ИСТИНА

The rare-earth element (REE) group includes 17 elements (Sc, Y, La–Lu), of which 16 are found in nature. Determination of natural REE levels in soils is essential for fundamental studies (specifically, for researches into the soil formation processes) and for ecological monitoring [1, 2]. Given that soil is a complex multi-element matrix where REEs are found in trace quantities only, the interference of matrix elements is likely to distort the results obtainable by any method of chemical analysis. It is therefore critical to eliminate inter-element interferences in the most widely used methods (ICP-AES, ICP-MS). This may be achieved by improving sample preparation or by using mathematical methods in data processing techniques. Typically, various separation and concentration methods are used to separate REEs from the matrix [3]; however, this unavoidably results in overly complicated methods and much longer analysis times. The simplest mathematical technique is to use inter-element interference ratios to remove distortions [4]. This paper discusses a number of options for inter-element interference elimination in REE determination in soils, with the use of ICP-AES without separation or concentration. We have used melting with lithium metaborate for decomposition and measured interference ratios for all REE signals (except Pm), as well as Th, for approximately 120 wavelengths for the following elements: Al, Ba, Ca, Fe, K, Li (as LiBO2), Mg, Mn, Na, Si, Sr, Ti, V, Zr, Ce, Nd and Pr. We have then used all these ratios to determine REEs in standard reference material SP-2 (sod podzol). Additionally, we have analysed essexite SGD-2 to verify the results for any elements that are not attested in SP-2. Our results are satisfactorily consistent with the existing data for the majority of REEs. This opens up further possibilities for a more accurate evaluation of specific elements; specifically, an evaluation of the impact of V, Ti, Zr and Al on the cerium signal helps to avoid over-valuations discussed in the existing literature [5]. As a result, we are offering a methodology for evaluating REEs in soils with the use of ICP-AES without separation or concentration. References 1. Vodyanitskii, Y.N. and Savichev, A.T. Lanthanides in Soils: X-Ray Determination, Spread in Background and Contaminated Soils in Russia // Geochemistry - Earth's System Processes / Dr. Dionisios Panagiotaras (Ed.). Rijeka: InTech, 2012. 2. Henderson, P. General Geochemical Properties and Abundances of the Rare Earth Elements // Developments in Geochemistry. Elsevier, 1984. 3. Gorbatenko A.A., Revina E.I. A Review of Instrumental Methods for Determination of Rare Earth Elements // Inorganic Materials. 2015, Vol. 51, No. 14, pp. 1375 — 1388. 4. Jaron, I.; Kudowska, B.; Bulska, B. Determination of rare earth elements in geological samples by ICP-OES // Atomic Spectroscopy. 2000, № 21(3). pp. 105 — 110. 5. Vodyanitskii, Y.N. and Savichev, A.T. Possibilities of X-ray radiometric analysis in the determination of lanthanides in soils [In Russian] // Agrofizika. 2011, No. 3, pp. 15 — 21.