Determination of elemental composition of apatite crystals by LA ICP MS

Complete text of publication follows. Present work describes determination of elemental composition of apatite crystals with the use of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICP MS). Apatite is the most important representative mineral of phosphates with the most common formula written as Ca5(PO4)3OH. During the measurements the assumption was made about the content of 42.3 % P2O5 and 50.3-55.9 % CaO in the analyzed crystals. Apatite is one of few minerals that are produced and used by biological systems and it is the major component of the vertebrates' skeleton (above 60%) and tooth enamel (even 90%). A relatively rare form of apatite in which most of the OH groups are absent and containing many carbonate is a large component of bone material. In this work crystalline apatite was analyzed as models before archaeological bones measurements. The work was devoted to recognize the possibility of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) as a method for direct measurement of bulk composition of apatite samples. LA ICP MS has been used widely to measure the chemical composition of small amounts of solid samples in many fields (e.g. environmental, geological, and archaeological sciences). The method does not require special sample preparation such as sample dissolution or even polishing. Therefore the method is very fast and gives large amount of information in the relatively short time. The method offers a spatial resolution from 10 to few hundred μm. Eight apatite crystals were analyzed. All crystals were divided into 3 pieces and analyzed by means of either LA ICP MS (using two different wavelengths if laser during ablation) or ICP MS after digestion. Analytical signals of LA ICP MS were for registered during one point or single line ablation mode, what delivered the information about the sample inhomogeneity. For the final analysis the amount of 11 independent repetitions of analysis were found to be required for obtaining the results comparable with ICP MS analysis. The authors kindly acknowledge the financial support from the Ministry of Science and High Education of Poland (No. N N204 241734).