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Flow injection–chemiluminescence determination of phenol using potassium permanganate and formaldehyde system
Spectrochimica Acta Part A 66 (2007) 58–62
Flow injection–chemiluminescence determination of phenol using potassium permanganate and formaldehyde system Wei Cao a,b , Xuemin Mu a , Jinghe Yang b,∗ , Wenbo Shi a , Yongcun Zheng a a
b
School of Chemistry and Chemical Engineering, Jinan University, Jinan 250022, China Key Laboratory of Colloid and Interface Chemistry, (Shandong University), Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China Received 20 October 2005; accepted 15 February 2006
Abstract It is found that phenol can react with potassium permanganate in the acidic medium and produce chemiluminescence, which is greatly enhanced by formaldehyde. The optimum conditions for this chemiluminescent reaction are in detail studied using a flow injection system. The experiments indicate that under optimum conditions, the chemiluminescence intensity is linearly related to the concentration of phenol in the range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detection limit (3σ) of 3 × 10−9 g mL−1 . The relative standard deviation is 1.2% for 4.0 × 10−7 g mL−1 phenol solution in 11 repeated measurements. This method has the advantages of simple operation, fast response and high sensitivity. The method is successfully applied to the determination of phenol in the waste water. © 2006 Elsevier B.V. All rights reserved. Keywords: Phenol; Chemiluminescence; Flow injection; Potassium permanganate; Formaldehyde
1. Introduction The phenol is one of important industrial chemical; it is widely used as disinfectants, components of insecticides, herbicides and synthetic fibers. On the other hand, phenol is one of the environmental pollutants; the development of a sensitive and selective method for the determination of phenols in environmental chemistry is required. The methods for determination of phenol are mainly based on spectrophotometry [1–3], chromatography [4–6] and electroanalytical method [7–9]. Although these methods have their respective advantages, but there also exist some different shortcomings, such as the sensitivity of the method is not very high, the procedure is time-consuming or it is not suitable for automatic and continuous analysis. Flow injection–chemiluminescence (CL) method is known to be a powerful analytical technique that possesses low detection limit, a wide linear dynamic range and relatively simple and inexpensive instrumentation [10,11], especially potassium permanganate system has got greater development recently because reagent is cheap and available easily [12–17]. The potassium
∗
Corresponding author. Tel.: +86 53188365459; fax: +86 53188564464. E-mail address: [email protected] (J. Yang).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2006.02.021
permanganate can oxidize the phenol in acidic medium and produce weak chemiluminescence with a detection limit of only 3 × 10−7 g mL−1 for the phenol [14]. In this paper, it is found that the CL signal between permanganate and phenol is greatly enhanced by the formaldehyde (HCHO), the chemiluminescence intensity is linearly related to the concentration of phenol in the range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detection limit (3σ) of 3 × 10−9 g mL−1 . Therefore, a sensitive flow injection–CL method for the determination of phenol is proposed. The method is successfully applied to the determination of phenol in waste water, and the results are satisfactory. 2. Experimental 2.1. Apparatus An FIA-3110 flow injection system with CL detection (Titan Instrumental Company, Beijing, China) was used for the CL study; the flow injection manifold is shown schematically in Fig. 1. Two peristaltic pumps were used to deliver all solutions at a flow rate of 3.75 mL min−1 for potassium permanganate and HCl solution or 1.25 mL min−1 for phenol and formaldehyde solution. PTFE tubing (0.8 mm i.d.) was used to connect all components in the flow system. Sample was injected through
W. Cao et al. / Spectrochimica Acta Part A 66 (2007) 58–62
59
Table 1 Effect of media Media
Fig. 1. Schematic diagram of flow injection CL analyzer. (a) Phenol solution; (b) formaldehyde solution; (c) KMnO4 solution; (d) HCl solution; (P) peristaltic pump; (V) sample injection valve; (C) flow cell; (W) waste; (HV) high voltage; (PMT) photomultiplier tube; (PC) personal computer.
an eight-way injection valve fitted with a 100 L sample loop. The CL signal produced in the flow cell (10 cm × 1 mm i.d. spiral glass tubing) was detected using a luminometer (manufactured exclusively for Perkin-Elmer by Labsphere Instrumental Company). 2.2. Reagents and solutions The stock standard solution (1.00 × 10−3 g mL−1 ) of phenol was prepared by dissolving phenol in water. The solution should be stable for at least 30 days and kept in a refrigerator. Working standard solutions of phenol were prepared by appropriate dilution of this stock standard solution with water before use. Working solutions of KMnO4 (8.0 × 10−4 mol L−1 ) were prepared freshly by diluting potassium permanganate stock solution (5.0 × 10−3 mol L−1 ) with water. Formaldehyde solution (8%, v/v) was prepared in water. All chemicals were of analytical-reagent grade, and doubly distilled water was used throughout the experiments. 2.3. Procedure The reagent stream KMnO4 solution (8.0 × 10−4 mol L−1 ) and HCl solution (2.0 mol L−1 ) were used as the oxidizer and formaldehyde solution was used as the enhancement reagent. The CL signal was recorded by injection of 100 L of working standard solution of phenol and formaldehyde solution (8%, v/v) into streaming potassium permanganate and HCl solution, and the CL peak height was then measured for quantification.
Phosphorous acid Sulfuric acid Nitric acid Hydrochloric acid Perchloric acid
Intensity of the CL Phenol and HCHO
HCHO
1.9 5.3 8.0 9.3 10.9
0.11 0.79 1.03 0.89 2.06
Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (1.0 × 10−3 mol L−1 ); 2.0 mol L−1 different acids.
3. Results and discussion 3.1. Selection of acid type and concentration The CL reaction of the phenol is examined in KMnO4 – HCHO–H+ system by using phosphatic acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid as the reaction media. The results are shown in Table 1. The results show that the stronger CL signal and weaker background are obtained in hydrochloric acid. The effect of hydrochloric acid concentration on the CL of this system was investigated and is shown in Fig. 2. It can be seen that 2.0 mol L−1 hydrochloric acid is suitable for the phenol to get the maximum CL signal. 3.2. Selection of potassium permanganate concentration The effect of potassium permanganate concentration on the CL intensity of this system has been examined in the range of 2.0 × 10−4 to 2.0 × 10−3 mol L−1 , and the results are shown in Fig. 3. It can be seen that the CL intensity increases with the increase of potassium permanganate concentration in lower concentration range (<6.0 × 10−4 mol L−1 ), then reaches the maximum and remains constant in the con-
2.4. Sample pretreatment To a 100 mL sample solution, 1 mL of 0.1 g mL−1 CuSO4 solution was added, then the pH of the solution was adjusted to 4 with 1.5 mol L−1 phosphoric acid. The test solution was placed in a 250 mL short neck Kjeldahl flask containing boiling tips and was distilled using a mantle heater and a 35 cm long Liebig condenser with a 100 mL volumetric flask as a receiver. The distillation was interrupted when the volume of distillate became about 90 mL, and 10 mL of water was added to the Kjeldahl flask. Then distillation was restarted and continued until the distillate reached the mark of the receiver. The distillate obtained was subjected to chemiluminescence to determine phenol as described above.
Fig. 2. The effect of HCl concentration. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (1.0 × 10−3 mol L−1 ).
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Fig. 3. The effect of potassium permanganate concentration. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); HCl solution (2 mol L−1 ).
centration range of 6.0 × 10−4 to 1.0 × 10−3 mol L−1 . While the concentration of potassium permanganate is larger than 1.0 × 10−3 mol L−1 , the CL intensity of this system decreases with the increase of potassium permanganate concentration. Therefore, 8.0 × 10−4 mol L−1 of potassium permanganate is selected for further research.
Fig. 5. The effect of flow rates of phenol and HCHO. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (8.0 × 10−4 mol L−1 ); HCl solution (2 mol L−1 ); flow rate of KMnO4 and HCl: 3.75 mL min−1 .
3.4. Selection of flow rate
It is found that the CL signal of phenol–KMnO4 in acidic solution can be enhanced by formaldehyde, the effect of formaldehyde concentration on CL intensity is examined and the results are shown in Fig. 4. It can be seen that the formaldehyde can enhance CL intensities of the systems with or without phenol. The maximum CL difference (ICL ) between the systems with and without phenol is obtained when formaldehyde concentration is in the range 8.0–9.6%; thus, 8.0% formaldehyde is selected for further research.
The flow rates of phenol and HCHO, potassium permanganate and hydrochloric acid solution were investigated in the range of 0.4–2.5 and 2.5–4.6 mL min−1 . The results are shown in Figs. 5 and 6. It can be seen that the CL intensity increases with increasing the flow rate of phenol and HCHO before 0.8 mL min−1 , after which the CL intensity reaches the maximum and remains constant. So, 1.25 mL min−1 is selected for the flow rates of phenol and HCHO solution. The CL intensity increases with the increase of flow rates of potassium permanganate and hydrochloric acid solution in the lower flow rates range (<3.75 mL min−1 ), then reaches the maximum and remains constant in the flow rates range of 3.75–4.6 mL min−1 . Therefore, 3.75 mL min−1 is selected for the flow rates of the potassium permanganate and hydrochloric acid solution for further research.
Fig. 4. The effect of formaldehyde concentration. (a) Phenol–KMnO4 –HCHO system; (b) KMnO4 –HCHO system; (c) I = Ia − Ib (Ia and Ib are the CL intensities of phenol–KMnO4 –HCHO and KMnO4 –HCHO systems, respectively). Conditions: phenol (1.0 × 10−5 g mL−1 ); KMnO4 solution (8.0 × 10−4 mol L−1 ); HCl solution (2 mol L−1 ).
Fig. 6. The effect of flow rates of KMnO4 and HCl. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (8.0 × 10−4 mol L−1 ); HCl solution (2 mol L−1 ); flow rate of phenol and HCHO: 1.25 mL min−1 .
3.3. Selection of formaldehyde concentration
W. Cao et al. / Spectrochimica Acta Part A 66 (2007) 58–62 Table 2 Tolerable limit of foreign species Species added K+ ,
Na+ ,
Tolerance ratio (species/phenol) +
NH4 Ca2+ , Mg2+ , Pb2+ Zn2+ , Al3+ , Cr3+ Cu2+ , Co2+ , Ni2+ , Mn2+ , Fe3+ SO4 2− , NO3 − PO4 3−
1000 100 10 1.0 1000 200
3.5. Interference The influences of some possibly co-existing materials in the sample of phenol and some inorganic ions on the CL intensity of the system are in detail investigated, and the results are shown in Table 2. The tolerable limit of a foreign species was taken as a relative error not greater than ±5% in the recovery at a concentration of 1.0 × 10−5 g mL−1 phenol. It can be seen from Table 2 that 1000-fold excess of K+ , Na+ and NH4 + ; 100-fold excess of Ca2+ , Mg2+ and Pb2+ ; 10-fold excess of Zn2+ , Al3+ and Cr3+ ; 1-fold excess of Cu2+ , Co2+ , Ni2+ , Mn2+ and Fe3+ ; 1000-fold excess of SO4 2− and NO3 − ; and 200-fold excess of PO4 3− do not interfere with the determination of phenol in this system. 3.6. Linear response range, detection limit and precision Under the above optimum conditions, the CL intensity is linearly related to the concentration of phenol in the range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detection limit (3σ) of 3 × 10−9 g mL−1 , the regression equation is I = 0.539 − 1.941 × 106 c, the correlation coefficient is r = 0.9996. The relative standard deviation is 1.2% for 4.0 × 10−7 g mL−1 phenol solution in 11 repeated measurements. 3.7. Determination of phenol in waste water Under the selected conditions, the proposed method is used to determine phenol in the sample of waste water and compared with 4-aminoantipyrine spectrophotometry [1]. The results are shown in Table 3. It can be seen that the accuracy and precision of the proposed method are satisfactory. 3.8. Possible reaction mechanism It was reported that KMnO4 could react with some reductants in the presence of formaldehyde to produce 1 O2 1 O2 (1 g 1 g ), a Table 3 Determination of phenol in waste water Sample
4-AAP method [1] (g mL−1 )
Proposed method (g mL−1 ) (n = 5)
R.S.D. (%)
1 2 3
1.68 × 10−6 4.01 × 10−7 6.38 × 10−7
1.63 × 10−6 4.08 × 10−7 6.32 × 10−7
2.0 3.2 1.6
61
complex oxygen molecule of single state, which could transform into 3 O2 (3 g ), a triplet state oxygen. During the transformation, it could produce CL and the formaldehyde could accelerate oxidation reaction rate [16,17]. The peak of chemiluminescence spectrum is at 630–640 nm, which is very similar to that of singlet oxygen chemiluminescence (630–650 nm). Thus, it was assumed that the phenol could also react with KMnO4 to produce CL, and the CL reaction could be accelerated by formaldehyde. Based on the above discussions, the possible reaction mechanism is suggested as following: MnO4 − + H+ + formaldehyde + phenol → 1 O2 (1 g ) + H2 O + Mn(II) + products 2 1 O 2 (1 g ) → 1 O 2 1 O 2 (1 g 1 g ) 1
O2 1 O2 (1 g 1 g ) → 23 O2 (3 g ) + hν
4. Conclusion It was found that in the acidic medium, the phenol could react with potassium permanganate and produce CL, which was enhanced by formaldehyde. Under the optimum conditions, a simple, fast response and sensitive CL method was developed for determination of phenol. The proposed method was used for determination of phenol in waste water and the results are satisfactory. Acknowledgements This work was supported by the Natural Science Foundation of China and the ShanDong Provincial Education Department of China. References [1] The Second Compilation Room of Standard Press of China, National Standards of Environmental Protection (Method of Water Analysis), Standard Press of China, Beijing, 2001, p. 130. [2] C.L. Kang, Y. Wang, R.B. Li, Y.G. Du, J. Li, B.W. Zhang, L.M. Zhou, Y.Z. Du, Microchem. J. 64 (2) (2000) 161. [3] I. Nukatsuka, S. Nakamura, K. Watanabe, K. Ohzeki, Anal. Sci. 16 (2000) 269. [4] M. Gyorik, Z. Herpai, I. Szecsenyi, L. Varga, J. Szigeti, J. Agric. Food Chem. 51 (2003) 5222. [5] E.M. Basova, V.M. Ivanov, K.V. Novikova, J. Anal. Chem. 57 (2002) 434. [6] M.S. Zhang, A.M. Wang, Fenxi Huaxue 27 (1999) 63. [7] H.S. Wang, A.M. Zhang, H. Cui, D.J. Liu, R.M. Liu, Microchem. J. 59 (1998) 448. [8] M.J. Christophersen, T.J. Cardwell, Anal. Chim. Acta 323 (1–3) (1996) 19. [9] Y. Lu, J. Ma, S. Cao, C. Xu, S. Hu, Fenxi KexueXuebao 12 (4) (1996) 323. [10] R.A. Agbaria, P.B. Oldham, M. McCarroll, L.B. McGown, I.M. Warner, Anal. Chem. 74 (2002) 3952.
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[11] P. Fletcher, K.N. Andrew, A.C. Calokerinos, S. Forbes, P.J. Worsfold, Luminescence 16 (1) (2001) 1. [12] B.J. Hindson, N.W. Barnett, Anal. Chim. Acta 445 (2001) 1. [13] W. Cao, J.H. Yang, C.X. Sun, Y.J. Chen, Q.F. Gao, Luminescence 20 (1) (2005) 20. [14] Y.X. Ding, J. ZhangZhou Teachers Coll. 14 (3) (2001) 45.
[15] L.Q. Li, Y.M. Zhou, M.L. Feng, J.R. Lu, J. Shandong Agric. Univ. 34 (3) (2003) 441. [16] G.N. Chen, F.X. Huang, X.P. Wu, Z.F. Zhao, J.P. Duan, Anal. Bioanal. Chem. 376 (6) (2003) 873. [17] M. Liu, Y.H. He, J.R. Lu, Fenxi Huaxue 33 (4) (2005) 535.
Flow injection–chemiluminescence determination of phenol using potassium permanganate and formaldehyde system Wei Cao a,b , Xuemin Mu a , Jinghe Yang b,∗ , Wenbo Shi a , Yongcun Zheng a a
b
School of Chemistry and Chemical Engineering, Jinan University, Jinan 250022, China Key Laboratory of Colloid and Interface Chemistry, (Shandong University), Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China Received 20 October 2005; accepted 15 February 2006
Abstract It is found that phenol can react with potassium permanganate in the acidic medium and produce chemiluminescence, which is greatly enhanced by formaldehyde. The optimum conditions for this chemiluminescent reaction are in detail studied using a flow injection system. The experiments indicate that under optimum conditions, the chemiluminescence intensity is linearly related to the concentration of phenol in the range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detection limit (3σ) of 3 × 10−9 g mL−1 . The relative standard deviation is 1.2% for 4.0 × 10−7 g mL−1 phenol solution in 11 repeated measurements. This method has the advantages of simple operation, fast response and high sensitivity. The method is successfully applied to the determination of phenol in the waste water. © 2006 Elsevier B.V. All rights reserved. Keywords: Phenol; Chemiluminescence; Flow injection; Potassium permanganate; Formaldehyde
1. Introduction The phenol is one of important industrial chemical; it is widely used as disinfectants, components of insecticides, herbicides and synthetic fibers. On the other hand, phenol is one of the environmental pollutants; the development of a sensitive and selective method for the determination of phenols in environmental chemistry is required. The methods for determination of phenol are mainly based on spectrophotometry [1–3], chromatography [4–6] and electroanalytical method [7–9]. Although these methods have their respective advantages, but there also exist some different shortcomings, such as the sensitivity of the method is not very high, the procedure is time-consuming or it is not suitable for automatic and continuous analysis. Flow injection–chemiluminescence (CL) method is known to be a powerful analytical technique that possesses low detection limit, a wide linear dynamic range and relatively simple and inexpensive instrumentation [10,11], especially potassium permanganate system has got greater development recently because reagent is cheap and available easily [12–17]. The potassium
∗
Corresponding author. Tel.: +86 53188365459; fax: +86 53188564464. E-mail address: [email protected] (J. Yang).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2006.02.021
permanganate can oxidize the phenol in acidic medium and produce weak chemiluminescence with a detection limit of only 3 × 10−7 g mL−1 for the phenol [14]. In this paper, it is found that the CL signal between permanganate and phenol is greatly enhanced by the formaldehyde (HCHO), the chemiluminescence intensity is linearly related to the concentration of phenol in the range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detection limit (3σ) of 3 × 10−9 g mL−1 . Therefore, a sensitive flow injection–CL method for the determination of phenol is proposed. The method is successfully applied to the determination of phenol in waste water, and the results are satisfactory. 2. Experimental 2.1. Apparatus An FIA-3110 flow injection system with CL detection (Titan Instrumental Company, Beijing, China) was used for the CL study; the flow injection manifold is shown schematically in Fig. 1. Two peristaltic pumps were used to deliver all solutions at a flow rate of 3.75 mL min−1 for potassium permanganate and HCl solution or 1.25 mL min−1 for phenol and formaldehyde solution. PTFE tubing (0.8 mm i.d.) was used to connect all components in the flow system. Sample was injected through
W. Cao et al. / Spectrochimica Acta Part A 66 (2007) 58–62
59
Table 1 Effect of media Media
Fig. 1. Schematic diagram of flow injection CL analyzer. (a) Phenol solution; (b) formaldehyde solution; (c) KMnO4 solution; (d) HCl solution; (P) peristaltic pump; (V) sample injection valve; (C) flow cell; (W) waste; (HV) high voltage; (PMT) photomultiplier tube; (PC) personal computer.
an eight-way injection valve fitted with a 100 L sample loop. The CL signal produced in the flow cell (10 cm × 1 mm i.d. spiral glass tubing) was detected using a luminometer (manufactured exclusively for Perkin-Elmer by Labsphere Instrumental Company). 2.2. Reagents and solutions The stock standard solution (1.00 × 10−3 g mL−1 ) of phenol was prepared by dissolving phenol in water. The solution should be stable for at least 30 days and kept in a refrigerator. Working standard solutions of phenol were prepared by appropriate dilution of this stock standard solution with water before use. Working solutions of KMnO4 (8.0 × 10−4 mol L−1 ) were prepared freshly by diluting potassium permanganate stock solution (5.0 × 10−3 mol L−1 ) with water. Formaldehyde solution (8%, v/v) was prepared in water. All chemicals were of analytical-reagent grade, and doubly distilled water was used throughout the experiments. 2.3. Procedure The reagent stream KMnO4 solution (8.0 × 10−4 mol L−1 ) and HCl solution (2.0 mol L−1 ) were used as the oxidizer and formaldehyde solution was used as the enhancement reagent. The CL signal was recorded by injection of 100 L of working standard solution of phenol and formaldehyde solution (8%, v/v) into streaming potassium permanganate and HCl solution, and the CL peak height was then measured for quantification.
Phosphorous acid Sulfuric acid Nitric acid Hydrochloric acid Perchloric acid
Intensity of the CL Phenol and HCHO
HCHO
1.9 5.3 8.0 9.3 10.9
0.11 0.79 1.03 0.89 2.06
Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (1.0 × 10−3 mol L−1 ); 2.0 mol L−1 different acids.
3. Results and discussion 3.1. Selection of acid type and concentration The CL reaction of the phenol is examined in KMnO4 – HCHO–H+ system by using phosphatic acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid as the reaction media. The results are shown in Table 1. The results show that the stronger CL signal and weaker background are obtained in hydrochloric acid. The effect of hydrochloric acid concentration on the CL of this system was investigated and is shown in Fig. 2. It can be seen that 2.0 mol L−1 hydrochloric acid is suitable for the phenol to get the maximum CL signal. 3.2. Selection of potassium permanganate concentration The effect of potassium permanganate concentration on the CL intensity of this system has been examined in the range of 2.0 × 10−4 to 2.0 × 10−3 mol L−1 , and the results are shown in Fig. 3. It can be seen that the CL intensity increases with the increase of potassium permanganate concentration in lower concentration range (<6.0 × 10−4 mol L−1 ), then reaches the maximum and remains constant in the con-
2.4. Sample pretreatment To a 100 mL sample solution, 1 mL of 0.1 g mL−1 CuSO4 solution was added, then the pH of the solution was adjusted to 4 with 1.5 mol L−1 phosphoric acid. The test solution was placed in a 250 mL short neck Kjeldahl flask containing boiling tips and was distilled using a mantle heater and a 35 cm long Liebig condenser with a 100 mL volumetric flask as a receiver. The distillation was interrupted when the volume of distillate became about 90 mL, and 10 mL of water was added to the Kjeldahl flask. Then distillation was restarted and continued until the distillate reached the mark of the receiver. The distillate obtained was subjected to chemiluminescence to determine phenol as described above.
Fig. 2. The effect of HCl concentration. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (1.0 × 10−3 mol L−1 ).
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Fig. 3. The effect of potassium permanganate concentration. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); HCl solution (2 mol L−1 ).
centration range of 6.0 × 10−4 to 1.0 × 10−3 mol L−1 . While the concentration of potassium permanganate is larger than 1.0 × 10−3 mol L−1 , the CL intensity of this system decreases with the increase of potassium permanganate concentration. Therefore, 8.0 × 10−4 mol L−1 of potassium permanganate is selected for further research.
Fig. 5. The effect of flow rates of phenol and HCHO. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (8.0 × 10−4 mol L−1 ); HCl solution (2 mol L−1 ); flow rate of KMnO4 and HCl: 3.75 mL min−1 .
3.4. Selection of flow rate
It is found that the CL signal of phenol–KMnO4 in acidic solution can be enhanced by formaldehyde, the effect of formaldehyde concentration on CL intensity is examined and the results are shown in Fig. 4. It can be seen that the formaldehyde can enhance CL intensities of the systems with or without phenol. The maximum CL difference (ICL ) between the systems with and without phenol is obtained when formaldehyde concentration is in the range 8.0–9.6%; thus, 8.0% formaldehyde is selected for further research.
The flow rates of phenol and HCHO, potassium permanganate and hydrochloric acid solution were investigated in the range of 0.4–2.5 and 2.5–4.6 mL min−1 . The results are shown in Figs. 5 and 6. It can be seen that the CL intensity increases with increasing the flow rate of phenol and HCHO before 0.8 mL min−1 , after which the CL intensity reaches the maximum and remains constant. So, 1.25 mL min−1 is selected for the flow rates of phenol and HCHO solution. The CL intensity increases with the increase of flow rates of potassium permanganate and hydrochloric acid solution in the lower flow rates range (<3.75 mL min−1 ), then reaches the maximum and remains constant in the flow rates range of 3.75–4.6 mL min−1 . Therefore, 3.75 mL min−1 is selected for the flow rates of the potassium permanganate and hydrochloric acid solution for further research.
Fig. 4. The effect of formaldehyde concentration. (a) Phenol–KMnO4 –HCHO system; (b) KMnO4 –HCHO system; (c) I = Ia − Ib (Ia and Ib are the CL intensities of phenol–KMnO4 –HCHO and KMnO4 –HCHO systems, respectively). Conditions: phenol (1.0 × 10−5 g mL−1 ); KMnO4 solution (8.0 × 10−4 mol L−1 ); HCl solution (2 mol L−1 ).
Fig. 6. The effect of flow rates of KMnO4 and HCl. Conditions: phenol (1.0 × 10−5 g mL−1 ); formaldehyde solution (8%, v/v); KMnO4 solution (8.0 × 10−4 mol L−1 ); HCl solution (2 mol L−1 ); flow rate of phenol and HCHO: 1.25 mL min−1 .
3.3. Selection of formaldehyde concentration
W. Cao et al. / Spectrochimica Acta Part A 66 (2007) 58–62 Table 2 Tolerable limit of foreign species Species added K+ ,
Na+ ,
Tolerance ratio (species/phenol) +
NH4 Ca2+ , Mg2+ , Pb2+ Zn2+ , Al3+ , Cr3+ Cu2+ , Co2+ , Ni2+ , Mn2+ , Fe3+ SO4 2− , NO3 − PO4 3−
1000 100 10 1.0 1000 200
3.5. Interference The influences of some possibly co-existing materials in the sample of phenol and some inorganic ions on the CL intensity of the system are in detail investigated, and the results are shown in Table 2. The tolerable limit of a foreign species was taken as a relative error not greater than ±5% in the recovery at a concentration of 1.0 × 10−5 g mL−1 phenol. It can be seen from Table 2 that 1000-fold excess of K+ , Na+ and NH4 + ; 100-fold excess of Ca2+ , Mg2+ and Pb2+ ; 10-fold excess of Zn2+ , Al3+ and Cr3+ ; 1-fold excess of Cu2+ , Co2+ , Ni2+ , Mn2+ and Fe3+ ; 1000-fold excess of SO4 2− and NO3 − ; and 200-fold excess of PO4 3− do not interfere with the determination of phenol in this system. 3.6. Linear response range, detection limit and precision Under the above optimum conditions, the CL intensity is linearly related to the concentration of phenol in the range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detection limit (3σ) of 3 × 10−9 g mL−1 , the regression equation is I = 0.539 − 1.941 × 106 c, the correlation coefficient is r = 0.9996. The relative standard deviation is 1.2% for 4.0 × 10−7 g mL−1 phenol solution in 11 repeated measurements. 3.7. Determination of phenol in waste water Under the selected conditions, the proposed method is used to determine phenol in the sample of waste water and compared with 4-aminoantipyrine spectrophotometry [1]. The results are shown in Table 3. It can be seen that the accuracy and precision of the proposed method are satisfactory. 3.8. Possible reaction mechanism It was reported that KMnO4 could react with some reductants in the presence of formaldehyde to produce 1 O2 1 O2 (1 g 1 g ), a Table 3 Determination of phenol in waste water Sample
4-AAP method [1] (g mL−1 )
Proposed method (g mL−1 ) (n = 5)
R.S.D. (%)
1 2 3
1.68 × 10−6 4.01 × 10−7 6.38 × 10−7
1.63 × 10−6 4.08 × 10−7 6.32 × 10−7
2.0 3.2 1.6
61
complex oxygen molecule of single state, which could transform into 3 O2 (3 g ), a triplet state oxygen. During the transformation, it could produce CL and the formaldehyde could accelerate oxidation reaction rate [16,17]. The peak of chemiluminescence spectrum is at 630–640 nm, which is very similar to that of singlet oxygen chemiluminescence (630–650 nm). Thus, it was assumed that the phenol could also react with KMnO4 to produce CL, and the CL reaction could be accelerated by formaldehyde. Based on the above discussions, the possible reaction mechanism is suggested as following: MnO4 − + H+ + formaldehyde + phenol → 1 O2 (1 g ) + H2 O + Mn(II) + products 2 1 O 2 (1 g ) → 1 O 2 1 O 2 (1 g 1 g ) 1
O2 1 O2 (1 g 1 g ) → 23 O2 (3 g ) + hν
4. Conclusion It was found that in the acidic medium, the phenol could react with potassium permanganate and produce CL, which was enhanced by formaldehyde. Under the optimum conditions, a simple, fast response and sensitive CL method was developed for determination of phenol. The proposed method was used for determination of phenol in waste water and the results are satisfactory. Acknowledgements This work was supported by the Natural Science Foundation of China and the ShanDong Provincial Education Department of China. References [1] The Second Compilation Room of Standard Press of China, National Standards of Environmental Protection (Method of Water Analysis), Standard Press of China, Beijing, 2001, p. 130. [2] C.L. Kang, Y. Wang, R.B. Li, Y.G. Du, J. Li, B.W. Zhang, L.M. Zhou, Y.Z. Du, Microchem. J. 64 (2) (2000) 161. [3] I. Nukatsuka, S. Nakamura, K. Watanabe, K. Ohzeki, Anal. Sci. 16 (2000) 269. [4] M. Gyorik, Z. Herpai, I. Szecsenyi, L. Varga, J. Szigeti, J. Agric. Food Chem. 51 (2003) 5222. [5] E.M. Basova, V.M. Ivanov, K.V. Novikova, J. Anal. Chem. 57 (2002) 434. [6] M.S. Zhang, A.M. Wang, Fenxi Huaxue 27 (1999) 63. [7] H.S. Wang, A.M. Zhang, H. Cui, D.J. Liu, R.M. Liu, Microchem. J. 59 (1998) 448. [8] M.J. Christophersen, T.J. Cardwell, Anal. Chim. Acta 323 (1–3) (1996) 19. [9] Y. Lu, J. Ma, S. Cao, C. Xu, S. Hu, Fenxi KexueXuebao 12 (4) (1996) 323. [10] R.A. Agbaria, P.B. Oldham, M. McCarroll, L.B. McGown, I.M. Warner, Anal. Chem. 74 (2002) 3952.
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