Keywords
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| Diclofenac sodium, Rabeprazole sodium, Simultaneous equation, Q-Absorption ratio method, urea, hydrotropic agents. |
Introduction
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| The term hydrotropy has been used to designate the increase in solubility of various substances due to the presence of large amounts of additives. Various hydrotropic agents have been used to increase the aqueous solubility of large number of drugs. Hydrotropic solution may be a proper choice instead of using residual toxicity organic solvents like acetonitrile, methanol, dimethyl formamide and chloroform which cause residual toxicity. Hydrotropic agents like sodium benzoate, sodium salicylate, urea, nicotinamide, sodium glycinate, sodium ascorbate, and niacinamide, have been employed to increase the aqueous solubility’s of large number of water insoluble drugs[1-13] . Chemically Diclofenac sodium is, sodium (2-(2, 6- dichloroanilino) phenyl) acetic acid, used as analgesic and anti-inflammatory drug used in the treatment of rheumatoid arthritis, osteoarthritis and alkylosing spondylotis and also for a variety of nonrheumatic inflammatory conditions. Chemically Rabeprazole sodium is 2-([4-(3-methoxypropoxy)-3- methyl-2-pyridinyl]-methyl]sulfinyl]-1H benzimidazole sodium salt is an anti-ulcer drug in the class of proton pump inhibitors that reduce the production of acid by blocking the enzyme (hydrogen-potassium adenosine triphosphatase) in parietal cells and used to treat duodenal ulcers and erosive or ulcerative gastro esophageal reflux disease. Diclofenac sodium is official in IP, BP and USP, literature survey reveals HPLC[14-15], spectrophotometry[16-17], and fluorimetry[18-19] methods for determination of diclofenac sodium. Rabeprazole was not official in any pharmacopoeia, HPLC[20-21], LC-MS[22], and spectrophotometric[23-24] methods have been reported for the rabeprazole sodium. Diclofenac-Rabeprazole mixture is not yet official in any pharmacopoeia, there was no official methods for the estimation of both the drugs, HPLC method for the simultaneous estimation of rabeprazole and diclofenac sodium is reported. Diclofenac sodium alone has been reported to be estimated by using hydrotropic agents[25-26], to our knowledge there was no simultaneous spectrophotometric estimation using hydrotropic agents have been described for the simultaneous estimation of both drugs in tablets. In this report two methods based on simultaneous equation and QAbsorption ratio methods have been used to determine the diclofenac sodium and rabeprazole sodium. The following methods were validated according to ICH norms. |
Experimental
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| Chemicals and reagents |
| Rabeprazole and Diclofenac were standardized by official method reported in Indian Pharmacopoeia and the purity of the sample was found to be 99.1% and 98.9% for rabeprazole and diclofenac, respectively. Urea used is of analytical reagent grade and water used was doubly distilled from all glass apparatus. |
| Instrumentation |
| Spectrophotometric analysis was performed on ausing a 1cm quartz cell and band pass of 2nm. The instruments setting were 200-400nm for normal wavelength range. |
| Selection and preparation of hydrotropic solvent |
| From the solubility studies 5M urea solution was selected as hydrotropic agent for spectrophotometric analysis of rabeprazole and diclofenac, respectively in their tablet formulations, 5M urea solution was prepared by accurately weighing 15g in to a 50ml volumetric flask and the volume was made up to 50ml with distilled water. |
| Preparation of stock and standards for linearity |
| Stock solutions were prepared by dissolving rabeprazole sodium and diclofenac sodium in 5M urea as hydrotropic solubilizing agent separately to obtain a concentration of 1mg/1ml for each compound. The standard solutions for calibration curve were prepared by dilution of the stock solutions in distilled water to reach concentration ranges of 4- 28 μg/ml and 5-25μg/ml for rabeprazole sodium and diclofenac sodium, respectively. |
| Preparation of sample stock solution |
| Ten tablets containing rabeprazole sodium and diclofenac sodium as active ingredients were weighed and finely powdered in a glass mortar. A portion of the powder equivalent to about 10mg of rabeprazole sodium was weighed accurately, transferred to a 10ml volumetric flask and either suspended in 5M urea then shake for some time and the mixture was sonicated for 30min then flask was completed to volume with the same solvent. Then the mixtures was filtered, the filtered solution was diluted to get a concentration of 10μg/ml with distilled water. |
| UV-spectrophotometric methods |
| Simultaneous equation method |
| This method of analysis was based on the absorption of drugs rabeprazole sodium and diclofenac sodium at the wavelength maxima of each other. Two wavelengths were selected for the development of the simultaneous equations at 285nm and 276nm (fig 1&2) for Rabeprazole and Diclofenac respectively. The absorptivity values E (1%, 1cm) were determined for two drugs at all selected wavelengths. The concentration of two drugs in mixture was calculated by using following equations. |
| CX = (A2 ay1-A1 ay2)/(ax2 ay1-ax1 ay2) |
| CY = (A1 ax2-A2 ax1)/ (ax2 ay1-ax1 ay2) |
| Where, Cx and Cy are the concentrations of rabeprazole and diclofenac respectively in mixture and in sample solutions. A1 and A2 are the absorbencies of sample at 285nm and 276nm, respectively, ax1 and ax2 are the absorptivity of rabeprazole at 285nm and 276nm. All standard and sample solutions absorbance was measured at 285nm and 275nm with their respective blanks. |
| Q-Absorption ratio method |
| This method is applicable to the drugs that obey Beer’s law at all wavelengths and the ratio of absorbance at any two wavelengths is a constant value, independent of concentration and path length. The solutions of 25μg/ml and 24μg/ml for diclofenac sodium and rabeprazole were scanned in the wavelength range of 400 to 200nm to obtain overlain spectra (fig 5). Two wavelengths, 281nm as iso absorptive point and 276nm (λmax of diclofenac sodium) were selected for the formation of Qabsorbance ratio equation. The calibration curves were determined in the concentration range of 5- 25μg/ml and 4-28μgml for diclofenac sodium and rabeprazole sodium respectively. The absorptivity coefficients of each drug at both the wavelengths were determined. The concentration of the individual components, Cx and Cy can be calculated by using the following equations. |
| Cx = (QM-QY/QX-QY) x (A1/ax1) |
| CY = (QM-QX/QY-QX) x (A2/ay1) |
| Where A1 and A2 are absorbance of sample solution at iso-absorptive point 281nm and 276nm λmax of diclofenac sodium respectively, ax1 and ax2 are the absorptivities of the rabeprazole at 281nm and 276nm respectively and ay1 and ay2 are the absorptivities of the diclofenac at 281nm and 276nm respectively. |
| Validation of UV- visible spectrophotometric methods |
| Linearity and range |
| Five aliquots of each drug solutions were taken from standard stock solution and transferred to 10ml volumetric flask to get a final concentration of 5, 10, 15, 20 and 25 μg/ml of diclofenac and 4, 8, 12, 16 and 20, 24 and 28μg/ml of rabeprazole and the volume was completed with the distilled water and each flask content was measured to determine the absorbance at all the selected wavelength. For simultaneous equation method the absorbance of all standard solutions were measured at 276nm and 285nm, the calibration curves of absorbance vs. concentration was plotted and correlation coefficient and regression line equations for both rabeprazole and diclofenac sodium were determined. For Q-Absorption ratio method the wave lengths selected were 281nm (iso absorptive point) and 276nm (λmax of diclofenac). The absorbance at these two wavelengths for all standard solutions of both rabeprazole and diclofenac were measured and the calibration curves and linear regression equation of rabeprazole and diclofenac at 281nm and 276nm were determined. |
| Precision |
| In intraday study concentration of two drugs were calculated on the same day at an interval of one hour. In inter day study the concentration of drug contents were calculated on three different days study expresses with in laboratory variation in different days. In both intra and inter-day precision study for the methods %RSD were calculated. |
| Accuracy |
| Accuracy of the developed method was confirmed by doing recovery study as per ICH norms at three different concentration levels 80%, 100%, 120% and the values were measured at all wavelengths for rabeprazole and diclofenac sodium. This operation was done in triplicate. From the recovery study it was clear that the method is very accurate for quantitative estimation of rabeprazole and diclofenac sodium in tablet dosage forms as the statistical results were within the acceptance range. |
| Limit of Detection and Limit of Quantification |
| The limit of detection and limit of quantification of diclofenac and rabeprazole by proposed methods were determined using calibration standards.LOD and LOQ were calculated as 3.3σ/S and 10σ/S, respectively, where S is the slope of the calibration curve and σ is the standard deviation of response. |
Results and discussions
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| Linearity and range |
| The linearity of rabeprazole sodium and diclofenac sodium were found to be in the range of 4-2μg/ml and 5-25μg/ml with correlation coefficient of 0.999 and 0.998 for rabeprazole and diclofenac, respectively for simultaneous method, for QAbsorption ratio method linearity was found to be 4- 28μg/ml with correlation coefficients of 0.999 and0.999 at 281nm and 276nm for rabeprazole sodium, the calibration data with %RSD for both the methods shown in (table-1, 2, 3, 4, 5, 6 and 10) and calibration curves are shown in (figure 3, 4, 6, 7, 8 and 9). |
| Precision |
| %RSD found for the simultaneous equation method in the range of 1.23-1.6 for rabeprazole and 1.005- 1.78 for diclofenac. The %RSD found for QAbsorption ratio method in the range of 1.02-2.05 (281nm) and 1.27-2.94 (276nm) for rabeprazole, 1.06-1.83(281nm) and 1.00-2.1(276nm) for diclofenac sodium, respectively as shown in Table 7. |
| Accuracy |
| Accuracy of the methods was confirmed by doing recovery studies from marketed formulation at three concentration levels of standard addition. The %recoveries found for the simultaneous equation method was 99.3-100.1 and 99.04-99 for rabeprazole and diclofenac simultaneously. For Q-Absorption ratio method the %recoveries found to be 99.9-100.1 and 98.8-99.1 for rabeprazole and diclofenac, respectively as shown in table 8. |
| Limit of Detection and Limit of Quantification |
| The limit of detection found to be 0.517 and 0.517 for simultaneous equation method for both rabeprazole and diclofenac sodium, respectively, the limit of quantification found to be 1.724 and 1.724 for both rabeprazole and diclofenac sodium, respectively. For Q-Absorption ratio method the limit of detection found to be 0.611 at (281nm), 0.675 at (276nm) and 0.642 at (281nm), 0.651 at (276nm) for rabeprazole and diclofenac, respectively, the limit of quantification found to be 2.172 at (281nm) and 1.923 at (276nm), 2.412 at (281nm) and 2.172 at (276nm) for both rabeprazole and diclofenac sodium as shown in table 9. |
| Analysis of marketed formulation (RCLONAC tablets) by UV spectrophotometric method |
| The percentage of rabeprazole sodium and diclofenac in the estimated formulation was found to be 98.75% and 98.62% for rabeprazole and diclofenac sodium, respectively for simultaneous equation method. For Q-Absorption ratio method the percentage of rabeprazole sodium and diclofenac in the estimated formulation was found to be 99.5 and 98.75% as shown in table 10. |
Conclusions
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| The present paper describes application of hydrotropic solubilization phenomenon for the simultaneous estimation of rabeprazole sodium and diclofenac sodium by simultaneous equation method and Q-Absorption ratio method. Both the drugs showed good linearity and regression values for their respective wavelengths. Hence the proposed methods are new, simple, cost effective, and free from pollution. It is concluded that the described methods have the potential for the application in the quality control laboratories. |
Acknowledgement
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| The authors wish to thank the authorities of Chalapathi institutes and Principal N.Rama Rao for suggestion and P.V. Suresh for helping me in literature survey. |
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Conflict of Interest
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| NIL |
Source of Support:
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| NONE |
Tables at a glance
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Figures at a glance
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