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Simultaneous determination of methocarbamol and ibuprofen or diclofenac potassium using mean centering of the ratio spectra method

Simultaneous determination of methocarbamol and ibuprofen or diclofenac potassium using mean... Acta Pharm. 62 (2012) 191­200 DOI: 10.2478/v10007-012-0016-z Original research paper NOURUDDIN WAGEIH ALI1* MAHA AHAMD HEGAZY2 MOHAMED ABDELKAWY2 EGLAL ABDELAHAMID ABDELALEEM1 1 Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy Beni-Suef University, Beni-Suef, Egypt Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt Accurate and sensitive methods were developed for simultaneous determination of methocarbamol and ibuprofen or diclofenac potassium in their binary mixtures, and in the presence of a methocarbamol related substance (guaifenesin) using mean centering of the ratio spectra method. The results obtained were statistically compared with the reported HPLC methods; no significant difference between the proposed methods and the reported methods was found regarding either accuracy or precision. Keywords: methocarbamol, diclofenac potassium, ibuprofen, mean centering of ratio spectra, guaifenesin Accepted April 16, 2012 Methocarbamol (ME), 2-hydroxy-3-(2-methoxyphenoxy) propyl carbamate (Fig. 1a), is a centrally acting skeletal muscle relaxant whose action may be due to its general depressant effects on the CNS. It is used as an adjunct in the short-term symptomatic treatment of painful muscle spasms associated with musculoskeletal conditions and is sometimes given with analgesics for musculoskeletal pain treatment (1, 2). Ibuprofen (IB), 2-(4-isobutylphenyl) propionic acid (Fig. 1b), and diclofenac potassium (DI), potassium [o-(2,6-dichloroanilino)phenyl] acetate (Fig. 1c), are non-steroidal drugs with anti-inflammatory, antipyretic and analgesic properties (1). ME formulated with either IB or DI is frequently prescribed to alleviate pain associated with muscle spasm. Guaifenesin (GU), 3-(2-methoxyphenoxy)-propane-1,2-diol (Fig. 1d), is considered as a substance related to ME (1). Moreover, GU may be produced by ME hydrolysis, especially in alkaline medium, and hence it is also considered to be the main degradation product of ME (2). * Correspondence; e-mail: dr.nourali@hotmail.com a) c) CO2K O H3CO OH NH2 NH Cl Cl b) CH3 CH3 COOH H3C Fig 1. Chemical structure of: a) methocarbamol, b) ibuprofen, c) diclofenac potassium. There are many reports on the determination of ME, IB, DI and GU separately or in combination with other drugs. Only a few methods have been reported for determination of either ME and IB or ME and DI in binary mixtures (3­12). Only one method has been reported for determination of ME and DI in the presence of GU (13). This is an HPLC method that uses gradient elution and different wavelengths. Non of the reported spectrophotometric methods can be applied for simultaneous determination of binary mixtures of ME and IB. No methods have been reported for determination of ME and IB in the presence of GU. Therefore, the objective of this work was to develop, simple, a sensitive and selective method for the determination of ME and its related substance GU in ternary mixtures with IB and DI. This is the first report on the determination of ME and IB in the presence of GU. EXPERIMENTAL Standard samples and reagents Standard ME and DI with certified purity of 99.80 and 99.97 %, respectively, were kindly supplied by October Pharma S.A.E., Egypt. Standard IB with certified purity of 100.06 % was kindly supplied by El Kahira Co., Cairo, Egypt. Standard GU with certified purity of 99.95 % was kindly supplied by RAMEDA Co., Egypt. All other reagents and chemicals used were of analytical grade and were used without further purification. Methanol HPLC grade was from SDS, France. Pharmaceutical formulations Ibuflex® tablets were manufactured by Global Napi Pharmaceuticals. Each tablet is claimed to contain 750 mg of ME and 400 mg of IB. Dimra® tablets were manufactured by October Pharma S.A.E., Egypt. Each tablet is claimed to contain 500 mg of ME and 50 mg of DI. Instruments and conditions A double beam UV-Visible spectrophotometer (Shimadzu, Japan) model UV-1601 PC with a quartz cell of 1 cm pathlength, connected to an IBM compatible computer, was used. The software was UVPC personal spectroscopy software version 3.7. All computations were performed in Matlab for WindowsTM version 6.5. For HPLC analyses (3, 4), an HPLC (Shimadzu) instrument equipped with a model series LC-10 ADVP pump, SCL-10 AVP controller, DGU-12 A degasser and SPD-10 AVP UV-VIS detector was used. Separation and quantitation were made on a 250 ´ 4.6 mm (i.d.) RP C18 column (4.6 mm particle size). Standard solutions Stock solutions for each of ME, IB and DI (1 mg mL­1) were prepared by dissolving pure powder in methanol. The latter were diluted to 10 mg mL­1 with 0.1 mol L­1 HCl. Each stock solution of ME, IB and DI was separately diluted ten times with methanol to get a 100 mg mL­1 working solution of each of them. Analytical procedures The absorption spectra of 10 mg mL­1 of each of ME, DI, IB and GU in 0.1 mol L­1 HCl were recorded over the range 200­400 nm using 0.1 mol L­1 HCl as blank. Linearity and calibration curves. ­ Aliquots equivalent to 40­200 mg ME and 40­220 mg IB were transferred from their working standard solutions (100 mg mL­1) into two series of 10-mL volumetric flasks, the volume was made up to the mark with 0.1 mol L­1 HCl to obtain final concentration solutions of 4­20 mg mL­1 for ME and 4­22 mg mL­1 for IB. Absorption spectra of the resulting solutions were measured in the range of 210­240 nm. Scanned spectra of ME were divided by the absorption spectrum of 4 mg mL­1 of IB; the same was applied to the spectra of IB divided by 4 mg mL­1 ME spectrum and the obtained ratio spectra were mean centered for ME and IB mixture. The mean centered values at 218.4 nm for both ME and IB were recorded and plotted vs. the corresponding concentrations. Regression equations were then computed. Aliquots from working standard solutions (100 mg mL­1) equivalent to 40­200 mg ME and 30­120 mg DI were also transferred into two series of 10-mL volumetric flasks and the volume was made up with 0.1 mol L­1 HCl to get final solutions of 4­20 mg mL­1 for ME and 3­12 mg mL­1 for DI. Absorption spectra of the resulting solutions were measured in the range of 220­285 nm. Scanned spectra of ME were divided by the absorption spectrum of 6 mg mL­1 of DI while the spectra of DI were divided by the absorption spectrum of 18 mg mL­1 of ME and the obtained ratio spectra were mean centered. The mean centered values at 279.4 and 260.6 nm for ME and at 260.8 nm for DI were plotted vs. the corresponding concentrations, and regression equations were computed. Analysis of laboratory prepared mixtures. ­ Different mixtures containing ME and IB or DI in different ratios were prepared. The procedure for each mixture was followed as mentioned above. Concentrations of ME, IB, DI and GU were calculated by the corresponding regression equation. Application to pharmaceutical preparations. ­ Ten tablets of Ibuflex® were accurately weighed, then thoroughly powdered and mixed. An accurate weight of mixed powder equivalent to 750 mg of ME and 400 mg of IB was transferred into a 250-mL beaker, 50 mL methanol were added and stirred magnetically for 10 minutes. The solution was filtered into a 100-mL volumetric flask, and the volume was made up with methanol to obtain a stock solution of concentration equivalent to 7.5 and 4 mg mL­1 of ME and IB, respectively. Appropriate tenfold dilution of this stock solution was made to prepare a solution equivalent to 75 and 40 mg mL­1 of ME and IB, respectively. The procedure detailed under linearity and construction of the calibration curve for each mixture was followed as mentioned above. Concentrations of ME and IB were calculated by the corresponding regression equation. a) Absorbance 0.000 200.0 270.0 Wevelength (nm) 340.0 b) Absorbance 0.000 200.0 270.0 Wevelength (nm) 340.0 Fig. 2. Zero-order absorption spectra in 0.1 mol L­1 HCl for: a) 10 mg mL­1 methocarbamol (.........), 10 mg mL­1 guaifenesin (-) and 10 mg mL­1 ibuprofen (- ­ - ­ -), b) 10 mg mL­1 methocarbamol (.........), 10 mg mL­1 guaifenesin (_) and 10 mg mL­1 diclofenac potassium (- ­ - ­ -). Table I. Regression parameters of the proposed MCR methods for determination of ME with IB or DI Diclofenac potassium 260.8 3­12 100.0 ± 1.0 1.0/2 0.9 1.0 Parameter l (nm) Calibration range (mg mL­1) Model accuracy LOD/LOQ (mg mL­1) Intra-day RSD (%) Inter-day RSD (%) Methocarbamol 218.4 4­20 100.0 ± 0.9 1.5/3.5 0.9 1.2 Ibuprofen 218.4 4­22 100.0 ± 1.6 1.5/3.5 0.9 1.8 Methocarbamol 260.6 4­20 100.0 ± 1.6 1.5/3 0.9 1.1 279.4 4­20 100.2 ± 1.7 1.5/3 0.9 1.1 As for Ibuflex® tablets, an appropriate dilution of stock solution was made to prepare a solution equivalent to 75 and 40 mg mL­1 of ME and DI, respectively. RESULTS AND DISCUSSION The focus of this work was to develop simple, sensitive and accurate analytical methods for simultaneous determination of ME and IB or DI in their binary mixtures. Mean centering of the ratio spectra method (MCR, 14) was applied for simultaneous determination of the studied binary mixtures without prior separation steps. MCR method has the advantage of eliminating the derivative steps and therefore the signal-to-noise ratio is not degraded. Method development and optimization The zero-order absorption spectra of ME and IB or ME and DI mixtures show severe overlapping (Figs. 2a,b), which did not allow us to use direct spectrophotometric measurements for simultaneous determination of ME and IB or DI. The effect of divisor concentration on the analytical parameters such as slope, intercept and correlation coefficient was also tested. For the first mixture, 4 mg mL­1 of IB and ME was used as a divisor for determination of both ME and IB at 218.4 nm. For the the second mixture 6 mg mL­1 of DI was used as a divisor for determination of ME at 260.6 nm and 279.4 nm while 18 mg mL­1 of ME was used as a divisor for determination of DI at 260.8 nm. The chosen divisior concentrations gave good results for the slope, intercept and correlation coefficient of calibration graphs as well as for selectivity. Method validation Method validation was performed according to ICH the guidelines (15) for proposed methods. Linearity of the proposed methods was evaluated and it was evident in the range of 4­20 mg mL­1, 4­22 mg mL­1 for ME and IB, respectively, in the first mixture and 4­20 mg 196 Standard additions Added (mg L­1) Recovery (%) Dimra® tablets 98.0 100.2 99.2 DI Mean ± SDa 102.2 100.9 97.7 ME Mean ± SDa 100.1 ± 0.9 7.00 8.00 10.00 101.0 ± 0.9 6.00 7.50 8.00 Found (mg mL­1)b 8.00 9.00 10.00 Found (mg L­1)b Recovery (%)c Added (mg mL­1) Pharmaceutical formulation Standard additions Recovery (%) 98.2 103.1 101.9 6.00 7.50 9.00 98.6 102.4 103.3 7.84 9.02 9.92 99.1 ± 1.1 6.13 7.57 8.79 100.2 ± 2.3 5.89 7.73 8.15 101.0 ± 2.6 6.90 8.19 10.33 101.4 ± 2.5 Reported HPLC method (3) IB 99.9 0.9 6 100.0 1.0 6 ME DI Proposed MCR method ME 260.6 279.4 Reported HPLC method (4) DI 99.8 1.6 6 ME 99.8 1.7 6 100.0 1.0 7 1.119 (2.200) 2.369 (4.387) 100.0 1.6 6 0.530 (2.228) 1.048 (5.050) 100.2 1.6 6 1.879 (2.228) 1.009 (5.050) Table II. Determination of ME and IB and ME and DI in commercial tablets by the proposed MCR methods and application of the standard addition technique Pharmaceutical formulation Ibuflex® tablets Recovery (%)a IB Mean ± SDa 99.7 ± 1.1 ME Mean ± SDa 100.8 ± 1.3 n = 3, n = 6. Table III. Statistical analysis of the proposed MCR methods and the reported methods for determination of ME, IB and DI in their pure powdered form Proposed MCR method IB ME Mean SD n Student's t-value F-value 100.0 1.6 8 1.149 (2.178) 2.664 (4.875) 100.0 0.9 9 1.054 (2.160) 0.882 (4.818) In parentheses one the tabulated t- and F-values p = 0.05. mL­1, 3­12 mg mL­1 for ME and DI, respectively in the second mixture (Figs. 3a-d). The regression equations for the proposed methods were calculated and found to be: R1 = 0.9999 for ME at 218.4 nm, Y1 = 0.0825 g1 ­ 0.0612 Y2 = 0.0726 g2 + 0.0165 Y3 = 0.0463 g3 ­ 0.0104 Y4 = 0.0785 g4 ­ 0.0173 Y5 = 0.3412 g5 + 0.0548 R2 = 0.9996 for IB at 218.4 nm, R3 = 0.9997 for ME at 260.6 nm, R4 = 0.9997 for ME at 279.4 nm, R5 = 0.9997 for DI at 260.8 nm where, Y1 and Y2 are peak amplitudes at the selected wavelengths for ME and IB, respectively, while Y3, Y4 and Y5 are peak amplitudes at the selected wavelengths for ME (two wavelengths) and DI, respectively; g1 and g2 are the concentrations in mg mL­1 for ME and IB, respectively, while g3, g4 and g5 are the concentrations in mg mL­1 for ME (at a) 1.5 1 b) 2 218.4 nm 1.5 218.4 nm 214 218 222 226 230 234 238 242 0.5 0 ­0.5 ­1 ­1.5 ­2 210 1 0.5 0 ­0.5 ­1 210 c) 5 260.8 nm 4 1.5 d) 2 279.4 nm 3 2 1 0 ­1 ­2 220 1 0.5 0 ­0.5 260.6 nm ­1 220 Fig. 3. The mean centered first ratio absorption spectra in 0.1 mol L­1 HCl for: a) ibuprofen in range 4­22 mg mL­1 using the spectrum of 4 mg mL­1 ME as a divisor, b) methocarbamol in range 4­20 mg mL­1 using the spectrum of 4 mg mL­1 IB as a divisor, c) diclofenac potassium in range 3­12 mg mL­1 using the spectrum of 18 mg mL­1 of ME as a divisor, d) methocarbamol in range 4­20mg mL­1 using the spectrum of 6 mg mL­1 of DI as a divisor. the the the the the corresponding wavelengths) and DI, respectively, whereas R1, R2, R3, R4 and R5 are the respective correlation coefficients at the selected wavelengths. Good linearity is evident from the high value of the correlation coefficients (Table I). Precision of the proposed methods is shown in Table I. Model accuracy of the proposed methods was checked by applying the proposed methods to determination of pure samples of the studied compounds and was found to be 100.0 % for ME and IB and 100.0 and 100.2 % for ME and DI, respectively. Concentrations were calculated from the corresponding regression equations and the results are shown in Table I. Accuracy was further assessed by applying the standard additions technique on Ibuflex® and Dimra® tablets where good recoveries were obtained, revealing no interference from excipients and good accuracy of the proposed methods (99.1 and 100.3 % for IB and ME, respectively, and 101 and 100.1 % for DI and ME, respectively, Table II). Specificity of the proposed methods is evident from the spectra shown in Figs. 3a-d. Robustness of the proposed methods was evaluated in the development phase where the effect of different factors on mean centering of the ratio spectra methods was studied to obtain optimum parameters for complete separation (data not shown). Table III shows statistical comparison of the results obtained by the proposed methods and the reported HPLC methods (3, 4). The calculated t- and F-values are lower than the theoretical ones, indicating that there is no significant difference between the proposed methods and the reported method with respect to accuracy and precision. CONCLUSIONS The proposed methods are simple, selective and precise and could be easily applied for simultaneous determination of ME and IB or ME and DI in their binary mixtures. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Pharmaceutica de Gruyter

Simultaneous determination of methocarbamol and ibuprofen or diclofenac potassium using mean centering of the ratio spectra method

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de Gruyter
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Copyright © 2012 by the
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1330-0075
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10.2478/v10007-012-0016-z
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Abstract

Acta Pharm. 62 (2012) 191­200 DOI: 10.2478/v10007-012-0016-z Original research paper NOURUDDIN WAGEIH ALI1* MAHA AHAMD HEGAZY2 MOHAMED ABDELKAWY2 EGLAL ABDELAHAMID ABDELALEEM1 1 Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy Beni-Suef University, Beni-Suef, Egypt Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt Accurate and sensitive methods were developed for simultaneous determination of methocarbamol and ibuprofen or diclofenac potassium in their binary mixtures, and in the presence of a methocarbamol related substance (guaifenesin) using mean centering of the ratio spectra method. The results obtained were statistically compared with the reported HPLC methods; no significant difference between the proposed methods and the reported methods was found regarding either accuracy or precision. Keywords: methocarbamol, diclofenac potassium, ibuprofen, mean centering of ratio spectra, guaifenesin Accepted April 16, 2012 Methocarbamol (ME), 2-hydroxy-3-(2-methoxyphenoxy) propyl carbamate (Fig. 1a), is a centrally acting skeletal muscle relaxant whose action may be due to its general depressant effects on the CNS. It is used as an adjunct in the short-term symptomatic treatment of painful muscle spasms associated with musculoskeletal conditions and is sometimes given with analgesics for musculoskeletal pain treatment (1, 2). Ibuprofen (IB), 2-(4-isobutylphenyl) propionic acid (Fig. 1b), and diclofenac potassium (DI), potassium [o-(2,6-dichloroanilino)phenyl] acetate (Fig. 1c), are non-steroidal drugs with anti-inflammatory, antipyretic and analgesic properties (1). ME formulated with either IB or DI is frequently prescribed to alleviate pain associated with muscle spasm. Guaifenesin (GU), 3-(2-methoxyphenoxy)-propane-1,2-diol (Fig. 1d), is considered as a substance related to ME (1). Moreover, GU may be produced by ME hydrolysis, especially in alkaline medium, and hence it is also considered to be the main degradation product of ME (2). * Correspondence; e-mail: dr.nourali@hotmail.com a) c) CO2K O H3CO OH NH2 NH Cl Cl b) CH3 CH3 COOH H3C Fig 1. Chemical structure of: a) methocarbamol, b) ibuprofen, c) diclofenac potassium. There are many reports on the determination of ME, IB, DI and GU separately or in combination with other drugs. Only a few methods have been reported for determination of either ME and IB or ME and DI in binary mixtures (3­12). Only one method has been reported for determination of ME and DI in the presence of GU (13). This is an HPLC method that uses gradient elution and different wavelengths. Non of the reported spectrophotometric methods can be applied for simultaneous determination of binary mixtures of ME and IB. No methods have been reported for determination of ME and IB in the presence of GU. Therefore, the objective of this work was to develop, simple, a sensitive and selective method for the determination of ME and its related substance GU in ternary mixtures with IB and DI. This is the first report on the determination of ME and IB in the presence of GU. EXPERIMENTAL Standard samples and reagents Standard ME and DI with certified purity of 99.80 and 99.97 %, respectively, were kindly supplied by October Pharma S.A.E., Egypt. Standard IB with certified purity of 100.06 % was kindly supplied by El Kahira Co., Cairo, Egypt. Standard GU with certified purity of 99.95 % was kindly supplied by RAMEDA Co., Egypt. All other reagents and chemicals used were of analytical grade and were used without further purification. Methanol HPLC grade was from SDS, France. Pharmaceutical formulations Ibuflex® tablets were manufactured by Global Napi Pharmaceuticals. Each tablet is claimed to contain 750 mg of ME and 400 mg of IB. Dimra® tablets were manufactured by October Pharma S.A.E., Egypt. Each tablet is claimed to contain 500 mg of ME and 50 mg of DI. Instruments and conditions A double beam UV-Visible spectrophotometer (Shimadzu, Japan) model UV-1601 PC with a quartz cell of 1 cm pathlength, connected to an IBM compatible computer, was used. The software was UVPC personal spectroscopy software version 3.7. All computations were performed in Matlab for WindowsTM version 6.5. For HPLC analyses (3, 4), an HPLC (Shimadzu) instrument equipped with a model series LC-10 ADVP pump, SCL-10 AVP controller, DGU-12 A degasser and SPD-10 AVP UV-VIS detector was used. Separation and quantitation were made on a 250 ´ 4.6 mm (i.d.) RP C18 column (4.6 mm particle size). Standard solutions Stock solutions for each of ME, IB and DI (1 mg mL­1) were prepared by dissolving pure powder in methanol. The latter were diluted to 10 mg mL­1 with 0.1 mol L­1 HCl. Each stock solution of ME, IB and DI was separately diluted ten times with methanol to get a 100 mg mL­1 working solution of each of them. Analytical procedures The absorption spectra of 10 mg mL­1 of each of ME, DI, IB and GU in 0.1 mol L­1 HCl were recorded over the range 200­400 nm using 0.1 mol L­1 HCl as blank. Linearity and calibration curves. ­ Aliquots equivalent to 40­200 mg ME and 40­220 mg IB were transferred from their working standard solutions (100 mg mL­1) into two series of 10-mL volumetric flasks, the volume was made up to the mark with 0.1 mol L­1 HCl to obtain final concentration solutions of 4­20 mg mL­1 for ME and 4­22 mg mL­1 for IB. Absorption spectra of the resulting solutions were measured in the range of 210­240 nm. Scanned spectra of ME were divided by the absorption spectrum of 4 mg mL­1 of IB; the same was applied to the spectra of IB divided by 4 mg mL­1 ME spectrum and the obtained ratio spectra were mean centered for ME and IB mixture. The mean centered values at 218.4 nm for both ME and IB were recorded and plotted vs. the corresponding concentrations. Regression equations were then computed. Aliquots from working standard solutions (100 mg mL­1) equivalent to 40­200 mg ME and 30­120 mg DI were also transferred into two series of 10-mL volumetric flasks and the volume was made up with 0.1 mol L­1 HCl to get final solutions of 4­20 mg mL­1 for ME and 3­12 mg mL­1 for DI. Absorption spectra of the resulting solutions were measured in the range of 220­285 nm. Scanned spectra of ME were divided by the absorption spectrum of 6 mg mL­1 of DI while the spectra of DI were divided by the absorption spectrum of 18 mg mL­1 of ME and the obtained ratio spectra were mean centered. The mean centered values at 279.4 and 260.6 nm for ME and at 260.8 nm for DI were plotted vs. the corresponding concentrations, and regression equations were computed. Analysis of laboratory prepared mixtures. ­ Different mixtures containing ME and IB or DI in different ratios were prepared. The procedure for each mixture was followed as mentioned above. Concentrations of ME, IB, DI and GU were calculated by the corresponding regression equation. Application to pharmaceutical preparations. ­ Ten tablets of Ibuflex® were accurately weighed, then thoroughly powdered and mixed. An accurate weight of mixed powder equivalent to 750 mg of ME and 400 mg of IB was transferred into a 250-mL beaker, 50 mL methanol were added and stirred magnetically for 10 minutes. The solution was filtered into a 100-mL volumetric flask, and the volume was made up with methanol to obtain a stock solution of concentration equivalent to 7.5 and 4 mg mL­1 of ME and IB, respectively. Appropriate tenfold dilution of this stock solution was made to prepare a solution equivalent to 75 and 40 mg mL­1 of ME and IB, respectively. The procedure detailed under linearity and construction of the calibration curve for each mixture was followed as mentioned above. Concentrations of ME and IB were calculated by the corresponding regression equation. a) Absorbance 0.000 200.0 270.0 Wevelength (nm) 340.0 b) Absorbance 0.000 200.0 270.0 Wevelength (nm) 340.0 Fig. 2. Zero-order absorption spectra in 0.1 mol L­1 HCl for: a) 10 mg mL­1 methocarbamol (.........), 10 mg mL­1 guaifenesin (-) and 10 mg mL­1 ibuprofen (- ­ - ­ -), b) 10 mg mL­1 methocarbamol (.........), 10 mg mL­1 guaifenesin (_) and 10 mg mL­1 diclofenac potassium (- ­ - ­ -). Table I. Regression parameters of the proposed MCR methods for determination of ME with IB or DI Diclofenac potassium 260.8 3­12 100.0 ± 1.0 1.0/2 0.9 1.0 Parameter l (nm) Calibration range (mg mL­1) Model accuracy LOD/LOQ (mg mL­1) Intra-day RSD (%) Inter-day RSD (%) Methocarbamol 218.4 4­20 100.0 ± 0.9 1.5/3.5 0.9 1.2 Ibuprofen 218.4 4­22 100.0 ± 1.6 1.5/3.5 0.9 1.8 Methocarbamol 260.6 4­20 100.0 ± 1.6 1.5/3 0.9 1.1 279.4 4­20 100.2 ± 1.7 1.5/3 0.9 1.1 As for Ibuflex® tablets, an appropriate dilution of stock solution was made to prepare a solution equivalent to 75 and 40 mg mL­1 of ME and DI, respectively. RESULTS AND DISCUSSION The focus of this work was to develop simple, sensitive and accurate analytical methods for simultaneous determination of ME and IB or DI in their binary mixtures. Mean centering of the ratio spectra method (MCR, 14) was applied for simultaneous determination of the studied binary mixtures without prior separation steps. MCR method has the advantage of eliminating the derivative steps and therefore the signal-to-noise ratio is not degraded. Method development and optimization The zero-order absorption spectra of ME and IB or ME and DI mixtures show severe overlapping (Figs. 2a,b), which did not allow us to use direct spectrophotometric measurements for simultaneous determination of ME and IB or DI. The effect of divisor concentration on the analytical parameters such as slope, intercept and correlation coefficient was also tested. For the first mixture, 4 mg mL­1 of IB and ME was used as a divisor for determination of both ME and IB at 218.4 nm. For the the second mixture 6 mg mL­1 of DI was used as a divisor for determination of ME at 260.6 nm and 279.4 nm while 18 mg mL­1 of ME was used as a divisor for determination of DI at 260.8 nm. The chosen divisior concentrations gave good results for the slope, intercept and correlation coefficient of calibration graphs as well as for selectivity. Method validation Method validation was performed according to ICH the guidelines (15) for proposed methods. Linearity of the proposed methods was evaluated and it was evident in the range of 4­20 mg mL­1, 4­22 mg mL­1 for ME and IB, respectively, in the first mixture and 4­20 mg 196 Standard additions Added (mg L­1) Recovery (%) Dimra® tablets 98.0 100.2 99.2 DI Mean ± SDa 102.2 100.9 97.7 ME Mean ± SDa 100.1 ± 0.9 7.00 8.00 10.00 101.0 ± 0.9 6.00 7.50 8.00 Found (mg mL­1)b 8.00 9.00 10.00 Found (mg L­1)b Recovery (%)c Added (mg mL­1) Pharmaceutical formulation Standard additions Recovery (%) 98.2 103.1 101.9 6.00 7.50 9.00 98.6 102.4 103.3 7.84 9.02 9.92 99.1 ± 1.1 6.13 7.57 8.79 100.2 ± 2.3 5.89 7.73 8.15 101.0 ± 2.6 6.90 8.19 10.33 101.4 ± 2.5 Reported HPLC method (3) IB 99.9 0.9 6 100.0 1.0 6 ME DI Proposed MCR method ME 260.6 279.4 Reported HPLC method (4) DI 99.8 1.6 6 ME 99.8 1.7 6 100.0 1.0 7 1.119 (2.200) 2.369 (4.387) 100.0 1.6 6 0.530 (2.228) 1.048 (5.050) 100.2 1.6 6 1.879 (2.228) 1.009 (5.050) Table II. Determination of ME and IB and ME and DI in commercial tablets by the proposed MCR methods and application of the standard addition technique Pharmaceutical formulation Ibuflex® tablets Recovery (%)a IB Mean ± SDa 99.7 ± 1.1 ME Mean ± SDa 100.8 ± 1.3 n = 3, n = 6. Table III. Statistical analysis of the proposed MCR methods and the reported methods for determination of ME, IB and DI in their pure powdered form Proposed MCR method IB ME Mean SD n Student's t-value F-value 100.0 1.6 8 1.149 (2.178) 2.664 (4.875) 100.0 0.9 9 1.054 (2.160) 0.882 (4.818) In parentheses one the tabulated t- and F-values p = 0.05. mL­1, 3­12 mg mL­1 for ME and DI, respectively in the second mixture (Figs. 3a-d). The regression equations for the proposed methods were calculated and found to be: R1 = 0.9999 for ME at 218.4 nm, Y1 = 0.0825 g1 ­ 0.0612 Y2 = 0.0726 g2 + 0.0165 Y3 = 0.0463 g3 ­ 0.0104 Y4 = 0.0785 g4 ­ 0.0173 Y5 = 0.3412 g5 + 0.0548 R2 = 0.9996 for IB at 218.4 nm, R3 = 0.9997 for ME at 260.6 nm, R4 = 0.9997 for ME at 279.4 nm, R5 = 0.9997 for DI at 260.8 nm where, Y1 and Y2 are peak amplitudes at the selected wavelengths for ME and IB, respectively, while Y3, Y4 and Y5 are peak amplitudes at the selected wavelengths for ME (two wavelengths) and DI, respectively; g1 and g2 are the concentrations in mg mL­1 for ME and IB, respectively, while g3, g4 and g5 are the concentrations in mg mL­1 for ME (at a) 1.5 1 b) 2 218.4 nm 1.5 218.4 nm 214 218 222 226 230 234 238 242 0.5 0 ­0.5 ­1 ­1.5 ­2 210 1 0.5 0 ­0.5 ­1 210 c) 5 260.8 nm 4 1.5 d) 2 279.4 nm 3 2 1 0 ­1 ­2 220 1 0.5 0 ­0.5 260.6 nm ­1 220 Fig. 3. The mean centered first ratio absorption spectra in 0.1 mol L­1 HCl for: a) ibuprofen in range 4­22 mg mL­1 using the spectrum of 4 mg mL­1 ME as a divisor, b) methocarbamol in range 4­20 mg mL­1 using the spectrum of 4 mg mL­1 IB as a divisor, c) diclofenac potassium in range 3­12 mg mL­1 using the spectrum of 18 mg mL­1 of ME as a divisor, d) methocarbamol in range 4­20mg mL­1 using the spectrum of 6 mg mL­1 of DI as a divisor. the the the the the corresponding wavelengths) and DI, respectively, whereas R1, R2, R3, R4 and R5 are the respective correlation coefficients at the selected wavelengths. Good linearity is evident from the high value of the correlation coefficients (Table I). Precision of the proposed methods is shown in Table I. Model accuracy of the proposed methods was checked by applying the proposed methods to determination of pure samples of the studied compounds and was found to be 100.0 % for ME and IB and 100.0 and 100.2 % for ME and DI, respectively. Concentrations were calculated from the corresponding regression equations and the results are shown in Table I. Accuracy was further assessed by applying the standard additions technique on Ibuflex® and Dimra® tablets where good recoveries were obtained, revealing no interference from excipients and good accuracy of the proposed methods (99.1 and 100.3 % for IB and ME, respectively, and 101 and 100.1 % for DI and ME, respectively, Table II). Specificity of the proposed methods is evident from the spectra shown in Figs. 3a-d. Robustness of the proposed methods was evaluated in the development phase where the effect of different factors on mean centering of the ratio spectra methods was studied to obtain optimum parameters for complete separation (data not shown). Table III shows statistical comparison of the results obtained by the proposed methods and the reported HPLC methods (3, 4). The calculated t- and F-values are lower than the theoretical ones, indicating that there is no significant difference between the proposed methods and the reported method with respect to accuracy and precision. CONCLUSIONS The proposed methods are simple, selective and precise and could be easily applied for simultaneous determination of ME and IB or ME and DI in their binary mixtures.

Journal

Acta Pharmaceutica – de Gruyter

Published: Jun 1, 2012

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