Multielement Determination of Rare Earth Elements in Geochemical Samples by Liquid Chromatography/ Inductively Coupled Plasma Mass Spectrometry
Recently, inductively coupled plasma mass spectrometry (ICP-MS) has been increasingly used for trace elements in various samples because ICP-MS generally provides much better detection limits by 2 -4 orders of magnitude for most elements. 1 However, it is noted here that since matrix effects are often serious in ICP-MS, ICP-AES is still useful for the determination of major, minor and some trace elements, when the concentrations of these analyte elements are higher than 1 µg/ml in the analysis
... ml in the analysis solution. In addition, ICP-AES provides better analytical precision than does ICP-MS. Thus, it is desirable to use ICP-MS and ICP-AES, depending on the concentration levels of the analyte elements as well as analytical purposes. The concentrations and distribution patterns of rare earth elements (REEs), for example in rock samples, generally provide important information about the geochemical evolution and origins of magmatic rocks. Thus, REEs in geological or geochemical samples, such as rocks, sediments and soils, have been determined by neutron activation analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES), and thermal-ionization mass spectrometry. 1 The present authors previously reported on the determinations of REEs in rock samples 2,3 and rare earth ores 4 by con-ventional ICP-AES with pneumatic nebulization. In addition, we explored the combined LC (liquid chromatography)/ICP-AES system as the analytical method for the determination of REEs in rock samples and REE oxides, where a monochromator system for single-element detection 5,6 and a polychromator system for simultaneous multielement detection 7 were employed. In these LC/ICP-AES systems, the main purpose of using LC was to separate the coexisting diverse elements and REEs in rock and other samples so as to eliminate interelement spectral interferences. Recently, ion chromatography combined with ICP-MS was applied to the determination of REEs. 8 The present authors also reported a LC/ICP-MS system for the chromatographic determination of REEs. 9 Since ICP-MS generally provides much better detection sensitivities for REEs than does ICP-AES 10,11 , the analytical results for REEs obtained by the LC/ICP-MS system appeared to be more reliable than those by the LC/ICP-AES system. 9,12 Thus, in the present experiment the determination of REEs in geological samples has been investigated in more detail by the LC/ICP-MS system. Furthermore, ICP-AES and the LC/ICP-AES system were also used for determining the matrix elements and for investigating the separation efficiencies of the matrix elements from REEs in the sample solutions. A system of liquid chromatography combined with inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the determination of rare earth elements (REEs) in geochemical standard reference samples. In liquid chromatography, a strong ion-exchange resin was employed as a stationary phase and ammonium lactate was used as a mobile phase. Multielement detection by ICP-MS was performed in the peak hopping mode to measure the chromatograms for all REEs at the corresponding mass numbers. REEs in the standard rock sample (GSJ JB-1) and the standard sediment sample (Pond Sediment; NIES No.2) were determined by the present measurement system without any correction of the matrix effect and polyatomic ion interferences.