Procedure for separating Fe from geological matrices to carry out isotopic analyses

We propose a simple procedure for separating and purifying Fe (and other metals) from geological matrices without the use of ionic exchange chromatography. This technique, in fact, may yield isotopic fractionation of the sample (Johnson and Beard, 1999; Schoenberg and von Blanckenburg, 2005). The sample is dissolved with HNO3 1.5 N to obtain a solution of pH between 2.5 and 3. Then, let H2S bubble through the solution for about 1 h, thus metal sulfides can precipitate completely under stationary conditions. After the solution is filtered and sul- fides are rinsed, they are dissolved with HCl 6 N. The different metals can be precipitated selectively by adding NH4OH and adjusting properly the pH. Lastly, the precipitates are filtered, rinsed and treated for carrying out TIMS analysis. To test effectiveness of the described procedure, the J–M iron standard was repeatedly analyzed. The isotopic results are shown in Table 1. It is evident that the analytical data obtained are of good quality, being particularly comparable with those carried out by Johnson and Beard (1999).