A time-of-flight resonance ionization mass spectrometer for elemental analysis of precious metals in minerals

Abstract

An instrument for time-of-flight resonance ionization mass spectrometry (TOF-RIMS) developed at the Advanced Mineral Technology Laboratory (Ontario, Canada) is described which has been applied to the quantitative trace analysis of metals in minerals. The instrument incorporates new pulsed ion optics which provide fast switching of polarity and potentials of acceleration and ion lens optics between the two consecutive laser ablation and laser photoionization steps. Pulsed mode operation allows the time-of-flight mass spectrometer to be operated at higher laser ablation powers with more efficient suppression of the primary ions which are a source of noise that degrades the ultimate sensitivity of detection. The performance of the TOF-RIMS apparatus was assessed by analyzing trace amounts of gold (Au) in sulphide, iron oxide, and silicate mineral samples. Quantification of the TOF-RIMS measurements was established on the basis of calibration curves obtained using reference samples covering three orders of magnitude in concentration. Reproducible minimum detection limits (2σ) of ⩽10 parts per billion with a precision of ∼±15% were obtained.