Ultra-sensitive isotopic analysis by resonance ionization mass spectrometry

A high-powered pulsed dye laser has been interfaced to a commercial ion microprobe mass analyzer. This combination should provide ultra-high sensitivity for isotope ratio measurements of selected elements in environmental samples. The technique is an outgrowth of resonance ionization mass spectrometry which has demonstrated high precision for isotope ratio determinations of uranium and plutonium using thermal filament atomization. Sputter atomization using a pulsed argon ion beam represents a significant improvement in efficiency because the temporal overlap between the atom cloud and the laser pulse can approach 100%. This, coupled with the high ionization efficiency of laser induced resonance ionization methods, promises an analytical sensitivity which is significantly better than other microprobe techniques. A description of the experimental set-up is given along with the modifications to the ion microprobe instrument which were necessary to obtain acceptable ion extraction efficiency. Also shown are results for samarium and uranium demonstrating the optical and mass spectra obtained