Characterization of Geological Certified Reference Materials by Inductively Coupled Plasma-Mass Spectrometry

A rapid, safe, and efficient microwave-assisted acid digestion method is reported to determine thirty-six elements in three international geological reference materials and two in-house reference materials using high resolution inductively coupled plasma mass spectrometry. This method was also employed to determine the radiogenic isotopic composition of Sr and Nd in two geological reference materials by multicollector inductively coupled plasma mass spectrometry. In order to ascertain the most suitable preparation method, four microwave-assisted digestion procedures were compared. The presence of insoluble fluorides on the recoveries of Ba, Rb, Sr and rare earth elements was resolved through sequential evaporation at 80 degrees Celsius followed by microwave digestion. Digestion methods without using HClO₄ or H₃BO₃ and using only H₃BO₃ were unsuitable due to lower recoveries and higher procedural blanks, respectively. Digestion methods that involved the use of HCl-HNO₃-HF and HCl-HNO₃-HF-HClO₄ were most suitable, resulting in better recoveries of the elements. However, the HCl-HNO₃-HF method was preferred compared to HCl-HNO₃-HF-HClO₄ because the former avoids the use of HClO₄ and thus was used in measurements of the radiogenic isotopes of Sr and Nd. The optimized method was used to verify the reference values for the isotopic compositions of Sr and Nd in geological standard reference materials.