOF/TOF mass spectrometer with a Nd:YAG smart beam laser at the University of York in York, UK, and a SNAP averaging algorithm was used to obtain monoisotopic masses (C 4.9384, N 1.3577, O 1.4773, S 0.0417, H 7.7583). Raw spectral data has been uploaded here.

Funding

New Frontiers in Research Fund, Award: NFRFE-2018-00066

Natural Sciences and Engineering Research Council of Canada, Award: RGPIN-2019-04145