Analytica Chimica Acta 452 (2002) Received 20 September 2000; received in revised form 14 August 2001; accepted 26 September 2001

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1 Analytica Chimica Acta 452 (2002) Column solid-phase extraction with Chromosorb-102 resin and determination of trace elements in water and sediment samples by flame atomic absorption spectrometry Sibel Saraçoğlu a, Latif Elçi b, a Department of Chemistry, Faculty of Art and Science, Erciyes University, TR Kayseri, Turkey b Department of Chemistry, Faculty of Art and Science, Pamukkale University, TR Denizli, Turkey Received 20 September 2000; received in revised form 14 August 2001; accepted 26 September 2001 Abstract A column, solid-phase extraction (SPE), preconcentration method was developed for determination of Bi, Cd, Co, Cu, Fe, Ni and Pb ions in drinking water, sea water and sediment samples by flame atomic absorption spectrometry. The procedure is based on retention of analytes in the form of pyrrolidine dithiocarbamate complexes on a short column of Chromosorb-102 resin from buffered sample solution and then their elution from the resin column with acetone. Several parameters, such as ph of the sample solution, amount of Chromosorb-102 resin, amount of ligand, volume of sample and eluent, type of eluent, flow rates of sample and eluent, governing the efficiency and throughput of the method were evaluated. The effects of divers ions on the preconcentration were also investigated. The recoveries were >95%. The developed method was applied to the determination of trace metal ions in drinking water, sea water and sediment samples, with satisfactory results. The 3 detection limits for Cd, Cu, Fe, Ni and Pb and were found to be as 0.10, 0.44, 11, 3.6, and 10 gl 1, respectively. The relative standard deviation of the determination was <10%. The procedure was validated by the analysis of a standard reference material sediment (GBW 07309) and by use of a method based on coprecipitation Elsevier Science B.V. All rights reserved. Keywords: Solid-phase extraction; Trace metals; Water and sediment samples; Flame atomic absorption spectrometry; Pyrrolidine dithiocarbamate; Cobalt; Cadmium; Copper; Iron; Nickel; Lead 1. Introduction Flame atomic absorption spectrometry (FAAS) has been widely used for determination of trace metal ions, because of the relatively simple and inexpensive equipment required. However, the direct determination of metal ions at trace levels by FAAS is limited due to their low concentrations and matrix interferences. In trace analysis, therefore, a preconcentration and/or separation of trace elements from the matrix Corresponding author. Tel.: address: elci@pamukkale.edu.tr (L. Elçi). is frequently necessary to improve the detection limit and selectivity for their determination by FAAS. For this, several methods have been proposed and used for preconcentration and separation of trace elements according to the nature of the samples, the concentrations of the analytes and the measurement techniques [1,2]. They include ion exchange [3,4], coprecipitation [5,6], solvent extraction [7] and adsorption [8 10]. Among the various preconcentration methods, solid-phase extraction (SPE) is one of the most effective multielement preconcentration methods because of simplicity, rapidity and ability to attain a high concentration factor. Until now, XAD resins [11 15], /02/$ see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S (01)

2 78 S. Saraçoğlu, L. Elçi / Analytica Chimica Acta 452 (2002) activated carbon [16 18], ion-exchange resins [19,20], chelating resins [21] and various polymers have been used as solid-phase material.for SPE, it would appear that most successful general approach is to use a hydrophobic solid-phase extractant for the retention of non-polar derivatives of the examined analytes. According to our knowledge, the various non-polar gas chromatography (GC) stationary phase materials have not been investigated in detail for use in SPE preconcentration procedures. Chromosorb-102 resin (a styrene-divinylbenzene copolymer) has been extensively used in gas chromatographic separation of organic compounds [22 24]. It was first used for determination of lead with a combination of flow injection SPE and FAAS in our previous study [10]. The purpose of the present study is to demonstrate the feasibility of using Chromosorb-102 resin as a solid-phase extractant for preconcentration of copper, iron, nickel, cadmium and lead found at trace level in drinking water, sea water and sediment samples. In the procedure, the analytes were retained in the form of pyrrolidine dithiocarbamate complexes on a short column of Chromosorb-102 resin from a buffered sample solution and then eluted from the resin column with acetone. In the development of the procedure, several parameters relevant to the retention and elution of the analytes were examined. 2. Experimental 2.1. Apparatus A Perkin-Elmer model 3110 atomic absorption spectrometer equipped with Perkin-Elmer single element hollow cathode lamps and an air acetylene burner was used for the determination of metals. The instrumental parameters were those recommended by the manufacturer. The wavelengths (nm) selected for the determination of the analytes were as follows: Cu, 324.8; Fe, 248.3; Ni, 232.0; Co, 240.7; Pb, 283.3; Bi, 323.1; and Cd, To determine the analytes in the concentrated solutions, a 100 l aliquot of the solution was introduced to the nebulizer by an injection method [25]. A model Nel ph 900 digital ph meter equipped with a combined glass calomel electrode was used for the ph adjustments Reagent and solution Reagents were of analytical reagent grade unless stated otherwise. All solutions were prepared in double distilled, deionized water. Standard solutions (1000 mg l 1 ) of the elements were prepared from appropriate amounts of nitrate salts in 1% HNO 3 and further diluted daily prior to use. A 0.05% (m/v) ammonium pyrrolidine dithiocarbomate (APDC) solution using solid APDC purchased from Sigma was prepared daily in water. Pure acetone from Merck was used as an eluent. The following buffer solutions were used for a preconcentration procedure: KCl/HCl buffer for ph 1; PO 4 3 /HPO 4 buffer for ph 2 and 3; CH 3 COO /CH 3 COOH buffer for ph 5 and 6; borate buffer for ph 7; NH 3 /NH 4 + buffer for ph Chromosorb-102 resin (Phase Separations Inc., Norwalk, CT) was used as the solid-phase extractant. It is a porous styrene-divinylbenzene copolymer having a surface area in the range of m 2 g 1 and mesh particle size. This hydrophobic resin can be used in a ph range from 0 to Method development The stopcock of the glass column (100 mm 10 mm) was covered with a fritted glass disc. A total of 500 mg of Chromosorb-102 resin was slurried in water, then poured into the column. A small amount of glass wool was placed on the disc to prevent loss of the resin beads during sample loading. The bed height of resin in the column was ca. 1.5 cm. It was washed successively with water, acetone and water. The column was preconditioned by passing a blank solution prior to use. After each use, the resin in the column was washed with a large volume of water and stored in water for the next experiment. The performance of the column method was tested with model solution before its application to the samples. A total of 25 ml of the model solution containing 5 g of Cd, 10 g each of Co, Cu, Fe and Ni and 20 g each of Bi and Pb was buffered to the desired ph. Three millilitre of 0.05% (m/v) APDC solution was added to this solution. It was loaded to 1 Johns Manville Chromosorb Porous Polymer Supports Catalogue.

3 S. Saraçoğlu, L. Elçi / Analytica Chimica Acta 452 (2002) the top of the preconditioned column and gravitationally passed through at a flow rate of 2 ml min 1. The column was washed with 5 10 ml of blank solution prepared with the corresponding buffer solution. The retained metal ions were eluted with 10 ml of acetone. The effluent was evaporated to near dryness on a hot plate adjusted to ca C and then cooled. It was diluted to 2 or 10 ml with 1 M HNO 3. The analytes in the final solution were determined by FAAS Analysis of drinking water, sea water and sediment Drinking tap water samples taken from our research laboratory were analysed without pre-treatment. To determine trace metals in the water sample, the preconcentration procedure given above was used for 600 ml of the drinking water. The surface sea water samples were collected in pre-washed polyethylene bottles from dirty region of İskenderun Bay, Turkey (Mediterranean Sea) in October The bottles were cleaned with detergent, double distilled deionized water, dilute nitric acid and double distilled deionized water, in sequence. The samples were immediately filtered through a Millipore cellulose nitrate membrane, pore size 45 m, acidified to ph 3 with hydrochloric acid and stored in precleaned polyethylene bottles. The samples were analysed by the preconcentration procedure given above, within 2 weeks after collection. For the analysis, the sample containing 600 ml of the acidified sea water was firstly neutralised and then buffered to the desired ph. For sediment analysis, a portion ( mg) of the certified sediment sample (NRC-CRM GBW from China) was accurately weighed into a 50-ml container (or beaker) and aqua regia (12 ml concentrated hydrochloric acid and 4 ml of concentrated nitric acid) was added to the sample. The container was covered with a watch glass and the mixture was evaporated on a hot plate at ca. 95 C almost to dryness. Then 8 ml of aqua regia was added to the residue and the mixture was again evaporated to dryness. After cooling, resulting mixture was filtered through a Advantec Toyo 5A filter paper. The sample was diluted to 10 ml with distilled water. The sample was analysed by the preconcentration procedure given above. The water samples were also analysed using a coprecipitation method based on the use of cerium(iv) hydroxide as a carrier. For this analysis, 600 g of Ce(IV) as sulphate was added to 750 ml of the water sample. The ph of the solution was adjusted to 10.5 with 1 mol l 1 NaOH. After 20 min, the precipitate was collected on a cellulose nitrate membrane filter of 0.45 m size and 47 mm diameter. The membrane loaded with the precipitate was dissolved in 0.5 ml of concentrated nitric acid and the solution obtained was diluted to 2 or 5 ml with water. To determine the analytes, 100 l of this final solution was injected into the flame AAS nebulizer [26]. 3. Results and discussion 3.1. Effect of some parameters on preconcentration The effect of the ph on the retention of metal APDC complexes on the Chromosorb-102 resin column was studied by applying of the proposed procedure at different ph values. The results (Fig. 1) indicate that the recoveries, 95%, are quantitative for Bi and Cd in the ph range 3 8, Co, Cu and Ni in the ph range 4 6, Fe in the ph range 5 6, and Pb in the ph range of 3 9. Consequently, ph 6 was used in further experiments. To test the effect of resin amount for quantitative retention of analytes, different amounts of Chromosorb-102 from 300 to 700 mg were added to the column. The procedure was applied to the model solutions by use of these columns. Quantitative recoveries for all the examined analytes were obtained in range mg of resin. Quantitative retention was not obtained with amounts of resin smaller than 400 mg. On the other hand, resin amount larger than 600 mg prevented the elution of the quantitatively retained chelates by 10 ml of acetone. Accordingly, the column was filled with 500 mg of Chromosorb-102 resin in further experiments. The ligand concentration plays an important role in the retention of the analytes because in its absence the resin does not retain completely the metal ions. However, excess APDC prevents the retentions of metal ions due to sorptive competitions between metal APDC chelates and APDC itself on the resin. Therefore, the influence of APDC concentration on the retention of the examined metal ions was investigated

4 80 S. Saraçoğlu, L. Elçi / Analytica Chimica Acta 452 (2002) Fig. 1. Effect of ph on retention of metal APDC complexes. in the range of to M APDC using a series of model solution containing the analytes, given in the method development section. The retentions of analytes with increasing concentration of APDC increased up to M. The retention was quantitative, 95%, for Cu, Fe and Ni in the range to M APDC, and for Co in the range to APDC. Quantitative retentions of Pb, Cd and Bi were obtained in the ranges to , to and to M APDC, respectively. So, the amount of ligand was chosen as Min further experiments. The recoveries obtained for sample solution without APDC were <10%. Since the retention of elements on an adsorbent depends on the flow rate of the metal solution, the influence of flow rate for sample solutions on the retention of the trace metals was investigated under the optimum conditions. From Table 1, it can be seen that retentions of Bi, Cd, Co, Fe and Pb as APDC complexes were independent of flow rates from 2 to 12 ml min 1.At flow rates >7.5 ml min 1, the decreased retentions of Cu and Ni can be interpreted as resulting from slow adsorption. To obtain quantitative recovery, the effect of eluent types on preconcentration was investigated using various eluting solutions. The volume of eluent was Table 1 Effect of flow rate for sample on retention of metal APDC complexes (n = 3) Flow rate (ml min 1 ) Recovery (%) ml. The results are shown in Table 2. Quantitative recoveries of the examined analytes were obtained with acetone. Recoveries with 1 M HNO 3 in acetone were quantitative for Cd, Co, Fe and Pb. Quantitative Table 2 Effect of eluent types on retention of metal APDC complexes (n = 3) Eluent type Recovery (%) 1 M HNO M HCl M HNO 3 in acetone Acetone

5 S. Saraçoğlu, L. Elçi / Analytica Chimica Acta 452 (2002) Table 3 Effect of eluent volume on retention of metal APDC complexes (n = 3; eluent:acetone) Eluent volume (ml) Recovery (%) recoveries were not obtained with aqueous 1 M HNO 3 and 1 M HCl. Thus, acetone was used as eluent in all further experiments. The effect of the eluent volume on the recoveries was also evaluated. As can be seen from Table 3, the recoveries of metal ions approach quantitative values when using 10 ml acetone. In order to deal with real samples containing very low concentrations of trace metal ions, the maximum applicable sample volume must be determined. Therefore, the effect of the sample volume on the recoveries was investigated. Table 4 indicates that the retention of all the examined metal ions is not affected by sample volume up to 600 ml. After 600 ml of sample volume, recovery values <95% for Fe and Bi were obtained. In this study, therefore, the final solution volume was 2 ml and the highest concentration factor was 300 for a 600 ml sample volume Effect of matrix ions on preconcentration In order to evaluate the feasibility of the method for water analysis, the effects of some alkali and alkaline Table 4 Effect of sample volume on retention of metal APDC complexes (n = 3) Sample volume (ml) Recovery (%) Table 5 Influence of matrix ions on retention of metal APDC complexes (n = 3) a Matrix ions Tolerance limits (mg l 1 ) Na K Ca Mg Cl SO a Bi not studied. Concentration of matrix ion in eluted solution (mg l 1 ) earth metal cations and some anions found as major components in natural water samples (Na +,K +,Ca 2+, Mg 2+,Cl,SO 4 2 ) were investigated. Table 5 showed that the recovery of the investigated trace metal ions, other than Bi, was not affected by a solution containing the indicated high concentrations of the matrix ions. Table 5 also shows very low recoveries for the matrix ions, which are helpful in the determinations of the trace heavy metals. The results are desirable in view of applications to samples with high salt content, and reflects the lack of complexation with APDC of these matrix ions. The reported tolerance limit is defined as the ion concentration causing a relative error <±5%. The tolerance limits are higher than the concentrations of Na +,K +,Mg 2+ and Cl in sea water [27] Analytical performance A sediment reference material (GBW from China) was used for method validation. The sediment sample was dissolved according to the procedure given in the experimental section. The SPE procedure was applied to the sediment solution. As seen in Table 6, the results were compared with the certified values Table 6 Determination of Co, Cu, Pb and Cd in a certified sediment sample (GBW 07309), (n = 5) Analyte Concentration of metal ( gg 1 ) Certified Found, (x ± ts)/ n Cu ± 2.02 Co ± 0.61 Pb ± 0.63 Cd ± 1.09

6 82 S. Saraçoğlu, L. Elçi / Analytica Chimica Acta 452 (2002) Table 7 Recovery of metal spikes from 600 ml of drinking water (n = 3) Element Added ( gl 1 ) Found ( gl 1 ) Recovery (%) Cu Fe Pb using a t-test at 95% confidence limits (C.L.). Good agreement was obtained between the estimated content by the proposed method and the certified values for Co, Cu and Pb, but not for Cd. This result also indicates that the developed SPE method for Co, Cu and Pb is not affected by potential interferences from the major matrix elements of the analysed sediment, including Al (5.6%); Fe (4.78%); Mg (1.43%); Ca (3.82%); Na (1.07%); and K (1.65%). The reason of the large positive error for Cd might probably be associated with interference of sediment constituents, such as silicate and aluminium. The correctness of the procedure was confirmed by the recoveries of spiked analytes from the 600 ml drinking water sample. The results are shown in Table 7. In addition, the accuracy of the SPE procedure was also checked by analysis of drinking and sea water samples by the reference method based on coprecipi- tation with cerium(iv) hydroxide (Table 8). There is no significant difference at 95% C.L., between the results obtained with two methods, with the exception of Fe and Cd. The reproducibility of the proposed SPE FAAS procedure was measured. The relative standard deviations (n = 3) were found to be 10% for Cu, 5% Fe and 3% Pb for the drinking water sample and 6.7% for Cd, 0.4% for Cu, 0.69% for Fe, 5.5% for Ni and 2.7% for Pb for the sea water sample. The detection limits of the investigated elements based on three times the standard deviation of the blank (N = 20) for Cd, Cu, Fe, Ni and Pb were found to be 0.10, 0.44, 11, 3.6 and 10 gl 1, respectively Applications Firstly, the method was applied to a certified sediment sample. As can be seen from Table 6, there is a good agreement between the certified values and analytical results, except for Cd. The proposed method was applied to the analysis of a drinking water sample, with satisfactory results for Cu and Pb (Table 8). The concentrations of Bi, Cd, Co and Ni were not determined due to their very low values. The method was also applied to the determination of Cd, Cu, Fe, Ni and Pb in a sea water sample (Table 8). The concentrations of Bi and Co were not determined due to their low concentrations. Again, the results for Cu and Pb were satisfactory, but not those for Fe, Ni and Cd. The accuracy of the results given in Table 7 was demonstrated by use of a coprecipitation procedure based on use of cerium(iv) hydroxide [26]. For the Table 8 Determination of Cu, Fe, Pb, Ni and Cd in drinking and sea water samples a Analytes Concentration of metals, x ± ts/ n ( gl 1 ) Drinking water Sea water Present method Reference method [26] Present method Reference method [27] Cu 1.96 ± 0.24 (6) 1.97 ± 0.19 (6) 1.13 ± 0.01 (5) 1.04 ± 0.07 (6) Fe 3.08 ± 0.15 (7) 4.00 ± 0.20 (6) 7.47 ± 0.08 (4) ± 0.77 (5) Pb 1.78 ± 0.07 (5) 1.84 ± 0.18 (5) 0.47 ± 0.01 (6) 0.52 ± 0.06 (4) Ni n.d. n.d ± 0.22 (5) 3.56 ± 0.43 (4) Cd n.d. n.d ± 0.26 (6) 5.38 ± 0.37 (6) a The values in parenthesis are number of replicate analyses; n.d.: not determined.

7 S. Saraçoğlu, L. Elçi / Analytica Chimica Acta 452 (2002) two methods, except for Fe and Cd, there are no significant differences at the 95% C.L. 4. Conclusions Chromosorb-102 resin shows excellent sorption for Bi, Cd, Co, Cu, Fe, Ni and Pb with APDC and poor sorption for alkali and alkaline earth element metals. Only 0.5 g of the resin is needed and repeated use is possible for preconcentration trace elements. Therefore, it is considered that the method is applicable to the preconcentration of trace elements in drinking, river, lake, sea and waste waters. No doubt the proposed procedure could be combined with other instrumental determination techniques. References [1] A. Mizuike, Enrichment Techniques for Trace Analysis, Springer, Heidelberg, [2] J. Minczevski, J. Chwastowsko, R. Dybezynski, Separation and Preconcentration methods in Inorganic Analysis, Ellis Horwood, Chichester, [3] T. Kiriyoma, R. Kuroda, Fresenius Z. Anal. Chem. 332 (1988) 338. [4] J. Kubova, V. Neveral, V. Stresko, J. Anal. Atomic. Spectr. 9 (1994) 241. [5] R.E. Santelli, M. Gallego, M. Varcarcel, Anal. Chem. 61 (1989) [6] L. Elçi, S. Saraçoğlu, Talanta 46 (1998) [7] P.L. Malvankar, V.M. Shinde, Analyst 116 (1991) [8] M. Soylak, L. Elçi, Int. J. Environ. Anal. Chem. 66 (1997) 51. [9] M. Hıraide, J. Hori, Anal. Sci. 15 (1999) [10] L. Elçi, Z. Arslan, J.F. Tyson, Spectrochim. Acta Part B 55 (2000) [11] L. Elçi, M. Soylak, M. Doğan, Fresenius J. Anal. Chim. 340 (1992) 175. [12] L. Elçi, Anal. Lett. 26 (1993) 5. [13] A. Tunçeli, A.R. Türker, Anal. Sci. 16 (2000) 81. [14] Y. Sakai, N. Mori, Talanta 33 (1986) 161. [15] S.L.C. Ferreira, C.F. Brito, A.F. Dantas, N.M.L. Araujo, A.C.S. Costa, Talanta 48 (1999) [16] M. Soylak, İ. Narin, L. Elçi, M. Dogan, Trace Elements Electrol. 16 (1999) 131. [17] L. Elçi, M. Doğan, Fresenius Z. Anal. Chem. 330 (1988) 610. [18] M. Kimura, K. Kawanami, Talanta 26 (1979) 901. [19] P.E. Carrero, J.F. Tyson, Analyst 122 (1997) 915. [20] K. Anezaki, X. Chen, T. Ogasawara, I. Nukatsuka, K. Ohzeki, Anal. Sci. 14 (1998) 523. [21] D.W. Lee, C.H. Eum, I.H. Lee, S.J. Jean, Anal. Sci. 4 (1988) 504. [22] A. Dravnieks, B.K. Krotoszynski, J. Whitfield, A. O Donnell, T. Burgwald, Environ. Sci. Technol. 5 (1971) [23] T.C. Thomas, J.N. Seiber, Bull. Environ. Cont. Toxical. 12 (1974) 17. [24] L.D. Butler, M.F. Burke, J. Chromatogr. Sci. 14 (1976) 117. [25] L. Elçi, S. Kartal, A. Ülgen, M. Doğan, P. Doğan, DOGA-Tr. J. Chem. 14 (1990) 294. [26] Ü. Divrikli, L. Elçi, Anal. Chim. Acta, 2001, accepted for publication. [27] V.L. Snoeying, D. Jenkins, Water Chemistry, Wiley, New York, 1980.