Synthesis and characterization of a poly(aminophosphonic acid) chelating resin

53

Analytrca ChlmrcaActa, 264 (1992) 53-58 Elsevler Science Pubhshers B V , Amsterdam

Synthesis and characterization of a poly(aminophosphonic acid) chelating resin M C Yebra-Bmrrun,

A BermeJo-Barrera

and M P Bermejo-Barrera

Department of Analyhcal Chemistry, Nutrrtron and Bromatology, Chemrrtry Faculty, Unruers~tyof Santtago de Compostela, 157064anttago de Compostela &am) (Recewed 2nd January

1991, revtsed

manuscnpt received 20th January 1992)

Abstract

Prehmmary mvesttgatlons on the apphcatlon of a polystyrene macroretlcular, cross-lmked poly(ammophosphomc acld) resm for the concentration of trace metals from aqueous solutions are reported The pH dependence of metal-resm chelation was determmed for M&I), Ca(II), Fe(III), CrtIII), N1(11),Cu(II), Pb(II), Zn(II) and M&I) The resm exhlblts no affnuty for the alkah metals tested over the pH range 1-14 The resm selectlvlty and capacity were determmed at pH 5 Metals were easily recovered by elutlon with 3 M hydrochloric acid and determmed m the eluate by flame atomx absorption spectrometry Keywords Atomic absorption spectrometry, tlon, Trace metals, Waters

Sample preparation,

Metal chelating resms have found wldespread apphcab&ty owmg to their selectlvlty Different functlonal kroups have been lmmoblltzed on styrene-drvmylbenzene matrlces by chemical reactions A large number of chelating polymers have been developed Polystyrene-divmylbenzene copolymer IS an extensively used matrix for chelating polymers because it 1s readily avallable and sufficiently durable Moyers and Fritz [I] synthesized resms contammg a propylenedlaminetetraa~tlc acid functIona group Phllhps and Fr&z [2] utilized hydroxamic aad resins for bmdmg metal tons Alexandratos et al [3] synthesized and characterized resins with phosphomc aad/phosphonate ester hgands and phosphomc aad/tertlary amme hgands on a polystyrene supCorrespondence to Prof Dr M P BermeJo-Barrera, Department of AnalytIcal Chemistry, Nutrltlon and Bromatology, Chemlstxy Faculty, Umverstty of Santiago de Compostela, 15706-Santiago de Compostela (Spam) ~3-2670/92/$05

Polfiammophosphomc

aad) resm, Preconcentra-

port Yokoyama et al [4] prepared and studied the chelation properties of polystyrene-dwmylbenzene copolymer resms contammg pyndylammes, sahcyfamme and 2-thenylamme Ueda et al [5] separated and concentrated lead, uramum and copper using polystyrene resms functlonallzed with azobenzylphosphomc acid hgands Szczepamak and Slepak [6,71 synthesized a chelatmg ion exchanger contammg ammomethanephosphomc acid with a styrene-dlvmylbenzene support and studied the separation of bland tervalent catlons by elutlon with perchlonc acid Petrov et al [S] prepared and compared ion exchangers containing ammophosphomc, ammophosphonate and ammophosphmlc groups However, m these studies apphcatlons of the synthesized resins were not presented Myasoedova and Sawm [9] and Smu-nov and Makarova [lo] reviewed chelating sorbents and their use m analytlcal chemistry and speclflc ion exchangers with functional groups, respectively

00 @ 1992 - Elsevter Science Publishers B V All nghts reserved

MC

54

The mam hmmatlon of most resms 1s that they are based on a mlcroretlcular copolymer matrix This means that the resin undergoes major changes that can disrupt the umform packmg of the resin m a column In addltlon, with low degrees of swelling the rate of ion-exchange reactions becomes slow, which 1s undesirable m chromatography Macroretlcular skeletons exhibit a large inner surface area and owing to their structure, exchangers with this skeleton type are much more resistant to osmotic shock They also exhlblt a smaller swelling difference m polar and non-polar solvents, a smaller loss of volume durmg drying and higher oxldatlon resistance Furthermore, reactions connected with mtroducmg the morgamc groups into the skeleton occur more easdy and with a higher yield m comparison with mlcroretlcular resins (styrene-dlvmylbenzene skeleton) [ 111 In this paper, a newly prepared selective macroreticular ion exchanger (with an Amberhte XAD4 support) containing ammophosphomc acid groups 1s reported This type of resin has a chelatmg ablhty for multi-charged metal ions [ 121 The preparation of this chelating resin and the exammatlon of its capacity, selectivity towards metal ions and apphcatlon to determmatlon of trace metals m waters are presented

EXPERIMENTAL

Apparatus

Glass chromatographlc columns (300 mm x 20 mm 1 d 1, a Crlson standard pH meter with electrode (Ingold U455) and a Perkm-Elmer Model 5000 atomic absorption spectrometer with an au-acetylene flame and hollow-cathode lamps were used All chemical appliances, such as bottles, columns, flasks and tubes, were treated with 10% nitric acid overnight and rinsed twice with ultrapure water before use Reagents and solutions

All chemicals were of analytical-reagent grade and ultrapure water [ 18 3 mQ cm specific reststlv-

Yebra-Bzumm et al /Anal

Chm Acta 264 (1992) 53-58

lty, obtained with a M&-Q water purlflcatlon system (Mllhpore)] was used throughout Reagents used for the synthesis of the resin were Amberhte XAD-4 resm (20-60-mesh macroporous polystyrene adsorbent having a hrgh surface area of 725 m2 g-l), chloromethyl methyl ether, tm(IV) chloride, l,Cdloxane, concentrated hydrochloric acid, l,Zdlammoethane, 01 M sodium hydroxide solution, phosphorous acid (70%, sp gr 14339) and formaldehyde (37% aqueous solution) Metal salts were used to prepare 1000 pg ml-’ stock metal ion solutions The appropriate amounts of the salts were dissolved m 1 M nitric acid These standard solutions were stored m polypropylene bottles Resm synthesis Chloromethylatwn of Amberhte XAD-4 resuz In

a typical experiment under reflux, chloromethyl methyl ether (100 ml) was added to copolymer beads (25 g), which were allowed to swell at room temperature for 1 h and then warmed while being stirred On addition of 50 ml of the ether contammg 7 6 g of tm(IV) chloride, the mixture boiled, and it was kept at reflwr temperature for 1 h The product was cooled, filtered off and washed with caution with 100 ml of aqueous droxane (30%, v/v>, 50 ml of aqueous dloxane containing 10% (v/v) of concentrated hydrochloric acid and flnally with as much dloxane alone as necessary for the filtrate to clear The resin was dried by heating to 90°C Ammatlon of chloromethylated resm A 25-g amount of chloromethylated resm as swollen m dloxane (50 ml) for 1 h at room temperature, then 200 ml of 1,Zdlammoethane were added and the mixture was kept slightly warmed for 2 days with intermittent shakmg The product was cooled, filtered off and washed with 0 1 M sodmm hydroxide solution and finally with ultrapure water The resin was dried by heatmg to 90°C Synthesm of poly (ammophosphonu: actd) resin

To 25 g of ammated resin, 175 ml of concentrated hydrochloric acid and 175 ml of phosphorous acid were added, then the murture was heated to reflux temperature with stlrrmg On reaching this temperature, 225 ml of 37% aqueous formalde-

MC

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et al /Anal

Chm

Acta 264 (1992) 53-58

55

hyde solution were added dropwlse and the reaction murture was kept at reflux temperature for a further 1 h The product was cooled, filtered off and washed with ultrapure water The resin was dried by heatmg to 90°C

condltlons recommended by the instrument manufacturer and the wavelengths used were Cu 324 8, Fe 248 3, Pb 217 0, Mg 285 2, Mn 279 5, Zn 213 9, Cr 357 9, N1232 1 and Ca 422 7 nm Analytrcal applrcatlon deter-mm&on of trace metals m waters The resm was used for the preconcentratlon of trace amounts of metals in natural waters, followed by determmatlon by flame AAS The resin (3 g) was loaded into a column and rinsed with ultrapure water at pH 5 A natural water sample (1 1, pH 5) was passed through the column at a flow-rate of 3 5 ml mm-l After washing the column with ultrapure water (pH 51, the metal ions retained were eluted with 3 M HCl (25 ml) at a flow-rate of 1 ml mm-’ and determined by flame AAS

Composmon of synthesrzed resm The total nitrogen content (0 57%) m the ammophosphomc resin was determined by microanalysis and the content of phosphorus 069%) was determined by digestion of the resin and spectrophotometrlc determmatlon of phosphorus by the molybdenum blue method [13] In order to determine the stability of the resin with use, the contents of mtrogen and phosphorus m a resm used several times were determined The results showed that these contents did not change with use of the resin (N = 0 39%, P = 164%) Pre1;mmat-ystudres The sorption of various metals was studied by a dynamic method, passing solutions of the metal through a 300 mm X 20 mm 1 d column packed with the resin First 25 ml of ultrapure water and the metal standard solution at the chosen pH were passed through the resin, which was then washed with ultrapure water at the same pH and eluted with 25 ml of a suitable dilute acid Blanks of ultrapure water were processed usmg the same procedure as for the metal standards The degree of sorption was found by flame atomic-absorption spectrometrlc (AAS) detemunation of the test element m the effluent from the column and m the solution obtained by elutlon An air-acetylene flame was used under the

TABLE

RESULTS

AND DISCUSSION

Study of metal zons retamed on the reszn This study was carried out prlmarlly as a screening process to determme which metals would form complexes with the resin ammophosphonic acid groups For all the metals tested, considerable retention of metal ions from solution occurred except for Na+, K+ and Rb+, which exhibited no affinity for the resm Effect of PI-Ion degree of sorptzon Fixed amounts of the metals m 25 ml of solution at pH 1-14 for all the metals were passed throught the column packed with the resm The

1

Effect of pH on recovery of metals a PH

cu (o/o)

Fe (%o)

Pb (%)

Mn (%I

Mg (o/o)

Zn (o/o)

Ca (%)

NI (o/o)

Cr (%)

1 3 5 7 9 11 14

400 97 4 98 8 1000 990 824 81 1

93 7 98 0 974 89 7 80 7 708 58 1

04 886 1000 1000 1000 993 84 1

00 1000 99 8 98 8 93 7 69 9 58 1

78 95 4 1000 1000 1000 93 7 800

00 95 9 1000 969 1000 1000 514

100 1000 1000 1000 1000 1000 998

50 13 2 1000 98 1 98 1 55 3 402

15 7 1000 1000 847 73 9 45 4 213

a Flow-rates

sorption, 3 5 ml mm-‘,

elutlon, 1 ml mm-’

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Yebra-Bwrun

et al /Anal

Chrm Acta 264 (1992) 53-58

TABLE 2 Percentage uptake on the resm as a function of concentration each of the Indicated metals

of hydrochlorx

acid (eluent) from solutions contammg

1 pg ml-’

[HaI (M)

cu (%o)

Fe (%I

Pb (%)N

Mn (%I

Mg (%I

zn (%)

Ca (%I

NI (%I

Cr (%o)

025 0 50 100 300 400 600

93 9 93 9 93 9 985 966 965

18 1 20 2 94 5 917 96 1 72 8

95 96 97 98 99 98

910 910 926 97 1 99 9 97 8

824 902 882 997 976 967

1000 1000 1000 1000 1000 97 6

923 893 963 966 1000 999

1000 1000 1000 1000 1000 1000

836 85 9 848 99 1 906 896

2 2 9 7 9 5

degree of retention of the metal ions tested as a function of pH 1s shown m Table 1 Almost all the metals were retained between 90 and 100% at pH 5 Therefore, pH 5 was selected for subsequent work Elutlon condhons

This study was done m order to choose a suitable reagent able to release the metals from the resin Metal solutions containing Cu 100, Fe 75, Pb 250, Mg 7 5, Mn 25, Zn 12 5, Cr 63, N124 and Ca 75 pg m 25 ml at pH 5 were passed through the column packed with the resin and eluted with 25 ml of 2-4 M acetic acid or 0 l-6 M hydrochloric acid Acetic acid at concentrations up to 4 M and m an amount of 25 ml was able to release only about the 5 4% of the copper The use of hydrochloric acid was therefore tested it allowed almost quantitative release of all the metals tested when used at concentration of 3 M (25 ml> (Table 2) Therefore, 25 ml of 3 M hydrochloric acid was selected for use as the eluent for all the metals

Effect offlow-rate The flow-rate affects the time allowed for the

mteractlons that have to take place between the metal and the chelatmg material and therefore may well exert an effect on the uptake efficiency With all the other condltlons maintained constant, the flow-rates of sorption and elutlon were studied The effects of flow-rate on the sorption of copper at pH 5 and its elutlon with 3 M HCl of copper were studied m the range 0 5-3 5 ml mm-’ It was found, as expected, that the uptake yield 1s a function of the flow-rate (Table 3) The results show that the flow-rate of elutlon must be lower than the flow-rate of passage of the standard (sorption of copper) The flow-rates chosen were therefore sorption at 3 5 ml mm-’ and elution at 1 ml mm-’ Total sorption capacrty The capacity of the resin 1s one of the factors

that determines how much resm will be needed

TABLE

4

Total sorption Element

TABLE 3 Effect of flow-rates used for retention 10ns on recovery (o/o) a Flow-rate

and elutlon

for retention

of metal

(ml mm - ‘1

Flow-rate for elutlon (ml mm-‘)

05

1

35

05 1 35

98 9 98 6 902

98 9 98 5 902

98 6 98 5 900

a Study with 100 pg of Cu(II) at pH 5 and elutlon with 3 M HCl

of

CUUI) FeUII) Pb(I1) Mn(II) Mg(II) Zn(II) Ca(II) Nl(II) CrUII)

capacity

of the resm

Sorption

capacity

pg g-t

gmol

500 315 1000 125 75 75 125 625 250

787 672 483 227 3 10 1 15 3 12 10 65 481

g-’

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Chun Acta 264 (1992) 53-58

TABLE 5 Competltlve recovery m relation to the concentration of metals Amount of resm (9)

Metal Ion concentration (pg ml-‘)

Recovery (%) CU

Fe

Pb

Mn

Mg

Zn

Ca

Nl

Cr

1

05 1 3

98 6 98 3 98 1

915 62 1 404

98 5 98 5 98 1

974 97 2 96 9

998 998 96 1

1000 99 6 96 4

96 8 965 96 5

1000 993 983

99 3 95 6 70 9

3

05 1 3

98 7 98 5 98 5

97 5 911 96 9

98 6 98 4 98 5

97 4 974 97 1

998 991 995

1000 998 98 6

969 967 963

1000 1000 99 6

99 2 98 I 916

for the quantltatlve removal of a particular metal Ion from solution This was determined at pH 5 using standard solutions containing 100-1200 pg of each metal ion, elutmg with 3 M hydrochloric acid The metals m the eluates were then determined by flame AAS Table 4 lists the capacity values expressed as pmol g-’ of resm for all the metals tested Resin-metal

were carried out at pH 5 AAS was used for the determmatlon of the metal ion concentrations The results of a competltlve study with all the metals, carried out to determine If certam metals would enhance or mhlblt the upEke of other metals, are shown m Table 5 As can be seen, FeUII) needs at least 3 g of resm quantitative retention Therefore, an amount of 3 g of resin was chosen to retam all the metals studied

selectlvrty

Depending on the composltlon of the sample, the selectivity of the resin for certain metals will determine how much resin 1s needed to remove all the metals present m the sample The selectlvsty of the resm for all the metals tested was determined with 1 and 3 g of resm m the column Volumes of 25 ml of stock metal ion solutions containing 0 5, 1 and 3 pg ml-’ of each metal were passed through the resin and eluted with 3 M hydrochloric acid All of the selectlvlty studies

Appllcatlon to analyst of natural water The feaslblhty of simultaneously collectmg and

determining Z&I), Fe(III), Mn(II), C&I), Nr(II), Pb(II), Cr(III), Mg(I1) and Ca(I1) m mineral water was evaluated with a spiked water sample (1 1, pH 5) containing matrix elements at natural water levels [14] The recoveries of the spiked metals (12-75 pg) were about 99%) when using the poly(ammophosphomc aad) resin wth a macroreticular support (3 g) Chelex-100 recovered

TABLE 6 Preconcentratlon

and detemunatlon

Source

of trace amounts of metals m mmeral waters a

Concentration of metal found fig 1-l

Verin (Orense) Verin (Orense) Mondariz (Pontevedra) Mondariz (Pontevedra) Sarrla (Lug01 a Bottle material plastic

/Jgml-’

Zn

Fe

Mn

CU

N1

Pb

Cr

Mg

Ca

305 664 95 193 80

415 30 7 35 0 33 6 251

84 17 I 19 3 31 8 95

20 5 12 8 22 1 28 2 19 8

60 53 53 74 53

146 15 9 146 113 173

23 41 32 32 23

68 37 72 56 20

83 71 118 219 94

58

Zn(II), Cu(I1) and Nl(II) above 97 6% at pH 7 6 [15] and with a sea water matm recovered Cr(III), Mn(II), Fe(III), N1(11), Cu(I1) and Zn(I1) to the extents of 25 f lo%, 86 f 2 5%, 90 f 15%, 95 f 6%, 88 A-3% and 100 f 5%, respectively [16] Elutlon with 3 M hydrochloric acid (25 ml) was suitable for the determination of the metals by flame AAS The real water samples examined various brands of bottled Gahclan mineral waters The results obtained for the determmatlon of metals m these mineral waters are given m Table 6 corlcluslons These prehmmary mvestlgatlons indicate that the poly(ammophosphomc acid) resin 1s apphcable to the preconcentratlon of trace metals from aqueous solutions The resin exhibits no affinity for the alkali metals tested The uptake of trace metals was found to be about 99% or better for most metals over a pH range that includes the pH values of most natural water systems The capacity of the resin IS also high enough for use m the simultaneous concentration and determmatlon of all the metals studled and the flow-rate of sorption 1s relatively rapid Preparation of the resin 1s easy and rapid and elutlon with hydrochloric acid 1s more advantageous than elutlon with the perchlorlc acid proposed by Szczepamak and Slepak [6], as the resin can be used repeatedly more than twenty times with identical results, requiring only regeneration by washing with 6 M hydrochloric acid (50 ml)

MC Yebra-Bwrrun et al /Anal Chum Acta 264 (1992) 53-58

and then SIXtimes with ultrapure water, moreover, perchlorlc acid can be unfavourable m the direct determmatlon of metals m eluates by flame AAS

REFERENCES 1 E M Moyers and J S Fritz, Anal Chem , 49 (1977) 418 2 R J Phdhps and J S Fritz, Anal Chum Acta, 139 (1982) 237 3 S D Alexandratos, D R Qudlen and M D Bates, Macromolecules, 20 (1987) 1191 4 T Yokoyama, A IOkuchl and TM IOmura, Bull Chem Sot Jpn , 56 (1983) 463 5 K Ueda, Y Sato, 0 Yoshlmura and Y Yamamoto, Analyst, 113 (1988) 777 6 W Szczepamak and J Slepak, Chem Anal (Warsaw), 18 (1973) 1019 7 W Szczepamak, Chem Anal (Warsaw), 19 (1974) 869 8 K.A Petrov, L V Treshchahna, V M Chlzhov and A I Nesterchuk, Vysokomol Soedm , Ser A, 18 (1976) 1540 9 V G Myasoedova and S B Sawm, Zh Anal Khlm , 37 (1982) 499 10 A V Smlrnov and S B Makarova, Przem Chem ,63 (1984) 121 11 M Marhol, m G Svehla (Ed ), Wdson and Wdson’s Comprehensive Analytical Chemistry, Vol XIV, Elsevler, Amsterdam, 1982, p 23 12 K Moedrltzer and RR Iram, J Org Chem, 31 (1966) 1603 13 M C Yebra, M L Mella, A BermeJo and M Fermindez, paper presented at the XXIII Reunu5n Bienal de la Real Socledad Espaiiola de Quimlca, Salamanca, 1990 14 H J M Bowen, Environmental Chemistry of the Elements, Academic, London, 1979, p 15 15 J P Rdey and D Taylor, Anal Chum Acta, 40 (1968) 479 16 P Bomfortl, R Ferraroh, P Grlglen, D Heltal and G Quelrazza, Anal Chum Acta, 162 (1984) 33