Use of Electrospray Ionization Mass Spectrometry (ESI-MS) for the Study of Metal (III) Extraction by Dialkyl Phosphoric Acid

P2-31

Use of Electrospray Ionization Mass Spectrometry (ESI-MS) for the study of metal (III) extraction by dialkyl phosphoric acid

E. Leclerc1, L. Berthon1, X. Heres1, B. Gannaz1, C. Berthon2, J.M. Adnet1

1CEA Valrhô, DEN/DRCP/SCPS/LCSE, B.P. 171, 30207 Bagnols sur Cèze, France 2CEA Valrhô, DEN/DRCP/SCPS/LCAM, B.P. 171, 30207 Bagnols sur Cèze, France

Abstract –In the framework of nuclear waste reprocessing, separation processes of minor actinide from fission product are developed by CEA. In order to understand the mechanism involved in the extraction process, the complexes ligand - metallic cations formed in organic phase has been characterized. This paper deals with the extraction of lanthanides (III) and actinides (III) cations by dialkyl phosphoric acid (the bis- 1,3-dimethylbutylphosphoric acid). The associative properties of the extractant were studied, the complexes (metal-ligand) present in organic phase were identified and the interactions ligand-metal were characterized. The electrospray ionization -mass spectrometry (ESI-MS) was used to investigate organic solutions, and the results are compared with those obtained by other techniques like NMR, IRTF and distribution ratio studies.

INTRODUCTION HBDMBP concentration was measured by To improve the management of radioactive acido-basic titration. Water concentration was wastes generated by spent nuclear fuel titrated by Karl Fisher analysis. reprocessing, CEA has undertaken the Aqueous phase: development of a liquid-liquid extraction process - pH 3 solution: glycolic acid 0.6 mol/L which has the objective, in particular, to separate adjusted to pH 3 with NaOH. the minor actinides [Am(III) and Cm(III)] from - europium solution: dissolution of europium high-level liquid waste [1] Dialkylphosphoric (III) nitrate in pH 3 solution. acid, like di(2-ethylhexyl)phosphoric acid The organic and aqueous solutions were shaked (HDEHP), proved to be a very efficient together at 25°C during 15 minutes and then extracting agent in the separation of trivalent centrifuged during 5 minutes and separated. lanthanides and actinides [2, 3]. Several - ESI-MS: A Brucker Esquire LC mass dialkylphosphoric acid have been tested to spectrometer was used. separate lanthanides from actinides using a Organic phase were contacted with the combination of buffer and complexant in appropriate aqueous phase (Vaq = 4 Vorg). aqueous phase. This present work deals with the Without metal, the organic phase was diluted extraction of the trivalent lanthanides and 1/10000e in acetonitrile/water (1:1 v/v). actinides by the bis-1,3-dimethylbutylphosphoric Eu-HBDMBP complex characterization: the acid (HBDMBP) diluted in dodecane. organic phase was diluted 1/10e in ethanol and The associative properties of the extractant were 1/100e in water/acetonitrile (1:1 v/v). studied, the complex (Metal-ligand) present in - NMR: A Unity Inova 400 MHz spectrometer organic phase were identified and the interaction was used. ligand - metal were characterized. - Distribution ratio studies: The ESI-MS technique was chosen to analyze Organic phases are contacted with the organic solutions. Indeed, the ‘gentle’ nature of appropriate aqueous phases (Vaq = Vorg) spiked the ESI [4] process allowed obtaining with 241Am(III) and 152Eu(III) at 25°C. An information about associative properties of the aliquots of each phases was then taken for organic molecule and providing structure, gamma counting (E = 59.64 keV for 241Am and stoichiometry of ligand-metal complexes in E = 121.8 keV for 152Eu). solution [5, 6]. The results are compared with - IRTF: a Brucker Equinox 55 those obtained by other techniques like NMR, spectrophotometer was used. IRTF and distribution ratio studies. AGGREGATION OF HBDMBP EXPERIMENTAL Dialkylphosphoric acids are considered to exist - Extraction conditions: as dimeric species in a non polar solvent [7, 8]. Organic phase: HBDMBP was diluted in The aggregation of the extractant in the organic dodecane. phase is expressed as:

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n HL (HL)n Therefore, the plot of log(C( 1- )) vs. log(C( - n)) gives a straight line with slope n and the and characterized by the aggregation constant ordinate log(Kn/(( 1- n)^(n-1))). The slope of the Kn. The aggregation of HBDMBP in dodecane at plot log(C( 1- )) against log(C( - n)) is equal to 25°C is studied after contact with a pH=3 2 and the ordinate is -0.0205. -1 aqueous phase. Then n=2 and the constant K2 = 3.0±0.2 L.mol . The Fig. 2 presents the speciation diagram Electrospray Ionization - Mass Spectrometry (monomer, dimer of HBDMBP) and water The Fig. 1 shows the positive mass spectrum of concentration in organic phase vs. HBDMBP HBDMBP. The ions at m/z 289, 533, 821 and concentration: one H2O molecule seems interact + + 1087 correspond respectively to LNa , L2H , with one dimer molecule. + + L3Na and L4Na with L corresponds to

+ 1,2 HBDMBP molecule. The dimeric form (L2H ) is the main species. dimer 1 H2O

Intens. 6 L x10 / l 0,8 o 1.0 m 533.2 + n i

L2H n o i 0,6 t monomer a r t n

0.8 e c n

o 0,4 C

0.6 0,2 y t i s

n 0

e 0 0,5 1 1,5 2 2,5 3 3,5 t 0.4 HBDMBP Concentration (mol/L) n

I 555.2 Fig. 2. Speciation diagram for HBDMBP diluted

0.2 + in dodecane at 25 °C after contact with a pH=3 + L3Na 99.0 LNa 820.9 + 289.2 aqueous phase. 267.0 351.3 L Na 4 1087.3 0.0 200 400 600 800 1000 m/z +MS m/z CHARACTERIZATION OF THE METAL- Fig. 1. ESI mass spectrum in the positive HBDMBP COMPLEXES ionization mode of HBDMBP 10-2 mol.L-1 This part deals with the extraction of metal diluted at 1/10000 in water/acetonitrile (1:1 v/v), nitrate by HBDMBP in pH=3 aqueous phase. cone voltage 30 V. Electrospray Ionization - Mass Spectrometry The positive ionization mode mass spectrum of NMR NMR can be used for aggregation studies [8, 9]. the organic phase is reported Fig. 3. Three ions at The chemical shift of 31P was measured as a m/z = 1215.5, 1481.6 and 1747.7 are particularly interesting and correspond respectively to function of the HBDMBP concentration. A shift + + + from -1.7 ppm for diluted solution to -4.5ppm for [EuL2(L-H)2] , [EuL3(L-H)2] and [EuL4(L-H)2] species (with L = HBDMBP). The most concentrated solution was observed. This gap is + enough to have a good precision for the abundant species is [EuL2(L-H)2] . An increase of the skimmer voltage leads to a disappearance determination of the dimerization constant. + + of the [EuL3(L-H)2] and [EuL4(L-H)2] (Fig. 4). The mass action law model is considered and This shows that the complex with four leads to the following equation: HBDMBP is the most stable species and the two others are probably species generated during the ≈ ’ ∆ Kn ÷ ionization step. log(C(δ1 −δ )) = n log(C(δ − δ n ))+ log∆ (n−1) ÷ « (δ1 − δ n ) ◊ In order to have more information about the With structure and the stability of the complexes, the - C: extractant concentration (mol.L-1), fragmentation of each of them has been studied - : experimental chemical shift, (Fig. 5 and 6). + - 1: chemical shift for the monomeric form (null The fragmentation of [EuL2(L-H)2] (Fig. 5) concentration), leads to three more important species at m/z = - n: chemical shift for the micellar form (infinite 1131.5 (loss of C6H12), m/z = 1047.4 concentration), (elimination of two C6H12 groups) and m/z = - n: aggregation number, 949.5 (loss of a HBDMBP molecule). The - Kn is the aggregation constant. weaker intensity of the peak issuing from the

ATALANTE 2004 Nîmes (France) June 21-25, 2004 2 P2-31 loss of HBDMBP compared of the intensity of molecule of HBDMBP (two in the case of + the peak issuing from the loss of C6H12 show that [EuL4(L-H)2] ) (Fig. 6) and lead to an ion at m/z the interaction Eu-HBDMBP is very strong = 1215.6 (1213.5 for 151Eu) which corresponds to + because it is easier to break an oxygen-carbon [EuL2(L-H)2] . bond than a metal-ligand bond.

Intens. Intens. + + I n te n s. [EuL (L-H) ] 14814181.6,6 [EuL (L-H) ] 14791479.,66 x 1 0 5 3 2 3 2 6000 + T=triester 200 533. L H 2 L=HBDMBP [ESupLec(tLre-H M)S]+2 1 .0 99.1 3 2 de2 [EuL (L-H) ]+ MS spe3ctrum2 2 + 5000 Spectre MS + [EuL (L-H) ] [EuL (L-H) ] 4 2 4 2 + 1745.7 + de [E2uL4(L-H)2] 1745,7 0 .8 [EuL (L-H) ] 2 2 150 MS spectrum

+ 1212155.6 ,6 TH y 4000 t

351.3 i 0 .6 s y t + n L5K i

+ e

L4Na 1369 t s

n 3000 100

1087 I + n 0 .4 [EuL2(L-H)2] + + e LNa [EuL2(L-H)2] t 289.2 + 1213,5 617.3 TLH 1215 n + + I 0 .2 L3Na [EuL4(L-H)2] + 2000 -L [EuL3(L-H)2] 821.1 1747 -L -L 1481 50

0 .0

2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 m /z 1000 + M S m/z

1393.4 0 0

1200 1250 1300 1350 1400 1450 1500 m/z 1200 1300 1400 1500 1600 1700 1800 m/z Fig. 3. Positive ESI mass spectrum of the organic m/z m/z 2 + phase after dilution 1/10 in ethanol and 1/100 in Fig. 6. MS spectrum of [EuL3(L-H)2] and + water/acetonitrile (1:1 v/v), cone voltage 30 V. [EuL4(L-H)2] complexes of the extracted Organic phase: HBDMBP 0.01 mol/L in dodecane. organic phase diluted at 1/10 in ethanol and at Aqueous phase: europium nitrate 0.05mol/L pH=3. 1/100 in water/acetonitrile (1:1 v/v). (T is an impurity of HBDMBP synthesis) Fragmentation amplitude set at 0.45 for [EuL3(L- + + H)2] and at 0.65 for [EuL4(L-H)2] . 4,0E+05

60000 + [EuL2(L-H)2] 3,5E+05 50000 Electrospray mass spectrometry shows that the 40000 3,0E+05 30000 most stable complex has four HBDMBP 20000 2,5E+05 10000 molecules strongly bonded to the metal. Two y t i

s 0

n 2,0E+05

e 20 30 40 50 60 t n I minor complexes are observed and are probably

1,5E+05 + [EuL4(L-H)2] generated during the ionization process in which

1,0E+05 one or two further HBDMBP molecules

+ 5,0E+04 [EuL3(L-H)2] surrounding the metal.

0,0E+00 20 30 40 50 60 70 80 90 100 Skimmer 1 (V) Extraction equilibrium + Fig. 4. Intensity of the [EuL2(L-H)2] , [EuL3(L- The distribution ratio of Am(III) and Eu(III) + + H)2] and [EuL4(L-H)2] vs. voltage of skimmer were measured as a function of the acidity and 1 (skimmer 2 voltage set at 10V). Trap Drive set the extractant concentration. at 50. Organic phase complexes diluted at 1/10 HBDMBP exists in organic phase as monomeric in ethanol and at 1/100 in water/acetonitrile (1:1 and dimeric form. Then, two extraction v/v). equilibriums can be considered:

Intens. M x+ + x + z L M (L H ) L xH + 1500 1131.5 ( ) − + Spectre MS2 de [EuL (L-H) ]+ x z HP = phosphoric a2cid 2 HP =[E AUcLid(eL -pHh)o]+spMhSo2risqpueectrum 2 2 x+ ≈ x + y ’ + 1250 M + ∆ ÷L M (L − H ) x Ly + xH « 2 ◊ 2 + 1000 [EuL2(L-H)2] y

t i

s n e t 750 n I 1215.5 The plots log(DAm or DEu) vs. pH are two straight + 1047.4 [EuP2 (HP)2] -84 500 -C6H12 lines with a slope of 3. This implies . Fig. 7 462.8 + x = 3 444.8 [EuL (L-H)2] 963.3 shows the effect of the concentration of 250 879.2

546.8 630.9 795.2 -L HBDMBP on the distribution ratio of Eu and 0 300 400 500 600 700 800 900 1000 1100 1200 m/z m/z Am. The slope value of the extractant dependencies

2 + measured for diluted solution (lower than 0.1 Fig. 5. MS spectrum of [EuL2(L-H)2] complex mol.L-1) is equal to 3. In these concentrations the of the extracted organic phase diluted at 1/10 in dimeric form can be negligible and metal is ethanol and at 1/100 in water/acetonitrile (1:1 extracted by 3 HBDMBP monomers. v/v). Fragmentation amplitude set at 0.95. + Contrary to [EuL2(L-H)2] , the complexes + + [EuL3(L-H)2] and [EuL4(L-H)2] loose easily a

ATALANTE 2004 Nîmes (France) June 21-25, 2004 3 P2-31 6 . 0 -1 1000 HBDMBP 1.5 mol.L in dodecane -1

5 contacted with glycolic acid 0.6 mol.L P-O-H, P-O-C st . 0 HBDMBP 1.5 mol.L-1 in dodecane -1 100 contacted 5 times with Eu 0.01 mol.L 4 . 0 s t i P-O-Eu st. n U

10 e c n 3

Eu . a 0 b r P O st. Bonded o s

b with Eu A M

D 1 2 . 0 Am PO st.

0,1 1 . 0

0,01 Slope = 3 1500 1400 1300 1200 1100 1000 900 800 700 Wavenumber cm-1

0,001 Fi Cg:\Doc.um8ents a.nd SetItingns\el20f305r9\Maes drocuementds\IR\IR eriac\HBbDMBPs 15o (a glyrcolipque).0t i o HBDnMBP 1.5Ms ( ap glyceoliquec) t r Rg=a460 Ohmo LasfA0 2= / 0L4a/sH2B00 =4 12 BV DMBP 0,001 0,01 0,1 1 -1 C:\Documents and Settings\el203059\M-e1s documents\IR\IR eric\HBDMBP 15 (Eu 0,01M) 5 ext.0 HBDMBP 1.5M ( Eu 0,01M) 5ext Rg=460 Ohm 0 2L/a0s4A/2 0=0 L4asB = 12 V CHBDMBP (mol.L ) 1.5 mol.L in dodecane after contact with an

Fig. 7. Distribution ration of Am(III) and Eu(III) a queous phase. vs. HBDMBP concentration in dodecane. Red: aqueous phase pH 3 without europium. -1 Temperature: 25 °C, aqueous phase pH=3. P ink: europium 0.01 mol.L in aqueous phase p H3. The decrease of the slope at higher concentration of extractant can be explain by the presence of The 2 forms (monomer and dimer) participate to dimeric form which is significant and the extraction of the metal. For diluted solution participates to the metal extraction. Two (lower than 0.1 mol.L-1), one complex is present extraction equilibriums can be considered: M (L − H ) but for more concentrated solution a 3 3+ + further complex M (L − H ) 3 L1 is probably M + 3L M (L − H ) 3 + 3H present. Metal is linked to the ligand via the ≈ ’ + 3+ 3 + y M (L − H ) Ly + 3H M + ∆ ÷L2 3 oxygen of the P=O and P-O(-H) group. « 2 ◊ Further investigations will be needed to complete the characterization of the organic phase in The mass spectrometry shows the presence of concentrated media. complex with 4 ligands around the metal, this agree with the presence of [M(L-H) L] issuing 3 REFERENCES from the extraction of metal by 2 dimers (y=1). 1. C. Madic, M.J. Hudson, J.O. Liljenzin, J.P. Glatz, R. Nannicini, A. Facchini, Z. Kolarik, Infrared Spectroscopy R. Odoj, Final Report, EUR-19149, (2000). Fig. 8 present IRTF spectra of organic phase 2. G. D. Del Cul, W.D. Bond, L.M. Toth, G.D. before and after extraction of europium (III). G. D. S. Dai, D.H. Metcalf, Oak Ridge Some characteristic absorption bands are National Laboratory, TM-12785, (1994). modified with the presence of europium. The -1 3. Z. Kolarik, Proceedings of the International P O stretching band at 1230 cm decrease and Solvent Extraction Conference, La Hague, a new band at 1200 cm-1 appears and France, 753-761, (1971). corresponds to the P O bonded to Eu. 4. A.T. Blades, P. Jayaweera, M.G. Ikonomou, Moreover, the intensity of the P-O-H and P-O-C P. Kebarle, Int. J. Mass Spectrom. Ion antisymmetric stretching band at 1015 cm-1 -1 Process., 101, 325-336, (1990). decrease and a new band at 1100 cm appears 5. C. Lamouroux, C. Moulin, J.C. Tabet, C.K. which corresponds to the P-O-Eu stretching. Jankowski, Rapid Commun. Mass Spectrom. These results show that europium is linked via 14, 1869-1877, (2000) oxygen from the P=O and P-O(-H) group to 6. S. Colette, B. Amekraz, C. Madic, L. HBDMBP. This is agree with the work of Berthon, G. Cote, C. Moulin, Inorg. Chem , Peppard for HDEHP [10]. 42, 2215-2226, (2003). 7. L. Ki-an, S. Muralidharan, H. Freiser, Solv. CONCLUSION Extr. Ion Exch., 3(6), 895-908 (1985). In pH 3 aqueous phase condition, the HBDMBP 8. D. Pattee, C. Musikas, A. Faure, C. molecule self associate to form dimer in -1 Chachaty, J. Less-Common metals, 122, dodecane (K2=3.0 L.mol ) which extract one 295-302, (1986). water molecule. 9. A. Faure, A.M. Tistchenko, T. Zemb, and C. Chachaty; J. Phys. Chem., 89, 3373-3378, (1985). 10. D.F. Peppard, J.R. Ferraro, J. Inorg. Nucl. Chem., 10, 275-288, (1959).

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