A Novel Stability Indicating Rp-Uplc-Dad Method for Determination of Metformin and Empagliflozin in Bulk and Tablet Dosage form

The objective of the present work was to develop and validate a novel stability indicating RP-UPLC-DAD method for the simultaneous analysis of Metformin and Empagliflozin in bulk and tablet dosage form. This new RP-UPLC method has superior in technology to formal Reverse phaseHPLC with retention time, solvent utilization, resolution and less cost. The peak area separation was accomplished on a Waters model UPLC system equipped with PDA detector and autosampler. A volume of 5 μL of sample and standard were injected into the column and all analytes were separated by using the mobile phase contains mixture 0.1% ortho phosphoric acid buffer (the pH was adjusted to 3.4 with 0.1 N NaOH) and methanol in the ratio 40:60% v/v at a flow rate of 0.25ml/ min through C18 BEH(Ethylene Bridged Hybrid) UPLC (100mm x 2.1mm ,1.8μm) at 350C column temperature and the detector wavelength was set at 254 nm. The system suitable parameters such as tailing factor , resolution and plate count of two drugs were 1.16 , 1.37 ;3.47 ;2314.34 and 4723 respectively. Retention time and peak area and of Metformin and Empagliflozin were found to be 0.882 & 3.471, 4887835 & 163463 respectively. Regression equation shows an r value (correlation coefficient) of greater than 0.999 for Metformin and Empagliflozin. Percent recovery of Metformin and Empagliflozin was found to be 99.92%-100.12% & 100.12%-100.56% respectively .Both Metformin and Empagliflozin were subjected to stress conditions such as acidic, basic, oxidative, thermal and photo degradation but substantial degradation was observed in acid studies. The newly developed RP-UPLC-DAD chromatographic method was validated with regard of system suitability, linearity, robustness, accuracy, , LOD ,precision and LOQ.


INTRODUCTION
Metformin is now established as a first choice drug for all type 2 diabetes mellitus patients, except when not tolerated or contraindicated it suppress hepatic gluconeogenesis and glucose output from liver.This is the major action responsible for lowering of blood glucose in diabetics.Enhance insulin mediated glucose uptake and disposal in skeletal muscle and fat.Insulin resistance exhibited by type II diabetics is thus overcome [1][2] .Worldwide most of the patients with type II diabetes mellitus are commonly accomplished with a singular-agent therapy, generally metformin and it is a good and most commonly used antihyperglycemic agent which enhance the glucose margin in type 2 diabetes patients, lowering both postprandial and basal plasma glucose.Metformin molecular formula C 4 H 11 N 5 .HCl was and molecular weight 165.62 [3][4][5][6] it is a white crystalline compound ,Structure of Metformin shown in Fig 1.
Practically all the glucose particles filtered at the glomerulus and it is reabsorbed in the proximal tubules The major transporter which accomplishes this is sodium glucose cotransporter-2 ,whose inhibition induces glycosuria and lowers blood glucose in type 2 DM, as well as causes weight loss.This SGLT-2 inhibitor Empagliflozin has been recently tested in type 2 DM patients .After single daily dose it lowers blood glucose levels 7-9 .Fast estimation of Metfor min and Empagliflozin in with more difference in label claims (Empagliflozin for 5 mg and Metformin for 500 mg) with short run time is a good challenge.For UPLC based analysis , the method of decreasing assays time effectively while resolving analytes from degraded products is often attained with column with small particles.L i t e r a t u r e s u r vey b r i n g s o u t t h a t Empagliflozin is determined by UV spectrophotometric method [12][13][14] , RP-HPLC method [15][16][17][18] , very less chromatographic methods were available for simultaneous determination of Metformin and Empagliflozin in bulk and tablet dosage form by using RP-HPLC [19][20][21][22][23][24] , UPLC 25 .

Empagliflozin chemically, n-Glucitol
The analytical method development and validation of Metformin and Empagliflozin using Gas liquid /Mass spectrometry and Liquid chromatography /Mass spectrometry were expensive and very delicate methods as compared with the UPLC for general analysis, hence it needs to use this UPLC -DAD technique for determination of stability studies by using RP-UPLC-DAD method Metformin and Empagliflozin in bulk and tablet dosage form.

Instrumentation and Equipments
The UPLC waters system was used for the stability indicating method development and method validation .It consists of binary solvent manager with connected with photo diode array detector (MA,USA) controlled with Empower software and auto sampler and auto injector.C18 BEH (Ethylene Bridged Hybrid) UPLC (100mm x 2.1mm ,1.7µm) column was used

Solution preparations
Preparation of mobile phase 0.1% ortho phosphoric acid buf/fer solution was accurately prepared by taking 1 ml ortho phosphoric acid in 1000 ml volumetric flask and dissolved it in water then made up to the mark by adjust the pH of solution to pH =3.4 with 0.1 N NaOH solution.Then filtered the resulting solution through 0.45µ filter under vacuum filtration.Mixture of ortho phosphoric acid buffer and methanol in the ratio 40:60% v/v was taken in a flask, degassed in ultrasonic water bath for 5 minutes allowed to cool at room temperature and then filtered through 0.45 µ filter under vacuum filtration.This prepared mobile phase was used as diluent.Preparation of standard solution W e i g h e a c c u r a t e l y a n d t r a n s f e r 100 g Metformin and 10 mg Empagliflozin working standard into a 10 ml clean dry volumetric flask and add about 7 ml of and sonicated to dissolve it totally and make up the volume to the up mark with the diluent.(Stock solution).After that pipette out 0.3 ml of the above solutions into a 10ml dry volumetric flask and dilute up to the mark with diluent.

Preparation of sample solution
Weighe accurately 10 tablets crush in mortar and pestle and transfer equivalent to 500mg Metformin and 5mg Empagliflozin sample into a 10 ml clean dry volumetric flask add about 7 ml of diluent and sonicated it up to 30 mins to dissolve it completely and make up the volume up to the mark with with the diluent.Then it is filtered through 0.44 micron injection filter.After that pipette out 0.3 ml of Metformin and Empagliflozin from the above stock solution into a 10ml dry volumetric flask and dilute up to the mark with diluent and inject 5 mL of the standard and sample into the RP-UPLC system.

Chromatographic conditions
Chromatographic column used was C18

Method validation System suitability parameters
A system suitability test method was expressed based on the parameters results obtained in different chromatograms.The concentration of standard solution was 300 µg/ml for Metformin and 30 µg/ml for Empagliflozin respectively.The efficiency of column resolute from the analyte peak >20, 000, the tailing factor <5.0% and resolution between peaks of two drugs should be >1.5.

Precision
Precision was evaluated by studying the intermediate precision and repeatability .Precision of each sample was determined by six replicate injections at a concentration of 100µg/ml of Metformin and 10 µg/ml of Empagliflozin respectively.

Accuracy
To evaluate the accuracy of proposed method, recovery studies were conducted, it is determined in three times at three different levels of concentration i.e. 80%, 100%, 120% in tablet dosage and bulk form.

Linearity
The linearity of analytical method was determined by measuring different concentrations of standard solutions to Metformin (25-125 µg/ml) and Empagliflozin (15-75 µg/ml).The calibration curve was obtained by plotting concentration of sample solutions on X-axis and and mean peak areas on Y-axis.

Sensitivity
Sensitivity of the proposed analytical method was determined in terms of limit of limit of quantitation (LOQ) and detection (LOD) .LOQ =10×ASD/S and LOD=3.3×ASD/S.In order to determine both parameters, concentration in the lower part of the linear range of calibration curve were used.

Robustness
The robustness method measures the method capability to it will not affected by very small, but if any deliberate changes in optimized chromatographic conditions was examined by testing influence of small deliberate changes in, change in mobile phase composition (90% to 110%), flow rate (± 0.2 ml/min), column temperature (±5 0 C) using 100µg/ml Metformin and 10 µg/ml Empagliflozin.

Stability studies
In this stability studies , Metformin and Empagliflozin were exposed to different chemical and physical degradation conditions such as 0.1 N HCl (acid degradation), 0.1% N NaoH (base degradation), 30% H 2 O 2 (oxidative degradation),heat (thermal degradation) and Ultra violet light (radiation decay) for defined time intevels ,and then diluted similar as standard stock dilution, and then repragentative chromatograms were obtained .The percentage of degradation compounds were calculated from the peak areas of the Metformin and Empagliflozin chromatograms.In the study of base or acid degradation, an amount of equivalent to powdered sample to 100mg Metformin and 10 mg Empagliflozin was transferred into 10 ml dry volumetric flask and add 3 ml of freshly prepared 0.1 N NaOH or 0.1 N HCl .thenshaken well and allowed for 24 hours at a temperature of 60 0 C.Then filtered the totel solution through 0.45µ filter into 10 ml standard flasks and neutralized the un reacted acid or base i.e 0.1 N HCl or 0.1N NaOH and made up to the mark.In case of oxidative degradation same amount of sample was transferred into 10 ml volumetric flask, add 3 ml of freshly prepared 30%

Fig. 8: Oxidative degradation chromatogram of Metformin and Empagliflozin
H 2 O 2 and kept at 75 0 C for 48 hours and filtered the totel solution through 0.45µ filter and made up to the mark.In the study of thermal decay or Ultra violet light -light degradation , precisely same quantity of sample was transferred into clean and dry watch glass,placed in an hot air oven at 110 0 C .In the study of photo degradation precisely same amount of sample was transferred into 10 ml volumetric flask kept at sunlight for 48 hours and then made up to the mark with diluents.

UPLC method development
UPLC is a new analytical technique used for determination of pharmaceutical formulations and separations mostly in combined drugs and dosage forms .The main plan of this work was to develop a novel stability indicating RP-UPLC method for estimation of Metformin and Empagliflozin.Initial trails were conducted during UPLC method development for optimizing different parameters on the system suitability of the method.
After trying different columns like, cyano, PFP, C8 the last chance of the stationary phase that gave a good resolution and eluting all peaks with better separation was reverse phase C18 BEH UPLC (100mm x 2.1mm 1.8µm particle size) column, this column was only showing retention time less than 1.5 minutes.The the organic solvents acetonitrile and methanol were tried for analytical method development.Compare with acetonitrile, methanol was showing good peak separations and less column back pressure.As we need to analysis of compounds, tried with different mobile phases like phosphate buffer, formic acid, trifloroacetic acid ortho phosphoric acid.In acid hydrolysis drugs were showing good peak separation and shape .Finally the good results were obtained by use of mixture of 0.1% ortho phosphoric acid (pHof the buffer adjusted to 3.4 with 0.1 N NaOH) and methanol in the ratio 40:60% v/v at a flow rate of 0.25ml/min through C18 BEH(Ethylene Bridged Hybrid) UPLC (100mm x 2.1mm, 1.8µm) at 35 0 C column temperature and the detector wavelength was set at 254 nm.Under the optimum chromatographic conditions, the retention times obtained for Metformin and Empagliflozin were 0.882 and 3.471 min, respectively.Optimized standard chromatogram for Metformin and Empagliflozin were expressed in figure 3.

Method validation System suitability
System suitability parameters such as resolution,tailing factor, plate count and resolution for two drugs were found to be 3.47; 1.16 and 1.37 ;2314.34 and 4723 respectively.Peak area and retention time of Metformin and Empagliflozin were found to be 4887835 & 163463, 0.882 & 3.471 respectively.The results of system suitability were expressed in Table 1.
For repeatability and intermediate precision assessment, %RSD was calculated.All the samples exhibited RSD values < 2 % confirming that the analytical method was precise.The results of precision were expressed in Table 2.

Accuracy
The acceptable percentage recovery of Metformin and Empagliflozin in bulk and tablet dosage form ranged from 99.92%-100.12% and 100.14%-100.56% respectively.The results are tabulated in Table 3.