THE FORMATION OF TRACE ELEMENT-ENRICHED PARTICULATES DURING LASER-ABLATION OF REFRACTORY MATERIALS

Scanning electron microscopy of the laser ablation products from two r efractory materials (NIST Standard 610 Glass and mammal tooth) reveale d the presence of particulates which were significantly (five- to > 50 0-fold) enriched in certain trace elements compared to the original sa mple. Their formation depended on the elemental composition and refrac toriness of the sample: the products from NIST 610 Glass included Au, Ag, Pb, Bi, Cu and Zn particles, white a non-refractory target (a copp er coin) did not produce any enriched particulates. Based on their siz e (up to 9 mu m diameter) and within-particle dement heterogeneity, th e most likely mechanism for their formation is zone refinement (migrat ion and segregation) of trace elements within the melted portion of th e sample, followed by ejection of element-enriched molten droplets by laser shock. Transport and ionization of the particulates would accoun t for the order of magnitude spikes observed in the signals of these e lements. Using the frequency and magnitude of the spikes as an indicat ion of enriched particulate formation, analysis of 17 elements during ablation of NIST 610 Glass suggested that in general there was an inve rse exponential relationship between particulate formation and the mel ting point of the element oxide. Trace element-enriched particulates h ave several implications for laser ablation-inductively coupled plasma -mass spectroscopy analyses, including isotopic ratio determinations, analytical precision, the degree of non-representative sampling, and e lement fractionation during transport.