Development of New Desolvating Sample Introduction System for Precise Isotopic Analysis of Fe by Multiple Collector-ICP-MS

Abstract

A new desolvating sample introduction system has been developed for precise isotopic ratio measurements of 56 Fe/ 54 Fe using a multiple collector-inductively coupled plasma-mass spectrometry (MC-ICPMS). The production of 56 ArO ions could be significantly reduced by a removal of water vapour using a membrane filter. Sample aerosol was directly heated up by a rod-heater through glass tubing, aiming at a higher separation efficiency of the water vapour from sample aerosol. This direct-heating technique could minimize the length of the membrane filter for desolvation down to the 300 350 mm level, which was almost order of magnitude shorter than that of conventional desolvating system using the membrane filter. The shorter membrane filter results in smaller memory effect as well as shorter washout time of the signal down to 2 3 minutes, which was at the 1/3 1/5 level compared with the conventional desolvating system. This is a very pleasing result because we can take full advantage of the rapidness of the analysis achieved by the ICP-MS technique, even with the desolvating sample-introduction system. The resulting instrumental sensitivity achieved here was identical to that obtained by the conventional solution nebulisation (2 V/µg g 1), indicative of no significant loss of analytes during the desolvating stage. In order to evaluate the analytical capability of the present sample introduction technique, the 56 Fe/ 54 Fe isotopic ratio for an Fe isotopic standard reference material (IRMM-014 SRM) was measured. The precision in the 56 Fe/ 54 Fe ratio measurements achieved from 2 µg of Fe was 0.04 (2SD, n 60 5 runs), which was significantly smaller than the isotopic variation in the 56 Fe/ 54 Fe ratio typically found in nature.

Atomic spectrometry update. Atomic mass spectrometry

“…Directly heating the sample using a rod heater in a new membrane filter desolvating sample introduction system reduced by an order of magnitude the length of membrane filter required compared with conventional membrane filter desolvation systems. 102 This resulted in fewer memory effects and a shorter washout time and improved the precision of 56 Fe : 54 Fe ratio measurement by MC-ICP-MS to 0.04%. The membrane filter removed water vapour and thereby reduced production of 40 Ar 16 O + ions.…”