A NOVEL UV SPECTROPHOTOMETRIC METHOD FOR SIMULTANEOUS ESTIMATION OF METOPROLOL TARTRATE AND ATORVASTATIN CALCIUM BASED ON ABSORBANCE CORRECTION PRINCIPLE

A novel, economical UV spectroscopic method for the simultaneous estimation of metoprolol and atorvastatin has been developed based on the absorbance correction principle. UV Spectrophotometric methods are rapid and economical and the absorbance correction principle is increasingly being employed for analysis as a convenient UV method of analysis. Methanol was used as solvent and water as diluent throughout the analysis. The wavelengths of 244.8 nm (λ max of atorvastatin) and 221.4 nm (λ max of metoprolol) were selected as λ 1 and λ 2 respectively. The method was validated as per ICH guidelines and was found to be accurate, precise, sensitive, and robust. The % assay value for the synthetic mixture was found to be 99.10% for metoprolol and 98.18% for atorvastatin which was within the acceptance value of 90 – 110%. The developed UV spectroscopic method is thus a valuable quality control tool in analysis.


INTRODUCTION
Two peril factors fundamental to cardiovascular diseases are hyperlipidemia and hypertension. These are the leading cause of death the world over. 1 Fixed dose combinations are in demand today due to convenience, better patient compliance, and fewer side effects. 2 Metoprolol tartrate (MET) (Fig.-1) and atorvastatin calcium (ATS) (Fig.-2) are used for the treatment of hypertension associated with hyperlipidemia. Literature survey reveals that some spectroscopic methods [3][4][5][6][7][8][9][10][11][12][13][14][15] and chromatographic methods like GC-MS 16 , RP-HPLC [17][18][19][20][21] , and RP-UPLC 22 have been reported for the analysis of metoprolol tartrate and atorvastatin calcium either individually or in combination. There has been a renewed interest in UV Spectrophotometric methods due to the methods being economical and rapid. The absorbance correction principle is increasingly being employed for analysis as a convenient UV method of analysis. Hence, the development of a cost-effective, UV method for the simultaneous estimation of the two drugs based on the Absorbance Correction Principle would be beneficial in the analysis of the drugs.

EXPERIMENTAL
Active pharmaceutical ingredients, metoprolol tartrate, and atorvastatin calcium were obtained as gifts from Shree Anand Life science, Ltd., Belagavi, Karnataka, India, and Zydus Cadila, Kundaim, Goa, India respectively. Methanol AR grade was used as a solvent and distilled water was employed as diluent throughout the analysis.
A NOVEL UV SPECTROPHOTOMETRIC METHOD P. Shelar et al.

Preparation of Working Standard Solution of Drugs
About 25mg of metoprolol tartrate and atorvastatin calcium were weighed accurately into two 25 ml volumetric flasks. The drugs were dissolved using methanol and the volume was adjusted with methanol to get a concentration of 1000µg/mL. Further, 10 mL was diluted with distilled water (100 µg/mL).

Preparation of Blank
Distilled water was used to dilute 10 mL of methanol to 100 mL and used as blank.

Preparation of Placebo Blank
About 25 mg of placebo powder was transferred into a 25mL volumetric flask and mixed with 15 mL of methanol. The solution was subjected to sonication for 10 minutes. The volume was adjusted with methanol and from the filtrate 1 mL was diluted to 10ml with distilled water.

Preparation of Synthetic Mixture
About 150 mg of placebo powder, 100 mg of atorvastatin calcium and 250 mg of metoprolol tartrate were intimately mixed using a glass mortar and pestle.

Selection of Analytical Wavelength
Scanning of the working standard solutions of MET and ATS was performed in the Ultraviolet region against the reference solution. Analytical wavelengths were obtained from the overlain spectra as follows: λ1 being the wavelength at which only one drug absorbs and λ2 being the wavelength at which both the drugs absorb.

Determination of Absorptivity
Absorptivity values for the drugs were calculated from the calibration curves recorded at predetermined wavelengths.

Method Validation
Validation of the developed analytical method was performed following the ICH guidelines. 23 Assay of Synthetic Mixture A synthetic mixture equivalent to 25 mg of metoprolol tartrate was weight into a volumetric flask o f 25 ml capacity. Methanol (15 mL) was added and the solution was subjected to sonication for 10 minutes. Methanol was added to adjust to volume, mixed, and filtered. 10 ml of filtrate was diluted to 100 mL with distilled water. Further 2 mL of solution was diluted to 10 mL using distilled water. The absorbance of the resultant solution was recorded at predetermined wavelengths. The percent purity of drugs in a synthetic mixture was calculated by the absorbance correction method.
The Concentration of Each Drug Was Determined By Following Equation A1 = ax1Cx, A2 = ax2Cxb +ay2Cy, Where, Cx is the concentration of ATS in g/1000 mL and Cy is the concentration of MET in g/1000 mL. A1 signifies the absorbance of the sample solution at λ1 and A2 signifies the absorbance of the sample solution at λ2. ax1 is the absorptivity of ATS at λ1, ax2 is the absorptivity of ATS at λ2 and ay2 is the absorptivity of MET at λ2.
A NOVEL UV SPECTROPHOTOMETRIC METHOD P. Shelar et al.

RESULTS AND DISCUSSION
Diluent was chosen based on the solubility of the drugs. As both MET and ATS were soluble in methanol, methanol was used to prepare standard stock solutions while further dilutions were done in distilled water.
The choice of analytical wavelengths was by scanning working standard solutions of MET and ATS in UV range against blank. The spectra showed λ max at 221.4 nm for MET and 244.8 nm for ATS. The spectra were overlain (Fig.-5), and analytical wavelengths were chosen as follows: λmax of ATS, 244.8 nm was chosen as λ1 (as MET showed nil absorbance at this wavelength) and 221.4 nm (λmax of MET) as λ2 as both the drugs showed satisfactory absorbance at this wavelength. Absorptivity values for both drugs were calculated by recording the absorbance of working standard solutions at predetermined wavelengths. The mean absorptivity for ATS was found to be 30.989 L/g/cm at 244.8 nm and 19.809 L/g/cm at 221.4 nm respectively, whereas for MET it was 23.949 L/g/cm at 221.4 nm.

Linearity
The solutions for linearity were prepared as per methodology and absorbance was measured at predetermined wavelengths. The calibration curves for the drugs are displayed in Fig.-4 and 5, and linearity data is shown in Table-

Precision
Solutions were prepared as per methodology and absorbance was recorded at predetermined wavelengths.
The results of precision studies are displayed in Table-2. The % RSD of precision study for MET and ATS was found to be within the acceptable limits of less than 2 %.

Accuracy
The results of the accuracy study are shown in Table-3. The % recovery at 80%, 100%, and 120% for MET and ATS was found to be within the acceptable criteria of 95 % -105 % establishing the accuracy of the developed method.

Limit of Detection and Quantitation
The data for LOD and LOQ measurements as shown in Table-4 proved that the developed method was sensitive.

Robustness
The data for robustness studies for change of instrument, analyst, and sonication time is displayed in Table-5. As seen deliberate changes introduced did not adversely affect the results of the analysis. Hence, the developed UV method for ATS and MET by absorbance correction method was found to be robust.

Assay of the Synthetic Mixture
The % assay values obtained are displayed in Table-6. As seen the % assay value for the synthetic mixture was 98.18% for ATS and 99.10% for MET which was within the acceptance criteria (90 -110%).

CONCLUSION
A novel, simple and economical UV spectroscopic method for the simultaneous analysis of metoprolol and atorvastatin has been developed and validated. In the developed UV spectroscopic method, methanol was employed as the solvent, and water was used as a diluent. ICH guidelines were followed for validation of the method. The Linear range was obtained in the c o n c e n t r a t i o n of 10 -100 µ g/mL for MET and 2 -100 µ g/mL for ATS respectively. The % assay value for the synthetic mixture was found to be 99.10% for metoprolol tartrate and 98.18% for atorvastatin calcium which met the acceptance criteria. The developed method can thus be a valuable quality control tool for the simultaneous analysis of the drugs.