Collection requirements for trace-element analyses of extraterrestrial samples

Trace-element abundances have proven important in understanding the evolution of and interrelationships between different meteorites. Preliminary investigations of the trace-element contents of interplanetary dust particles indicate that trace-element abundances will prove equally important in distinguishing between micrometeorites of different types, comparing the interplanetary dust to the meteorites, and assessing the degree of thermal alteration experienced either on the parent body or during the collection process. Sample collection, delivery, and curation must be accomplished in a manner to avoid contamination with even trace amounts of the elements to be analyzed. The present SXRF sensitivity for micrometeorite analysis is of order 1 femtogram, but anticipated improvements in sensitivity will require sample contamination substantially below this level. Sample collection and handling equipment should be constructed from materials selected for ultrahigh purity, and serious consideration should be given in selecting the particular set of elements from which the collection apparatus is composed so as not to compromise useful information.