We report methodological innovations and an initial application to retrieve Ca isotopic (delta Ca-44/40) compositions of (bio) apatite at high spatial resolution. We utilize laser-microsampling via laser-cut polygons followed by extraction of MU g-sized bioapatite fragments; and apply a 10(10) Omega resistor for Ca-40 and parafilm-dam loading tominimize in-run Ca isotope fractionation for TIMS analysis. We obtain identical internally-normalized TIMS Ca isotopic ratios for natural calcite, apatite and bone meal SRM1486 without chemical separation, suggesting no need of chemical purification of these materials for such analysis. Our Ca-42-Ca-48 double spike (DS) corrected delta Ca-44/40 values of standard solutions HPSnew, Fisher07 and bone meal SRM1486 are 0.70 +/- 0.18%, 1.03 +/- 0.20%, and -1.03 +/- 0.19% (2SD), relative to SRM915a, all well in line with published data. Solutions prepared from both laser-cut and non-laser cut Durango apatite have similar delta Ca-44/40 values (0.70 +/- 0.17%, 2SD), suggesting no resolvable Ca isotope fractionation effect induced from laser-cutting. A delta Ca-44/40 profile of a third molar from a modern human female, laser-sampled in the growth direction of the enamel apatite, reveals a 0.5% increase from age similar to 11 to similar to 11.5, followed by a 0.7% drop at age similar to 12 and a final return to enriched Ca-isotope compositions until age similar to 14. We surmise that the initial increase is related to her known phase-out of dairy products, whereas the drop may coincide with hormonal changes at the onset of her menstruation. The latter hints at a relationship between physiological change and d44/40Ca variation, and raises the need for proper evaluation of physiological effects on Ca isotopes before reliable environmental signals can be extracted from the large Ca-isotope variability previously observed in skeletal tissues. We also investigated the potential for Ca isotopic analysis using an IsoProbeMC-ICPMS in both solution and laser ablation (LA) modes. While the use of a collision cell almost completely removes Ar-40(+) interference on Ca-40(+), partially-resolved hydrocarbon interferences result in only similar to 30% useable peak flats, that potentially cause problems with peak jumping needed for analysis of Ca-46 and Ca-48. Furthermore, it is difficult to correct for Ti isobaric interferences so that analysis without chemical separation is challenging. In-situ Ca isotope analysis of natural calcite (SRM915b), aragonite and apatite by LA-MC-ICPMS shows substantialmatrix sensitivity, and therefore requires close matrix matching. (C) 2015 Elsevier B.V. All rights reserved.
