Development of new desolvating sample introduction system for precise isotopic analysis of Fe by multiple collector-ICP-MS

A new desolvating sample introduction system has been developed for precise isotopic ratio measurements of Fe-56/Fe-54 using a multiple collector-inductively coupled plasma-mass spectrometry (MC-ICPMS). The production of (ArO+)-Ar-56 ions could be significantly reduced by a removal of water vapour rising 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 similar to 350 mm level, which was almost order of magnitude shorter than that of conventional desolvating system rising the membrane filter. The shorter membrane filter results in smaller memory effect as well as shorter washout time of the signal down to 2 similar to 3 Minutes, which was at the 1/3 similar to 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/mu g 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 Fe-56/Fe-54 isotopic ratio for an Fe isotopic standard reference material (IRMM-014 SRM) was measured. The precision in the Fe-56/Fe-54 ratio measurements achieved from 2 mu g of Fe was 0.04% (2SD, n = 60 x 5 runs), which was significantly smaller than the isotopic variation in die Fe-56/Fe-54 ratio typically found in nature.