Studies on some divalent metal α-isosaccharinic acid complexes

Radiochim. Acta 94, 363–368 (2006) / DOI 10.1524/ract.2006.94.6.363© by Oldenbourg Wissenschaftsverlag, München

Studies on some divalent metal α-isosaccharinic acid complexes

By Peter Warwick1,∗, Nick Evans1 and Sarah Vines2

1 Centre for Environmental Studies, Department of Chemistry, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK2 UK Nirex, Curie Avenue, Harwell, Didcot, Oxon, OX11 0RH, UK

(Received September 5, 2005; accepted in final form March 24, 2006)

ISA / Cadmium / Uranium / Cobalt / Stability constants

Summary. The presence of organic complexants, suchas α-isosaccharinic acid (ISA) in an intermediate-levelradioactive-waste (ILW) repository may have a detrimentaleffect on the sorption of radionuclides by forming organiccomplexes in solution. To assess this, stability constants arerequired for the complexes formed. Constants have been de-termined for the divalent metal ions, Cd2+, Co2+ and UO2

2+

with α-isosaccharinic acid (ISA) in near-neutral and alkalineconditions. The effect of these complexes on radionuclide sol-ubility in the near-field and alkaline-disturbed zone is shown.The constants were measured by the ion-exchange (Schubert)method [1] with the exception of U(VI) at pH 13.3, for whichthe solubility product method [2] was used. At pH 7 eachcomplex was of the form M1ISA1, with log β values sugges-tive of salt formation. At high pH, log β values were between13 and 20. The number of hydroxide ions involved in thecomplexation reactions was determined using Bjerrum plots,conductometric titrations and spectrophotometric methods [1].The constants have enabled speciation calculations to be per-formed showing the effect of ISA on the metal’s solubility.Solubility is predicted to increase in the presence of ISAfrom pH 9 to 13.5, suggesting that it may have an impacton radionuclide behaviour. The largest solubility increases arefor Cd and Co, the smallest for U(VI).

1. Introduction

The Nirex Phased Geological Repository Concept involvesthe use of a cementitious backfill to provide a chem-ical barrier to radionuclide migration from the near field.The backfill chemically conditions the porewater to pro-vide a high pH environment, under which the solubilityof many key radionuclides is low. The backfill also pro-vides a large surface area for radionuclide sorption. Thepresence of organic complexants in the porewater can po-tentially have a detrimental effect on both the solubilityand sorption of radionuclides, by the formation of or-ganic complexes in solution [3–5], thereby increasing theirmobility in near-field and alkaline-disturbed zone. Oneof the most important of these is 2-C-(hydroxymethyl)-3-deoxy-D-pentonic (α-isosaccharinic) acid (ISA). ISA,CO2HC(OH)(CH2OH)CH2CHOHCH2OH, is a polyhydrox-ylated carboxylic acid with potentially labile hydroxyl

*Author for correspondence (E-mail: [email protected]).

protons that can be displaced during metal complexationat high pH. Therefore, for performance assessment pur-poses it is necessary to determine stability constants forcomplexes formed between ISA and radionuclides of im-portance [6]. Some conditional stability constants with ISAhave been reported in the literature e.g. Th and Eu [7],Ni [1] and U(IV) [2], but there is a need for additional con-stants. This paper presents results for Cd, Co, and U(VI).The stoichiometries of the complexes were determined usingBjerrum plots, conductometric titrations [8] and spectropho-tometry [9]. Bjerrum plots [10] give the ratios of metal tohydroxide ions in the complexes formed. They also providethe information required to perform appropriate conduc-tometric titrations. These titrations determine the ratio ofmetal to ligand in the complexes and confirm the metal tohydroxide ratio obtained from the Bjerrum plots.

Stability constant derivation

The Schubert method was used for Co-ISA stability con-stants, as well as the U(VI)-ISA stability constant at lowpH. The method uses an ion exchange resin and the metalconcentration is determined in solution in the presence andabsence of ISA. The ligand concentration is in large excess,so the equilibrium free ligand concentration is assumed tobe equal to the initial one. The distribution ratio (D) whichdescribes the distribution of metal between resin [Mres] andsolution phase [Msol], in the presence of ligand, is:

D = [Mres][Msol] (1)

This can be shown to give the following relationship [1]:

D = [Mres][Mx+] (A +β[Mx+]n−1[L]z)

(2)

Where A = 1 + β1(OH)[OH−] + β2(OH)[OH−]2 + ... as dis-cussed by Maes et al. [11].

The distribution (D0) of metal in the absence of ligand is:

D0 = [Mres]A[Mx+] (3)

Which leads to the well known Schubert expression for com-plexes containing one cation (n = 1):

β =(

D0

D−1

)A

[ISA]z(4)

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364 P. Warwick, N. Evans and S. Vines

Or in its logarithmic form:

log

(D0

D−1

)A = log β + z log [L] (5)

However, if n = 2, and mixed-hydroxo complexes areformed, a different expression is obtained [1]. In this case:

β = A2 D0

[Msol][L]z[OH]y D

(D0

D−1

)(6)

Thus the stoichiometry must be determined prior to themeasurement of the stability constant.

The solubility product approach was used for the deter-mination of the U(VI)-ISA stability constant at high pH. Themethod involved three stages:

(i) precipitation and ageing of amorphous UO2,(ii) equilibration of the oxide with the ligand and,(iii) measurement of supernatant solution activities.

In the first stage uranyl nitrate (UO2(NO3)2) solution,containing a tracer amount of 233U, was allowed to precip-itate. The precipitate was aged for 2 weeks. This reactionmay be represented as:

2UO22+ +2Na+6OH−� Na2U2O7 +3H2O

Hydroxo species can also be formed in solution and aretaken account of in the ‘A’ term in the same way as forthe Schubert method. This was calculated on the assump-tion that the significant species present were UO2(OH)4

2−(aq)

and UO2(OH)3−

(aq). The stability constants used were thosein the NIST database (log β(UO2(OH)4

2−) = 22.2 and

log β(UO2(OH)3−) = 22.2). Since water and the uranium

solid phases have unit activities, a pseudo solubility product(Ksp) was obtained. In the second stage, the solid was treatedwith ISA. Hence, the total dissolved uranium concentrationin the presence of ligand was equated to:

[U]total = [UO22+]A +[UO2ISA]

Blank samples without ligand were run to obtain a valuefor the solubility product for the precipitate, in this caseNa2U2O7 (am). A value of log Ksp = −57.51 was obtained.More details of this approach are given in Warwick et al. [1].

2. Experimental

Deionised water produced by a Barnstead NANOpure ultra-pure water purification system and AR reagents were usedthroughout. ISA lactone was prepared using the proceduredescribed by Whistler and BeMiller [12]. The radionuclides(109Cd, 57Co, 233U) were purchased from Amersham. Theresin used was BioRad 50W-X2 cation exchange resin con-ditioned to its sodium form. pH was measured using anOrion 720A meter with a glass electrode, which was cali-brated using an Aldrich volumetric standard sodium hydrox-ide solution. Spectrophotometric absorbances, were meas-ured using 1 cm silica cells in a Philips PU8730 UV/Visspectrophotometer. A Jenway 4310 meter was used to meas-ure conductivity. β-emitting isotopes were counted by li-quid scintillation counting in a Canberra Packard TRI-Carb2750TR/LL, using Ecoscint cocktail. Gamma-emitters werecounted on a Packard Cobra II Auto-Gamma.

2.1 Measurement of stoichiometry

2.1.1 Bjerrum plots

Bjerrum plots were constructed by adding varying amountsof NaOH (0.1 mol dm−3) to a mixture of metal chloride(0.01 mol dm−3) and NaISA (0.01 mol dm−3) to produce so-lutions containing M : OH− ratios from 0 to 4. Each solu-tion was adjusted to I = 0.1 mol dm−3 using KNO3. After14 days at 25 ◦C, the pH was measured and plotted againstM : OH− ratio.

2.1.2 Conductometric titrations

Three conductometric titrations were performed for eachmetal. In type A, 1 cm3 aliquots of metal chloride(0.1 mol dm−3) were added to 20 cm3 of 0.1 mol dm−3

sodium ISA and the conductance measured after each add-ition. In type B, excess NaISA (60 cm3) was added to 20 cm3

of NaOH (0.1 mol dm−3) and titrated with metal chloride. Intype C, 10 cm3 of NaISA were titrated with metal chlorideand NaOH (0.2 mol dm−3) simultaneously. After correctingfor dilution the results were expressed graphically.

2.1.3 Precipitate absorption method

Solutions containing Co (0.01 mol dm−3), excess NaISA(0.05 mol dm−3), and varying amounts of NAOH to giveOH− to Co mole ratios up to 4 : 1 were adjusted with0.1 mol dm−3 potassium nitrate to provide constant ionicstrength and equilibrated for a week, under nitrogen, to pre-vent auto-oxidation at high pH. Absorbances were measuredat 281 nm after filtration.

2.2 Measurement of stability constants

2.2.1 The Schubert method

All measurements were made at 25 ◦C. The experimentswere performed in 20 cm3 polypropylene vials containing1000 mg of resin. Each datum point was measured with fivereplicates. 15 cm3 aliquots of ISA solution, varying from10−1 to 10−6 mol dm−3, adjusted to the required pH withsodium hydroxide, were spiked with 107Cd, 57Co or 233U giv-ing a metal concentration between 10−8 and 10−9 mol dm−3,and equilibrated in a shaker bath for 72 hours. One setof vials had no resin, in order to determine whethermetal sorbed to the vial walls. 1 cm3 of supernatant liquidwas withdrawn, through a 0.45 µm filter, and the activitymeasured.

2.2.2 The Solubility product approach

Samples of amorphous Na2U2O7 were precipitated inNALGENE vials by mixing 5 cm3 of carbonate free NaOH(2.0 mol dm−3) and 2 cm3 of UO2(NO3)2 solution(0.01 mol dm−3; containing 233U tracer giving an activity ofca. 12 MBq dm−3). After two weeks, a 1 cm3 solution ofsodium ISA was added to the vials. Ten replicates wereperformed. The vials were shaken intermittently for twoweeks. In the experiments undertaken to obtain Ksp the su-pernatant activity was determined without ligand present ateach pH. All experiments were carried out at 25 ◦C and an



Studies on some divalent metal α-isosaccharinic acid complexes 365

ionic strength of I = 0.3. After two weeks, 5 cm3 of the su-pernatants were filtered off using a 0.45 µm syringe filter.3 cm3 were discarded to waste to allow for sorption ontothe filter etc. Specific activities (d.p.m. cm−3) were deter-mined using liquid scintillation counting in Ecoscint in glassvials. In many cases the measured activities were close tothe detection limits. Consequently long counting times wereused, the counting windows were carefully selected and thebackground sample matrices were closely matched to thesamples.

3. Results

3.1 Bjerrum plots for the determination ofstoichiometry

Cadmium isosaccharinate (Cd−ISA) appeared to form atleast two different complexes over the pH range 6–13.3.Below pH 7.9, a colourless soluble complex was formed.Above 7.9, an insoluble white precipitate occurred, whichpartially dissolved above pH 11. There was no evidence forOH− participation in the formation of the soluble complex.There was evidence for a 1 : 2 Cd : OH− ratio in the complex,as shown by the inflexion in the plot.

For Cobalt, at pH < 3 a soluble pink species wasformed. As the pH was raised, at pH = 3 a pink precipitatewas produced which partially re-dissolved above pH 8.4.The Bjerrum plot indicates a 1 : 2 Co : OH− ratio in thiscomplex.

For U(VI) at near-neutral pH, a soluble yellow specieswas formed which persisted up to pH 13. No evidence wasfound of OH− participation in the complex.

3.2 Conductometric titrations for the determinationof stoichiometry

For cadmium Fig. 2 shows evidence (Cd line A) of the for-mation of a 1 : 1 complex (Cd : ISA), shown by the changein gradient from 0.55 to 0.52 at 20 cm3 Cd solution added.Line B shows a Cd : OH− ratio of 1 : 2 in the complex(change at 10 cm3 from −0.46 to 0.39). Line C shows theformation of a complex with a Cd : ISA ratio of 1 : 1, whenthere are two OH− to every Cd2+ (change from 0.61 to 0.52at 9 cm3).

Figure 3 shows the formation of a cobalt-ISA complexwith a Co : ISA ratio of 1 : 1, (shown by the change in gra-

Fig. 1. Bjerrum plots for Cd, Co and U(VI).

Fig. 2. Conductometric titrations for Cd.

Fig. 3. Conductometric titrations for Co.

dient from 0.84 to 0.67 at 20 cm3 cobalt solution added) inthe absence of hydroxide ions. Line B shows a Co : OH− ionratio of 1 : 2 in the complex (change in gradient from −0.24to 0.18 at 10 cm3). Line C indicates the formation of a com-plex with a Co : ISA ratio of 1 : 1 when there were two OH−

ions to every cobalt (gradient change from 0.56 to 0.32 at10 cm3).

In the case of U(VI), line A in Fig. 4 shows evidenceof complex formation between uranium(VI) and ISA withmetal to ligand ratio of 1 : 1, shown by the inflexion from0.36 to 0.32 in the gradient at 10 cm3 uranium(VI) solutionadded. Line B shows the formation of a complex with a ura-nium(VI) to hydroxide ion ratio of 4 : 1 (change in gradientfrom −0.70 to 0.41 at 5 cm3).

Fig. 4. Conductometric titrations for U(VI).




3.3 Spectrophotometric studies for the determinationof stoichiometry

Only cobalt showed an absorbance peak for the complex(281 nm), which was sufficiently separated from the metaland its hydrolysis products to enable spectrophotometricmethods to be used for analysis.

3.3.1 Precipitate absorbance method for determinationof stoichiometry

Absorbances were measured at high pH with differingCo : OH− ratios. The minimum in Fig. 5 showed that theprecipitated complex contains a mole ratio of 1 : 2.

Summary of stoichiometric results

Table 1. Summary of stoichiometric results from acidic and near-neutral pH values.

Metal Cd Co U(VI)

Solution Colourless Pink YellowpH < 7.9 < 3 7Bjerrum plot No OH− No OH− No OH−

Conductometric Cd : ISA 1 : 1 Co : ISA 1 : 1 U : ISA 1 : 1Schubert Slope Co : ISA 1 : 1Species formed CdISA+ CoISA+ UO2ISA+

Table 2. Summary of stoichiometric results from high pH range.

Metal Cd Co U(VI)

Description White ppt Purple ppt Yellow SolutionpH > 11 > 8.4 13.5Precipitate Co : OH 1 : 2AbsorbanceBjerrum plot Cd : OH 1 : 2 Co : OH 1 : 2 No OHConductometric Cd : OH 1 : 2 Cd : ISA 1 : 1 Co : OH 1 : 2

Co : ISA 1 : 1 U : ISA 1 : 1 U : OH 1 : 4Schubert Slope Cd : ISA 1 : 1Species formed a CdISA(OH)2 CoISA(OH)2 UO2ISA(OH)4

a: Charges omitted from species formed.

Table 3. Summary of stoichiometric results from intermediate pHrange.

Metal Cd Co

Description White precipitate Pink precipitatepH 7.9–11 3–8.4Precipitate Absorbance Co : OH 1 : 2Bjerrum plot Cd : OH 1 : 1.5 Co : OH 1 : 2Conductometric Cd : ISA 1 : 1 Co : OH 1 : 2

Cd : OH 1 : 2 Co : ISA 1 : 1Schubert Slope Cd : ISA 1 : 1Species formed CdISA(OH)2 CoISA(OH)2

3.4 Measurement of stability constants

It has been assumed that stoichiometries measured at rela-tively high concentrations can be used in the calculation ofstability constants measured using relatively low metal con-centrations.

Fig. 5. Precipitate absorbance method for cobalt ISA.

3.4.1 Cadmium

At pH 7, the stoichiometry of the complex was determinedto be 1 : 1 i.e. CdISA. The derived value, using equation (5),for the stability constant was log β = 2.9 ± 0.6. The con-stants for all other complexes of the form M1L1 were cal-culated using this equation. The side-reaction-coefficient(A term) was calculated on the assumption that the sig-nificant species present were Cd2+

(aq) and CdOH+(aq). The

stability constants used were those in the NIST [13] database(log β = 3.9). All speciations were performed using the pro-gramme JCHESS [14]. Fig. 6 shows the distribution of Cdbetween the supernatant solution and resin, with fit curvesshown to highlight each set of data. The values of D wereused to calculate β from equation (5). The measured con-stants remain conditional until the pKa values for the hy-droxy groups on the ISA are determined.

At pH = 10, the stoichiometry of the complex was deter-mined to be CdISA(OH)2. Using

β =(

D0

D−1

)A

[ISA][OH]2

the calculated value for the stability constant was log β =11.7 ± 1.1. The constants for all other complexes of theform M1L1(OH)n were calculated using this equation. TheA term calculation assumed that the significant species

Fig. 6. Distribution of Cd between supernatant and ion exchange resin.



Studies on some divalent metal α-isosaccharinic acid complexes 367

were Cd(OH)2 (aq) and Cd(OH)+(aq). The constants used

to calculate the A term were log β(Cd(OH)2) = 7.7 andlog β(CdOH+) = 3.9. At pH = 13.3, the complex was de-termined to be CdISA(OH)2. Using the same equation thederived value for the stability constant was log β = 11.5±0.1. The significant species present were assumed to beCd(OH)2 (aq), Cd(OH)3

−(aq) and Cd(OH)4

2−(aq). The constants

used were log β(Cd(OH)2) = 7.7, log β(Cd(OH)3−) = 10.3

and log β(Cd(OH)42-) = 8.7.

3.4.2 Cobalt

The variation of D with ISA concentration is shown inFig. 7. At pH 7, the stoichiometry of the complex was de-termined to be CoISA. The derived value for the stabilityconstant was log β = 1.2±0.1. The A term was calculatedon the assumption that the only significant species presentwas Co2+

(aq). The Schubert plot also indicated that the ratioof metal to ligand is 1 : 1. At pH 10, the stoichiometry wasdetermined to be CoISA(OH)2. The derived value for theconstant was log β = 10.8±1.2. The A term calculation as-sumed the significant species present was Co(OH)3

−(aq). The

constant used was (log β = 10.5 [13]). At pH 13.3, the com-plex was determined to be CoISA(OH)2. The derived valuewas log β = 12.4±0.8. It was assumed that the significantspecies was again Co(OH)3

−(aq).

3.4.3 Uranium (VI)

The variation of D with ISA concentration is shownin Fig. 8. At pH 7 the complex was determined to beUO2ISA. The derived value for the stability constant waslog β = 6.5 ± 0.2. The A term was calculated on the as-sumption that the significant species present were UO2

2+(aq),

UO2OH+(aq), and UO2(OH)2 (aq). The stability constants used

were those in the NIST and CHESS databases respectively(log βUO2OH+

(aq) = 7.7 and log βUO2(OH)2 = 17.25).

3.4.4 Uranium (VI) ISA at High pH

This constant was measured using the solubility prod-uct approach. Samples without ligand were measured to

Fig. 7. Distribution of Co between supernatant and ion exchange resin.

Fig. 8. Distribution of U(VI) between supernatant and ion exchangeresin.

obtain a value for the solubility product for the precipi-tate (Na2U2O7 (am)). A value of log Ksp = −57.5 was ob-tained. The side-reaction-coefficient (A term) was cal-culated on the assumption that the significant speciespresent were UO2(OH)4

2−(aq) and UO2(OH)3

−(aq). The sta-

bility constants used were those in the NIST database(log β(UO2(OH)4

2−) = 22.2 and log β(UO2(OH)3

−) = 22.2).

Determination of a conditional stability constant, using themethod in Warwick et al. [5] gave a value of log β = 18.8±1.6 for uranium(VI) ISA at high pH.

4. Discussion

The measured constants are shown in Table 4. Each com-plex formed at near-neutral pH was of the form M1ISA1,with log β values in a range suggestive of salt formation, ex-cept the oxycation UO2

2+ for which log β = 6.5. In all casesOH− ions have been involved in the formation of complexesat high pH. It is not clear whether the OH group was co-ordinated to the cation in addition to the ISA, or if chelatecomplexes were formed with the consequent elimination ofhydrogen ions from the ligand, e.g. the equation for the for-mation of the Cd complex at high pH could be:

Cd2+ + ISA− +2OH− → CdISA− +2H2O or

Cd2+ + ISA− +2OH− → CdISA(OH)23− +2H+

More work is required to determine which of these pos-sibilities is applicable to each complex [5]. However, forthe purposes of consistency in this paper the stoichiometryof the complexes has been written as though the hydroxylgroups are co-ordinated to the metal. At pH 13.3 the con-stants were in the region log β = 10–14, with 2OH− ionsbeing involved in their formation, apart, again, from U(VI).

These constants have enabled speciation calculationsto be performed using the computer programme JCHESS,showing the effect of ISA on the solubility of the metals.

Table 4. logβ values of complexes.

Cation Near-Neutral pH pH 10 High pH

Cd2+ 2.9 ±0.6 11.7±1.1 11.5±0.1Co2+ 1.2 ±0.1 10.8±1.2 12.4±0.8UO2

2+ 6.50±0.2 18.8±1.6




Fig. 9. Variation of solubility enhancement factor with pH.

Of particular interest to PA is the effect of ISA in the near-field and the alkaline-disturbed-zone. In order to show this,a solubility enhancement factor was determined; calculatedfrom:

Enhancement Factor =metal solubility in presence of ISA (mol dm−3)

metal solubility in absence of ISA (mol dm−3)

Figure 9 shows the variation of enhancement factor againstpH for all di- and trivalent cations for which log β values areknown. Metal solubility is enhanced between pH 9 and 13.5,indicating that ISA may have a major impact on the fate ofradionuclides in the near-field of a cementitious repository.The largest enhancements are for Co (> 1000×), Ni, andCd. The enhancement for Co and Ni falls at higher pH ashydrolysis products become more significant. The smallesteffect is on U(VI).

Acknowledgment. This work was performed at Loughborough Univer-sity under contract to UK Nirex. The principal authors would like tothank UK Nirex for their support.

References

1. Warwick, P., Evans, N., Hall, A. Vines, S.: Complexation of Ni(II)by α-isosaccharinic acid and gluconic acid from pH 7 to pH 13.Radiochim. Acta 91, 233 (2003).

2. Warwick, P., Evans, N., Hall, A. Vines, S.: Stability constants ofuranium(IV)-α-isosaccharinic acid and gluconic acid complexes.Radiochim. Acta 92, 897 (2004).

3. Ilett, D. J., Pilkington, N. J., Tweed, C. J.: Complexation of ra-dionuclides, proceedings of the royal society of chemistry/NirexSymposium, The chemistry of deep disposal of radioactive waste.Loughborough University, Loughborough, UK (1997).

4. Bourbon, X., Toulhoat, P.: Influence of organic degradation prod-ucts on the solubilisation of radionuclides in intermediate and lowlevel radioactive wastes. Radiochim. Acta 74, 319 (1996).

5. Greenfield, B. F., Hurdus, M. H., Spindler, M. W., Thomason, H. P.:The effects of the products from the anaerobic degradation of cel-lulose on the solubility and sorption of radioelements in the nearfield. Nirex report NSS/R376, Nirex, Didcot, UK (1999).

6. Nirex Generic Disposal System Specification. Nirex, Didcot, UK(2000)

7. Vercammen, K., Glaus, M., Van Loon L.: Complexation of Th(IV)and Eu(III) by α-isosaccharinic acid under alkaline conditions.Radiochim. Acta 89, 393 (2001).

8. Joyce, L. G., Pickering, W. F.: An investigation of the metal glu-conate system. Aust. J. Chem. 18, 783 (1965).

9. Ashton J. F., Pickering W. F.: Cobalt(II) gluconate complexes.Aust. J. Chem. 23, 1367 (1970).

10. Rossotti, F. J. C., Rossotti, H.: The determination of stability con-stants and other equilibrium constants in solution. McGraw-Hill,New York (1961).

11. Maes, A., De Brabandere, J. Cremers, A.: A modified schubertmethod for the measurement of the stability of europium humicacid complexes in alkaline conditions. Radiochim. Acta. 44/45,51 (1988).

12. Whistler, R. L., BeMiller, J. N.: α-D-isosaccharino-1,4-lactone. In:Methods in carbohydrate chemistry. Vol. 2 Reactions of carbo-hydrates. (Wolfram, M. L., BeMiller, J. N., eds.) Academic Press,New York (1963) p. 477.

13. Martell, A. E., Smith, R. M.: Critical Stability Constants. Vol. 3,Plenum Press, New York (1989).

14. Van der Lee, J.: JCHESS Software for geochemistry, hydrol-ogy and environmental science. Ecole des Mines de Paris,Fontainebleau, France (2002).



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