822 ION-EXCHANGE FILMS FOR ELEMENT CONCENTRATION IN X-RAY FLUORESCENCE ANALYSIS WITH TOTAL REFLECTION OF THE PRIMARY BEAM. Abstract A.P.Morovov, L.D.Danilin, V.V.Zhmailo, Yu.V.Ignatiev, A.E.Lakhtikov, V.V.Nazarov, M.G.Vasin, V.V.Chulkov, V.N.Funin Russian Federal Nuclear Center - VNIIEF, Sarov, Nizhni Novgorod region, Russia otd46jexpd.vniief.ru Tentative results of studies dedicated to development of submicron films of ion-exchange materials for element separation and concentration in TXRF are presented. A technique to produce 0.1-l urn films was developed. Some sorption properties of such films were studied. Film characteristics were measured on the laboratory mock-up of a TXRF spectrometer. Introduction X-ray fluorescence analysis with total reflection of the primary beam (TXRF) is successfully used at present for trace element detection in various environmental objects /l-3/. Different methods of preliminary concentration are used in this method for analysis of samples of complex compounds to eliminate the influence of basic elements of the materials under study on detection limits of impurities. In many cases this procedure is cumbersome and complicated /4/. The possibility of applying thin films of ion-exchange materials for element separation and concentration in TXRF is under study at VNIIEF currently. The proposed concentration method simplifies, in some cases, sample preparation procedure, and thus produces concentrate in a light organic matrix convenient for studies both by TXRF and usual XRF methods. Since traditional ion-exchange materials represent, as a rule, insoluble polymer structures, methods to produce polychelates in the form of solutions for subsequent production of thin films selective for gold, platinum, metals and d-elements series are developed. Some preliminary results of these studies are presented in the report. 1. Equipment used for experimental investigations The investigations are carried out on the laboratory mock-up of a TXRF spectrometer, the diagram of which is shown in Fig. 1 /5/. Serial x-ray apparatus DRON-1 with BSV-9 tube is used as the radiation source. Voltage on the tube is V=SOkV, current is 1=20mA. Tubes with MO and W anodes are used. Sample characteristic radiation is. recorded by a Si(Li) detector (manufactured by Canberra ). The detector energy resolution is 155 ev for quantum energy 5.9 kev. Silicon crystal sensitive surface area is 12 mm2. Detector with highly pure Ge (HPGe) crystal is used to control primary beam and x-ray optical elements adjustment. Optical scheme elements are adjusted by remote control step motors. Linear displacement step is M 0.5 pm, while angular step is = 0.01 mrad.
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823 Monitor detector x-ray Slit diaphragm Two-mirror monochromator 80 - a a a 300 360 500 A Fig. 1. Block diagram of optics system with two-mirror monochromator Sample excitation by monochromatic radiation is used in the scheme. Monochromator based on a multilayer W-C structure with a layer period of about 50 A is used to cut the monochromatic line out of the spectrum. Monochromator consists either of one multilayer mirror or of a block of two multilayer mirrors. Spectra of x-radiation formed by the described monochromators are shown in Fig. 2. Single-mirror monochromator was used in most of studies due to its high aperture ratio and adjustment simplicity. 100000 1 I / / / h D. 10000 1000 100 10 1 w 2 4 6 8 10 12 14 Energy, kev I 7: 16 18 20 22 Fig.2. X-ray tube spectra formed by different monochromators: 1 - initial MO-anode spectra; 2 - spectrum formed by single W-C mirror; 3 - spectrum formed by two W-C mirrors block. The measurement system is based on a PC; CAMAC equipment is used for data recording and control.
824 2. Studies of thin-film sorbents Chlorinated polymer-based matrices were used in development of thin-film ion-exchange materials synthesis technology. The produced matrices are attributed to the class of ammonium polymer salts soluble in various organic solvents and forming relatively strong films /6/. Various soluble sorbents containing groups of rhodanine, 3,5-dimethylpyrazole, 8- mercaptoquinoline, tenoiltrifluoroacetone and other chelate structures were produced on the basis of chlorinated polymer matrices. It was shown by methods of IR spectroscopy that the synthesized substances are individual chemical compounds rather than mechanical mixtures. Trial samples of ion-exchange films were produced from the synthesized polymers and used in a series of preliminary experiments on sorption of cadmium, gold, platinum and other metals from solutions. Films 0.1-l pm thick were studied. The measurements showed (see Fig. 3) that contrast of analytical lines in spectra obtained from 0.1 pm films in TXRF geometry (film on quartz substrate) is approximately 10 times higher than that of spectra obtained from the same free films. 25. 20 3 E +j 15 tj a I! e 10 z iii w 5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Energy, kev Fig.3. Spectra of film fluorescence on TR mirror (curve 1) and in free state (curve 2). Angular dependence of element fluorescence in the film on a substrate differs significantly from that for samples produced by evaporation of a drop of liquid. Fluorescence intensity for the film reaches its maximum in the angle range 0<%9,, (Fig. 4). To clarify this effect the film samples were measured on EXTRA-II spectrometer (GKSS, Forschungszentrum, Geesthacht, Germany, group of H.Schwenke). The results of the measurements were processed using the program package developed at the GKSS for investigation of surfaces with the TXRF method. The results obtained allowed the assumption that sorbed elements were contained in the surface layer of the film - 10 nm thick.
825 I I / CJ l i I I I I I *I 1, I I / : 2 600.s?.s 8 s 400 8 s 2 200 1 1,25 L5 1,75 2 2,25 2,5 2,75 slope angle, mrad * Fig.4. Fluorescence intensity as a function of slope angle for film samples in TR geometry: 1 - polycarbonate film; 2 - sample produced by solution drop evaporation; Si - quartz substrate. -i 5 7000'- cd. 6000.. 8000, I g 5000 -- '0 4000 -- 5 3000 -- 5 2000 -- F 1000 ~- / 6? 01, 0 10 20 30 40 50 60 Gold concentration in solution, Mg/ml Fig.5. Sorption efficiency as a function of element concentration in solution. Sorption time is 60 minutes.
826 * 35000 ; 30000 0 10 20 30 40 50 60 Sorption time, minutes Fig. 6. Sorption efficiency as a function of sorption time. Au concentration in solution is 111.5 pg/ml.
827 5 s t b a aj 3 E 2 U 1000 100 10 1 ~j ~~/$~l j/ -,--+A-?Y- -II-.~-, / I +- t - -;- - -;- - iiu1fw -:-I.;--:- = II:= I- -- - I- - I, k -- x y I y I- - g 2: z I._ z -/_~ +I; 1 : I ; L -1. -, 9K-- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 I- -I- Energy, kev -I-.- / Fig. 7. Au-containing film fluorescence spectrum. + Free film, PVC-rhodanine, V=2.0 ml, [HCL]=lM/l, [Au]=1 11.5 pg/ml. t=60 min., 1000 pi 1-c -_,, ---,_--,---,--,~~,Ir~~~~~~~~~~~~~~~~--+-~~~~ i ~ i ~ ~ ~ ~_-i--~ ~ i~-~--~--l--l-~i--,~-~,---,---,---,---,--~--~--~--~--~--+-~+-~+-~-c--,~-~,~--,---,---,---,----1-~--i--~---1---i--i-~-c---i-~-c-- 100,---,---,IIl,_f_,,r_l --,- -l--+zi+--+--+--fz - 1,- - -,- - -,- - -,- - -,- - -,- - + - - + - - -f - - + - - + ~~,~~;~r+-- -z --- -------------------------------------- I ------------------------ r-3 - -- --i I - --------~--~-- -I--, I I I I, 1 / I / 1 I / I--!-- -,---,--_I I I -/---,-- / i-ni--i--i--+--+--+--~--~- / ~ : ;:I lb&j t- t:: I, I / / 1, / I I I I I I I I I I I I / I _=,==Il===l===l==n=r~=*ti==3jgr~ll==*=~~- -nbr=zr-$ + --,-- :-- 1,- - I!---I- Ii 1.f..l...r... ~-.1 L - L c - i IIIr:l c---i-- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Energy, kev Fig. 8. Au-containing film fluorescence spectrum. Free film, PVC-rhodanine, V=5.0 ml, [HCL]=lM/l, [Au]=l. 1 p.g/ml. t=60 min.,
828 The studies on sorption of gold from 1 N HCl on - 1 micron films were carried out using the produced chelate PVC-rhodanine. Sorption efficiency as a function of Au (III) concentration C for sorption time t = const, and as a function of sorption time t for C = const is shown in Figs. 5 and 6 respectively. Sorption efficiency is a linear function of concentration up to about 20-25 pg/ml. For concentrations - 30 pg/ml sorbent saturation, probably, takes place; that can be related to either low capacity of the latter, or to operation of surface layers. Sorption efficiency falls sharply with concentration (Fig. 7,8), that is in qualitative agreement with sorption as a function of sorbed element concentration. Conclusion The equipment and method for production of ion-exchange materials in the form of thin and super-thin films were developed. Films of various thickness were produced on the basis of synthesized soluble polychelates and used in preliminary experiments on sorption of metals from solutions. The experiments carried out show that sorption of metals takes place. These results are in qualitative agreement with the general idea of element sorption from solution by usual ionexchange materials. However, preliminary data indicate that the mechanism of ion sorption by thin films has specific features. The work was carried out under the ISTC contract #286-96. The authors would like to thank the experts of the GKSS Institut fiir Physik H.Schwenke, JKnoth, H.Schneider for studies of film sorbents characteristics and discussion of results. References 1. Y.Yoneda, T.Horiuchi Rev. Sci. Znstr., 197 1, vol. 42(7), p. 1069. 2. H.Aiginger, P.Wobrauschek Nucl. Instr. and Meth., 1974, vol. 114, p. 157. 3. JKnoth, HSchwenke, Z.Fresenius Anal. Chem., 1978, vol. 291, p. 200. 4. A.Prange Spectrochimica Acta 44B, 1989, p.437 5. A.P.Morovov, M.G.Vasin, Yu.I.Vinogradov, V.V.Zhmailo, Yu.V.Ignatiev, A.E.Lakhtikov, V.V.Nazarov, V.N.Funin, V.V.Chulkov Voprosy Atomnoi Nauki i Telhniki (VANT), Series Nuclear Reactor Physics, PMNS - XI, 1997. 6. M.A.Askaorov, A.G.Dzhalilov Ionogenic polymers synthesis. FAN, Tashkent, 1978, p.160.