The formation of a chelate complex of antimony(III) with o-chlorophenylfluorone (CPF) was used for the spectrophotometric determination of antimony. The spectral correction technique was applied to characterize the complexation and the determination of SbIII. Results have shown that complex Sb(CPF)2H2O was formed and its stepwise stability constants were determined to be logK1 = 6.44 and logK2 = 5.81. The molar absorptivities of the complex at pH = 4.5 and at 540 nm were ε1 = 1.38×104 and ε2 = 3.46×104 dm3 mol–1 cm–1. The method is characterised by selectivity in the presence of the mixture of thiourea, triethanolamine and ethylenebis(oxyethylenenitrilo)-tetraacetic acid. The limit of detection is 0.03 µg cm–3 of SbIII. Analysis of wastewater samples was performed with satisfactory results. </p

Jian-Wei Fan

Lu-Ting Pan

Tian Li

Xiang-Hu Liu

English

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 * Author to whom correspondence should be addressed. (E-mail: fanjianwei@tongji.edu.cn) CROATICA CHEMICA ACTA CCACAA, ISSN 0011-1643, e-ISSN 1334-417X Croat. Chem. Acta 82 (3) (2009) 619–622. CCA-3354  Original Scientific Paper  Complexation between Antimony and o-Chlorophenylfluorone and its Application to Determination of Antimony in Wastewater  Lu-Ting Pan, Xiang-Hu Liu, Tian Li, and Jian-Wei Fan* State Key Laboratory of Pollution Control and Resource Reuse Research, College of Environmental Science and Engineering, Tongji University, Shanghai-200092, P. R. China RECEIVED MARCH 11, 2005; REVISED JUNE 20, 2008; ACCEPTED JULY 15, 2008   Abstract. The formation of a chelate complex of antimony(III) with o-chlorophenylfluorone (CPF) was used for the spectrophotometric determination of antimony. The spectral correction technique was applied to characterize the complexation and the determination of SbIII. Results have shown that complex Sb(CPF)2H2O was formed and its stepwise stability constants were determined to be logK1 =6.44 and logK2 =5.81. The molar absorptivities of the complex at pH=4.5 and at 540 nm were 1 =1.38104 and 2 =3.46104 dm3 mol–1 cm–1. The method is characterised by selectivity in the presence of the mixture of thiourea, triethanolamine and ethylenebis(oxyethylenenitrilo)-tetraacetic acid. The limit of detection is 0.03 g cm–3 of SbIII. Analysis of wastewater samples was performed with satisfactory results.  Keywords: spectral correction technique, o-chlorophenylfluorone, spectrophotometry, determination of antimony, wastewater   INTRODUCTION Antimony is rare in nature and unpolluted water typi-cally contains less than 1 ng cm–3 of Sb. It often exists in wastewater discharged from metallurgical, ore dres-sing, and electroplating, printing, leather-manufacturing, pharmaceutical factories. Sb belongs to the group of non-essential elements and its toxicity is comparable to arsenic and bismuth. The United States Environmental Protection Agency (EPA) lists Sb and its compounds as the priority pollutants. Most common current methods for the determination of SbIII species in aqueous solution include hydride generation atomic absorption spectros-copy,1 GC-MS,2 differential pulse stripping voltamme-try 3,4 etc. Only a few spectrophotometric methods are applied to detection of antimony, e.g., some ordinary spectrophotometric methods,5 kinetic spectrophotome-tric methods6,7 and first-derivative spectrophotometric method.8 These methods are also used along with some other technologies, e.g., partial least squares method,9 flow injection,10 and solvent extraction.11 Compared to other methods, the spectrophotometric method has its advantages, such as low cost, simple operation, easy spread and wide application. Up to now, it has been stu-died extensively, particularly in the developing countries.  The purpose of the present work is to investigate the complexation between antimony(III) and o-chloro-phenylfluorone (CPF) by the spectral correction techni-que, which has greatly improved determination of metal ions instead of ordinary spectrophotometry.12, 13 The SbIII-CPF complex was used to detect antimony concen-tration in wastewater and the effect of other metal ions on SbIII determination was studied.   EXPERIMENTAL Apparatus and Reagents A double-beam spectrophotometer, Model Lambda-25 (Perkin-Elmer, USA), with UV WinLab software (Ver-sion 2.85.04), was used for absorption measurements. The solution pH was measured with a pH meter Model pHS-25 (Shanghai Precise Science Instruments, China). Antimony(III) stock solution (1.000 mg cm3) was prepared by dissolving 1.000 g of high-purity antimony (> 99.9 %, A. R., Shanghai Chemicals, China) in 25 cm3 of sulfuric acid (A. R., Shanghai Chemicals, China) and heating for dissolution, and the volume was made up to 1000 cm3 with deionized water. Working solutions were obtained by suitable dilution of the stock solution with deionized water. CPF (1.00 mol cm–3) was used. The solution was prepared as described earlier.14 620 L.-T. Pan et al., Complexation between Antimony and o-Chlorophenylfluorone Croat. Chem. Acta 82 (2009) 619. Surfactant solutions (all with surfactant mass frac-tion, w = 1 %) were prepared: Triton X-100, cetyltri-methylammonium bromide (CTAB) and sodium do-decyl benzene sulfonate (SDBS) (Shanghai Chemical Regents Co., China Medicals). The masking reagent was prepared by mixing 5 g of thiourea, 4 cm3 of tri-ethanolamine (A. R., Zhengzhou Chemicals, China) and 4 g of ethylenebis(oxyethylenenitrilo)-tetraacetic acid (EGTA, A. R., Fudan University, China) and diluting it to 200 cm3 with deionized water. Complex Characterization 20.0 g of SbIII was placed in a 25-cm3 volumetric flask. 2.5 cm3 of acetate buffer solution, pH = 4.5,15 1 cm3 of a surfactant solution and a known volume of 1.00 mol cm–3 CPF were added. The volume was made up to the mark with water and the solution was mixed well. After 10 min, solution absorbances were measured at 430 and 540 nm against a reagent blank, respectively. The constants were calculated as described earlier.16 Determination of SbIII.17 50 cm3 of a wastewater sample solution was mixed with 10 cm3 of concentrated sulfuric acid. The mixture was heated until evaporated to the volume of about 10 cm3, then neutralized with 10 % (w) NaOH and filtered. Filtrate solution was diluted to 50 cm3. Suitable aliquots of sample solution were analyzed for antimony as describe above.  RESULTS AND DISCUSSION Absorption spectra of CPF and its SbIII-CPF complex solutions recorded against water have their maxima at 496 and 540 nm, in case of pH = 4.5, in the presence of Triton X-100 (Figure 1, curves 1 and 2). However, in the absorption spectra of the SbIII-CPF complex record-ed against a reagent blank the valley is located at 430 nm (Figure 1, curve 3). Both 430 and 540 nm were therefore selected as work wavelengths so as to reach a maximal peak-valley interval. The influence of CPF addition on the solutions containing 0.80 g cm–3 SbIII was examined. Absor-bances remain maximally constant when CPF concen-tration is higher than 0.016 mol cm–3. The effective fraction () of CPF and the composition ratio () of CPF to SbIII calculated according to literature16 are shown in Figure 2. From curve 1,  increases from 58 % up to 90 % with increasing the CPF concentration from 0.006 to 0.016 mol cm–3 and then decreases after further increasing it above 0.016 mol cm–3.  almost remains a constant maximum at 2 when CPF concentration is higher than 0.016 mol cm–3. As a result, the Sb(CPF)2H2O complex can be formed.  By varying the solution pH between 3.0 and 7.5, the peak-valley absorbance interval remains a constant maximum between pH = 3 and 5, As a result, pH = 4.5 acetate buffer solution was added in this work.  The presence of surfactants might provide a higher complexation ability with a catalytic field.18 Three types of surfactants: Triton X-100 as non-ionic surfactant, CTAB as cationic surfactant and SDBS as anion surfactant were Figure 1. Absorption spectra of the CPF and SbIII-CPF com-plex solutions at pH = 4.5 in the presence of Triton X-100(w = 0.04 %): (1) CPF, 0.040 mol cm–3, (2) SbIII, 16 g cm–3;CPF, 0.010 mol cm–3, (3) SbIII, 0.80 g cm–3; CPF, 0.040 molcm–3. Both 1 and 2 against water and 3 against a reagent blank. 400 450 500 550 6000.00.10.20.30.40.50.60.70.8-0.050.000.050.100.150.20  / nmAbsorbance 123AbsorbanceFigure 2. Variations of  and  of the solutions initially con-taining 0.80 g cm–3 SbIII and CPF between 0.006 and 0.120mol cm–3. 0.00 0.03 0.06 0.09 0.120204060800.51.01.52.02.5c(CPF) / mol dm3(CPF, SbIII) (CPF) / %12L.-T. Pan et al., Complexation between Antimony and o-Chlorophenylfluorone 621 Croat. Chem. Acta 82 (2009) 619. added and their effects on the interval between peak and valley absorptions of the complex solution were meas-ured. Triton X-100 gives the longest interval. The light-absorption of SbIII-CPF solution approaches a maximum while more than 0.5 cm3 of 1 % (w) Triton X-100 is present. Hence, 1.0 cm3 of 1 % Triton X-100 was added in this work.  The effect of time indicated that the reaction was complete in 5 min in the presence of Triton X-100 and the absorbance of the solution remained almost constant for at least 2 h.  The stepwise stability constant (Kn) and the step-wise absorptivity (n) of the complex were calculated.16 Two solutions were prepared: one contained 0.80 g cm–3 of SbIII and 0.006 mol cm–3 of CPF and the other 0.80 g cm–3 of SbIII and 0.012 mol cm–3 of CPF. Results are given as follows: logK1 = 6.44, logK2 = 5.81, 1 = 1.38  104 and 2 = 3.46  104 dm3 mol–1 cm–1 at 540 nm at 15 C in the medium of ionic strength Ic = 0.01 mol dm–3. Thus, logK = 12.25. From 2, the complex reaction is sensitive. A series of standard solutions containing SbIII (be-tween 0 and 40.0 g) were prepared and the absorbance of each solution was measured. The regression equa-tions at 540 nm are: Ac = 0.0169x – 0.006 (R = 0.9996) and A = 0.0150x – 0.006 (R = 0.9957), where x is the Sb concentration expressed in g cm–3. From the R values and the line scopes, both the accuracy and sensi-tivity of the spectral correction technique are better than those of ordinary spectrophotometry.  Six replicated determinations of a standard solu-tion containing 5.00 g of SbIII were carried out. The mean  standard deviation and relative standard devia-tion were 4.98  0.11 g, and 2.2 % by the proposed method. However, they were 4.81  0.35 g, and 7.3 % by the single wavelength spectrophotometry. The limit of detection (LOD), defined as the average of 10 repli-cated blanks plus 3 times of the standard deviation of the blank,19 was calculated to be 0.03 g cm–3 SbIII. Once the masking reagent as a mixture of thiourea, triethanolamine and EGTA was added, none of the following ions will affect the direct determination of 10.0 g of SbIII (< 5 % error): 1000 g of Cl–, SO42–, NO3–, F–, PO43–, NH4+, CaII, MgII, BaII, CuII; 300 g of HgII, CdII; 150 g of LaII, AuIII; 60 g of NiII, CoII, SnII, AgI, PtIV, CrIII, ZnII; 20 g of MnII, AlIII and 10 g of VV, TiIV, FeII, GeIV. Sample Analysis  To test the method, two wastewater samples were ana-lyzed. They were obtained from a metallurgic plant (sample #1) and an electroplating workshop (sample #2). Before determination, every sample must be pre-treated according to the mentioned procedures. Analysis results of (Table 1) were in good agreement with those obtained by atomic fluorescence spectrophotometry (AFS). The recommended method is accurate and feasi-ble in the section of determination of antimony in wastewater.    CONCLUSION Formation of the SbIII-CPF complex has been studied by the spectral correction technique. The recommended method is simple, sensitive and selective for the deter-mination of SbIII. The advantage of the present proce-dure is that it does not require many reagents and has a low RSD value. The relative standard deviation for six replicate measurements of 5.00 g cm–3 of anti-mony(III) was 2.2 %, whereas single wavelength spec-trophotometry gave a RSD value 7.3 %. The method has been applied to determine antimony in wastewater sam-ples with acceptable results.  Acknowledgements. Financial support from the National Key Technology R&D Program of China (No. 2008BAJ08B13) is gratefully acknowledged. Table 1. Determination of antimony in wastewater. Conditions: cCPF = 0.040 mol dm–3, pH = 4.5 Sample  (Sb)(a)/μg cm–3 RSD/% Recovery /% Added FoundProp. meth.(b) AFS(c) #1 0 0.628 ± 0.04 0.622 ± 0.032 6.4   1.25 1.88 ± 0.03 1.91 ± 0.04 1.59 100 #2 0 1.24 ± 0.03 1.12 ± 0.04 2.4   1.25 2.56 ± 0.04 2.44 ± 0.05 1.56 106 (a) Average of four determinations (b) Proposed method (c) Atomic fluorescence spectrometry  622 L.-T. Pan et al., Complexation between Antimony and o-Chlorophenylfluorone Croat. Chem. Acta 82 (2009) 619. REFERENCES 1. M. O. Andreae, J. F. Asmonde, P. Foster, and D. L. Van’t, Anal. Chem. 53 (1981) 1766–1771. 2. M. Dodd, S. A. Pergantis, W. R. Cullen, H. Li, G. K. Eigendorf, and K. J. Reimer, Analyst 121 (1996) 223–228. 3. G. E. Batley, and T. M. Florence, Electroanal. Chem. Interfacial. Electrochem. 55 (1974) 23–26. 4. A. P. Waller and W. F. Pickering, Talanta 42 (1995) 197–204. 5. A. N. Tripathi and K. S. Patel, Fresenius J. Anal. Chem. 360 (1998) 270–272. 6. A. Afkhami, T. Madtakian, and A. Abdolmaleki, Croat. Chem. 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Sci. Technol. 32 (2004) 77–91. 19. V. Thomsen, D. Schatzlein and D. Mercuro, Spectroscopy (Ams-terdam). 18 (2003) 112–114.   SAŽETAK Kompleks antimona s o-klorofenilfluoronom i njegova primjena za određivanje antimona u otpadnim vodama  Lu-Ting Pan, Xiang-Hu Liu, Tian Li i Jian-Wei Fan  State Key Laboratory of Pollution Control and Resource Reuse Research, College of Environmental Science and Engineering, Tongji University, Shanghai-200092, P. R. China  Formiranje kelatnog kompleksa između antimona(III) i o-klorofenilfluorona (CPF) upotrebljeno je za spektrofo-tometrijsko određivanje antimona, pri čemu je korištena tehnika korekcije spektara. Rezultati su pokazali da nas-taje kompleks sastava Sb(CPF)2H2O čije su sukcesivne konstante stabilnosti iznosile logK1 =6,44 i logK2 =5,81, a molarne apsorptivnosti 1 =1,38104 i 2 =3,46104 dm3 mol–1 cm–1, pri 540 nm i pH=4,5. Metoda je selektivna u prisutnosti smjese tiouree, trietanolamina i etilenbis(oksietilennitrilo)-tetraoctene kiseline. Granica detekcije za SbIII je iznosila 0,03 g cm–3. Analizom uzoraka otpadnih voda dobiveni su zadovoljavajući rezultati. 

Complexation between Antimony and o-Chlorophenylfluorone and its Application to Determination of Antimony in Wastewater

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