A comparison of pretreatment methods for the analysis of phosphate oxygen isotope ratios in bioapatite

Abstract

RATIONALE:The integrity of the biological phosphate oxygen isotope (d 18 O p ) signal is thought to be contingent upon the complete removal of competing sources of oxygen such as associated organic matter. A range of pretreatment methods to purify phosphate material from competing sources of oxygen has been reported, with contradictory evidence on the usefulness and efficiency of one or another. Yet, a systematic comparison of these techniques for bioapatite phosphate has not been conducted. METHODS: Chemical and thermal pretreatment techniques were tested for their effectiveness at removing organic matter and the likelihood that they modify original d 18 O values. The test was performed in inorganic (synthetic apatite and a phosphorite rock) and organic (bone and tooth tissues) phosphate materials for which we had an expectation of the actual original d 18 O p value. Analysis of nitrogen content (wt.%), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were employed. RESULTS: We detected variable efficiency at removing organic matter between pretreatment methods with no correlation to any specific structural change. The d 18 O p results showed considerable variation between samples pretreated with the different methods and the untreated samples, with a compositional range of up to 4.5 % in the bone samples. Variations of the d 18 O p values within error were found for tooth enamel, phosphorite rock and inorganic apatite. CONCLUSIONS: We recommend a cautious approach when interpreting and comparing d 18 O p data from bone samples treated with different pretreatment protocols. In general, the untreated samples seem to show d 18 O p values closer to the expected ones. According to our results, pretreatment is completely unnecessary in highly mineralized tissues. Copyright

Stable oxygen isotopes of dental biomineral: differentiation at the intra- and inter-tissue level of modern shark teeth

“…Enameloid also contains only about 1 -3 wt% of collagen, as opposed to up to 20 wt% of collagen in dentine. Organic material is characterized by 18 O-depleted values compared with the bioapatite biomineral (Enax et al 2012;Grimes & Pellegrini 2013); therefore, in the case of an insufficient cleaning, any oxygen coming from residual organic matter would produce proportionally lower d 18 O values in the dentine, and this is supported by our results. It is important to take in consideration ontogenetic aspects and time frame of shark tooth development, which may contribute to the so-called "vital effects" on the isotopic compositions of dental biomineral (Risnes 1990;Weiner & Dove 2004;Gillis & Donoghue 2007).…”

“…The carbonate fraction can be subjected to dissolution during the pre-treatment, as H 2 O 2 solution acts as acid, and therefore the total original d 18 O of the dentine can proportionally be more shifted. Grimes & Pellegrini (2013) report that concentrated H 2 O 2 pre-treatment can have 1.5‰ till 4.5‰ effect on the d 18 O of modern teeth. As a result, lower and significantly more variable d 18 O of the dentine in our case may be caused by the potential loss of carbonate fraction during the cleaning process.…”

“…tissue-specific crystallinity, chemical composition and unequal amount of integrated organic compounds (see Wiedemann-Bidlack et al 2008;Enax et al 2012). Differences in these parameters may be responsible for tissue-specific behaviour of the biomineral, during sample preparation when exposed to certain chemical agents (Grimes & Pellegrini 2013), and during data acquisition. X-ray diffractometry (Enax et al 2012) indicates extremely high crystallinity in shark enameloid, and the nanocrystalline structure of dentine biomineral, which also has higher carbonate content (see Daclusi & Kerebel 1980;Kesmez et al 2004).…”

Multi-factorialin vivostable isotope fractionation: causes, correlations, consequences and applications

“…So, plants can have different phosphate pools, in which individual approaches to oxygen isotopic equilibration with water are observed [80]. Even the pre-treatment of the samples is of importance [81].…”

Finding Vikings with Isotope Analysis: The View from Wet and Windy Islands

“…Bone and enamel samples were taken as powder using a handheld dental drill and burr and processed to produce silver phosphate (Ag 3 PO 4 ) using a modification of Stephan (2000) as described in Grimes and Pellegrini (2013). Samples weighing approximately 10-20 mg were pretreated in 2.3% NaOCl followed by 0.125 M NaOH for 24 hours.…”