Simultaneous Spectrophotometric Determination of Benzyl Alcohol and Diclofenac in Pharmaceutical Formulations by Chemometrics Method

Transcription

1 Journal of the Chinese Chemical Society, 005, 5, Simultaneous Spectrophotometric Determination of Benzyl Alcohol and Diclofenac in Pharmaceutical Formulations by Chemometrics Method Jahanbakhsh Ghasemi, a * Ali Niazi a and Sirous Ghobadi b a Chemistry Department, Faculty of Sciences, Razi University, Kermanshah, Iran b Biology Department, Faculty of Sciences, Razi University, Kermanshah, Iran Diclofenac sodium (DS) is a drug with analgesic, antipyretic, and anti-inflammatory properties. It is present in numerous pharmaceutical preparations. In injectable forms, it is usually accompanied by benzyl alcohol (BA) as an excipient, which is used as a blocking anesthetic (4%) and an antiseptic (4-10%). In this work a spectrophotometric methodology was applied in order to determine benzyl alcohol and diclofenac in injectable formulations by applying a multivariate calibration method. By a multivariate calibration method such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. In this study, the concentration model is based on absorption spectra in the nm range for 5 different mixtures of benzyl alcohol and diclofenac. Calibration matrix contains and 1-50 g ml -1 for benzyl alcohol and diclofenac, respectively. The root mean square errors of prediction (RMSEP) for benzyl alcohol and diclofenac were and , respectively. The proposed method was validated by using a set of synthetic sample mixtures and subsequently applied to simultaneous determination of benzyl alcohol and diclofenac in two different pharmaceutical formulations. Keywords: Benzyl alcohol; Diclofenac; Spectrophotometry; Partial least squares. INTRODUCTION Diclofenac sodium (DS), sodium salt of [-(,6-dichlorophenyl)amino]phenyl]acetic acid, is a potent non-steroidal anti-inflammatory agent for treatment of rheumatoid arthritis. The pharmacological effects of this drug are thought to be related to the inhibition of the conversion of arachidonic acid to prostaglandins, which are the mediators of the inflammatory process. 1, Diclofenac sodium is usually accompanied by benzyl alcohol (BA) as an excipient when used in injectable form. 1 Even though benzyl alcohol is present as an excipient, it is important that its concentration dose not exceed limit values for each formulation type, since it can produce fatal toxic syndromes, allergies, and undesirable effects over the nervous system. Generally, benzyl alcohol is quantitatively determined by gas chromatography and diclofenac sodium has been determined by a variety of analytical techniques, such as gas chromatography, 3 differential scanning calorimetry, 4,5 spectrophotometry, 6,7 spectrofluorimetry, 8 and liquid chromatography. 9 Simultaneous determination of benzyl alcohol and diclofenac sodium in pharmaceutical preparations containing benzyl alcohol and diclofenac sodium 10,11 was achieved by derivative methods. Spectral overlap and non-specific irrelevant absorption affect the interpretation of data for even the simplest-component drug systems, leading to variable intercepts on the absorbance axis and systematic errors in the graphs of absorbance versus concentration. These drugs present partially overlapping spectra. Derivative techniques and multivariate calibration such as partial least squares (PLS) have been devised for the analysis of mixtures with overlapping spectra. 1,13 The advantage of multicomponent analysis using partial least squares is the speed of the interest in a mixture, as a separation step can be avoided. The theory and application of partial least squares (PLS) in spectrometry have been discussed by several workers Several multicomponent determinations based on the application of these methods to spectrophotometric data have been reported in the literature The aim of this paper is to evaluate the possibility of using the partial least squares method for simultaneous determination of benzyl alcohol and diclofenac (Fig. 1), in pharmaceutical formulations. * Corresponding author. jahan.ghasemi@tataa.com

2 1050 J. Chin. Chem. Soc., Vol. 5, No. 5, 005 Ghasemi et al. EXPERIMENTAL SECTION Instrumentation and Software A Hewlett-Packard 8453 diode array spectrophotometer controlled by a Hewlett-Packard computer and equipped witha1cmpathlength quartz cell was used for UV-vis spectra acquisition. Data acquisition between 30 and 30 nm was performed with the UV-Vis ChemStation program (Agilent Technologies), running under Windows XP. A Metrohm 69 ph-meter furnished with a combined glass-saturated calomel electrode was calibrated with at least two buffer solutions at ph 3.00 and The data were treated in an AMD 000 XP (56 Mb RAM) microcomputer using MATLAB software, version 6.5 (The MathWorks). Partial least squares (PLS) calculus was carried out in the PLS-Toolbox, version.0 (Eigenvectors Company). Reagents and Standard Solutions All chemicals used were of analytical-reagent grade. Subboiling, distilled water was used throughout the work. Stock solutions (1000 g ml -1 ) of benzyl alcohol and diclofenac sodium (Merck) were prepared by direct weighing the required amount of commercially available reagents. The composition of the 3 ml commercial injectable form is: diclofenac sodium 75 mg and excipients (mannitol, sodium metabisulfite, benzyl alcohol (4%), propylene glycol, sodium hydroxide sufficient amount for ph 8.4, and distilled water apyrogene). Procedure and Sample Preparation Known amounts of the standard solutions were placed in a 10-mL volumetric flask and diluted to the final volume with deionized water (final ph 8.4). The final concentration of these solutions varied between and 1-50 gml -1 for benzyl alcohol and diclofenac, respectively. An amount of about 1 ml of the injectable form (mentioned above) of diclofenac sodium accurately dissolved in an appropriate amount of water. The sample was transferred into a 10-mL calibrated flask and diluted to volume and treated as described above for the standard drug solution. RESULTS AND DISCUSSION Fig. shows the absorption spectra in aqueous solution of benzyl alcohol and diclofenac separately at ph 8.4. The simultaneous determination of benzyl alcohol and diclofenac in mixtures by conventional spectrophotometric methods is hindered by strong spectral overlap throughout the wavelength range. Such a determination could theoretically be facilitated by the use of partial least squares method. Conventional univariate calibration In order to establish the optimal measurement conditions for the joint determination, we used the univariate method to investigate the effect of experimental variables on the absorption spectra for the drugs studied. We first checked the stability of the two analytes in aqueous solution. For this purpose, we recorded the UV absorbance spectra for solutions of benzyl alcohol and diclofenac as a function of time and found that the spectra of benzyl alcohol and diclofenac did not vary appreciably over a period of a few days provided that the solutions were kept at room temperature in the dark. As our aim is to determine benzyl alcohol and diclofenac in injectable formulation, and ph must be 8.4, therefore, a sufficient amount of sodium hydroxide is added to all solutions to maintain ph at 8.4. The temperature was found to CH COONa Cl NH CH OH Cl Diclofenac Sodium Benzyl Alcohol Fig. 1. Structural formulate of benzyl alcohol and diclofenac sodium. Fig.. Absorption spectra of the benzyl alcohol (90 g ml -1 ), and diclofenac (40 gml -1 ).

3 Determination of Benzyl Alcohol and Diclofenac J. Chin. Chem. Soc., Vol. 5, No. 5, have no appreciable effect on the spectra of the analytes, and thus 5 C was chosen for the subsequent work. Individual calibration curves were constructed with several points (Fig. 3), as absorbance vs. analytes concentration in the range of and 1-50 gml -1 for benzyl alcohol and diclofenac, respectively. The wavelengths used to generate calibration curves were 50 and 76.5 nm for benzyl alcohol and diclofenac, respectively. Linear regression results, line equations, and R are also shown in Fig. 3. Calibration and prediction data sets Multivariate calibration methods are suitable for the analysis of large numbers of samples. However, they are not advisable for the determination of large numbers of analytes because of the complexity of the calibration matrix. Moreover, the sample preparation and analysis are the most expensive steps in the multivariate calibration procedure. Multivariate calibration methods such as partial least squares (PLS) require suitable experimental design of the standards belonging to the calibration set in order to provide good predictions. The calibration matrix was designed over the concentration ranges of and 1-50 g ml -1 for benzyl alcohol and diclofenac, respectively. The calibration matrix used for the analysis is shown in Table 1. For the prediction step, 1 prepared mixtures that were not included in the previous set were employed as an independent test (see Table ). To ensure that the prediction and real samples are in the subspace of the training set, the score plot of first principal component vs. second was sketched and all the samples are spanned with the training set scores. Selection of the optimum number of factors The optimum number of factors (latent variables) to be Table 1. Concentration data of the training set for twocomponents systems (g ml -1 ) BA DS BA DS BA DS Fig. 3. Analytical curve for univariate determination of benzyl alcohol and diclofenac. Table. Added and found results of the synthetic mixtures of benzyl alcohol (BA) and diclofenac sodium (DS) by PLS (g ml -1 ) Added Found Recovery (%) BA DS BA DS BA DS

4 105 J. Chin. Chem. Soc., Vol. 5, No. 5, 005 Ghasemi et al. included in the calibration model was determined by computing the prediction error sum of squares (PRESS) for crossvalidation models using a high number of factors (half the number of total standard + 1), which is defined as follows: PRESS ( y yˆ ) i i where y i is the reference concentration for the ith sample and y i represents the estimated concentration. The cross-validation method is employed to eliminate only one sample at a time and then PLS calibrates the remaining standard spectra. 1 By using this calibration the concentration of the sample left out was predicted. This process was repeated until each standard had been left out once. One reasonable choice for the optimum number of factors would be the number that yielded the minimum PRESS. Since there is a finite number of samples in the training set, in many cases the minimum PRESS value causes overfitting for unknown samples that were not included in the model. A solution to this problem has been suggested by Haaland et al in which the PRESS values for all previous factors are compared with the PRESS value at the minimum. The F- statistical test can be used to determine the significance of PRESS values greater than the minimum. The maximum number of factors used to calculate the optimum PRESS was selected as 13, and the optimum number of factors obtained by PLS model are summarized in Table 3. In all cases, the number of factors for the first PRESS values whose F-ratio probability drops below 0.75 was selected as the optimum. Determination of benzyl alcohol and diclofenac in synthetic mixtures The predictive ability of the method was determined using 1 two-component mixtures (their compositions are given Table 3. Statistical parameters of the optimized matrix using the PLS Analytes NPC* PRESS RMSEP RSEP (%) Benzyl alcohol Diclofenac * Number of principal components. in Table ). The results obtained by applying PLS algorithm to twelve synthetic samples are listed in Table, which also show the recovery for the synthetic series of benzyl alcohol and diclofenac mixtures. As can be seen, the recovery was also quite acceptable. Statistical parameters For the evaluation of the predictive ability of a multivariate calibration model, the root mean square error of prediction (RMSEP) and relative standard error of prediction (RSEP) can be used: 31 RMSEP n i1 RSEP(%) 100 ( y y ) pred n n i1 where y pred and y obs are the predicted concentration and the observed value of the concentration in the sample, respectively, and n is the number of samples in the validation set. The values of RMSEP and RSEP (%) for benzyl alcohol and diclofenac are summarized in Table 3. Determination of benzyl alcohol and diclofenac in pharmaceutical formulations To assess the reliability of the method, two commercial pharmaceutical preparations were analysed. Table 4 shows obs ( y y ) pred obs obs ( y ) Table 4. Simultaneous determination of benzyl alcohol (BA) and diclofenac (DS) in pharmaceutical preparations using the PLS. These formulations contain 75 mg diclofenac sodium and 10 mg benzyl alcohol Pharmaceutical preparations Amount Found (mg SD a ) Recovery (%) Amount Found (mg SD a ) Recovery (%) DS DS BA BA Chemidarou b 7. (.37) ( 3.08) 98.3 Voltaren c 74.1 ( 3.77) ( 3.68) 94.0 a Relative standard deviation for n = 3 b Ampoules (from Chemidarou, Ltd.) c Ampoules (from Voltaren Ltd.)

5 Determination of Benzyl Alcohol and Diclofenac J. Chin. Chem. Soc., Vol. 5, No. 5, the results obtained as well as the composition of the drug formulations. The validation of the method has been carried out by comparing with labeled amounts. As can be seen, the recovery was quantitative and there were no significant differences between the amounts obtained from this method and labeled amounts. The plots of the prediction concentration versus actual values are shown in Fig. 4 for benzyl alcohol and diclofenac (line equations and R values are also shown). quality control of their manufacture. The ensuring methods are simple, precise, and affordable; also, they require no complex pretreatment or chromatographic separation of the samples containing the active ingredients to be determined. The method is a viable alternative to the existing analytical methods for routine analyses. Received October 7, 004. CONCLUSION Based on the results obtained in this work, application of the PLS to the absorbance spectra produced by benzyl alcohol and diclofenac during their simultaneous determination in pharmaceutical preparations is an effective means for Fig. 4. Plots of predicted concentration versus actual concentration for benzyl alcohol and diclofenac by PLS. REFERENCES 1. Boylan, J. C.; Cooper, J.; Chowhan, Z. T. Handbook of Pharmaceutical Excipients; American Pharmaceutical Association: Washington, Ghosh, J. A textbook of pharmaceutical chemistry; S. Chand and Company LTD: New Delhi, Clarke s Isolation and Identification of Drugs, nd ed., The Pharmaceutical Press: London, Bucci, R.; Magri, A. D.; Magri, A. L. Fresenius J Anal. Chem. 1998, 36, Palomo, M. E.; Ballesteros, M. P.; Frutos, P. J. Pharm. Biomed. Anal. 1999, 1, Botello, J. C.; Perez-Caballero, G. Talanta 1995, 4, Ortega-Barrales, P.; Ruiz-Medina, A.; Fernandez-De Cordova, M. L.; Molina-Diaz, A. Anal. Sci. 1999, 15, Arancibia, J. A.; Escandar, G. M. Analyst 1999, 14, Mayer, B. X.; Namiranian, K.; Dehghnyar, P.; Stroth, R.; Mascher, H.; Muller, M. J. Pharm. Biomed. Anal. 003, 33, de Micalizzi, Y. C.; Pappano, N. B.; Debattista, N. B. Talanta 1998, 47, Ghasemi, J.; Niazi, A.; Ghobadi, S. Chem. Pharm. J. 005, In Press. 1. Martens, H.; Naes, T. Multivariate Calibration; John Wiley: New York, Martens, H.; Martens, M. Multivariate Analysis of Quality: An Introduction; John Wiley: New York, Geladi, P.; Kowalski, B. R. Anal. Chim. Acta 1986, 185, Beebe, K. R.; Kowalski, B. R. Anal. Chem. 1987, 59, 1007A. 16. Haaland, D. M.; Thomas, E. V. Anal. Chem. 1988, 60, Haaland, D. M.; Thomas, E. V. Anal. Chem. 1988, 60, Haaland, D. M.; Thomas, E. V. Anal. Chem. 1990, 6, Brereton, R. G. Analyst 000, 15, Ghasemi, J.; Niazi, A. Microchem. J. 001, 68,1. 1. Ghasemi, J.; Niazi, A.; Safavi, A. Anal. Lett. 001, 34, Ghasemi, J.; Amini, R.; Niazi, A. Anal. Lett. 00, 35, Ghasemi, J.; Mohammadi, D. E. Microchem. J. 00, 71,1.

6 1054 J. Chin. Chem. Soc., Vol. 5, No. 5, 005 Ghasemi et al. 4. Ghasemi, J.; Niazi, A.; Leardi, R. Talanta 003, 59, Ghasemi, J.; Shahabadi, N.; Seraji, H. R. Anal. Chim. Acta 004, 510, Ghasemi, J.; Niazi, A. Talanta 004, In Press. 7. Espinosa-Mansilla, A.; Duran-Meras, I.; Salinas, F. J. Pharm. Biomed. Anal. 1998, 17, Navalon, A.; Blanc, R.; del Olmo, M.; Vilchez, J. L. Talanta 1999, 48, Ribone, M. E.; Pagani, A. P.; Olivieri, A. C. J. Pharm. Biomed. Anal. 000, 3, Walash, M. I.; Sharaf-El-Din, M. K.; Metwally, M. E. S.; Shabana, M. R. J. Chin. Chem. Soc. 005, 5, Wiberg, K.; Sterner-Molin, A.; Jacobsson, S. P. Talanta 004, 6, 567.