Mkdpsr13 by Dr DPS RATHORE

Exploration and Research for Atomic Minerals Vol. 23, 2013, pp. 217-225

AMBERLITE XAD-2 FUNCTIONALIZED WITH PHENOLIC LIGANDS AS METAL ION EXTRACTANTS: A REVIEW Manjeet Kumar1 and D. P. S. Rathore2 Chemical Laboratory, Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, New Delhi1, Nagpur2 E-mail: manjeetkumar.amd.gov.in

Abstract The designing and characterization of promising chelating resins based on Amberlite XAD-2 and their analytical applications are discussed in this review paper. The chelating resins synthesized in the author’s laboratory were also discussed alongwith comparison with other preconcentrating matrices. Keywords: Amberlite XAD - 2, Metal ion extractants, Review, Phenolic ligands

INTRODUCTION

at micro and trace levels continue to be of The estimation of metal ions at a very low current interest and a challenging problem at concentration level is considered very important many instances. in the context of geochemical explorations, Moreover, the upsurge of new environmental monitoring, biosorption, clinical information about the toxicity of several metal and forensic analysis, high purity material ions has made the metal estimation at a further designing and other miscellaneous applications. lower concentration level absolutely essential The need for preconcentration of trace metal and preconcentration a greater necessity if ions in aqueous solutions or in other matrices common analytical methods like flame atomic results from the following two important absorption spectrometry have to be used. factors: Similarly, the increased interest in high purity (i) Many times, direct application of instrumental analytical methods to complex samples is restricted due to the concentration of analyte being below the detection limits due to unfavourable signal to noise ratio.

materials during last few decades has also encouraged new initiatives in trace metal analysis like coupling of a preconcentration/ separation procedure with the instrumental measurements.

To cope up with the newly emerging (ii) The analysis of the trace elements where challenges, separation and preconcentration of large and variable matrix interferences metal ions are often coupled with the would otherwise preclude reliable analysis. instrumental methods. There are number of i.e., when methods do not have necessary instrumental techniques employed for the selectivity, sensitivity or freedom from matrix determination of metal ions. These include interferences. In all such cases the inductively coupled plasma - atomic emission preconcentration / separation of the metal ions spectrometry (ICP – AES), inductively coupled to be analysed is essential. Thus separation/ plasma - mass spectrometry (ICP – MS), atomic enrichment of metal ions from complex matrices fluorescence spectrometry (AFS), X-ray (e.g., water from various sources) selectively fluorescence (XRF), neutron activation analysis 217

Manjeet Kumar and D. P. S. Rathore

(NAA), fluorimetry, ion chromatography (IC) and flame or electrothermal atomic absorption spectrometry (Flame or ET – AAS). However, the desirable stringent requirements of accuracy, sensitivity, versatility and specificity in the analysis have to be kept in mind before any such endeavor. Atomic absorption spectrometry (flame and graphite furnace) on coupling with a preconcentration method may easily result in a fast, accurate, economical and sensitive method, suitable for micro and trace analysis. The methods commonly used for analyte separation/ preconcentration include: (i) Evaporation, (ii) Co-precipitation, (iii) Liquid-liquid extraction), and

extraction

(solvent

(iv) Solid-liquid extraction ((a) ion exchange, and (b) chelating ion exchange resins). On evaporation, matrix effects (total dissolved salts) are increased, thereby creating problem during nebulization of the solution, while in co-precipitation, several factors may contribute to lack of quantitative recovery in addition to the solubility of the precipitate. Although solvent extraction is one of the most popular techniques for the separation of metal ions but has limited application in enriching trace amounts of ions present in dilute solutions. This is because the degree of extraction decreases as the aqueous-to-organic phase ratio is increased, effectively limiting the sample size used and the preconcentration factor achieved. The attainment of equilibrium may take several hours. The mutual solubility of two phases, emulsion formation, toxic nature of organic solvents and handling of large volume of organic solvent, which is inflammable, are other disadvantages. Many times multi-step extraction is also necessary for complete recovery.

On the other hand, ion exchangers are insoluble solid materials, which contain exchangeable cations or anions. These ions can be exchanged for a stoichiometrically equivalent amount of other ions initially present in an electrolyte solution when an ion exchanger is brought into contact with it. While chelating ion exchange resins represent an important category of synthetic resins frequently employed to selectively preconcentrate metal ions from large sample volume, followed by determination with an element specific detectors. Ion exchange chromatography and chelating ion exchangers both have been used extensively for preconcentration and separation of metal ions. These resins do not work in the same way as conventional cationic or anionic resins. The methods commonly used for analyte separation/ preconcentration include: evaporation, coprecipitation, liquid-liquid extraction (solvent extraction), and solid-liquid extraction (ion exchange, and chelating ion exchange resins). The chelating resins have been found useful for separation and preconcentration of not only transition, alkaline earth, rare-earth, and uranium metal ions but are also useful in organic synthesis, polymer drug graft, and catalysis. A number of references [1-12] detailing with the separation/ preconcentration of metals ions by chelating resins have appeared in the last two decades. Chelating polymeric resins: Chelating ion exchange resins have received considerable attention owing to their inherent advantages over simple ion exchangers, i.e., their greater selectivity to bind metal ions. They are also designated as “functionalized polymers”, “chelating sorbents”, “chelating resins” and “chelating polymeric resins”. They are generally prepared by immobilizing a chelating ligand onto a support matrix through physical sorption or chemical spacer/ coupler. The kind of metal ion and the ligand strictly determine the bond

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Amberlite XAD-2 Functionalized with Phenolic Ligands as Metal Ion Extractants: A Review

length and angle between the central metal ion CH 2 —) spacer is generated through the and the coordination ligands in metal chloromethylation of ligand or polymer matrix complexes. followed by Friedel Crafts alkylation with an appropriate moiety. The azo (—N=N—) spacer Chelating resins sorb metal ions through is created when Amberlite XAD-2, (having chelation. The term chelate effect refers to the polystyrene divinylbenzene skeleton) after fact that a chelated complex, i.e., one formed cleansing was nitrated and thereafter the nitro by a bidentate or a multidentate ligand, is more groups were reduced to get the amino polymer. stable than the corresponding complex with It was then diazotized and resulting diazonium monodentate ligands. The greater the number salt was coupled with phenolic ligands in of points of attachment of ligand to the metal weakly alkaline media or amino ligands in ion, the greater is the stability of the complex. weakly acidic media. Chelating/ functionalized groups are usually capable of interacting with a large number of Characterisation of chelating resins and metals forming a five / six membered chelate their metal complexes: The characterizations ring, but the stability of the formed complexes of newly synthesized chelating resins involve differs and depends on sorption conditions. use of analytical and physico-chemical techniques. The physical methods are of Synthesis of chelating polymeric resins: greater importance as the selectivity is Chelating resins based on organic polymers considered to depend on the chelating may either have functional groups in their functional groups, which determines the polymeric skeleton or modified by chelating coordination behaviour of these groups ligand that is immobilized by physical towards the metal ions and the geometry adsorption onto them via p -p dispersion forces around the metal ions. and/ or ion exchange, or chemical bonding. The chelating resins developed through physical Analytical applications of amberlite XAD-2 adsorption on polymer matrices suffer from based functionalized polymers: The ligand leaching problem and offers restricted combination of porous (less cross-linked) reusability of the resin. Nevertheless, their easy polymeric supports and multifunctional ligands preparation is definitely an advantage. The (preferably of small molecular size) appear to anchoring of ligands on these polymers be suitable for designing such resins. through covalent bonding is attained, either by Amberlite XAD-2 is commercially available, covalently immobilized on them directly or via sufficiently macro-porous, mechanically and chemical spacer/ coupler. The methylene (— chemically stable. They are not highly crossCH 2—) spacer and azo (—N=N—) spacer are linked and therefore may be good supports for commonly used. The immobilization of ligands designing the desired chelating resins [13-15]. through covalent linkage on the polymer The ligands chosen viz. o-aminophenol (o-AP) matrix as a pendant group with or without and tiron (TIR) has small molecular size and spacer offers much wider ranges of pyrogallol (PG), quinalizarin (QA) and 2possibilities in fabricating chelating resins and Thenoyl Tri fluoro acetone (TTA) has multiple consequently their tailoring for applications sites for coordination. Amberlite XAD-2 has (such as a preconcentrating matrix for metal been covalently linked to four ligands (Figure ions) becomes possible. The methylene (— 1) through azo spacer.

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Manjeet Kumar and D. P. S. Rathore

SYNTHESIS OF AMBERLITEXAD-2 BASED CHELATING RESINS

Fig. 1. Synthesis of Amberlite XAD-2 based chelating resins

The non-ionic Amberlite XAD-2 has been coated with a variety of chelating ligands. Pyrocatechol violet (2) impregnated Amberlite XAD-2 has been used to preconcentrate Pb(II), In(II), Zn(II) and Cd(II) before their determination by AAS. Preconcentration factor was found to be 100 except for Pb for which the factor was ~80. 4-(2-Pyridylazo) resorcinol (3) coated Amberlite XAD-2 has been studied for its analytical applications. It has been found

suitable in the presence of tetraethylenepentamine for the separation of silver from copper ores prior to its determination by AAS. Willis and Sangster have studied Amberlite XAD-2 as adsorbent for extracting Fe-1,10-phenanthroline complex. A preconcentration factor of ~200 for Fe can be achieved by using different eluents like methanol and methanol-hydroxyl ammonium chloride for eluting the adsorbed complex.

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Amberlite XAD-2 Functionalized with Phenolic Ligands as Metal Ion Extractants: A Review

Vernon and Eccles have immobilized 8hydroxyquinoline (4) and salicylic acid (7) on Amberlite XAD-2 through the formation of an azo linkage between polymer matrix and the ligands but they neither characterized the resins properly nor explored their metal enrichment property in detail. Amberlite XAD-2 functionalized via azo coupling with Alizarin Red-S (8), Salicylic acid (7) and pyrocatechol violet (2) have been used for metal enrichment. With Alizarin Red-S immobilized resin, separation and preconcentration of Cd, Ni, Pb and Zn were carried out in pH range 3-6. The metal ions were eluted with 1-4 M HCl or HNO3. Its sorption capacity is between 100 and 8-Hydroxyquinoline (4) and 8hydroxyquinoline-5-sulphonic acid (5) impregnated Amberlite XAD-2 and Bio-Rad AG MP-1 have been used to enrich Ca(II), Cd(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) before their determination by ICP-AES. The enrichment factor was ~100 with detection limits of 0.1 (Mg) to 25.0 (Pb) mg/L. 500 mg/g resin and preconcentration factor 40 for all the metals studied. Salicylic acid Eriochrome Blue-Black R (6) modified Amberlite XAD-2 was used to impregnated Amberlite XAD-2 has been preconcentrate Zn(II) and Pb(II) at pH 5.0 and investigated for the retention of Cr(III), Fe(III), 4.0-6.0 respectively with a recovery of 98-100 Co(II), Ni(II), Cu(II), Zn(II), Ga(III), In(III), % (using 2-4 M HCl or HNO3 as an eluent). Pb(II) and Bi(III). It has been used to The sorption capacity for Zn and Pb is 1146 preconcentrate Ni(II) selectively before its and 461 mg/g respectively and preconcentration determination with AAS and flow injection factor between 150 and 200. The resins coupled AAS. The limit of determination is 0.1 containing ligands 7 and 8 were applied to water Îźg/L. samples for the collection of these four metal ions. The recovery is good with a RSD value 4.7-10.1 %. Amberlite XAD-2 functionalized with pyrocatechol violet was employed to enrich Cd(II), Ni(II), Pb(II), and Zn(II) ions prior to their determination by FAAS. The optimum pH for their sorption is 5, 5-7, 4 and 3 respectively. The preconcentration factor for them varies between 20-60. In their

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Manjeet Kumar and D. P. S. Rathore

collection (1 mg/L of each metal ion), F-, NO3and PO4- ions do not interfere upto 0.1-0.5 M level. The sorption capacities for these metal ions vary between 0.6 and 1.4 mg/g of resin. For enrichment of Cu(II), Zn(II) and Pb(II) from aqueous solutions, Jain et al. have used ovanillin thiosemicarbazone (o-VTSC) (9) immobilized Amberlite XAD-2 and found that the preconcentration factor was 90, 140 and 100 respectively. The sorption capacity is between 850 and 2000 mg/g of resin and loading half time, (t1/2) 26, 5 and 11 min. respectively for the three metals. o- VTSC chelating resin, having O, N and S binding sites, was also utilized for sequential chromatographic separation of Th(IV) and U(VI) from river water and geological standard samples, prior to their determination by spectrophotometry, and ICPAES and GF-AAS, respectively. The preconcentration factor of 105 and 100, sorption capacity of 1600 and 1525 mg/g resin and loading half time of 7 and 10 min. was found for these two metals. Detection limit achieved is 100 ng/mL.

been developed for extraction of Cd(II), Cu(II), Co(II), Fe(III), Ni(II), Pb(II) and Zn(II). The metals can be quantitatively sorbed in the pH range 4.0-7.0. The sorption capacity of the resin is between 23 and 310 mmol/g of resin, whereas preconcentration factor between 80 and 400 at concentration level 5-25 mg/L has been achieved. Xylenol orange coated Amberlite XAD-2 was used to preconcentrate Zn(II), Pb(II), Ni(II) and Cu(II) at mg/L levels from seawater.

1-(2-Pyridylazo)-2-naphthol (13) immobilized on Amberlite XAD-2 (through azo coupler) and calmagite (14) (through physical sorption) were used for separation and preconcentration of Ni(II) and Cu(II) in the pH range 6.0 - 11.5 and 3.7-10.0 respectively, prior to their determination by ICP-AES and FAAS. The sorption capacity for Ni(II) and Cu(II) was found to be 1.87 and 1.59 mmol/g (of resin) respectively with a preconcentration factor of around 50 for both. Preconcentration of trace metals [Cd, Hg, Ni, Co, Cu and Zn] on 2(methylthio)aniline-functionalized XAD-2 was carried out from tap water and river water samples, prior to their determination by flame atomic absorption spectrometry. The recoveries were>96%. The procedure was validated by standard addition and analysis of a standard river sediment material (GBW 08301, China). Amberlite XAD-2 dispersed in the sample The limit of quantification for Cd, Hg, Ni, Co, was used for total sorption of metal ions (Cd, Cu and Zn were 0.041, 0.043, 0.052, 0.064, Co, Cu, Fe, Ni and Pb) previously complexed 0.058, 0.083 g/L, respectively. with ammonium pyrrolidene dithiocarbamate ligand solution buffered to pH 4.5. After filtration, the resin was recovered and redispersed by means of a non-ionic surfactant (Triton X-100). Metals retained were determined with the slurry-sampling technique coupled with ICP-AES detection. Oxine (8-hydroxyquinoline) (4) after Recently chromotropic acid (10), Pyrocatechol (11) and thiosalicylic acid(12) chloromethylation was coupled with Amberlite functionalized Amberlite XAD-2 resin have XAD-2 through Friedal-Crafts alkylation. It

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Amberlite XAD-2 Functionalized with Phenolic Ligands as Metal Ion Extractants: A Review

resulted in a chelating resin which was used to extraction of Pd, Pt and Rh in alloys and ores. concentrate free Mg(II) ions in the presence of The detection limits were 3-8 ng/mL for 1 min kinetically labile complexes of magnesium with of preconcentration. The copper (II) chelate of EDTA and oxalate. N-(dithiocarboxy) sarcosine is sorbed on a column of Amberlite XAD-2 resin from a 0.1 M phosphate solution (pH~7) and stripped with an ammonia solution made in 60% methanol (pH~9). The absorbance of the eluted chelate is measured by spectrophotometry. The method is highly selective and was applied to seawater.

Cortina and Warshawsky have reviewed the recent developments in solid-liquid extraction by solvent-impregnated resins particularly organo-phosphorous extractants (D 2 EHPA, TIBP, DTMPPA, TOPO, TBP). Amberlite XAD-2, 4 and 7 resins have been used as support matrices. The Amberlite XAD2 systems are better than those based on Amberlite XAD-4 and 7. The recovery, separation and kinetics of sorption of platinum group metals with Alamine 336 impregnated Amberlite XAD-2 was studied by Rovira et al. Rh(III) is hardly extracted, whereas extraction of Pd(II) and Pt(IV) takes place due to the formation of (R3NH)2MCln complexes where n = 4 for Pd(II) and n = 6 for Pt(IV). Ferreira and Brito used Amberlite XAD-2 loaded with 2-(2thiazolylazo)-p-cresol (15) for separation and preconcentration of Co, followed by ICP-AES determination. They found that the capacity of the column was 3.75 mmol/g of resin with a preconcentration factor of ~ 100. 4-(n-octyl) diethylenetriamine 1 loaded Amberlite XAD-2 and 8 have been used for online solid phase

Amberlite XAD-2 also finds its utility in removing organic matter apart from metal enrichment. Wu and Gaind have reported that Tryptamine coated Amberlite XAD-2 resin is most efficient among several solid sorbent coated with Tryptamine and used for the collection of airborne phenylisocyanate in workplace. Amberlite XAD-2 has also been used as such for separation, enrichment and determination of human fecal bile acids, rapid detection and quantification of basic drugs, extraction of mutagens, determination of methaqualone in blood plasma, extraction of carbamate insecticides from natural water, isolation and concentration of organophosphorus pesticides from drinking water, isolation of drugs from autopsy material, estimation of testosterone binding capacity in the serum, extraction of steroid diconjugates and determination of plasma aldosterone by radioimmunoassay and separation of organic acids like carboxylic acids, sulphonic acids and amino acids. Inter-comparison of sorption capacities, preconcentration factor and loading half time of Amberlite XAD-2 based preconcentrating matrices are tabulated in Table 1, 2 and 3 respectively.

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Manjeet Kumar and D. P. S. Rathore Table 1. Inter-comparison of sorption capacities of Amberlite XAD-2 based preconcentrating matrices

Metal ion (mmol g-1)

Immobilized ligand Cu

Tiron o-Aminophenol Pyrogallol Quinalizarin o-Vanillinthiosemicarbazone 1-(2- Pyridylazo)-2naphthol Alizarin Red â&#x20AC;&#x201C; S Pyrocatechol violet Salicylic aci Calmagite 2-(2-Thiazolylazo)p-cresol Chromotropic acid

Support: Amberlite XAD-2 110.2 214.6 60.3 169.7 182.0 100.3 32.4 58.0 55.2 16.0 45.0 69.6 69.7 32.4 69.4 82.1 82.7 18.9 27.5 25.5 21.7 17.1 9.2

220.3 53.0 71.3 49.6

84.5 30.4 46.4 15.1

13.3

9.65

22.9

6.4

1.10 1.6

11.3 -

2.4 -

1.9 1.5 10.5 -

7.8 6.6 2.2 -

21.6 17.5 -

133.8

83.2

3.7 65.2

103.4

186.3 147.6

58.0

Table 2. Comparison of preconcentration factor of Amberlite XAD-2 functionalised resins with other preconcentrating matrices Immobilized ligand

Metal ion Cu

o-Aminophenol Tiron Pyrogallol Quinalizarin o-Vanllinthiosemi -carbazone 1-(2- Pyridylazo)-2 -naphthol Alizarin Red Pyrocatechol violet Salicylic acid Calmagite 2-(2-Thiazolylazo) -p-cresol Chromotropic acid Thiosalicylic acid Pyrocatechol Dithiocarbamate

50 200 65 100

50 50 40 50

Support : Amberlite XAD-2 100 65 40 40 55 150 25 180 65 65 120 25 160 120 40 50 100 65

80 140 -

150 70 65

90 a

100 a

140 a

100 b

â&#x20AC;&#x201C;S 50

50 -

40 -

40 18 -

40 23 140 -

40 60 180 -

40 -

100 200 100 20

100 100 200 200 20

150 180 200 20

200 200 200 20

200 100 200 20

200 200 100 20

120 400 80 20

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Amberlite XAD-2 Functionalized with Phenolic Ligands as Metal Ion Extractants: A Review

Table 3. Comparison of Loading Half Time, t1/2 or Time for Saturation (min.) Immobilized ligand

Tiron o-Aminophenol Pyrogallol Quinalizarin o-Vanillinthiosemicarbazone Pyrocatechol violet

Metal ion Cu

2.9 (10) 14.0 2.6 8.5

3.6 (10) 8.0 2.3 5.3

Support : Amberlite XAD-2 2.9 3.8 4.0 2.9 (10) (10) (10) (10) 10.0 15.0 18.0 11.0 2.7 3.0 3.3 2.1 10.2 15.0 7.4

26 10 (100) -

12h

Chromotropic acid 2.9 2.6 4.3 (minimum time for saturation in bracket)

CONCLUSION

3.2 (10) 2.5 14.1

2.8 (10) 2.0 -

3.6 (10) 2.8 6.3

5 10 (30) 12h

10 52

11 10 (45) -

3.4

3.2

2.4

5.8

7. C. Kantipuly, S. Katragadda, A. Chow and H. D. Gresser, (1990). Talanta, v. 37, p. 491.

In the present paper critical review has been presented on Amberlite XAD-2 8. D. Bilba, D. Bejan and L. Tofan, (1998). Croatia Chim. Acta, v. 71, p.155. functionalized with phenolic ligands as metal ion extractants with their synthesis, 9. B. S. Garg, R. K. Sharma, N. Bhojak and S. Mittal, (1999). Microchem. J., v. 61, p. 94. characterization and analytical applications in natural waters and synthetic systems. 10. C. Y. Liu and K.L. Cheng, Chelating polymers, in “Facets of Coordination ACKNOWLEDGEMENT Chemistry”, (eds.) B. V. Agarwala and K. N. Munshi, (1993). World Scientific, The authors wish to thank Shri P. S. Singapur, Ch. 10, pp. 123-135. Parihar, Director, Additional Director (OP-II), Regional Director, NR and Head, Chemistry 11. D. E. Leyden and W. Wegscheider, (1981). Analytical Chemistry, v. 53, 1059A. Group and Incharge, Chemistry Lab., NR, AMD for kind permission to publish. 12. G. Schmuckler, (1965). Talanta v. 12, p. 281.

REFERENCES

13. M. Kumar, Ph. D. thesis entitled “Amberlite XAD-2 Functionalized with Phenolic 1. R. S. S. Murthy, J. Holzbecher and D. E. Ligands as Metal Ion Extractants” submitted Ryan, (1982). Rev. Anal. Chem., v. 6, p. 113. to Indian Institute of Technology, Delhi in July, 2001 and references therein. 2. S. K. Sahni and J. Reedijk, (1984). Coord. Chem. Rev., v. 59, p. 1. 14. M. Kumar, D. P. S. Rathore and A. K. Singh, (2000). Analyst, v. 125, p. 1221; (2000). Talanta,v. 51, p. 1187; (2001). Mikrochimica Acta, v. 137, p. 127; Fresenius J., (2001). Analytical Chemistry, v. 370, p. 377.

3. K. Schwochau, (1984). Top. Curr. Chem., v. 124, p. 91. 4. M. Kumar, (1994). Analyst, v. 119, p. 2013. 5. G. V. Myasoedova and S. B. Savvin, (1986). Crit. Rev. Anal. Chem., v.17, p.1. 6. P. Mac Carthy, R. W. Klusman and J. A. Rice, (1987). Anal. Chem., v. 59, 308R.

15. M. Kumar, (2007). Exploration and Research for Atomic Minerals, v. 17, pp.1520.

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