Saadiyah A. Dhahir; Huda J. Hussein

Abstract

A simple， cheap and sensitive spectrophotometric method for the determination of methyl paraben in pure and dosage form has been described. The Method is based on the diazotization of the drug by sodium nitrite in acidic medium at 5Co followed by coupling with orthoaminobenzoic acid to form orange color the product was stabilized and measured at 442 nm Beers law is obeyed in the concentration range of 1-9 μg？ml-1 with molar absorptivity of 1.6×106 L？mole-1？cm-1.， Sandells sensitivity were 0.0095 μg？cm-1， The detection limit were 0.0065 μg？ml-1， and The limit of Quantitation were 0.02μg？ml-1. All variables including the reagent concentration， reaction time， color stability period， and mole ratio were studied in order to optimize the reaction conditions. No interferences were observed Results of analysis were validated statistically and by recovery studies. These methods are successfully employed for the determination of methyl paraben in some oral solution. The developed method is easy to use and accurate for routine studies relative to HPLC and other techniques.

Key words： Determination； Spectrophotometric； Methyl paraben

INTRODUCTION

Methylparaben drug is Methyl p-hydroxybenzoate. It is a white or colourless powder crystals， very slightly soluble in water， freely soluble in alcohol and in methanol1. The formula structure explain below：

Methyl paraben， in particular， has been used extensively for more than 50 years due to its most favorable solubility properties compared to the higher chain alkyl hydroxybenzoates （Soni， Taylor， Greenberg， & Burdock， 2002； Giordano et al.， 1999）. Methyl paraben is none stimulating and nontoxic， and has a broad antibiotic spectrum. The compound is widely used as a preservative for foods， cosmetics and medicines. Those methyl paraben containing products caused contact dermatitis and drug hypersensitivity2（Mowad， 2000）. Most of the methods for their determination in cosmetics and pharmaceutical preparations are based on gas chromatography （GC） （Mannucci et al.， 1992； Aromdee& Rattandon， 2009； Shnmugan， Rajendran， Ralhakrishnan，& Tao， 2010； Han， Jia， Liu， Duan， & Chen， 2010）， highpressure liquid chromatography （HPLC） （Shabir， 2010； Boonleang & Tanthana， 2010； Kamble， Singh， & Singh， 2011； Krishnachaitanya， Israel， & Gowrisankar， 2011； Modi， Vairale， Sherikar， & Nalamothu， 2011） and fluorescence spectrometry （Blanco， Carretero， Peinado， & Guttierrez， 2000）.

1. EXPERIMENT

1.1 Apparatus

All spectrophotometric measurements were carried out using Computerize UV-Visible， shimadzu； silica glass cell of 1 cm thickness was used throughout this study.

1.2 Materials

Methylparaben stock standard solution 1000 μg？ml-1

was prepared by dissolving 0.1 g of pure methylparaben（SDI） in distilled water and diluting to the marked in 100 ml volumetric flask. Working standard solution 100μg？ml-1 was prepared by diluting 10 ml of this stock standard solution with distilled water in 100 ml volumetric flask.

Sodium nitrite solution 1% w/v was prepared by dissolving 1 g of sodium nitrite in distilled water and diluting to the marked in 100 ml volumetric flask.

Hydrochloric acid solution 1 M was prepared by diluting 43 ml of 11.64 M of concentrated hydrochloric acid （BHD） with distilled water in 500 ml volumetric flask.

Ortho-aminobenzoic 100 μg？ml-1 was prepared by dissolving 0.01 g of ortho-aminobenzoic in ethanol （BHD） and diluting with distilled water to the marked in 100 ml volumetric flask

Sodium hydroxide solution 1 M was prepared by dissolving 4. g of sodium hydroxide in distilled water and diluting to the marked in 100 ml volumetric flask.

1.3 Recommended Analytical Procedure

The 0.5 ml of Methylparaben standard solution 100μg？ml-1 and 0.5 ml of 1M sodium hydroxide solutions were added to 0.5 ml of of ortho-aminobenzoic and 0.5 ml of 1% sodium nitrite and 0.5 ml of 1M HCl were mixed in and completed with distilled water to the mark in 10 ml volumetric flask and shacked for 2 minutes， with shaking and cooling ice bath for 2 minutes， after 5 minutes the orange color is completely developed and the absorbance measurement was carried out at a wavelength at 442 nm， against a blank solution prepared in the same method but without Methylparaben

Oral Solution

a. Ketofen Syrup： 1.25 ml was taken from container containing 0.8 mg of methyl paraben in 100 ml and dissolved with 5ml ethanol and transferred into 100 ml volumetric flasks and diluted up to the mark with distilled water.

b. Cyprodien Syrup： 2 ml was taken from container containing 0.48 mg of methyl paraben was transferred into 100 ml volumetric flasks and diluted up to the mark with distilled water. Working standard solutions was prepared by suitable dilution for Ketofen Syrup and Cyprodien Syrup， the recommended procedure was used to determination methyl paraben.

3. RESULTS & DISCUSSION

3.1 Absorption Spectra

An orange-colored oxidizing coupling product with absorption maximum at 442 nm Figure 1 shows the spectra of orange product

3.1.1 Optimization of the Experimental Conditions

The effect of various variables on the color development was studied to get the optimum conditions for the determination of methyl paraben. In the subsequent experiments， 1ml of （100 μg？ml-1） methyl paraben solution with varies volumes 0.1% of sodium nitrite solution The optimum concentration of 0.1% sodium nitrite solution that gave maximum absorption at 442 nm versus reagents blanks was found to be 0.5 ml. Figure 2 explained these results. The effect of different volumes （0.1-1.0） ml of 1 M Hydrochloric acid solution， （0.1-1.0 ml） of 100 μg？ml-1 of ortho-aminobenzoic acid and （0.1-1） ml of 1 M sodium hydroxide solution were examined on the maximum absorbance of the azo dye.

It was found that 0.5 ml of （1 M） hydrochloric acid solution， 0.6 ml of （100 μg？ml-1） ortho-aminobenzoic acid solution and 0.6 ml of （1 M） sodium hydroxide solution were enough to obtain the maximum absorbance. The azo dye color was only formed in alkaline medium. Therefore， the effects of different alkaline solutions were studied such as potassium hydroxide， sodium hydroxide sodium carbonate， and ammonium hydroxide. It was found that sodium hydroxide is the most suitable alkaline medium to produce a maximum absorbance and was used in all subsequent experiments.

The stability of the dye was studied for 1 h following the mixing of the reagents. The colored azo dye developed rapidly after mixing and attained maximum absorbance about 4 min at room temperature. The color was stable for a period of 24 h. The effect of temperature on the diazotization and coupling reaction show that the absorbance of the azo dye remains constant in the range 0-40oC and decreases up to 30 oC. Therefore， it has been recommended to carry out reaction at zero temperature.

3.2 Calibration Graph

Employing the conditions described in the procedure， a linear calibration graph of methyl paraben is obtained（Figure 3）， which shows that Beers law is obeyed over the concentration range of 1-9 μg？ml-1 with correlation coefficient of 0.9998 and an intercept of 0.0297. The conditional molar absorptivity of the orange product formed was found to be 1.6x106 L？mol-1？cm-1. Sandells sensitivity were 0，0095 μg？cm-1， detection limit were 0，0065 μg？ml-1 and The limit of quantitation were 0，02 μg？ml-1.

3.2.1 Effect of Interference

The effects of some foreign ions which often accompany this drug in pharmaceutical products were studied by adding different amounts of foreign ions to 10μg/ml of methyl paraben. The color was developed following the recommended procedure described earlier. It was observed that the Arabic Gum， glucose， Fructose， sodium acetate， Urea， NaCl， and O-Cresol were not interfering with the determination at levels found in dosage form.

3.2.2 Structure of the Dye

The stoicheiometry of the reaction between Methyl paraben and ortho-aminobenzoic acid was investigated using Job method （Skoog， Holler， & Crouch， 2007）； the results obtained Figure 4 show that 1：1 drug to reagent was formed at 442 nm.

4.2 Evaluate the Results of the Proposed Method For the evaluating the results of the proposed method comparing with the standard method （Kebbekus & Mitra， 1998， pp.23-24） to determine the efficiency and success in the estimate Due to unavailable of the standard method in the British Pharmacopoeia， there for Standard addition method was used for determination of methyl paraben in Ketofen Syrup and. Cyprodien Syrup preparation The results shown in Figures 6-7 shows that the results of standard addition method agree well with the proposed method， indicating that the method is selective and free from interference.

CONCLUSION

The proposed methods were found to be simple， economical， selective and sensitive. The statistical parameters and recovery study data clearly indicate no interference. Hence， these methods could be considered for the determination of methyl paraben in the quality control laboratories

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