Pm. Outridge et Rd. Evans, EFFECT OF LASER PARAMETERS AND TOOTH TYPE ON THE ABLATION OF TRACE-METALS FROM MAMMALIAN TEETH, Journal of analytical atomic spectrometry, 10(9), 1995, pp. 595-600
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.