Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 2(12), 6-10, December (2012) Res.J.Chem. Sci. International Science Congress Association 6 Spectrophotometric Determination of Phenol in Micellar MediumGupta Nirja, Parmar Prachi* and Pillai Ajai Department of Chemistry, Govt. V.Y.T. Autonomous College Durg, Chhattisgarh, INDIAAvailable online at: www.isca.in Received 4th May 2012, revised 26th May 2012, accepted 14th September 2012Abstract A simple and sensitive spectrophotometeric method for the determination of Phenol based on its oxidation by N-bromophthalimide (NBP) is proposed. The resulting bromoderivative of phenol oxidizes leucocrystal violet to crystal violet in aqueous medium, the absorbance of which is measured at 595 nm. The colour intensifies with the addition of surfactant, cetyltrimethyl ammonium bromide (CTAB). Beer’s law is obeyed in the range of 0.02 – 0.22 µg mL-1 of phenol. The molar absorbtivity of the dye is found to be 3.13 x 10 l mol-1 cm-1 and sandell’s sensitivity as calculated from the slope is found to be 3x10-4 µg cm-2 The method has been successfully applied for the determination of phenol in coke oven effluents and the result obtained, compares well with other reported methods. Keywords: Non extractive spectrophotometric, Phenol, NBP, LCV. Introduction Phenols are toxic substances, widely used in the manufacture of synthetic phenolic resins, dyes, plastics, lamp black paints, air fresheners, paper soaps, paint removers etc. It is introduced into the environment through industrial discharges from coke oven plants, petroleum refineries, drug manufacturing units, antioxidants and dye industries1-2Phenol traces are also found in automobile exhaust, tobacco smoke and occasionally in hospital air. Exposure to high concentration of phenol in air for long duration is reported to cause paralysis and severe injury to heart, liver, kidney and lungs and in some cases may cause death also4-5. OSHA (occupational safety and health administration) has set a limit of 5 ppm in air, for workers during 8 hour work shifts. The US Environmental Protection Agency recommends rejection of water for drinking purpose which contains more than 1 µg of phenol/litre. Wide applicability and toxicity of phenol has resulted in many methods for their detection and determination. The methods used for the determination of phenol include flow injection, GC-FID with SPME, chemiluminescence, HPLC10, electrochemical methods11, GC-MS12, solvent extraction13 X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) nitrogen-gas adsorption method14, granular activated carbon15. Several spectrophotometric methods involving reagents like p-aminophenol16, 4-aminoantipyrine17, N-hydroxyl-N, N-diphenylbenzamidine18, sodium nitro-prusside19 have also been reported for its determination. In the present communication a spectrophotometeric method for determination of phenol is elaborated. The method is based on oxidation of phenol20 by NBP to form a bromo derivative which is subsequently reacted with LCV in micellar medium. The method has been successfully applied for the determination of phenol in real samples. Material and MethodsApparatus: A Systronics Spectrophotometer 106 was used for spectral measurements. Systronics pH meter, model 331 was used for pH measurements. All chemicals used were of analytical reagent grade and double distilled water was used for dilution. Reagents: Phenol Stock (Merck): 1 mg mL-1 stock solution of phenol is prepared in 5% ethanolic solution. Working standards were prepared by the appropriate dilution of the stock. Leucocrystal violet (LCV) [Eastman Kodak Co.]: 250 mg of Leucocrystal Violet (4,4’,4’’ methyldynetris (N, N’Dimethylaniline) was dissolved in 200 mL of distilled water containing 3 mL 85% phosphoric acid (Merck) and the volume was made upto 1 litre with distilled water and was stored in amber coloured bottle away from sunlight. N- Bromophthalimide (NBP) [Loba chemie]: 0.04 g NBP was dissolved in 8 mL acetic acid and the volume was made up to 25 mL with double distilled water and was stored in amber coloured bottle. 0.5% Sodium hydroxide: 2 g sodium hydroxide in 100 mL distilled water. Buffer solution: Buffer solution of pH 4 ±0.1 was prepared by dissolving 17.01 g potassium hydrogen phosphate in 490 mL water followed by drop wise addition of 85% phosphoric acid until the pH becomes 4 ±0.1 and volume was made up to the mark in 500 mL standard flask. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 2(12), 6-10, December (2012) Res. J. Chem. Sci. International Science Congress Association 7 CTAB Surfactant (Loba Chemie): 10-2 M solution was prepared by dissolving 0.3644 g CTAB in 100 mL distilled water. Procedure: Preparation of calibration curve: To aliquots of working standards containing 0.5 – 5.0 µg of phenol, 1mL of NBP was added and warmed slightly. After 2 minutes, 1mL of buffer was added and stirred gently. To this 1 mL of LCV followed by 0.5 mL of 0.5% NaOH and 1mL of CTAB was added and mixed. The solution was diluted up to 25 mL and kept at 30C for full colour development. An intense violet coloured dye having maximum absorption at 595 nm was obtained at ~ 4pH. Results and DiscussionSpectral characteristics: The absorption spectra of the coloured product formed in the proposed reaction shows maximum absorbance at 595 nm against reagent blank, which gave negligible absorbance at this wavelength. Adherence to Beer’s law Molar absorptivity and Sandell’s sensitivity: Beer’s law is obeyed over the concentration in the range of 0.02 -0.22 µg mL-1 of phenol. Molar absorptivity and Sandell’s sensitivity for the aqueous solution were found to be 3.13 x 10 L mol-1 cm-1 and 3 x 10-4 µg cm-2 respectively. Effect of Reagent concentration: Best results were obtained while using 1 mL each of NBP and buffer. It was observed that for maximum absorbance 1 mL of LCV was sufficient. There was no change at higher concentration, whereas at lower concentration there was decrease in absorbance values. Effect of surfactant: Addition of surfactant increased the intensity of violet coloured dye for which 1 mL of 10-2 M CTAB solution was necessary. Sensitivity was affected below and above this concentration. Order of addition of reagents: The order of addition of reagents is crucial. Addition of reagents in the order NBP, buffer solution, NaOH, LCV and then CTAB gave constant and maximum absorbance. If surfactant is added before addition of sodium hydroxide, sensitivity was affected. Effect of Time and Temperature: Temperature between 35-45 C was found to be the most suitable for obtaining maximum absorbance values. Above and below this range, absorbance was markedly affected. It was found that 10 minutes time was sufficient for complete colour development and the colour was stable for several days. Effect of pH: The most suitable range of pH was found to be between 4 to 4.5 for the formation of crystal violet from LCV. This was maintained by using phosphate buffer and sodium hydroxide. It was found that 1 mL of phosphate buffer and 0.5 mL of 0.1 M sodium hydroxide solution was required for maximum colour development. Increase of pH above 5.0 caused turbidity while below 3.5, no colour was observed. Reproducibility: The reproducibility of the method was checked by six replicate analysis of the solution containing 3 µg per 25 mL of phenol. The standard deviation and relative standard deviation data are summarized in table 1. Table-1 Optical characteristics, precision and accuracy of the method Optical characteristics Results  max (nm) 595 Limit of Beer’s Law (µg mL - 1 ) 0.02 – 0.2 Molar absorptivity ( L mol - 1 cm - 1 ) 3.13 x 10 5 Sandell’s sensitivity 3 x 10 - 4 Standard deviation ± 0.0063 Relative standard deviation 1.21 Effect of Foreign species: To check the validity of the method, effects of several species commonly found along with phenol, on the reaction were studied. This was done by addition of known amount of these species to 3 µg phenol prior to its analysis by the proposed method. The tolerance limits for various interfering species are shown in table 2. Table-2 Effect of diverse ions Foreign Species Tolerance level* (µg mL - 1) Methanol ,Ethanol ,Benzene 1000 Toluene 300 Formaldehyde , aniline 300 o-nitrophenol 70 o-cresol, p-cresol, m-cresol 800 Hg 2+ , Ca 2+ , Pb 2+ 850 Al 3+ ,Fe 3 + 1200 PO 4 3 - , SO 4 2 - , CH 3 COO - 1400 S 2 – 100 *causing an error of ±2% in absorbance value Reaction mechanism: Reaction mechanisms suggested for the proposed system are as follows: 1. Phenol + NBT Tribromophenol Tribromophenol + LCV CV Colourless Blue colour 2. Phenol + NBT Br Br + LCV CV Colourless Blue colour If the reaction were to proceed by the liberation of bromine, then addition of mercury acetate would have resulted in a change in absorbance values as mercury acetate is known to destroy bromine21. However no change in the absorbance values has been observed upon addition mercury acetate thus confirming that the reaction proceeds by formation of tribromophenol. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 2(12), 6-10, December (2012) Res. J. Chem. Sci. International Science Congress Association 8 Application: To check the validity of the method, it was applied for the determination of phenol in real samples like polluted water and coke oven effluents. Table-3 Determination of phenol in water samples Samples Amount of phenol found in (µgmL - 1) Proposed Method Reported Method Polluted river water W1 0.780 0.750 W2 1.02 1.00 W3 1.08 1.01 Coke oven effluent W4 2.12 2.08 W5 3.14 3.11 W6 3.75 3.71 Determination of phenol is polluted water: Coke oven effluents and samples from river water, which receives these effluents were collected and analysed by the proposed method. Since these samples contain oil, tar, and other organic compounds, alkaline hydrolysis was done at pH 11-12 and then extracted with carbon tetrachloride in 2x5 mL portion. The organic layer containing tar and oil was discarded. Aqueous portion was warmed briefly on a water bath to remove excess of carbon tetrachloride. After cooling, it was filtered through Whatman no-41 and analyzed by the proposed and reported method22. ConclusionThe present method for the determination of phenol is simple, sensitive and avoids the use of hazardous chemicals. This method can be compared favorably with other reported methods in table-4. The method can be successfully applied to the trace determination of phenol in polluted water. Table-4 Comparison with other spectrophotometric methodsMethod max(nm) Beer’s law range ( µg mL-1 )Remarks 4- amino antipyrene 23 510 0.2 – 2 Metal ion interfere, long Waiting time. p-nitroaniline 24 530 0.1 – 0.4 Reagent is carcinogenic p – anisidine, NCS 25 650 0.05 – 0.4 Colored reagent blank, higher temp. required Sodium nitropruside, hydroxylamine hydrochloride 19700 0.05 – 5.0 Interference of metal ions, less sensitive NCS – Ammonia 26 670 0.3 – 2.04 Less sensitive, metal ion interfere Vanadium , N-hydroxyl- N,N’-diphenylbenzamidine 18600 0.03 Extractive method NBT, LCV (proposed method ) 595 0.02 – 0.22 Non extractive, less time taking, non toxic reagent used, higher colour stability Figure-1 Absorption spectra of colour compound Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 2(12), 6-10, December (2012) Res. J. Chem. Sci. International Science Congress Association 9 Figure-2 Calibration curve for the determination of Phenol Acknowledgement The authors are thankful to DST-FIST for instrumental support and Department of Chemistry, Govt V.Y.T. P G Autonomous College Durg, for providing laboratory facilities. References 1.James J. Schauer, Michael J. Kleeman, Glen R.C., Bernd R.T. Simoneit, Environ. Sci. Technol.,35, 1716-1728 ( 2001)2.James W. Moore, Ramamoorthy S., Organic Chemicals in Natural Waters: Applied Monitoring and Impact Assessment, (Springer Verlag NewYork), (1984)3.Marcelo F. Pistonesi, María Susana Di Nezio, María Eugenia Centurión, Miriam E. Palomeque, Adriana G. Lista, Beatriz S. 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