Gas speciation, and [sup 13]C and [sup 18]O content of gases produced by laser sampling of carbonate

To determine the concentration of gaseous carbon- and oxygen-bearing species produced by laser ablation, an Ion Trap mass spectrometer (ITD) was added to a standard Nd-YAG laser microprobe system. Ultra-pure He carrier gas, flowing through a stainless steel flanged reaction chamber, sweeps laser-generated gases from the chamber during ablation. The gas is split prior to introduction in the ITD, allowing a small percentage of the effluent to enter the ITD while the majority is passed through two liquid nitrogen cold traps for collection of CO[sub 2] for standard stable isotope ratio analysis. Gas speciation is determined from multiple mass/charge spectral scans of the gas using the ITD. When lasing is performed at 30A in cw mode, the delta C-13 of laser-generated CO[sub 2] co-varies positively as a function of the CO[sub 2]/(CO+CO[sub 2]) ratio with values increasingly by 2% from 35 to 90% CO[sub 2]. As a general rule, the delta C-13 of CO[sub 2] is closest to that of the carbonate when CO[sub 2] ratios and yields are small. The delta O-18 of CO[sub 2] remains nearly constant throughout the range of CO[sub 2] ratios or yields investigated. When lasing is performed at 35A in Q-switch mode (5kHZ), themore » delta C-13 of CO[sub 2] decreases by 4% as the CO[sub 2] ratio increases from 40 to 60%. The delta C-13 of laser-generated CO[sub 2] approaches that of the carbonate as CO[sub 2] ratio increases and yield decreases. The delta O-18 of CO[sub 2] remains nearly constant throughout the range of CO[sub 2] ratios or yields investigated despite the fact that O[sub 2] comprises 10 to 21% of the laser-generated gas.« less