Improvements in RIMS isotope precision: applications to in situ atom-limited isotopic analysis

Resonance ionization mass spectrometry offers high sensitivity and elemental selectivity in microanalysis, but the isotopic precision attainable by this technique has been limited. Here we report instrumental modifications to improve the precision of RIMS isotope ratio measurements. Special attention must be paid to eliminating pulse-to-pulse variations in the time-of-flight mass spectrometer through which the photoions travel, and resonant excitation schemes must be chosen such that the resonance transitions can be substantially power-broadened to cover the isotope shifts. We report resonance ionization measurements of chromium isotope ratios with statistics-limited precision better than 1%.