Abstract:

The measured values of Mg isotope ratios using multi-collector inductively coupled plasma mass spectrometry may be effected by matrix elements to certain extent. Some geological samples such as those from the Baiyan Obo ore deposit may have exceptionally high contents of REE, Nb, Fe and Mn. An investigation of effects of matrix elements on Mg isotope ratio measurement has been carried out. The results show that the measured δ²⁶Mg deviates from true value when the matrix/Mg(mass fraction) is over 0.2. Thus it is necessary to resolve these matrix elements before determining the δ²⁶Mg value. Firstly, the protocols established for Mg purification are using AG MP-1 anion exchange resin and 2.5 mL 10 mol/L HCl+0.001% H₂O₂ reagents as loading medium and eluant, the first 2.5 mL eluant contains Mg but no Fe and Mn; and then using AG50W-X12 cation exchange resin and 2 mol/L HCl as loading medium and eluants, the eluant from 2-7 mL 2 mol/L contain Mg but no REE，Nb and other matrix elemts.

Key words: matrix effects, separation, Mg isotope, the sample with high REE-Nb-Fe-Mn;isotopes, Bayan Obo