Synthesis of polyacrylacylaminourea chelating fiber and properties of concentration and separation of trace metal ions from samples

Analytica Chimica Acta 427 (2001) 287–291

Synthesis of polyacrylacylaminourea chelating fiber and properties of concentration and separation of trace metal ions from samples Bolin Gong a,∗ , Xueqiang Li a , Fengrun Wang a , Haidong Xu a , Xijun Chang b a b

Department of Chemistry, Ningxia University, Yinchuan 750021 , PR China Department of Chemistry, Lanzhou University, Lanzhou 730000, PR China

Received 6 July 2000; received in revised form 12 September 2000; accepted 13 September 2000

Abstract A novel polyacrylacylaminourea chelating fiber is synthesized simply and rapidly from nitrilon (an acrylonitrile-based synthetic fiber) and used for the preconcentration and separation of trace In(III), Bi(III), Cr(III), V(V) and Ti(IV) ions from solution samples. The analyzed ions can be quantitatively concentrated by the fiber up to a flow rate of 10.0 ml min−1 at pH 3, and can also be desorbed with 10 ml of 2 M HCl + 2% thiourea from the fiber column with recoveries of 97–99%. The chelating fiber is reused for eight times, the recoveries of these ions are still over 92%, and 100–1000 times of excess of Fe(III), Al(III), Ca(II), Mg(II), Ni(II), Mn(II), Cu(II), Zn(II), and Cd(II) cause no interference in the determination of these ions by inductively-coupled plasma atomic emission spectrometry. The capacities of the fiber for the analytes are in the 0.23–1.17 mmol g−1 range. The results show the relative standard deviation for the determination of 50.0 ng ml−1 In(III) and Bi(III), 5.0 ng ml−1 Cr(III), V(V) and Ti(IV) are in the 0.5–3.2% range. The recoveries of a standard added in real solution samples are between 96 and 100%, and the concentration of each ion in mineral sample detected by the method is in good agreement with the certified value. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Concentration; Separation; Polyacrylacylaminourea chelating fiber; Indium; Bismuth; Chromium; Vanadium; Titanium

1. Introduction The preconcentration and separation of elements by use of chelating resins [1–4] or chelating fibers [5–8] have been reported. However, most of chelating resins or chelating fibers are used for preconcentration and determination of noble metal ions, the synthesis of the chelating resins or fibers usually takes a long time and the synthetic process is complicated. The chelating fibers could not be used for enrichment of trace

∗ Corresponding author. Tel.: +86-951-208-4892; fax: +86-951-207-7740. E-mail address: [email protected] (B. Gong).

element Cr(III) and the rate of uptake of metal ions is slow. In this paper, a new polyacrylacylaminourea chelating fiber is synthesized rapidly by a one-step reaction of nitrilon with aqueous aminourea. The structure of the chelating fiber is analyzed by using Fourier transform infrared spectroscopy (FT-IR) [9,10]. The properties of the chelating fiber for the preconcentration and separation of trace of aqueous In(III), Bi(III), Cr(III), V(V) and Ti(IV) from solution samples, as measured by inductively-coupled plasma atomic emission spectrometry (ICP-AES), are studied in details. The precision and the accuracy of the proposed method are achieved by analysis of a real sample solution and a mineral reference sample with satisfactory results.

0003-2670/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 3 - 2 6 7 0 ( 0 0 ) 0 1 1 9 8 - 3

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Scheme 1.

2. Experimental 2.1. Instruments and apparatus An ICP/6500 inductively coupled plasma spectrometer (Perkin-Elmer), a Model 170-sx FT-IR spectrometer (Nicolet), a Pore Size 9320 (Micromeritics Instrument Corporation), a Model 1106 Elemental Analyzer (Carlo Erba) are used and a Model pHs-3A digital pH meter (Analysis Instrument Factory at Beijing, China) is used. The adsorption column is a glass tube (15 cm length, 0.5 and 0.15 cm i.d. at the lower end) containing 0.2 g of polyacrylacylaminourea chelating fiber in high-purity water over-night, and in which a small pad of adsorbent cotton–wool has been placed beforehand. 2.2. Reagents and standards Nitrilon (Lanzhou Chemical Factory) is cut with scissors, washed with ethanol and distilled water, and the dried under an infrared drying lamp. Reagents of spectral and analytical purity are used for all experiments. The stock solutions of 1.00 mg ml−1 of the five and analyzed ions are prepared by dissolving spectroscopically pure In2 O3 , Bi2 O3 , Cr(NO3 )3 , NH4 VO3 and TiO2 , respectively, in dilute HNO3 . They are diluted and mixed to give stock standard solutions of 50.0 ␮g ml−1 for each of In and Bi and 5.0 ␮g ml−1 for each of Cr, V and Ti in 1.0 mol l−1 HNO3 , and the standard solutions are used for all experiments. 2.3. Synthesis and characterization of the chelating fiber A 25 g portion of dried nitrilon (contains 93% acrylonitrile, 5.7% methyl acrylate and 1.3% itaconic acid)

and 100 g 35% aminourea hydrochloride aqueous solution are placed in a three-necked flask. The mixture is adjusted to pH 7–8 with NaOH solution, and refluxed for 15 h at 80–90◦ C with slow stirring. The product is washed with distilled water until neutral and dried under IR irradiation. Thus, a gold-colored polyacrylacylaminourea chelating fiber is obtained, its nitrogen content determined by the Kjeldahl–Gunning method is 27.7%. The synthesis reaction can be briefly expressed by Scheme 1. According to the reference [9–11], the IR spectrum of the polyacrylacylaminourea chelating fiber can be assigned as follows: 3454.5 and 3342.2 (γ N–H2 and γ N–H), 2939.9 and 2868.1 (C–H of CH2 and CH), 1738.2 (γ C==O), 1628.9 (δ s NH2 ), 1457.3 (δ s CH2 ), 1250 (γ C–N of O==C–NH), 1170.4 (γ C–N of CH2 NH2 ), 1078.2 (δ C–N), 836.2 (δ NH2 ), 764.6 (δ P CH2 ), and 684.8 cm−1 (δ w NH2 ). (γ : stretching vibration; δ: bending vibration; δ s : scissor vibration; δ P : rocking vibration; δ w : wagging vibration). The IR spectrum of chelating fiber presents the N–H characteristic vibrational adsorption band (3342.2 cm−1 ). A comparison between the IR spectrum of the chelating fiber with that of nitrilon shows that the 2250.5 cm−1 of –CN vibrational adsorption band disappears. These observations demonstrate that the analytical functional groups have been attached to the fiber. 2.4. Analytical procedure The mixed standard solutions of In, Bi, Cr, V and Ti or real sample solutions are pipetted into beakers (100–1000 ml). The solutions are adjusted to pH 3 with clark-lubs buffer solution and pass through the adsorbing column at a flow rate of 10.0 ml min−1 . The analytes are desorbed from the columns with 10 ml of

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2 M HCl + 2% CS(NH2 )2 solution (50◦ C) at a flow rate of 4.0 ml min−1 . Subsequently, the ions in the 10 ml of eluate are determined by the ICP spectrometer. Spectrometer conditions are as follows. Forward power: 1100 W; viewing height: 15 mm; Ar plasma gas flow rate: 15 l min−1 ; Ar nebulizer gas flow rate: 1.0 l min−1 ; Ar auxiliary gas flow rate: 0.7 l min−1 ; wavelengths: In, 230.605 nm; Bi, 223.061 nm; Cr, 267.716 nm; V, 292.402 nm; Ti, 334.941 nm.

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3. Results

cedure, each column is eluted with 10 ml of 1–6 M HCl + 2% CS(NH2 )2 solution at 50◦ C. The results show that these elements can be quantitatively desorbed with 10 ml of 2 M HCl + 2% CS(NH2 )2 solution from columns with recoveries above 96%. However, it is also observed that when the concentration of the eluent is greater than 2 M HCl or the content of CS(NH2 )2 is greater than 2%, the ICP-AES results gradually decrease. This occurs because the nebulization rates are reduced relatively to the standard solutions.

3.1. Effect of acidity on adsorption

3.4. Influence of desorption flow rate

Equal concentrations of mixed standards are diluted to equal volumes and enrich through the columns in the pH range 1–7 as described above. The results show that trace Bi and In at pH 2–7; Cr and V at pH 3–6; Ti at pH 3 can be enriched quantitatively by the fiber with recoveries over 95% and that recoveries of all elements are higher than 97% at pH 3. In order to determine these elements simultaneously, pH 3 is selected as the enrichment acidity. In addition, at pH 3, K, Na, Ca, Mg, Ni(II), Cu(II), Co(II), Mn(II), Ga(III) and Be(II) are not adsorbed by the fiber column, La(III), Au(III), Hg(II), Cd(II) and Pb(II) are adsorbed only by 10–30%, Sb(III) and As(III) are enriched by 40–60%. However, because the fiber adsorbs In, Bi, Cr, V and Ti ions strongly, their enrichment are not influenced by these other ions either.

When the column procedure is used, the influence of the flow rate on desorption of the analytes from the columns with 10 ml of 2 M HCl + 2% CS(NH2 )2 is investigated. The results show that desorption recoveries of Bi, In and Ti are greater than 98% for the flow rate below or at 4.0 ml min−1 and that the recoveries of all elements are greater than 97% at flow rate 4.0 ml min−1 . A 4.0 ml min−1 flow rate is selected for the eluent flow rate.

3.2. Effect of flow rate on enrichment When the recommended procedure is used, the flow rate for preconcentration of the analytes on fiber column at pH 3.0 varies between 7.0 and 14.0 ml min−1 . The results show that In, Bi, Cr, V and Ti ions can be enriched quantitatively at flow rate below 11.0 ml min−1 with recoveries above 94% and that recoveries of all elements are higher than 97% at flow rate 10.0 ml min−1 . A 10.0 ml min−1 flow rate is selected for preconcentration velocity. 3.3. Influence of desorption acidity After the trace of In, Bi, Cr, V and Ti are enriched on the fiber column following the above pro-

3.5. Adsorption capacity and reuse property A 0.1 g portion of the fiber is placed in each of the five conical flasks. A stock solution of each of In, Bi, Cr, V and Ti ions is added to each flask and diluted to an equal volume of 100 ml. The acidity of each solution is adjusted to pH 3, and the vessels are shaken in a mechanical vibrator. The concentrations of the above ions in solution are measured at regular intervals of 10 min by ICP-AES until equilibrium is reached. Thus, the saturated adsorption capacity of the fiber is calculated. It is 0.39 mmol g−1 for In(III), 0.23 mmol g−1 for Bi(III), 0.52 mmol g−1 for Cr(III), 0.73 mmol g−1 for V(V), and 1.17 mmol g−1 for Ti(IV). When the fiber is used repeatedly (up to eight times) as described for the enrichment and determination of In, Bi, Cr, V and Ti ions (after these ions are desorbed from the fiber each time with 10 ml of 2 M HCl + 2% CS(NH2 )2 , the fiber column is washed to neutrality with distilled water), the adsorption efficiency is still higher than 92%. The chelating fiber after being used for eight times does not display obvious swelling effect.

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Table 1 Analytical results of a real sample solutiona Element

Concentration (ng ml) Found (n = 7)

In Bi Cr V Ti

80.0 51.5 – 6.3 8.7 a

± 2.5 ± 2.0 ± 0.3 ± 0.4

Added

Sum (n = 7)

50.0 50.0 5.0 5.0 5.0

129 ± 4.0 101 ± 3.0 5.0 ± 0.3 11.1 ± 0.4 13.6 ± 0.5

Recovery (%)

R.S.D. (%)

98.0 99.0 100 96.0 98.0

2.4 2.7 3.2 2.9 2.6

Added 0.1 g citric acid and 0.1 g NH2 OHHCl.

Table 2 Analytical results of real mineral sample solution Element In Bi Cr V Ti a

Concentration (%)

R.S.D. (%)

Specified value

Founda

0.030 0.023 0.210 0.010 –

0.029 0.024 0.215 0.010 –

3.8 4.2 0.8 3.2 –

Average of five determinations.

Different potential interfering ions (50.0 ␮g ml−1 each of Ca(II), Mg(II), Zn(II), Cu(II); 30.0 ␮g ml−1 each of Fe(III), Al(III) and 20.0 ␮g ml−1 each of Mn(II), Ni(II), Cd(II)) are added to dilute analytes standards (50.0 ng ml−1 each of In, Bi and 5.0 ng ml−1 each of Cr, V, Ti). The analytes are preconcentrated and determined as described above. The results show that 100–1000 times of excesses of these other ions cause little interference with the determination of In, Bi, Cr, V and Ti with recoveries in the 94.5–100% range. However, thousand times of excesses of Fe(III) and Al(III) interfere with the determination of In, Bi, Cr, V and Ti ions, and can be eliminated by adding shielding agent (citric acid and hydroxylamine hydrochloride).

times, are in the 96–100% range. The relative standard deviation (R.S.D.) is between 0.5 and 2.4%. The accuracy of the combined preconcentration — ICP procedure is checked by analyzing real waste water from a metal smelter using the standard addition method. The results in Table 1 show that the recoveries of In(III), Bi(III), Cr(III), V(V) and Ti(V) ions added to the sample are in the 96–100% range, R.S.D. are in the 2.4–3.2% range. In addition, a 0.100 g amount of a mineral reference sample is weighed accurately into a 100 ml beaker, 5 ml of (1+1) HCl+HNO3 is added. It is heated for 40 min with vibrating until the sample is dissolved completely. The solution is diluted to 100 ml with distilled water. Then 10 ml of this solution is analyzed according to the analytical procedure and the results are given in Table 2, it can be seen that the results are in good agreement with the values specified.

4. Analytical precision and accuracy

5. Conclusion

Under the selected conditions, the recoveries of traces of 50.0 ng ml−1 for each of In, Bi and 5.0 ng ml−1 for each of Cr, V, Ti in 1000 ml of solutions, enriched and determined simultaneously seven

A new polyacrylacylaminourea chelating fiber shows a higher adsorption selectivity for In(III), Bi(III), Cr(III), V(V) and Ti(IV) ions, and adsorbed ions can be readily desorbed from the fiber column by

3.6. Interference of other ions

B. Gong et al. / Analytica Chimica Acta 427 (2001) 287–291

a 10 ml of 2 M HCl + 2% thiourea solution. The fiber also presents the advantage of lower interference, higher adsorption capacity, better reuse ability and higher chemical mechanical stability, the synthesis of the fiber is simple and economical. Preconcentration by this fiber combined with ICP-AES can be applied to the determination of trace In, Bi, Cr, V and Ti ions in waster water and mineral reference samples with satisfactory results. Acknowledgements Supported by the Natural Science Foundation and the Science Committee Foundation and of Ningxia. References [1] C. Kantipuly, S. Katragadda, A. Chow, H.V. Gesser, Talanta 37 (1990) 491.

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[2] Z.X. Su, X.J. Chang, G.Y. Zhan, X.Y. Luo, Q.S. Pu, Anal. Chim. Acta 310 (1995) 493. [3] X.J. Chang, B.L. Gong, D. Yang, X.Y. Luo, Anal. Lett. 30 (1997) 2611. [4] N.M. Kuz’min, V.Z. Krasil’shchick, Zh. Anal. Khim. 43 (1988) 1349. [5] Y.X. Zhang, C.M. Wang, Y.M. Qu, Mikrochim. Acta, Part I 75 (1984) 291. [6] G.V. Myasoedova, I.I. Antokol’skaya, S.B. Savvin, Talanta 32 (1985) 1105. [7] X.J. Chang, Z.X. Su, G.Y. Zhan, X.Y. Luo, W.Y. Gao, Analyst 119 (1994) 1445. [8] G.V. Myasoedova, I.I. Antokol’skaya, O.P. Shvoeva, M.S. Mezhirov, S.B. Savin, Solvent Extr. Ion Exch. 6 (1988) 301. [9] Q.N. Dong, IR Spectra Methods, Publishing House of the Chemical Industry, Beijing, 1979, p. 160, 179, 195. [10] Y.Q. Cheng, IR Spectra Methods and Use, Publishing House of Shanghai University, Shanghai, 1993, p. 89, 72, 112. [11] B.L. He, W.Q. Huang, Ions Exchanger and Adsorption Resin, Publishing House of Shanghai Science and Education, Shanghai, 1995, pp. 90–130.