A rapid method for separating magnesium, iron and calcium from low-Mg rocks for precise measurement via MC-ICP-MS

Abstract

Magnesium (Mg), iron (Fe) and calcium (Ca)—key rock-forming elements—play critical roles in numerous geological processes, making them invaluable tracers in geochemical studies. However, conventional methods for their separation often involve a series of individual purification protocols and repeated column procedures. This study introduces a rapid chemical separation scheme for Fe, Mg and Ca, suitable for diverse rock types, especially for high-Ca and low-Mg samples. This protocol begins with precipitation to remove alkali metals (K and Na), followed by sequential separation of Fe, Mg, and Ca under varying acidic conditions using a single elution protocol with 1.5 mL of AGMP-50 resin. For samples with the Ca/Sr ratio less than 100, additionally a TODGA resin column is incorporated to further separate Ca from Sr. The purified Fe, Mg and Ca fractions exhibited high purity and low procedural blanks, enabling precise isotopic analysis by multi-collector inductively coupled plasma mass-spectrometry (MC-ICP-MS) using a sample-standard bracketing (SSB) method. The method's validity was confirmed through analysis of ten international geological reference materials, with results accurately reproducing published reference values. Therefore, the protocol's efficiency, reproducibility, and adaptability demonstrate its suitability for high-precision isotopic studies for a wide range of geological samples.