Microprobe two-step laser mass spectrometry as an analytical tool for meteoritic samples

Abstract

Abstract. Microprobe two-step laser mass spectrometry (/iL 2 MS) is a new mass spectrometric method in which the two essential steps of any mass spectrometric analysis, vaporization and ionization, are carried out using two independent laser sources. In the first step, the output of a pulsed infrared laser is focused on the sample to cause rapid heating in the spot area illuminated, which is typically 40 /zm by 40 /im. In the second step, the output of a pulsed ultraviolet laser causes (1+1) resonance-enhanced multiphoton ionization (REMPI) of those desorbed neutral molecules that (1) are able to absorb this UV wavelength and (2) whose ionization potential is less than the energy of two photons of this UV wavelength. The resulting ions are then mass analyzed in a reflectron time-of-flight apparatus. Under suitable conditions fragmentation can be avoided in both the vaporization and ionization steps so that μΙι 2 Μ8 can be applied to the analysis of a mixture of molecules. Applications of ^L 2 MS to meteorite samples are presented as a means of detecting trace amounts of certain organic molecules present in complex materials without prior sample preparation, extraction, purification, and separation steps. Moreover, this analysis can be carried out with micrometer spatial resolution so that in favorable cases the presence or absence of certain molecules can be correlated to mineralogical features of the sample.

Alkylation of polycyclic aromatic hydrocarbons in carbonaceous chondrites

“…A detailed description of this instrument is provided elsewhere (Clemett and Zare, 1997). Briefly, in the first step of the technique, a pulsed IR laser beam (10.6-m wavelength) is focused to a 40-m spot on the sample surface, releasing constituent sample molecules through thermal desorption.…”

Extracts of impact breccia samples from Sudbury, Gardnos, and Ries impact craters and the effects of aggregation on C60 detection

“…The L 2 MS technique is described in detail in Clemett and Zare (1997). It differs from SELDI and LDMS by temporally and spatially separating desorption and ionization and by the laser wavelengths employed.…”

Organic compound alteration during hypervelocity collection of carbonaceous materials in aerogel

“…A detailed description of the L 2 MS technique has been presented elsewhere (Kovalenko et al 1992;Clemett and Zare 1997), and is summarized here. Constituent neutral molecules of the sample are first desorbed with a pulsed infrared laser beam focused to a spot, adjustable to 10 or 40 µm in diameter for the µ-L 2 MS setup, using Er:YAG (2.94 µm) and CO 2 (10.6 µm) lasers, respectively.…”