Isotopic analysis of molybdenum by surface ionization mass spectrometry and a carbonization technique

A technique to increase and stabilize the ion production of molybdenum and some other elements has been developed in their isotopic analysis by single-filament surface ionization mass spectrometry. A mixture of the element (5--100 μg, dilute sulfuric acid solution) and five to ten as much glycerol (5 v/v % aqueous solution purified by ion exchange) was mounted on a ribbon filament and was charred in air to slightly wet tar, and then heated in the mass spectrometer ion source under a vacuum of--5x10-1 Torr to appropriate temperatures by slowly increasing the filament current. As the filament material, rhenium ribbon was suitable for Mo and Hf, and tantalum ribbon for Cr samples. The sample coated in the form of oxo-compounds was reduced possibly through intermediate or direct carbonization during mass spectrometry and the sample pretreatment outside or inside the instrument was shortened. Stable ion currents of 10-13 to 10-11 A for Mo+, Hf+, and Cr+ ions were obtained and found to be usable in routine isotopic analysis. (auth.)