EFFECT OF LASER PARAMETERS AND TOOTH TYPE ON THE ABLATION OF TRACE-METALS FROM MAMMALIAN TEETH

This study has shown that the analysis of trace metals in tooth materi al by laser ablation (LA) ICP-MS is wavelength-, beam energy- and matr ix-dependant. Ultraviolet (UV) light offers more promise for laser wor k with teeth, because it results in Ca-normalized signals for a number of metals which are greater than, or equal to, those obtainable with green light, and with less mass ablated and so less intra-instrument C a deposition. Two distinct types of ablation processes appear to occur with tooth material, Bulk ablation of metals, indicated by Ca-normali zed signals that are generally independant of beam energy, occurs at g reen light energies of >2-3 mJ and UV energies of >3-3.5 mJ. Below the se energy levels, selective thermal desoprtion (fractional ablation) o f metals is indicated by increasing Ca-normalized signals associated w ith declining rates of matrix removal, If fractional ablation could be achieved reproducibly, it may have potential for reducing Ca interfer ence effects during the ionization phase of LA-ICP-MS analysis of calc ified tissues, Walrus dentine and beluga cement appear to ablate in fu ndamentally different ways; these matrix effects are probably species- related, because beluga dentine and cement ablate similarly, In beluga teeth, increasing amounts of matrix are removed with increasing UV an d green beam energies up to the maximum levels of our laser, while the mass of walrus dentine removed is constant above UV energies of 3.8 m J and green energies of 7.0 mJ, This suggests the existence of a bulk ablation power density threshold in walrus dentine which, once attaine d, produces an ablating plasma that is not affected by increasing beam energy, Pulse rate is an important variable, with evidence of greatly reduced fractional ablation and more consistent Ca-normalized signals of metals at a pulse frequency of 5 Hz compared with 10 Hz.