Multi-elemental matrix-matched calcium hydroxyapatite reference materials for laser ablation: Evaluation on teeth by laser-induced breakdown spectroscopy

Laser ablation has become the most accepted method for direct sampling of solid materials, as in elemental trace analysis by laser-induced breakdown spectroscopy. However, the scarcity of matrix-matched standards or reference materials (such as NIST reference materials for instance) is an obstacle to quantitative analysis, particularly in the area of hard biological materials analysis, such as bones and teeth. If existing, the corresponding certified standards often consist of powders, then compacted as pellets which density, cohesive strength and dopant incorporation are not always representative of the samples under investigation, thereby casting serious uncertainties on calibration protocols. Here, we report on the synthesis of hydroxyapatite reference ceramic materials that can be doped controllably with various elements of interest. The fabrication process involves spiking during synthesis, prior to a hard sintering of pelletized ceramics. As a result, these materials have good chemical homogeneity and ablation properties that mimic those of naturally calcified biological tissues.