Determination of Iron Content in High Purity Rare Earth by Inductively Coupled Plasma-Tandem Mass Spectrometry

Because inductively coupled plasma mass spectrometry (ICP-MS) could not be used for determination of trace Fe in high purity rare earths, an inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) method was proposed. The mass spectral technique based on the oxygen reaction cell was used to optimize the instrument parameters, the flow rate of O-2 was adjusted to 2.0 mL/min, and the matrix injection concentration was determined to be 3.00 g/L, as well as the internal standard In was used for the calibration. Then, the isotope Fe-56(+) ion with abundance of 91.68% was selected as the analysis target. With Q(1) =56/Q(2) = 72, the collision reaction of O-2 with Fe-56(+) was carried out to generate the target product of (FeO+)-Fe-56-O-16, which performed effectively to eliminate the mass spectrum interference of polyatomic ion of (ArO+)-Ar-40-O-16, (CaO+)-Ca-40-O-16 and (ClOH+)-Cl-37-O-18. So that it could accurately determine the trace impurities of Fe content in 15 kinds of high purity rare earth oxide and 4 kinds of high purity rare earth metals of cerium, neodymium, yttrium, and praseodymium-neodymium. According to the selected analysis conditions, the linear correlation coefficient of the calibration curve was greater than 0.9999, the detection limit was 68 mu g/g, the relative standard deviations (RSD, n=11) were 2.1%-4.3%, and the recoveries were 95%-105%. This method is simple and environmentally friendly, and suitable for the rapid determination of trace of Fe in high purity rare earth metals and their oxides.