1. Introduction. Pharmazie 71 (2016) 683 ORIGINAL ARTICLES

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1 Pharmaceutical Chemistry Department 1, The Center for Drug Research and Development (CDRD) 2, Faculty of Pharmacy, British University in Egypt, El-Sherouk City; Analytical Chemistry Department 3, Faculty of Pharmacy, Ain Shams University, Abbassia, Cairo, Egypt A guide for using experimental design in chromatographic method development: applied to the analysis of selected anti-diabetic pharmaceutical combinations B. M. AYOUB 1, 2, O. ABDEL-AZIZ 3 Received June 11, 2016, accepted August 20, 2016 Bassam M. Ayoub, Pharmaceutical Chemistry Department, The Center for Drug Research and Development (CDRD), Faculty of Pharmacy, British University in Egypt, El-Sherouk City, Cairo 11837, Egypt bassam.ayoub@bue.edu.eg Pharmazie 71: (2016) doi: /ph A guide experimental design in chromatographic method development was described and applied successfully to the analysis of different recently approved anti-diabetic pharmaceutical combinations. Enhancement of UHPLC analysis of alogliptin benzoate either with pioglitazone hydrochloride or with metformin hydrochloride was achieved. The optimal chromatographic conditions were not attained by trial and error that requires a large number of experiments. Alternatively, a computer program was used as a systematic optimization strategy for the design of the experiment which accurately predicts the combined effect of different factors simultaneously. Resolution between peaks was studied by the proposed fractional factorial design approach performed by the Minitab Program using screening and optimization steps. Application of the central composite design was implemented. A Pareto chart was used to exclude the insignificant variables. Linearity ranges were found to be μg ml -1, 1-20 μg ml -1 and 1-32 μg ml -1 for alogliptin benzoate, pioglitazone hydrochloride and metformin hydrochloride, respectively. The proposed method is applicable for the analysis of six pharmaceutical dosage forms namely, Nesina, Actos, Glucophage, Oseni, Kazano and Actoplus MET tablets. 1. Introduction Most analytical approaches for chromatographic method development are holding the conditions constant except for the variable under investigation. A more advanced statistical method was applied in the present work handling the data to improve the understanding of the variables and extract the most useful information using the lowest possible number of runs. Chromatographic data processed by factorial design of experiment (DOE) included a reasonable number of samples and variables in order to achieve a good information output. Resolution between peaks was selected to monitor the efficiency of the chromatographic variables as increasing resolution means more separated peaks with high analysis outcomes. Improved medication compliance for diabetic patients is usually accomplished through combination therapy. Recently approved Oseni and Kazano tablets are examples for mixed therapy. Oseni is composed of alogliptin benzoate and pioglitazone hydrochloride while Kazano is composed of alogliptin benzoate and metformin (Saisho et al. 2015). Alogliptin benzoate (ALG), 2-({6-[(3R)-3-aminopiperidin-1-yl]- 3-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl}methyl) Fig. 1: Chemical structures of Alogliptin (a), Pioglitazone (b) and Metformin (c). 683

2 Table (1): Screening of the investigated variables Experiments A B C D E F A: Methanol: acetonitrile ratio B: Column temperature C: Buffer ratio in mobile phase D: Flow rate E: ph of the buffer F: Concentration of the ion pairing reagent Table (2): Alias structure using design generators showing the interaction between different factors 1 I + ABCE + ADEF + BCDF 2 A + BCE + DEF + ABCDF 3 B + ACE + CDF + ABDEF 4 C + ABE + BDF + ACDEF 5 D + AEF + BCF + ABCDE 6 E + ABC + ADF + BCDEF 7 F + ADE + BCD + ABCEF 8 AB + CE + ACDF + BDEF 9 AC + BE + ABDF + CDEF 10 AD + EF + ABCF + BCDE 11 AE + BC + DF + ABCDEF 12 AF + DE + ABCD + BCEF 13 BD + CF + ABEF + ACDE 14 BF + CD + ABDE + ACEF 15 ABD + ACF + BEF + CDE 16 ABF + ACD + BDE + CEF A Methanol:acetonitrile ratio B Column temperature C Buffer ratio in mobile phase D Flow rate E ph of the phosphate buffer F Concentration of the ion pairing reagent benzonitrile (Fig. 1a) belongs to dipeptidyl-peptidase-4 inhibitors. Pioglitazone hydrochloride (PGN), ((RS)-5-(4-[2-(5-ethylpyridin- 2-yl) ethoxy] benzyl) thiazolidine-2,4-dione (Fig. 1b) is a thiazolidinedione. Metformin hydrochloride (MET), N,N-dimethylimidodicarbonimidic diamide (Figure 1c) is a biguanide usually used in combination therapy of diabetes mellitus (Saisho et al. 2015). Some liquid chromatographic methods have been described for determination of ALG in tablets either with MET (Thangabalan et al. 2014; Kumar et al. 2013; Sri et al. 2013; Runja et al. 2016; Swathi et al. 2015, or with PGN (Kashyap and Srinivasa 2014; Neelima at al. 2014; Ahmed et al. 2014; Mabrouk et al. 2016). The present work describes the first UHPLC method for the simultaneous determination of ALG, PGN and MET in the recently approved pharmaceutical preparations 684 Oseni (ALG & PGN) and Kazano (ALG & MET). Moreover, the developed UHPLC method is suitable for further quality control applications of other pharmaceutical dosage forms namely, Nesina (ALG), Actos (PGN), Glucophage (MET) and Actoplus MET (PGN and MET) tablets. In addition, UHPLC operates at much higher pressure than HPLC with enhanced resolution between peaks and shorter run times accompanied with significant reduction in solvent use. Optimization of the chromatographic conditions was performed by DOE using Minitab program with the advantage of estimating more than one factor simultaneously (Hibbert 2012). Furthermore, the developed UHPLC method has the following major advantagees over the routine HPLC methods found in the literature for the determination of ALG either with MET or with PGN: simultaneous determination of three drugs using one validated method for the analysis of different pharmaceutical combinations, detection at more sensitive wavelengths for the studied drugs, better resolution between peaks, adjusted ph less than pka of the considered drugs by more than two units, higher sensitivity verified by lower LOD and LOQ values and high analysis outcomes. Finally, referring to the reported methods; detection of MET at 254 nm [Kumar et al. 2013) was not linear in the range applied and not accurate according to MET spectra which is approximately equal zero at 254 nm. Also, using mobile phases with ph values greater than 4 (Kumar et al. 2013; Runja et al. 2016) led to deformed peaks with low resolution in the preliminary trials. LOQ range of ALG (10-25 μg/ml) (Thangabalan et al. 2014; Kumar et al. 2013; Sri et al. 2013), was not applicable to Kazano tablet analysis with the ratio of (17 ALG: 500 MET) leading to an increase in the required concentration of MET with extreme peak deformation. Using detection wavelength of 290 nm (Swathi et al. 2015) failed to show any peaks for MET. 2. Investigations, results and discussion 2.1. Method development using central composite design (CCD) An experimental design was used successfully for optimization of chromatographic conditions. Fractional factorial design using the CCD was applied using Minitab software. The primary investigated isocratic elution showed good results. Increasing column temperature enhanced the resolution of the eluted peaks so it was studied in the DOE. A cyano column was used for determination of single gliptins (El-Bagary et al. 2012a,b) while C 18 column was used for determina-

3 Table (3): Optimization of the significant variables Experiments A B C D tion of different gliptins combinations (Ayoub 2015; El-Bagary et al. 2013), so a C 18 column was selected for the present work. The diode array detector was operated at 220 nm to enhance the simultaneous determination of the three drugs with high sensitivity, the other lambda max (λ max ) of the drugs was investigated using a diode array detector and showed lower sensitivity than 220 nm including 237 nm (λ max of MET), 269 nm (λ max of PGN) and 275 nm (λ max of ALG). Buffer ph was optimum in the acidic region (3 and 3.5) to ensure its value below the pka of the studied drugs by more than two as the studied drugs are hydrochloride and benzoate salts. Different parameters affecting the chromatographic conditions were screened using fractional factorial (1/4) experimental design (Table 1). The studied factors included: (A: methanol to acetonitrile ratio) with 0.5:1 ratio as the low level and 2:1 ratio as the high level, (B: Column temperature, 20 C as -1 and 50 C as +1), (C: Buffer ratio in the mobile phase, 50% as -1 and 90% as +1), (D: Flow rate, 0.1 as -1 and 0.5 as +1), (E: ph of the phosphate buffer, 3 as -1 and 4 as +1) and (F: concentration of the ion pairing reagent, 0.1% as -1 and 0.5% as +1). Alias structure (Table 2) was constructed using design generators (E=ABC, F=BCD) to show the interaction between the studied factors. The factors whose p-values were less than 0.05 were considered as statistically significant (Fig. 2). In the optimization step, response surface methodology (RSM) was applied (Table 3). The estimated regression coefficients of the analysis were calculated using coded units. CCD was composed of sixteen cube points and seven center points in the cube (Figs. 3-6). After interpretation of the developed pareto charts and contour plots, it was observed that ph of the buffer (between 3 and 4) and concentration of the ion pairing reagent were found statistically non-significant. Methanol: acetonitrile ratio and column temperature were optimum at the high level (+1) while the flow rate was optimum at the low level (-1). Amount of buffer was optimum at the high level for the resolution between the first two peaks (MET and ALG) and it was optimum at the low level for the resolution between the last two peaks (ALG and PGN) so the intermediate level (center point of the estimation) was used System suitability tests N (number of theoretical plates) was found to be 1884, 3653 and 4857 for MET, ALG and PGN respectively. T (tailing of peaks) was found to be 1.01, 1.02 and 1.04 for MET, ALG and PGN respectively. The resolution between MET and ALG peaks (R1) was equal to 4.24 while the resolution between ALG and PGN peaks (R2) was equal to Percent relative standard deviation (% RSD) of the peak areas and retention times for six repeated injections of the ternary mixture of the studied drugs was within the acceptable range ( ) which is below 1 % that guarantee a reproducible valid method Method validation according to ICH Linearity Linearity ranges were found to be 1-32 μg ml -1, μg ml -1 and 1-20 μg ml -1 for MET, ALG and PGN, respectively. The regression equations of calibration curves were computed. For MET (AUP = C μg/ml , r = 1), for ALG (AUP = C μg/ml , r = ) and for PGN (AUP = C μg/ml , r = ). The regression parameters were calculated. STEYX was found to be 0.14, and for MET, ALG and PGN, respectively. In addition, S b and S a values of ( ), ( ) and ( ) were acceptable for MET, ALG and PGN, respectively. Limit of detection (LOD) and limit of quantification (LOQ) showed values of ( μg/ml), ( μg/ml) and ( μg/ml) for MET, ALG and PGN, respectively. Where; STEYX is the residual standard deviation of the regression line, S b is the standard deviation of the slope, S a is the standard deviation of the intercept and S is the slope obtained from the calibration curve Accuracy and precision The validation samples prepared as described under were analyzed three times (n = 3) within the same day and also on three successive days. Accuracy of the results was verified through calculation of percent recoveries of five concentrations of each drug. Besides, accuracy of the results was confirmed by percent recovery of each drug in its laboratory prepared mixture. The mean of the percent recoveries of the validation samples and the laboratory prepared mixture was found to be ( % %), (99.96 % %) and ( % %) for MET, ALG and PGN, respectively. While precision was checked by percent relative standard deviation (% RSD) of the measured recoveries and found to be below 1 % for both intraday and interday precision Robustness Robustness was ascertained by studying the resolution factor between the two peaks of MET and ALG (R1) and also resolution between ALG and PGN peaks (R2). After changing flow rate from 0.1 ml min -1 to 0.98 ml min -1 and ml min -1, the resolution factors (R1 - R2) obtained were ( ), ( ) and ( ), respectively. While after changing the proportion of methanol from 30 % to be 29 % and 31 %, the resolution factors (R1 - R2) obtained were ( ), ( ) and ( ), respectively. Furthermore, when the previous modification was repeated using acetonitrile variation instead of methanol, (R1 - R2) obtained were ( ), ( ) and ( ), respectively. In addition, after the column temperature was changed from 50 C to 49 C and 51 C, (R1 - R2) obtained were ( ), ( ) and ( ), respectively. Finally, the value of the ph of the phosphate buffer was varied from 3.5 to 3.4 and 3.6, and the (R1 - R2) obtained were ( ), ( ) and ( ), respectively. There was no significant difference in the results indicating a good robustness of the proposed method. 685

4 ORIGINAL ARTICLES Fig. 2: Pareto charts of R1 and R2, (R1 represents the resolution between MET and ALG peaks while R2 represents the resolution between ALG and PGN peaks). Fig. 3: Contour plot of the resolution between MET and ALG peaks (R1) Specificity 2.4. Conclusion Specificity was checked by analyzing each drug in laboratory prepared mixtures and in pharmaceutical dosage forms (Fig. 7). The results obtained for the calculated concentrations including the mean of the recovery and the standard deviation were 98.68±1.66 %, 101.1±0.83 %, and 99.83±1.13 % for MET, ALG and PGN, respectively. The proposed UHPLC method is sensitive and robust for the simultaneous determination of ALG, PGN and MET using experimental design with the greater availability of statistical software. DOE was performed by Minitab Program as screening and optimization steps with the advantage of estimating more than one factor simultaneously 686

5 ORIGINAL ARTICLES Fig. 4: Surface plot of the resolution between MET and ALG peaks (R1). 687

6 Fig. 5: Contour plot of the resolution between ALG and PGN peaks (R2). Fig. 6: Surface plot of the resolution between ALG and PGN peaks (R2). in all their possible combinations. Central composite design was used to determine the significant variables and optimize the chromatographic conditions with the lowest number of runs. The method was applied successfully on the pharmaceutical dosage forms and will be of interest to the analysts in the area of drug control for the recently approved alogliptin combinations, Oseni and Kazano tablets, as one validated method applicable also on other dosage forms namely, Nesina, Actos, Glucophage and Actoplus MET tablets. It is worth to mention that the proposed work is the first method that applies UHPLC technique for the simultaneous analysis of the 688 three studied drugs rather than HPLC. UHPLC is advantageous in terms of withstanding the high system back pressure and fewer consumables. Also the method was developed after optimizing the chromatographic conditions using DOE. Using DOE is getting more attention as FDA guidelines recommend the use of DOE approach in analytical methods development (FDA 2009) to change the variables of the chromatographic conditions simultaneously over a set of planned experiments in which all factors are varied together while the traditional method development by change one factor at a time ignores interaction between several factors (Hibbert 2012).

7 Fig. 7: a) UHPLC chromatogram of a laboratory prepared mixture of MET (30 μg ml -1 ) at 2.3 min, ALG at 4.4 min (10 μg ml -1 ) and PGN (15 μg ml -1 ) at 8.3 min. b) UHPLC chromatogram of Oseni tablet containing ALG (34 μg ml -1 ) at 4.4 min and PGN (16.5 μg ml -1 ) at 8.3 min. c) UHPLC chromatogram of Kazano tablet containing MET (29.5 μg ml -1 ) at 2.3 min and ALG (1 μg ml -1 ) at 4.4 min. 3. Experimental 3.1. Instrumentation Thermo Fisher UPLC Model Ultimate (3000, USA), Symmetry Acclaim C 18 column ( mm, 2.2 μm), Diode array detector (3000 RS, USA), autosampler (3000 TRS, USA) and Elmasonic (S60H, Germany) were used Reagents, reference samples and working solutions Pharmaceutical grade MET, ALG and PGN certified to contain 99.7 %, 99.7 % and 99.8 %, respectively, Oseni tablets (34 mg of ALG and 16.5 mg of PGN) and Kazano tablets (17 mg of ALG and 500 mg of MET) were supplied from Takeda pharmaceutical company (Japan). HPLC grade acetonitrile and methanol were purchased from Fisher Scientific (UK). HPLC grade potassium dihydrogen phosphate and orthophosphoric acid were purchased from Sigma Aldrich (Germany). Working solutions of MET (40 μg ml -1 ), ALG (50 μg ml -1 ) and PGN (20 μg ml -1 ) were prepared using the mobile phase Chromatographic conditions The optimized mobile phase was a mixture of phosphate buffer ph (3.5), methanol and acetonitrile in the ratio of (70:20:10, v/v/v) using C 18 column as a stationary phase accompanied with ultraviolet detection at 220 nm, 50 C as the column temperature, 10 μl as the injection volume and 0.1 ml min -1 as the flow rate Sample preparation Two samples were prepared for Oseni and Kazano tablets separately. In each preparation, accurately weighed amounts of Oseni tablets (34 mg ALG, 16.5 mg PGN) and 689

8 Kazano tablets (1 mg ALG, 29.5 mg MET) were separately made up to 100 ml with methanol, sonicated, filtered, then ten milliliters of both Oseni and Kazano tablets extracts were separately transferred to different 100 ml volumetric flasks and finally completed to volume with the mobile phase. The final concentration of the diluted Oseni tablet extract is 34 μg ml -1 of ALG and 16.5 μg ml -1 of MET while the final concentration of the diluted Kazano tablet extract is 1 μg ml -1 of ALG and 29.5 μg ml -1 of MET Procedures Linearity Accurately measured aliquots of working solutions (prepared under 3.2) equivalent to μg, μg and μg of MET, ALG and PGN, respectively were transferred separately into a series of 10 ml volumetric flasks, completed to volume with the mobile phase to prepare calibrators equivalent to 1, 2, 4, 8, 16 and 32 μg ml -1 of MET, equivalent to 0.5, 5, 10, 20, 30 and 40 μg ml -1 of ALG and equivalent to 1, 2, 4, 8, 16 and 20 μg ml -1 of PGN. Ten micro liters were injected to the UHPLC system using chromatographic conditions mentioned under 3.3. The calibration curves were obtained for the three drugs Assay of MET, ALG and PGN in bulk, lab prepared mixture, Oseni and Kazano tablets The procedure mentioned under was repeated using validation samples equivalent to 3, 6, 12, 20 and 28 μg ml -1 of MET, equivalent to 2.5, 7.5, 15, 25 and 35 μg ml -1 of ALG and equivalent to 1.5, 3, 6, 12 and 18 μg ml -1 of PGN. Also a mixture of MET, ALG and PGN was prepared as a laboratory prepared mixture equivalent to (30 μg ml -1 of MET, 10 μg ml -1 of ALG and 15 μg ml -1 PGN) and analyzed by the same procedure. For assay of the drugs in Oseni and Kazano tablets, the procedure was applied on the sample solutions prepared under Precision of the method The validation samples prepared as described under were analyzed three times within the same day to examine repeatability of the method and on three successive days to check the intermediate precision Robustness of the method Flow rate was changed from 0.1 ml min -1 to 0.98 ml min -1 and ml min -1. The proportion of methanol (30%) was changed by ±1% to be 29% and 31%. Furthermore, the previous modification was repeated using acetonitrile variation instead of methanol variation. Column temperature was changed from 50 C to 49 C and 51 C. Finally, the value of the ph of the phosphate buffer was varied from 3.5 to 3.4 and 3.6. Acknowledgement: The present work was funded by The British University in Egypt. Conflicts of interest: None declared. 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