Determination of phenol in water by pervaporation–flow injection analysis

doi:10.1016/S0003-2670(00)00991-0

Analytica Chimica Acta

Volume 419, Issue 1, 15 August 2000, Pages 9-16

https://doi.org/10.1016/S0003-2670(00)00991-0 Get rights and content

Abstract

A pervaporation–flow injection method for the determination of phenol in aqueous samples is described. The method involves sample injection into a concentrated sodium chloride (25 wt.%) donor stream at pH 2 and stopping the flow of the acceptor stream containing 0.1 M KNO₃ and 0.01 M NaOH in the acceptor chamber of the pervaporation unit for 12 min. This period allows the completion of phenol transfer from the headspace of the donor chamber of the pervaporation unit through the membrane into the static solution in the acceptor chamber. After restarting the flow through the acceptor chamber the phenol concentration is detected amperometrically at a glassy carbon electrode set at +0.6 V. At 20°C the linear detection range was found to be 1–50 mg l⁻¹ with R.S.D. varying between 1 and 4% for n=3. The detection limit and sample throughput were determined as 0.9 mg l⁻¹ and 5 h⁻¹, respectively. Excellent agreement with the standard 4-aminoantipyrine (4-AAP) method was observed when validating the method with lake samples containing suspension and spiked with phenol.

Introduction

Phenols, defined as hydroxy derivatives of benzene and its condensed nuclei, may occur in domestic and industrial wastewaters, natural waters and potable water supplies as a result of their wide use in numerous commercial products including pesticides, wood preservatives, disinfectants, dyes [1] and fungicides [2]. Phenols are also by-products of industrial processes, such as petrochemical industries [3], paper pulp manufacturing [4] and coal liquefaction plants [5].

The importance of monitoring phenols in the aquatic environment is due to their toxicity to aquatic organisms even below the mg l⁻¹ level (e.g. pentachlorophenols [1]) and the production of odorous and objectionable taste to drinking water supplies and edible aquatic species at the μg l⁻¹ level (e.g. chlorophenols [6]).

A number of colorimetric methods for the quantitative determination of phenols in aqueous samples have been proposed [7], [8], [9], [10]. The most frequently used among them is based on the reaction of phenols with 4-aminoantipyrine (4-AAP) in the presence of an oxidant to form red-coloured compounds [7]. The result is expressed usually as ‘total phenols’. This method cannot detect nitro- and para-substituted phenols since they do not react with 4-AAP. This drawback was overcome by a flow injection (FI) based method with electrochemical detection developed by Christophersen and Cardwell [11]. Other FI based methods utilising membrane extraction-preconcentration were proposed for determination of phenols in oil, kerosene and naphtha [12].

Industrial and environmental phenol samples frequently contain emulsions, suspensions and various organic molecules. For this reason sample pretreatment is required which slows down the sample throughput considerably and increases the analysis cost. Recently, a technique called pervaporation–flow injection (PFI) has been successfully applied for the direct quantitative determination of volatile and semi-volatile analytes in sample types mentioned above [13]. The analytes evaporate into the headspace of the pervaporation module and diffuse through a membrane into the acceptor stream where detection takes place. Since there is no direct contact between the sample and the membrane, deterioration of the latter (e.g. clogging by particles or macromolecules) is avoided [14].

The aim of the present study is to develop a fast, sensitive and reliable on-line method for the determination of phenol in aqueous samples based on coupling PFI with electrochemical detection.

Section snippets

Solution preparation

All reagents (i.e. NaCl (Univar, Ajax Chemicals, Australia), H₂SO₄, KNO₃, Na₃PO₄, NaOH (BDH, Australia), KNO₃, K₄[Fe(CN)₆] (BDH, Australia), phenol (99% purity, Chem Services, PA, USA), 4-AAP (ICN Biomedicals, USA)) were of analytical grade and the corresponding stock solutions were prepared in nanopure deionised water (17.9 MΩ cm, Barnstead, USA).

The NaCl concentration in the donor stream was adjusted in the range from 0 to 25 wt.% by directly dissolving the appropriate amount of NaCl in

Results and discussion

The PFI system parameters that affect the sensitivity and reproducibility of the phenol determination were studied separately. Table 1 shows the range over which each parameter was investigated and its optimal value. In the following paragraphs, the influence of these parameters on the sensitivity, reproducibility and the sample throughput, where appropriate, is discussed. The experiments outlined were performed under the optimal conditions given in Table 1 unless stated otherwise.

Conclusions

The PFI method for detection of phenol proposed in the present paper is characterised by a linear detection range between 1 and 50 mg l⁻¹ with R.S.D. varying between 1 and 4% for n=3. The detection limit and sample throughput were determined as 0.9 mg l⁻¹ and 5 h⁻¹, respectively. The method was successfully used in the determination of phenol in natural water samples containing suspended particulate matter. The ability for direct determination of phenol in ‘dirty’ samples makes the PFI method an

Acknowledgements

The authors are grateful to the Australian Research Council for financial support and to La Trobe University for a scholarship for S. Sheikheldin.

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Determination of phenol in water by pervaporation–flow injection analysis

Abstract

Introduction

Section snippets

Solution preparation

Results and discussion

Conclusions

Acknowledgements

J. Chromatogr.

J. Chromatogr.

Anal. Chim. Acta

Anal. Chim. Acta

Anal. Chim. Acta

J. Chromatogr.

Anal. Chem.

J. Chromatogr. Sci.