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Preparation and analytical characterization of a chelating resin coated with 1-(2-pyridylazo)-2-naphthol
Talanta, Vol. 32, No. I, pp. 574476, 1985 Printed in Great Britain. All rights reserved
0039-9140/85$3.00+ 0.00 Copyright 0 1985Pergamon Press Ltd
PREPARATION AND ANALYTICAL CHARACTERIZATION OF A CHELATING RESIN COATED WITH 1-(2-PYRIDYLAZO)-2-NAPHTHOL J. CHWASTOWSKAand E. MOZER Department of Analytical Chemistry, Faculty of Chemistry, Technical University of Warsaw, Warsaw, Poland (Received 25 April 1984. Revised 6 December 1984. Accepted 1 February 1985)
chelating sorbent was obtained by deposition of I-(2-pyridylazo)-2-naphthol on Amberlite XAD-4. The analytical characteristics of the sorbent were established and optimum sorption conditions for Cu, Zn, Fe, Cd, Ni, and Pb under static and dynamic conditions were determined. The sorbent was applied to analysis of river water. After group separation of traces of metals on the sorbent and subsequent elution with hydrochloric acid, the metals were determined in the effluent by atomic-absorption Summary-A
Styrene-divinylbenzene copolymers with a large surface area and macroporous structure, such as Amberlite XAD, are capable of adsorbing water-soluble organic substances. This property has been successfully utilized for separation of various organic compounds in analysis of water,lA as well as for preparation of chelating sorbents by deposition of chelating reagents on Amberlite XAD as substrate. The method has been applied for preparation of a dithizone-coated resin (which was then used for isolation of mercury from sea-water)5 and of a resin coated with ferroin-type compounds.6 In this work Amberlite XAD4 was used as a substrate for deposition of l-(Zpyridylazo)2-naphthol (PAN), a heterocyclic azo compound capable of forming complexes with many metal ions. Polyurethane foams coated with PAN have already been reported as good sorbents for trace metals.7-9 EXPERIMENTAL Reagents
Standard I-mg/ml stock solutions of Fe, Pb, Ni, Cu, Zn and Cd were made by dissolving appropriate salts in distilled water suitably acidified to Drevent hvdrolvsis. and were further diluted ai required. PAN was u&d as-a 6.45% solution in methanol. Preparation of the sorbent
The copolymer was kept for one day in methanol, then filtered off and air-dried. PAN was deposited on the copolymer by two methods. In the first, a saturated solution of PAN in methanol (10 ml per g of resin) was passed at 1 ml/min through a column of Amberlite XAD-4, and the column was then washed with 5 bed-volumes of doubly distilled water. In the other, the resin was kept for 1 hr in a solution of PAN in methanol, with occasional stirring. The resin was then filtered off, washed with water, and air-dried. The amount of PAN deposited on the resin was estimated by determining spectrophotometrically the amount of PAN left in the solution and washings. It was found that 78% of the PAN had been retained in the resin, which corresponds to 0.054 mmole per g of dry Amberlite XAD-4.
Procedures The so&ion of various metals was studied under static conditions by shaking a solution of the metal with a weighed quantity of the sorbent in a separating funnel, and under dynamic conditions by passing a solution of the metal through a column of the sorbent. The static method was used in determination of the capacity and stability of the sorbent, the optimum sorption conditions (kinetics and pH), and the desorption conditions (stripping agent, its concentration, and shaking time). The dynamic method was applied in determining the optimum pH, flow-rate, and sample volume. The degree of sorption was found by atomic-absorption spectrophotometric determination of the test element in the effluent from the column and in the solution obtained by desorption. An air-acetylene flame was used under the conditions recommended by the instrument manufacturer, and the wavelengths (nmj used were: Cd-228.8, Cu324.7. Fe-248.3. Ni-232.0. Pb-217.0. Zn-213.9. Sorption kinetics (static c&ditions). A lo-ml portion of copper solution containing 75 peg of Cu at pfi 8.5 was shaken for 30. 60, and 90min with 1 e. of the sorbent in a separating fudnel.’ Desorption conditions. One-g portions of resin were shaken for 60min with lo-ml portions of copper solution (75 pg of Cu, pH 8.5), and then stripped by shaking for IS min with 10 ml of 2, 3 and 4M hydrochloric acid. Effect of pH on degree of sorption. Fixed amounts of the metals (Cu-75 pg, Fe+-66 pg, Cd-130 pg, Ni-70 pg, Zn-75 pg, Pb-100 pg) in 10 ml of solution, at pH 2-10 for copper and pH 5-10 for the other metals, were shaken with l-g portions of resin for 60 min. Total sorption capacity. This was determined at pH 8.S (assumed to be optimal for group separation of the test elements) with shaking for 60 min. The resin was separated, washed with water at pH 8.5, and stripped with 4M hydrochloric acid. The metals in the strippings were then determined by atomic-absorption spectrophotometry (AAS).
574
Sorption under dynamic conditions
Two columns, 9 and 6 mm in diameter respectively, were made with 2 g of the sorbent. A 200-ml portion of test solution at pH 8.5 and the concentration used in the static tests was passed through the resin, which was then washed with water at pH 8.5 and stripped with 10 ml of 4M hydrochloric acid. The metal stripped was determined by AAS.
575
SHORT COMMUNICATIONS
Table 1. Total sorption capacity of the sorbent
Element CU Fe Ni Zn Cd
fig 127 168 176 131 337
/.-.-._
mmole 0.002 0.003 0.003 0.002 0.003
The effect of flow-rate on the sorption of copper was studied for the range 1.5-20 ml/min. The influence of the solution volume on copper sorption was studied by passing 200, 500, 1000 and 2000 ml volumes of copper solution through the column at a constant rate of 10 ml/min. Analysis of water samples Water samples (1 or 2 1.)were filtered, adjusted to pH 8.0,
and passed at 5 ml/min through a column of 10 g of the chelating sorbent. The sorbed metals were eluted with 10 ml of 4M hydrochloric acid. The eluate was collected in a 25ml standard flask, diluted to volume and analysed by AAS, after dilution if necessary (e.g., for iron and zinc).
RESULTS AND DISCUSSION
Characteristics of the sorbent Preparation of the sorbent is easy and quick; the batch method gives more uniform deposition of the reagent. The sorbent is highly stable. All attempts to remove the PAN from the Amberlite XAD-4 with organic solvents failed. The stability is confirmed by the fact that the sorbent can be repeatedly used: eight successive sorptions on the same sorbent gave almost identical results. The total sorption capacity is not very high (Table l), which is typical for sorbents of this type.
PH
Fig. 1. Relationship between sorption and pH of solutions: l-Fe, 2-01, 3-Zn, 4-Cd, 5-Pb, 6-Ni.
stripped by shaking it with 4h4 hydrochloric acid for 15 min. Column method Table 2 shows that the column method gives more efficient overall sorption than the static method. Experiments with copper showed that varying the flow-rate in the range 1.5-20 ml/min did not affect the degree of sorption, which is advantageous for large volumes of sample, since a high flow-rate can be used to shorten the analysis time. The sample volume also does not affect performance with a fixed amount of resin and fixed total amount of metal. This is important for application to water analysis. Application to analysis of water Naturally occurring waters contain considerable amounts of sodium, potassium, magnesium and calcium salts, mainly the chlorides and sulphates. The influence of the major salts found in natural waters Table 3. Group column sorption of metals in presence of other elements (synthetic drinking water, 200 ml, pH 8.5)
Sorption under static conditions The study of the sorption kinetics showed that shaking for 1 hr is necessary for equilibrium to be reached. Figure 1 shows that pH g-9 is optimal for sorption of the elements studied. Under the batch conditions used, copper and iron are almost quantitatively sorbed, whereas lead, nickel, cadmium and zinc are only W-85% sorbed. All the elements retained by the sorbent are easily
Element
cu Cd Ni Pb
Zn Fe
Added, M
Sorbed, IQ?
Sorption, x
30 52 42 50 30 66
21 36 30 40 22 48
70 69 71 80 73 73
Table 2. Column sorption of metals (as a group in 200 ml of solution, pH 8.5) Amount sorbed Flow-rate 10 ml/min
Fe
Added, Irg 30 25
2 Pb Ni
30 52 100 28
Element
cu
TAL W-E
Flow-rate 15 ml/min
I PET
%
Pg
%
29.0 24.5
97 98
28.0 23.0
93 92
45.0 28.0
93 87 90 90
27.0 47.0 90.0 25.0
90 90 90
576
SHORT
COMMUNICATIONS
Table 4. Group column sorption of metals in presence of other elements (synthetic drinking water) at different pH values (200 ml of solution, flow-rate 5 ml/min) pH 8.5
pH 8.0
pH 7.0
Element
Added, ~8
Sorbed, 1(8
Sorption, %
Sorbed, Ix
Sorption, %
Sorbed, pg
Sorption, %
CU Fe Ni Zn Cd Pb
30 66 42 30 52 50
21 48 30 22 36 40
70 73 71 73 69 80
26 62 31 25 44 40
87 94 74 83 84 80
23 64 12 21 16 32
77 97 30 70 31 64
Table 5. Analysis of river water Found,* pgcgll. Element Zn CU Cd Fe Ni Pb
l-l. sample 56.3 2.1 <1 215 7.2 5.5
2-l. sample 56.0 2.0 <1 200 7.5 5.2
l-l. sample after mineralization 56.5 2.0
*Mean of 3 determinations.
on the sorption of metals on the PAN-XAD4
sorbent was therefore examined, with a synthetic water (formulated on the basis of the acceptable limits for drinking water) having the composition: Na+ 30, K+ 8, Mg*+ 40, Ca*+ 110, Cl- 248, and SO:- 158 mg/l. A lOO-ml portion of the synthetic water, to which a mixture of the elements under study had been added, was adjusted to pH 8.5 and passed at 5 ml/min through a column (9 mm diameter) of the sorbent. It was found (Table 3) that the degree of sorption was lower than that in the absence of the salts present in the synthetic water. This was thought to be due to competitive sorption of calcium and magnesium. Further examination showed that at pH 8.5 the degree of sorption is 35% for magnesium, and 25% for calcium, and it decreases with decreasing pH. Since the concentration of these two elements in water can be very large compared with that of the trace elements, they can easily block the active centres of the sorbent. This effect can in principle be counteracted by using a lower pH for sorption of the trace elements, and/or by using more sorbent. The sorption experiment was therefore repeated with the synthetic water/trace element mixture at pH 7.0 and 8.0 with 4 g of sorbent. The results (Table 4) show that use of pH 7 is not profitable because of the considerably decreased sorption efficiency for all the trace metals, especially nickel and cadmium. Use of pH 8.0 and even more sorbent seemed a reasonable compromise. Under these conditions the sorption of the trace elements is sufficiently effective, and the sorption of calcium is reduced to 15% and of magnesium to 22%. The procedure has been applied to analysis of river water (from the Jeziorka river). The water samples (1
and 2 1.) were passed through the column either directly after filtering or after preliminary mineralization by boiling with 15 ml of concentrated nitric acid for 30 min. The results obtained are given in Table 5 show that preliminary mineralization is not necessary. This fact may be attributed to the elements being sorbed from organic as well as inorganic compounds. The similarity of the results obtained for the two sizes of sample proves that the sorption capacity of the amount of resin used (10 g) was sufficient for the purpose. The cadmium content was so low that even after concentration from 2 litres of water its amount was below the limit of determination. The iron and zinc contents were high enough for their determination after 2-fold and 5-fold dilution, respectively, of the final solutions. REFERENCES
1. G. A. Junk, J. J. Richard, K. D. Greiser, D. Witiak, J. L. Witiak, M. D. Arguello, R. Vick, H. J. Svec, J. S. Fritz and G. V. Calder, J. Chromatog., 1974, 99, 745. 2. G. A. Junk, C. D. Chriswell, R. C. Chang, L. D. Kissinger, J. J. Richard, J. H. Fritz and H. J. Svec, 2. Anal. Chem., 1976, 282, 331. J. P. Riley and D. Taylor, Anal. Chim. Acta, 1969, 46, 307. J. Zerbe, Chem. Anal. Warsaw, 1979, 24, 85. A. C. Howard and N. N. Arbab-Zawar, Talanta, 1979, 26, 895. J. L. Lundgren and A. A. Schilt, Anal. Chem., 1977,49, 974. 7. T. Braun and M. N. Abbas, Anal. Chim. Acta, 1980, 119, 113. 8. I&m, ibid., 1982, 134, 321. 9. M. P. Maloney, G. J. Moody and J. D. R. Thomas, Analyst, 1980, 105, 1087.
0039-9140/85$3.00+ 0.00 Copyright 0 1985Pergamon Press Ltd
PREPARATION AND ANALYTICAL CHARACTERIZATION OF A CHELATING RESIN COATED WITH 1-(2-PYRIDYLAZO)-2-NAPHTHOL J. CHWASTOWSKAand E. MOZER Department of Analytical Chemistry, Faculty of Chemistry, Technical University of Warsaw, Warsaw, Poland (Received 25 April 1984. Revised 6 December 1984. Accepted 1 February 1985)
chelating sorbent was obtained by deposition of I-(2-pyridylazo)-2-naphthol on Amberlite XAD-4. The analytical characteristics of the sorbent were established and optimum sorption conditions for Cu, Zn, Fe, Cd, Ni, and Pb under static and dynamic conditions were determined. The sorbent was applied to analysis of river water. After group separation of traces of metals on the sorbent and subsequent elution with hydrochloric acid, the metals were determined in the effluent by atomic-absorption Summary-A
Styrene-divinylbenzene copolymers with a large surface area and macroporous structure, such as Amberlite XAD, are capable of adsorbing water-soluble organic substances. This property has been successfully utilized for separation of various organic compounds in analysis of water,lA as well as for preparation of chelating sorbents by deposition of chelating reagents on Amberlite XAD as substrate. The method has been applied for preparation of a dithizone-coated resin (which was then used for isolation of mercury from sea-water)5 and of a resin coated with ferroin-type compounds.6 In this work Amberlite XAD4 was used as a substrate for deposition of l-(Zpyridylazo)2-naphthol (PAN), a heterocyclic azo compound capable of forming complexes with many metal ions. Polyurethane foams coated with PAN have already been reported as good sorbents for trace metals.7-9 EXPERIMENTAL Reagents
Standard I-mg/ml stock solutions of Fe, Pb, Ni, Cu, Zn and Cd were made by dissolving appropriate salts in distilled water suitably acidified to Drevent hvdrolvsis. and were further diluted ai required. PAN was u&d as-a 6.45% solution in methanol. Preparation of the sorbent
The copolymer was kept for one day in methanol, then filtered off and air-dried. PAN was deposited on the copolymer by two methods. In the first, a saturated solution of PAN in methanol (10 ml per g of resin) was passed at 1 ml/min through a column of Amberlite XAD-4, and the column was then washed with 5 bed-volumes of doubly distilled water. In the other, the resin was kept for 1 hr in a solution of PAN in methanol, with occasional stirring. The resin was then filtered off, washed with water, and air-dried. The amount of PAN deposited on the resin was estimated by determining spectrophotometrically the amount of PAN left in the solution and washings. It was found that 78% of the PAN had been retained in the resin, which corresponds to 0.054 mmole per g of dry Amberlite XAD-4.
Procedures The so&ion of various metals was studied under static conditions by shaking a solution of the metal with a weighed quantity of the sorbent in a separating funnel, and under dynamic conditions by passing a solution of the metal through a column of the sorbent. The static method was used in determination of the capacity and stability of the sorbent, the optimum sorption conditions (kinetics and pH), and the desorption conditions (stripping agent, its concentration, and shaking time). The dynamic method was applied in determining the optimum pH, flow-rate, and sample volume. The degree of sorption was found by atomic-absorption spectrophotometric determination of the test element in the effluent from the column and in the solution obtained by desorption. An air-acetylene flame was used under the conditions recommended by the instrument manufacturer, and the wavelengths (nmj used were: Cd-228.8, Cu324.7. Fe-248.3. Ni-232.0. Pb-217.0. Zn-213.9. Sorption kinetics (static c&ditions). A lo-ml portion of copper solution containing 75 peg of Cu at pfi 8.5 was shaken for 30. 60, and 90min with 1 e. of the sorbent in a separating fudnel.’ Desorption conditions. One-g portions of resin were shaken for 60min with lo-ml portions of copper solution (75 pg of Cu, pH 8.5), and then stripped by shaking for IS min with 10 ml of 2, 3 and 4M hydrochloric acid. Effect of pH on degree of sorption. Fixed amounts of the metals (Cu-75 pg, Fe+-66 pg, Cd-130 pg, Ni-70 pg, Zn-75 pg, Pb-100 pg) in 10 ml of solution, at pH 2-10 for copper and pH 5-10 for the other metals, were shaken with l-g portions of resin for 60 min. Total sorption capacity. This was determined at pH 8.S (assumed to be optimal for group separation of the test elements) with shaking for 60 min. The resin was separated, washed with water at pH 8.5, and stripped with 4M hydrochloric acid. The metals in the strippings were then determined by atomic-absorption spectrophotometry (AAS).
574
Sorption under dynamic conditions
Two columns, 9 and 6 mm in diameter respectively, were made with 2 g of the sorbent. A 200-ml portion of test solution at pH 8.5 and the concentration used in the static tests was passed through the resin, which was then washed with water at pH 8.5 and stripped with 10 ml of 4M hydrochloric acid. The metal stripped was determined by AAS.
575
SHORT COMMUNICATIONS
Table 1. Total sorption capacity of the sorbent
Element CU Fe Ni Zn Cd
fig 127 168 176 131 337
/.-.-._
mmole 0.002 0.003 0.003 0.002 0.003
The effect of flow-rate on the sorption of copper was studied for the range 1.5-20 ml/min. The influence of the solution volume on copper sorption was studied by passing 200, 500, 1000 and 2000 ml volumes of copper solution through the column at a constant rate of 10 ml/min. Analysis of water samples Water samples (1 or 2 1.)were filtered, adjusted to pH 8.0,
and passed at 5 ml/min through a column of 10 g of the chelating sorbent. The sorbed metals were eluted with 10 ml of 4M hydrochloric acid. The eluate was collected in a 25ml standard flask, diluted to volume and analysed by AAS, after dilution if necessary (e.g., for iron and zinc).
RESULTS AND DISCUSSION
Characteristics of the sorbent Preparation of the sorbent is easy and quick; the batch method gives more uniform deposition of the reagent. The sorbent is highly stable. All attempts to remove the PAN from the Amberlite XAD-4 with organic solvents failed. The stability is confirmed by the fact that the sorbent can be repeatedly used: eight successive sorptions on the same sorbent gave almost identical results. The total sorption capacity is not very high (Table l), which is typical for sorbents of this type.
PH
Fig. 1. Relationship between sorption and pH of solutions: l-Fe, 2-01, 3-Zn, 4-Cd, 5-Pb, 6-Ni.
stripped by shaking it with 4h4 hydrochloric acid for 15 min. Column method Table 2 shows that the column method gives more efficient overall sorption than the static method. Experiments with copper showed that varying the flow-rate in the range 1.5-20 ml/min did not affect the degree of sorption, which is advantageous for large volumes of sample, since a high flow-rate can be used to shorten the analysis time. The sample volume also does not affect performance with a fixed amount of resin and fixed total amount of metal. This is important for application to water analysis. Application to analysis of water Naturally occurring waters contain considerable amounts of sodium, potassium, magnesium and calcium salts, mainly the chlorides and sulphates. The influence of the major salts found in natural waters Table 3. Group column sorption of metals in presence of other elements (synthetic drinking water, 200 ml, pH 8.5)
Sorption under static conditions The study of the sorption kinetics showed that shaking for 1 hr is necessary for equilibrium to be reached. Figure 1 shows that pH g-9 is optimal for sorption of the elements studied. Under the batch conditions used, copper and iron are almost quantitatively sorbed, whereas lead, nickel, cadmium and zinc are only W-85% sorbed. All the elements retained by the sorbent are easily
Element
cu Cd Ni Pb
Zn Fe
Added, M
Sorbed, IQ?
Sorption, x
30 52 42 50 30 66
21 36 30 40 22 48
70 69 71 80 73 73
Table 2. Column sorption of metals (as a group in 200 ml of solution, pH 8.5) Amount sorbed Flow-rate 10 ml/min
Fe
Added, Irg 30 25
2 Pb Ni
30 52 100 28
Element
cu
TAL W-E
Flow-rate 15 ml/min
I PET
%
Pg
%
29.0 24.5
97 98
28.0 23.0
93 92
45.0 28.0
93 87 90 90
27.0 47.0 90.0 25.0
90 90 90
576
SHORT
COMMUNICATIONS
Table 4. Group column sorption of metals in presence of other elements (synthetic drinking water) at different pH values (200 ml of solution, flow-rate 5 ml/min) pH 8.5
pH 8.0
pH 7.0
Element
Added, ~8
Sorbed, 1(8
Sorption, %
Sorbed, Ix
Sorption, %
Sorbed, pg
Sorption, %
CU Fe Ni Zn Cd Pb
30 66 42 30 52 50
21 48 30 22 36 40
70 73 71 73 69 80
26 62 31 25 44 40
87 94 74 83 84 80
23 64 12 21 16 32
77 97 30 70 31 64
Table 5. Analysis of river water Found,* pgcgll. Element Zn CU Cd Fe Ni Pb
l-l. sample 56.3 2.1 <1 215 7.2 5.5
2-l. sample 56.0 2.0 <1 200 7.5 5.2
l-l. sample after mineralization 56.5 2.0
*Mean of 3 determinations.
on the sorption of metals on the PAN-XAD4
sorbent was therefore examined, with a synthetic water (formulated on the basis of the acceptable limits for drinking water) having the composition: Na+ 30, K+ 8, Mg*+ 40, Ca*+ 110, Cl- 248, and SO:- 158 mg/l. A lOO-ml portion of the synthetic water, to which a mixture of the elements under study had been added, was adjusted to pH 8.5 and passed at 5 ml/min through a column (9 mm diameter) of the sorbent. It was found (Table 3) that the degree of sorption was lower than that in the absence of the salts present in the synthetic water. This was thought to be due to competitive sorption of calcium and magnesium. Further examination showed that at pH 8.5 the degree of sorption is 35% for magnesium, and 25% for calcium, and it decreases with decreasing pH. Since the concentration of these two elements in water can be very large compared with that of the trace elements, they can easily block the active centres of the sorbent. This effect can in principle be counteracted by using a lower pH for sorption of the trace elements, and/or by using more sorbent. The sorption experiment was therefore repeated with the synthetic water/trace element mixture at pH 7.0 and 8.0 with 4 g of sorbent. The results (Table 4) show that use of pH 7 is not profitable because of the considerably decreased sorption efficiency for all the trace metals, especially nickel and cadmium. Use of pH 8.0 and even more sorbent seemed a reasonable compromise. Under these conditions the sorption of the trace elements is sufficiently effective, and the sorption of calcium is reduced to 15% and of magnesium to 22%. The procedure has been applied to analysis of river water (from the Jeziorka river). The water samples (1
and 2 1.) were passed through the column either directly after filtering or after preliminary mineralization by boiling with 15 ml of concentrated nitric acid for 30 min. The results obtained are given in Table 5 show that preliminary mineralization is not necessary. This fact may be attributed to the elements being sorbed from organic as well as inorganic compounds. The similarity of the results obtained for the two sizes of sample proves that the sorption capacity of the amount of resin used (10 g) was sufficient for the purpose. The cadmium content was so low that even after concentration from 2 litres of water its amount was below the limit of determination. The iron and zinc contents were high enough for their determination after 2-fold and 5-fold dilution, respectively, of the final solutions. REFERENCES
1. G. A. Junk, J. J. Richard, K. D. Greiser, D. Witiak, J. L. Witiak, M. D. Arguello, R. Vick, H. J. Svec, J. S. Fritz and G. V. Calder, J. Chromatog., 1974, 99, 745. 2. G. A. Junk, C. D. Chriswell, R. C. Chang, L. D. Kissinger, J. J. Richard, J. H. Fritz and H. J. Svec, 2. Anal. Chem., 1976, 282, 331. J. P. Riley and D. Taylor, Anal. Chim. Acta, 1969, 46, 307. J. Zerbe, Chem. Anal. Warsaw, 1979, 24, 85. A. C. Howard and N. N. Arbab-Zawar, Talanta, 1979, 26, 895. J. L. Lundgren and A. A. Schilt, Anal. Chem., 1977,49, 974. 7. T. Braun and M. N. Abbas, Anal. Chim. Acta, 1980, 119, 113. 8. I&m, ibid., 1982, 134, 321. 9. M. P. Maloney, G. J. Moody and J. D. R. Thomas, Analyst, 1980, 105, 1087.