CO₂‐Laser Extraction‐Static Mass Spectrometry Analysis of Ultra‐Low Concentrations of Nitrogen in Silicates

Abstract

A new installation for the analysis of picomole quantities of nitrogen has been designed and constructed. It permits the simultaneous analysis of N and rare gases extracted from silicates by heating. The extraction procedure involves the use of a CO2 laser as a heater, and the analysis is made by static mass spectrometry using a high sensitivity, high resolution mass spectrometer. Procedural blanks of 2 picomoles N2 (60 picogram N) allow us to analyse routinely N in mg‐sized samples such as mantle‐derived and meteoritic minerals, and Lunar soil grains.

Primordial heavy noble gases in the pristine Paris carbonaceous chondrite

“…A second extraction step on fragment 4 released ≤1% of the total amounts of its noble gas contents (Table , , and ), in agreement with the fact that more than 99% of noble gases are extracted by CO 2 infrared laser heating when a spherule of molten silicate is obtained (Humbert et al. ).…”

“…The formation of a spherule of molten silicate indicated that the melting temperature of the sample had been reached, and that more than 99% of the gas had been extracted (Humbert et al. ). A re‐extraction was carried out on fragment 4, with negligible amounts of gas being released, in line with a complete extraction of the gas upon initial melting.…”

“…Droplets of pure ethanol were periodically deposited onto the saw to facilitate the removal of dust. The four pieces were then dried at 90°C for 1 h, before being weighted and set into the CO 2 infrared (k = 10.6 lm) laser extraction chamber (Humbert et al 2000) under high vacuum (10 À9 mbar) at 110°C for 2 days. This preheating of the sample allowed weakly bound atmospheric gases to be degassed prior to noble gas analysis.…”

Evidence for an early nitrogen isotopic evolution in the solar nebula from volatile analyses of a CAI from the CV3 chondrite NWA 8616

“…After leaving the samples under high vacuum (P ≤ 10 -8 Torr) for one week prior to analysis, they were heated individually with a continuous mode infrared CO 2 laser (λ = 10.6 μm). While three samples (#6, 10, 11) were heated to melting in a single step, two temperature steps (~600°C and fusion) were applied to all other samples by modulating the power of the laser and monitoring the heating procedure on a TV screen using a CCD camera (Humbert et al, 2000) (Fig. 2).…”

“…Noble gas (Ne and Ar) and nitrogen abundances and isotope ratios were determined by CO 2 laser extraction-static mass spectrometry (Humbert et al, 2000;Hashizume and Marty, 2004). The twelve CAI and two matrix fragments were loaded into different pits of the laser chamber connected to the purification line of the Micromass VG5400 mass spectrometer at the CRPG noble gas analytical facility.…”