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Spectrochimica Acta Part A 66 (2007) 58–62

Flow injection–chemiluminescence determination of phenol usingpotassium permanganate and formaldehyde system

Wei Cao a,b, Xuemin Mu a, Jinghe Yang b,∗, Wenbo Shi a, Yongcun Zheng a

a School of Chemistry and Chemical Engineering, Jinan University, Jinan 250022, Chinab 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

bstract

It is found that phenol can react with potassium permanganate in the acidic medium and produce chemiluminescence, which is greatly enhancedy formaldehyde. The optimum conditions for this chemiluminescent reaction are in detail studied using a flow injection system. The experimentsndicate that under optimum conditions, the chemiluminescence intensity is linearly related to the concentration of phenol in the range 5.0 × 10−9

o 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 solutionn 11 repeated measurements. This method has the advantages of simple operation, fast response and high sensitivity. The method is successfullypplied to the determination of phenol in the waste water.

2006 Elsevier B.V. All rights reserved.

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eywords: Phenol; Chemiluminescence; Flow injection; Potassium permangan

. Introduction

The phenol is one of important industrial chemical; it isidely used as disinfectants, components of insecticides, her-icides and synthetic fibers. On the other hand, phenol is onef the environmental pollutants; the development of a sensitivend selective method for the determination of phenols in envi-onmental chemistry is required. The methods for determinationf phenol are mainly based on spectrophotometry [1–3], chro-atography [4–6] and electroanalytical method [7–9]. Although

hese methods have their respective advantages, but there alsoxist some different shortcomings, such as the sensitivity of theethod is not very high, the procedure is time-consuming or it

s not suitable for automatic and continuous analysis.Flow injection–chemiluminescence (CL) method is known

o be a powerful analytical technique that possesses low detec-ion limit, a wide linear dynamic range and relatively simple and

nexpensive instrumentation [10,11], especially potassium per-anganate system has got greater development recently because

eagent is cheap and available easily [12–17]. The potassium

∗ Corresponding author. Tel.: +86 53188365459; fax: +86 53188564464.E-mail address: yjh@sdu.edu.cn (J. Yang).

IsFaaha

386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2006.02.021

ormaldehyde

ermanganate can oxidize the phenol in acidic medium and pro-uce weak chemiluminescence with a detection limit of only× 10−7 g mL−1 for the phenol [14]. In this paper, it is found

hat the CL signal between permanganate and phenol is greatlynhanced by the formaldehyde (HCHO), the chemilumines-ence intensity is linearly related to the concentration of phenoln the range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detec-ion limit (3σ) of 3 × 10−9 g mL−1. Therefore, a sensitive flownjection–CL method for the determination of phenol is pro-osed. The method is successfully applied to the determinationf phenol in waste water, and the results are satisfactory.

. Experimental

.1. Apparatus

An FIA-3110 flow injection system with CL detection (Titannstrumental Company, Beijing, China) was used for the CLtudy; the flow injection manifold is shown schematically inig. 1. Two peristaltic pumps were used to deliver all solutions

t a flow rate of 3.75 mL min−1 for potassium permanganatend HCl solution or 1.25 mL min−1 for phenol and formalde-yde solution. PTFE tubing (0.8 mm i.d.) was used to connectll components in the flow system. Sample was injected through

W. Cao et al. / Spectrochimica Acta Part A 66 (2007) 58–62 59

Fig. 1. Schematic diagram of flow injection CL analyzer. (a) Phenol solution;(p(

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Table 1Effect of media

Media Intensity of the CL

Phenol and HCHO HCHO

Phosphorous acid 1.9 0.11Sulfuric acid 5.3 0.79Nitric acid 8.0 1.03Hydrochloric acid 9.3 0.89Perchloric acid 10.9 2.06

CK

3

3

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trare shown in Fig. 3. It can be seen that the CL intensityincreases with the increase of potassium permanganate con-centration in lower concentration range (<6.0 × 10−4 mol L−1),then reaches the maximum and remains constant in the con-

b) formaldehyde solution; (c) KMnO4 solution; (d) HCl solution; (P) peristalticump; (V) sample injection valve; (C) flow cell; (W) waste; (HV) high voltage;PMT) photomultiplier tube; (PC) personal computer.

n eight-way injection valve fitted with a 100 �L sample loop.he CL signal produced in the flow cell (10 cm × 1 mm i.d. spirallass tubing) was detected using a luminometer (manufacturedxclusively for Perkin-Elmer by Labsphere Instrumental Com-any).

.2. Reagents and solutions

The stock standard solution (1.00 × 10−3 g mL−1) of phenolas prepared by dissolving phenol in water. The solution shoulde stable for at least 30 days and kept in a refrigerator. Work-ng standard solutions of phenol were prepared by appropriateilution of this stock standard solution with water before use.orking solutions of KMnO4 (8.0 × 10−4 mol L−1) were pre-

ared freshly by diluting potassium permanganate stock solution5.0 × 10−3 mol L−1) with water. Formaldehyde solution (8%,/v) was prepared in water.

All chemicals were of analytical-reagent grade, and doublyistilled water was used throughout the experiments.

.3. Procedure

The reagent stream KMnO4 solution (8.0 × 10−4 mol L−1)nd HCl solution (2.0 mol L−1) were used as the oxidizer andormaldehyde solution was used as the enhancement reagent.he CL signal was recorded by injection of 100 �L of workingtandard solution of phenol and formaldehyde solution (8%, v/v)nto streaming potassium permanganate and HCl solution, andhe CL peak height was then measured for quantification.

.4. Sample pretreatment

To a 100 mL sample solution, 1 mL of 0.1 g mL−1 CuSO4olution was added, then the pH of the solution was adjusted to 4ith 1.5 mol L−1 phosphoric acid. The test solution was placed

n a 250 mL short neck Kjeldahl flask containing boiling tipsnd was distilled using a mantle heater and a 35 cm long Liebigondenser with a 100 mL volumetric flask as a receiver. The dis-illation was interrupted when the volume of distillate becamebout 90 mL, and 10 mL of water was added to the Kjeldahl flask.

hen distillation was restarted and continued until the distillate

eached the mark of the receiver. The distillate obtained was sub-ected to chemiluminescence to determine phenol as describedbove.

FmL

onditions: phenol (1.0 × 10−5 g mL−1); formaldehyde solution (8%, v/v);MnO4 solution (1.0 × 10−3 mol L−1); 2.0 mol L−1 different acids.

. Results and discussion

.1. Selection of acid type and concentration

The CL reaction of the phenol is examined in KMnO4–CHO–H+ system by using phosphatic acid, sulfuric acid,ydrochloric acid, nitric acid and perchloric acid as the reac-ion media. The results are shown in Table 1. The resultshow that the stronger CL signal and weaker background arebtained in hydrochloric acid. The effect of hydrochloric acidoncentration on the CL of this system was investigated and ishown in Fig. 2. It can be seen that 2.0 mol L−1 hydrochloriccid is suitable for the phenol to get the maximum CL sig-al.

.2. Selection of potassium permanganate concentration

The effect of potassium permanganate concentration onhe CL intensity of this system has been examined in theange of 2.0 × 10−4 to 2.0 × 10−3 mol L−1, and the results

ig. 2. The effect of HCl concentration. Conditions: phenol (1.0 × 10−5gL−1); formaldehyde solution (8%, v/v); KMnO4 solution (1.0 × 10−3mol−1).

60 W. Cao et al. / Spectrochimica Acta Part A 66 (2007) 58–62

Fp(

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Fig. 5. The effect of flow rates of phenol and HCHO. Conditions: phe-nol (1.0 × 10−5 g mL−1); formaldehyde solution (8%, v/v); KMnO4 solution(3

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ig. 3. The effect of potassium permanganate concentration. Conditions:henol (1.0 × 10−5g mL−1); formaldehyde solution (8%, v/v); HCl solution2 mol L−1).

entration range of 6.0 × 10−4 to 1.0 × 10−3 mol L−1. Whilehe concentration of potassium permanganate is larger than.0 × 10−3 mol L−1, the CL intensity of this system decreasesith the increase of potassium permanganate concentration.herefore, 8.0 × 10−4 mol L−1 of potassium permanganate iselected for further research.

.3. Selection of formaldehyde concentration

It is found that the CL signal of phenol–KMnO4 in acidicolution can be enhanced by formaldehyde, the effect oformaldehyde concentration on CL intensity is examined andhe results are shown in Fig. 4. It can be seen that the formalde-yde can enhance CL intensities of the systems with or withouthenol. The maximum CL difference (�ICL) between the sys-

ems with and without phenol is obtained when formaldehydeoncentration is in the range 8.0–9.6%; thus, 8.0% formaldehydes selected for further research.

ig. 4. The effect of formaldehyde concentration. (a) Phenol–KMnO4–HCHOystem; (b) KMnO4–HCHO system; (c) �I = Ia − Ib (Ia and Ib are theL intensities of phenol–KMnO4–HCHO and KMnO4–HCHO systems,

espectively). Conditions: phenol (1.0 × 10−5g mL−1); KMnO4 solution8.0 × 10−4 mol L−1); HCl solution (2 mol L−1).

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8.0 × 10−4 mol L−1); HCl solution (2 mol L−1); flow rate of KMnO4 and HCl:.75 mL min−1.

.4. Selection of flow rate

The flow rates of phenol and HCHO, potassium perman-anate and hydrochloric acid solution were investigated in theange of 0.4–2.5 and 2.5–4.6 mL min−1. The results are shownn Figs. 5 and 6. It can be seen that the CL intensity increasesith increasing the flow rate of phenol and HCHO before.8 mL min−1, after which the CL intensity reaches the max-mum and remains constant. So, 1.25 mL min−1 is selected forhe flow rates of phenol and HCHO solution. The CL intensityncreases with the increase of flow rates of potassium per-anganate and hydrochloric acid solution in the lower flow

ates range (<3.75 mL min−1), then reaches the maximum andemains constant in the flow rates range of 3.75–4.6 mL min−1.herefore, 3.75 mL min−1 is selected for the flow rates of the

otassium permanganate and hydrochloric acid solution for fur-her research.

ig. 6. The effect of flow rates of KMnO4 and HCl. Conditions: phe-ol (1.0 × 10−5 g mL−1); formaldehyde solution (8%, v/v); KMnO4 solution8.0 × 10−4 mol L−1); HCl solution (2 mol L−1); flow rate of phenol and HCHO:.25 mL min−1.

W. Cao et al. / Spectrochimica Ac

Table 2Tolerable limit of foreign species

Species added Tolerance ratio (species/phenol)

K+, Na+, NH4+ 1000

Ca2+, Mg2+, Pb2+ 100Zn2+, Al3+, Cr3+ 10Cu2+, Co2+, Ni2+, Mn2+, Fe3+ 1.0SP

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.5. Interference

The influences of some possibly co-existing materials in theample of phenol and some inorganic ions on the CL intensity ofhe system are in detail investigated, and the results are shownn Table 2. The tolerable limit of a foreign species was takens a relative error not greater than ±5% in the recovery at aoncentration of 1.0 × 10−5 g mL−1 phenol. It can be seen fromable 2 that 1000-fold excess of K+, Na+ and NH4

+; 100-foldxcess of Ca2+, Mg2+ and Pb2+; 10-fold excess of Zn2+, Al3+

nd Cr3+; 1-fold excess of Cu2+, Co2+, Ni2+, Mn2+ and Fe3+;000-fold excess of SO4

2− and NO3−; and 200-fold excess of

O43− do not interfere with the determination of phenol in this

ystem.

.6. Linear response range, detection limit and precision

Under the above optimum conditions, the CL inten-ity is linearly related to the concentration of phenol inhe range 5.0 × 10−9 to 1.0 × 10−6 g mL−1 with a detec-ion limit (3σ) of 3 × 10−9 g mL−1, the regression equa-ion is I = 0.539 − 1.941 × 106c, the correlation coefficients r = 0.9996. The relative standard deviation is 1.2% for.0 × 10−7 g mL−1 phenol solution in 11 repeated measure-ents.

.7. Determination of phenol in waste water

Under the selected conditions, the proposed method is usedo determine phenol in the sample of waste water and comparedith 4-aminoantipyrine spectrophotometry [1]. The results are

hown in Table 3. It can be seen that the accuracy and precisionf the proposed method are satisfactory.

.8. Possible reaction mechanism

It was reported that KMnO4 could react with some reductantsn the presence of formaldehyde to produce 1O2

1O2(1�g1�g), a

able 3etermination of phenol in waste water

ample 4-AAP method[1] (g mL−1)

Proposed method(g mL−1) (n = 5)

R.S.D. (%)

1.68 × 10−6 1.63 × 10−6 2.04.01 × 10−7 4.08 × 10−7 3.26.38 × 10−7 6.32 × 10−7 1.6 [

ta Part A 66 (2007) 58–62 61

omplex oxygen molecule of single state, which could transformnto 3O2(3�g), a triplet state oxygen. During the transformation,t could produce CL and the formaldehyde could accelerate oxi-ation reaction rate [16,17]. The peak of chemiluminescencepectrum is at 630–640 nm, which is very similar to that ofinglet oxygen chemiluminescence (630–650 nm). Thus, it wasssumed that the phenol could also react with KMnO4 to produceL, and the CL reaction could be accelerated by formalde-yde.

Based on the above discussions, the possible reaction mech-nism is suggested as following:

nO4− + H+ + formaldehyde + phenol

→ 1O2(1�g) + H2O + Mn(II) + products

1O2(1�g) → 1O21O2(1�g

1�g)

O21O2(1�g

1�g) → 23O2(3�g) + hν

. Conclusion

It was found that in the acidic medium, the phenol couldeact with potassium permanganate and produce CL, which wasnhanced by formaldehyde. Under the optimum conditions, aimple, fast response and sensitive CL method was developedor determination of phenol. The proposed method was usedor determination of phenol in waste water and the results areatisfactory.

cknowledgements

This work was supported by the Natural Science Foundationf China and the ShanDong Provincial Education Departmentf China.

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