AN EDXRF AND WDXRF INTERCOMPARISON CASE STUDY: MAJOR ELEMENTS CONTENT OF DOBROGEA LOESS

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1 AN EDXRF AND WDXRF INTERCOMPARISON CASE STUDY: MAJOR ELEMENTS CONTENT OF DOBROGEA LOESS L.C. TUGULAN 1, JEANET GRADINARU 2, O.G. DULIU 3 1 Radioactive Waste Management Department Laboratory, Horia Hulubei Institute for Physics and Nuclear Engineering, Reactorului 30, RO , P.O.B. MG-6, Bucharest-Măgurele, Romania l.c.tugulan@yahoo.com 2 ArcelorMittal s.a. 1, Smardan str., , Galati, Romania 3 University of Bucharest, Department of Structure of Matter, Earth and Atmospheric Physics and Astrophysics, 405, Atomistilor str., Magurele (Ilfov), Romania o.duliu@upcmail.ro (corresponding author) Received July 10, 2015 The performances of two variants of XRF elemental analysis, i.e. the Energy Dispersive XRF (EDXRF) developed by the Radioactive Waste Management Department Laboratory (DMDR-Lab) at the National Institute for Physics and Nuclear Engineering and the Wavelength Dispersive XRF (WDXRD) developed by the Spectroscopy Laboratory (LS) in the ArcelorMittal Company, Galati were compared by analysing the content of major, rock forming elements of 10 samples of loess and paleosol collected from the Costinesti (South-Eastern Dobrogea) loess deposit. The results concerning the content of Na, Mg, Al, Si, K, Ca, Ti and Fe as determined by both methods were coincident within the experimental uncertainties as the t-test confirmed. Accordingly, the t parameter varied between and at p between and respectively. Key words: EDXRF, WDXRF, intercomparison, major elements, loess, t-test. PACS: Kv, Fj. 1. INTRODUCTION The X-ray fluorescence (XRF) spectrometric analysis actually represents a routine method to determine the content of elements whose order number is grater than 11 in a broad range of materials. Based on the analysis of the X-ray characteristic spectrum, XRF analysis could be performed in Wavelength Dispersive (WDXRF) or in Energy Dispersive (EDXRF) mode. WDXRF presents the advantage of a better energy resolution but needs relatively complex instrumentation. On contrary, the EDXRF spectrometer provided with silicon detectors and cooled by Peltier effect has a simpler construction but have a lower energy resolution with respect to previous ones [1]. But regardless these differences, both type of instruments have a broad range of concentrations from % to tens Rom. Journ. Phys., Vol. 61, Nos. 9-10, P , Bucharest, 2016 v.1.4* #2ad945ed

2 2 EDXRF and WDXRF intercomparison. Major elements content of Dobrogea loess 1627 of mg/kg, which, through a special configuration (equipping the installations with filters, targets and possibility of removing the air from the measuring chamber, etc.) can be reduced to about 1 µg/kg[1]. In view of this, the Radioactive Waste Management Department Laboratory (DMDR) with the Horia Hulubei National Institute for Physics and Nuclear Engineering has developed a protocol to determine by EDXRF with high accuracy the content of major, rock forming elements of both natural and man made solid materials. This procedure involve eight elements as oxides, e.g. Na 2 O, MgO, SiO 2, Al 2 O 3, K 2 O, CaO, TiO 2 and FeO. To validate it, an intercomparation regarding the same elements as determined by WDXRF in the Spectroscopy Laboratory of the Alcelor- Mittal Company in Galati was performed. In view of this, ten samples of loess and paleosol collected from the Costinesti (South-Eastern Dobrogea) loess deposit were investigated by both XRF techniques. Loess was chosen as this type of aeolian sediment formed by the accumulation of wind-blown dust during the last glaciations, could bring useful information regarding the past climatic conditions [2 4]. The results of this intercomparison will be further presented and discussed. 2. MATERIALS AND METHODS 2.1. LOESS SAMPLES Ten samples of soil and paleosol were collected from the sea-cliff, near the village of Costinesti (Dobrogea), by using a steel corer. as described in ref. [5]. The Costinesti loess deposit was chosen at it display a complete loess-paleosol sequence whose age varied from present to about ky, covering about four different glacial cycles [6] XRF DETERMINATIONS All EDXRF measurements were performed by using an Xenemetrix TM ltd. EX TM SDD model equipped with an EG 60 X-ray generator, with a maximum power of 300 W, at an anodic voltage of 60 kv and a maximum current 4.9 ma. The Silicon Drift Detector (SDD) with an area of 25 mm 2 was cooled by Peltier effect. All spectral analysis were performed by means of next 2.0.q.6 software. A set of six filters (Ti, Fe, W, Mo, Rh and Sn) and eight different secondary targets (Zr, Si, Ti, Fe, Ge, Mo, Sn and Gd) were used to get the optimal excitation conditions in the case of elements whose XRF peaks overlap. The instrument was periodically tested and calibrated by a set of discs made of pure elements (Al, Ti, Ti-Al-Cu, Cu, Mo and Sn) furnished by the manufacturer.

3 1628 L.C. Tugulan, Jeanet Gradinaru, O.G. Duliu 3 It should be remark that all EDXRF determinations were done in accordance with the recommendations contained in ref. [7, 8]. The system was calibrated by using : TILL-1 [9] (Geochemical Soil, CANMET Mining and Mineral Sciences Laboratories of Natural Resources, Canada), NCS DC (Stream Sediment, China Nation Analysis Centre for Iron and Steel) [10] and IAEA-SL-1 (Lake Sediment, International Atomic Energy Agency) [11]. The accuracy was checked by means of NCS DC (Lake deposit, China National Analysis Centre for Iron and Steel) [12]. For illustration, the XRF spectrum of the TILL-1 material used for calibration is reproduced in Fig. 1, while the Table 1 contains the best experimental conditions of Xenemetrix TM spectrometer used to determine the content of major elements. The content of each element was calculated by means of the following relation [13]: c i = I i,p E i m Abs corf prep (1) where: I i,p is the net pack-area corresponding to the element i, E i represents the spectrometer calibration factor for element i, m is the sample mass, Abs cor is the absorption correction factor, F prep corection coefficient due to the sample preparation. In this way, the relative combined uncertainty u c regarding the content of the element i was estimated by the following relation [13 15]: (uii,p ( uabscor ( uei ( ufprep u c = I i,p ) 2 + Abs cor ) 2 + E i ) 2 + F prep ) 2 (2) The final results concerning the contents as well as the relative uncertainty for each element calculated by means of Eq. (1) and (2) are reproduced in Table 2. In the case of WDXRF measurements, the best results were obtained by using an ARL TM 9900 Thermo Scientific TM XRF simultaneous-sequential spectrometer, able to analyse up to 90 elements from B to U in nearly any solid or liquid sample. The spectrometer is provided with a 75 µm Be window, Rh anode of X ray generator of the 6 th. A fully digitally mastered goniometer allows a fast acquisition up to o per minute. The presence of a built-in calibration system and of an appropriate software allow determining elemental content from few mg/kg to about 100 %, without any need of reference samples.

4 4 EDXRF and WDXRF intercomparison. Major elements content of Dobrogea loess 1629 Fig. 1 The XRF spectrum of the TILL-1 reference material 2.3. STATISTIC ASSAY The paired Student s t - test was used to check at which extent the experimental data regarding the content of major elements obtained by the two techniques, i.e WDXRF and EDXRF are similar. For this, the free-ware PAST [16] was used. Table 1 The experimental conditions used to determine the content of major elements by Xenemetrix TM spectrometer. a.p. -atmospheric pressure Element XRF I tube V tube Acquisition Target/filter Remarks (ma) kv time (s) Na Kα Si target Vacuum Mg Kα Rh Vacuum Al Kα Rh a.p. Si Kα Rh a.p. K Kα Ti target a.p. Ca Kα Ti target a.p. Ti Kα Fe filter a.p. Fe Kα Ti target a.p.

5 1630 L.C. Tugulan, Jeanet Gradinaru, O.G. Duliu 5 Table 2 The experimental results regarding the Costinesti loes/paleosol content of major elements as oxides (in %) determined by EDXRF Element Sample P1/2 P2 P3 P4 P4/5 P5 P5/6 P7 P8 P9 Na2O ± 0.33 ± 0.41 ± 0.45 ± 0.33 ± 0.34 ± 0.35 ± 0.30 ± 0.32 ± 0.38 ± 0.38 MgO ± 0.30 ± 0.38 ± 0.40 ± 0.30 ± 0.32 ± 0.31 ± 0.29 ± 0.29 ± 0.35 ± 0.34 Al2O ± 1.4 ± 1.4 ± 1.1 ± 1.6 ± 1.3 ± 1.5 ± 1.5 ± 1.2 ± 1.5 ± 1.7 SiO ± 6.4 ± 7.1 ± 6.8 ± 7.4 ± 6.1 ± 6.7 ± 7.1 ± 6.2 ± 6.4 ± 6.5 K2O ± 0.23 ± 0.24 ± 0.23 ± 0.23 ± 0.18 ± 0.22 ± 0.20 ± 0.20 ± 0.18 ± 0.20 CaO ± 1.00 ± 0.71 ± 0.85 ± 0.29 ± 1.42 ± 1.02 ± 0.72 ± 1.47 ± 0.91 ± 0.78 TiO ± 0.07 ± 0.08 ± 0.07 ± 0.09 ± 0.06 ± 0.07 ± 0.08 ± 0.06 ± 0.08 ± 0.08 FeO ± 0.59 ± 0.54 ± 0.57 ± 0.68 ± 0.62 ± 0.52 ± 0.58 ± 0.45 ± 0.62 ± 0.78

6 6 EDXRF and WDXRF intercomparison. Major elements content of Dobrogea loess 1631 Table 3 The experimental results regarding the Costinesti loes/paleosol content of major elements as oxides (in %) determined by WDXRF Element Sample P1/2 P2 P3 P4 P4/5 P5 P5/6 P7 P8 P9 Na2O ± 0.33 ± 0.35 ± 0.43 ± 0.31 ± 0.33 ± 0.33 ± 0.30 ± 0.33 ± 0.38 ± 0.36 MgO ± 0.31 ± 0.35 ± 0.39 ± 0.29 ± 0.30 ± 0.29 ± 0.26 ± 0.28 ± 0.34 ± 0.34 Al2O ± 1.5 ± 1.5 ± 1.5 ± 1.6 ± 1.5 ± 1.6 ± 1.5 ± 1.3 ± 1.6 ± 1.7 SiO ± 6.4 ± 6.8 ± 6.6 ± 7.0 ± 6.2 ± 6.4 ± 6.7 ± 6.2 ± 6.4 ± 6.1 K2O ± 0.23 ± 0.11 ± 0.23 ± 0.23 ± 0.22 ± 0.20 ± 0.21 ± 0.21 ± 0.20 ± 0.19 CaO ± 1.00 ± 0.63 ± 0.79 ± 0.26 ± 1.30 ± 1.00 ± 0.72 ± 1.50 ± 0.90 ± 0.76 TiO ± 0.07 ± 0.07 ± 0.07 ± 0.07 ± 0.07 ± 0.07 ± 0.07 ± 0.06 ± 0.07 ± 0.08 FeO ± 0.62 ± 0.61 ± 0.66 ± 0.76 ± 0.61 ± 0.64 ± 0.68 ± 0.54 ± 0.67 ± 0.88

7 1632 L.C. Tugulan, Jeanet Gradinaru, O.G. Duliu 7. Fig. 2 Two biplots of the content of silicon dioxide (left) and titanium dioxide (right) as determined by WDXRF vs. EDXRF illustrating the perfect correlation existing between the results obtained by the two techniques. 3. RESULTS AND DISCUSSION The experimental results concerning the content of eight major elements in all ten samples of loess and paleosol as determined by EDXRF and WDXRF together with corresponding combined uncertainties are reproduced in Table 2 and 3 respectively. At a first glance it results that both techniques gave similar, almost coincident with combined uncertainties results. This fact is well proved by the biplots of the experimental content of the same element as determined by EDXRF and WDXRF. For illustration, in Fig. 2 are reproduced two of them, corresponding to SiO 2 and TiO 2, the most abundant and the most spare elements respectively. In order to compare the results obtained by the two laboratories, first of all it was necessary to calculate the relative difference e i between the content of each Table 4 The final results of the paired Student s t test as well as the values of the p parameter - the probability the experimental results concerning the content of major elements in each sample to be the same. Sample P1/2 P2 P3 P4 P4/5 t -0,038-0,041-0,014-0,028-0,040 p 0,9699 0,9681 0,9892 0,9780 0,9688 Sample P5 P5/6 P7 P8 P9 t -0,038-0,035-0,039-0,045-0,034 p 0,9702 0,9724 0,9697 0,9649 0,9737

8 8 EDXRF and WDXRF intercomparison. Major elements content of Dobrogea loess 1633 element by means of the relation: e i = c i,edxrf c i,w DXRF c i,w DXRF (3) The final results showed that this difference varied between 0.4 and 6.8 %, i.e. slightly lower than the combined uncertainty of the EDXRF as well as WDXRF determination. Moreover, the results of a Students t t-test, whose results are reproduced in Table 4, were characterized of the values of the t - parameter between and , thus confirming the existing compatibility between the two techniques. The fact that the combined uncertainties are almost equal in the case of EDXRF and WDXRF indicate that in the case of major elements whose content is on the order of magnitude of percent or tens of percent both methods show similar performances. 4. CONCLUDING REMARKS Two different variants of the XRF spectrometry, i.e. EDXRF and WDXRF were used to determine the content of eight major, rock forming elements, in tens sample of loess and paleosol collected from the Costinesti (South-Eastern Dobrogea) loess deposit. Although the two set of determinations were performed in two different laboratories by using proper protocols, the final results showed to be very similar, fact attested not only by the coincidence of the mean values within one standard deviation of all elements, but also by a two-way t-test whose value of the t-parameter varied between and In this way, it could be considered that the elemental composition of each set of samples as obtained by the two laboratories were coincident with o probability between and REFERENCES 1. International Atomic Energy Agency (IAEA). Analytical applications of nuclear techniques. Vienna, Austria, STI/PUB/1181, ISBN (2004) 2. S. Gallet, B-M Jahn, B. Van Vliet Lanoe, A. Dia, E. Rossello, Earth Planet. Sci. Let. 156, 157 (1998). 3. J.A. Catt, Soils and Quaternary geology. A Handbook for Field Scientist, Oxford Sciences Publications, Clarendon Press, Oxford (1986). 4. G. Ujvari, A. Varga, B. Raucsik, J. Kovács (2014) Quat. Intern. 319, (2014); doi: /j.quaint L.C. Tugulan, O.G. Duliu, Rom. Rep. Phys. 66, (2014).

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