Calibration strategies for quantifying the Mn content of tooth and bone samples by LA-ICP-MS

There is a growing interest in using biomonitoring of tooth and bone specimens to assess human exposure to manganese (Mn). Information on historical exposure to Mn can be obtained through micro-spatial analysis of such specimens by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The principal aim of this study was to compare several calibration strategies for determining Mn content in tooth and bone by LA-ICP-MS including: (a) a six-point calibration curve based on synthesized hydroxyapatite (HA) materials, and single-point calibrations based on (b) NIST SRM 1400 Bone Ash, (c) NIST SRM 1486 Bone Meal, and (d) NIST SRM 612 Trace Elements in Glass. Performance was similar between different ICP-MS platforms (quadrupole ICP-MS, dynamic reaction cell ICP-MS, and sector field ICP-MS). Data based on calibration using the ⁵⁵Mn count rate were compared to that based on using the ⁵⁵Mn/⁴³Ca count rate ratio to obtain results as the Mn mass fraction. Reasonable performance was obtained by calibration using either SRM 612 or SRM 1400, in combination with the ⁵⁵Mn/⁴³Ca count rate ratio and using either the synthesized HA standards or SRM 1400 as calibrators, combined with ⁵⁵Mn count rate. By contrast, calibration based on SRM 1486 resulted in a systematic low bias. While there are several options for quantifying the Mn content of tooth and bone using LA-ICP-MS, users should be aware of the potential for strong matrix effects that may affect results. Overall, determining the ⁵⁵Mn/⁴³Ca count rate ratio, rather than the mass fraction, may represent a better approach for reporting the content of Mn in tooth and bone by LA-ICP-MS.