Study on Mass Spectrometry Interference of Potassium in Determination of Rare Earth Oxide and Chloride by Inductively Coupled Plasma Mass Spectrometry

The mass spectrometry interference in determination of potassium content in rare earth oxides and chlorides by inductively coupled plasma mass spectrometry (ICP-MS) was studied. Optimizing H2 flow rate in the collision reaction cell (CRC) of single quadrupole-ICP-MS (Q-ICP-MS) could effectively eliminate the mass spectrometry interference of 38Ar1H+ on 39K+. In the experiment, it was found that residual chlorine in the instrument and chlorine in rare earth chlorides could also cause abnormalities to the results. The interference mechanism of chlorine was thoroughly studied using triple quadrupole-ICP-MS (QQQ-ICP-MS). The chloride product ions were measured in both No gas and H2 tandem modes, and the results showed that 37Cl+ was the main form under no gas condition. However, in CRC of H2, about 97% of 37Cl+ was converted to 37Cl1H+2, which was the main reason for the abnormal results. Setting Q1=39, 37Cl+ could not pass the first mass analyzer or enter the CRC. The optimal flow rate for H2 was 6 mL/min and O2 was 0.75 mL/min. The detection limit of K in different matrices was 0.03–0.20 ng/mL. Signals were suppressed because of matrix effect. When the matrix was 1 mg/mL, standard curve method was used with Sc as internal standard. The relative standard deviations (n=7) of K content in Lu2O3 and LaCl3 were both less than 5%, and the recoveries were 95.9% to 105.0%. The standard addition method was used for Y2O3 at 5 mg/mL matrix concentration, and the results of H2 and O2 mode were 0.000073% and 0.000074%, respectively.