Spectrophotometric determination of Montelukast Sodium in pure form and in its pharmaceutical formulations

A simple, sensitive and rapid spectrophotometric method for determination of Montelukast Sodium (MON) in both pure form and pharmaceutical formulations was developed. This method was based on the oxidation of the studied drug in presence of acidic medium by a known excess of (Potassium bromide: Potassium bromate) (KBr:KBrO3) and subsequent determination of unreacted oxidant by reacting it with Crystal Violet (CV) dye [4 [bis [4 (dimethylamino) phenyl] methylidene] cyclohexa-2,5-dien-1-ylidene]-dimethylazanium to produce blue product at λmax. 592 nm. The linearity range was found to be (5-50)µg/ml and molar absorptivity 1.5691×104 L/mol.cm, correlation coefficient 0.9993 and the limit of detection 0.209 µg/ml. This method was successfully applied for the determination of (MON) in tablet formulation .


Introduction
Montelukast Na (Fig. 1), "used for the maintenance treatment of asthma and to relieve symptoms of seasonal allergies" [1,2] , and used to prevent wheezing, difficulty breathing, chest tightness, and coughing caused by asthma.Montelukast is also used to prevent bronchospasm (breathing difficulties) during exercise.It is also used to treat the symptoms of seasonal (occurs only at certain times of the year), and perennial (occurs all year round) allergic rhinitis (a condition associated with sneezing and stuffy, runny or itchy nose).It is in a class of medications called leukotriene receptor antagonists (LTRAs).It works by blocking the action of substances in the body that cause the symptoms of asthma and allergic rhinitis [3] .Molar mass is 608.169gm/mole, M.P. = 242.5 °C, is a hygroscopic, optically active, white to offwhite powder.Montelukast sodium is freely soluble in ethanol, methanol, and water and practically insoluble in acetonitrile, chemically known is sodium; [4] .Several methods have been proposed for determination of this drug, such as HPLC [5][6][7] , TLC [8,9] , HPTLC [10][11][12] , Voltammetry [13,14] , UV-Vis.Spectrophotometry [15][16][17][18] .

Fig. (1): Chemical Structures of Montelukast Na
The research aims to develop a simple, fast and economical spectrophotometric methods for determination of Montelukast Na by using dye with an oxidizing agent in the acid medium.

Procedures
After initial testing, optimal conditions were obtained, and the procedure involves transferring 0.5 ml of 500 µg/ml (MON) to a 10 ml volumetric flask, then adding 0.75 ml of the oxidizing agent (KBr: KBrO3) by diluting (2.5 to 100 ml), followed by adding 0.5 ml of 1.0 M HCl acid.After 15 minutes, 1.0 ml of Crystal Violet dye were added, and after 5 minutes, the volume is completed with ethanol to 10 ml, because after five minutes the color of the blank disappears, the highest absorption of the resulting compound (blue color) absorbs at 592 nm.

Procedures for "stoichiometric ratio"
The reaction of equivalence between this drug and the reagent (dye), have been estimated by carrying out "molar ratio" and "continuous variation method".In these methods, "equimolar" solutions of (MON 0.5 ml) and "CV dye" (7.7 × 10 -5 M) were used.In the first method varying aliquots of "CV dye" was added to constant aliquots of drug solution, final volumes (10ml) and the absorbance was measured at 592 nm, opposite the blank treated similarly.while in the latter method, a series of MON:CV dye solutions was kept at (5ml) (0:5, 0.5:4.5, 1:4, 1.5:3.5, 2:3, …… 5:0).

Application of the proposed methods
Ten tablets (2.465gm, 1.859gm and 2.040gm) respectively, from each preparation, were grinded into fine powder.An precisely weighed amount of powder was transferred into a beaker and then were shaken with 50 ml of solvent (ethanol) and filtered.The filtrates and the washings were collected in a 100ml volumetric flask.and diluted up to the mark with solvent to obtain final concentration of 1000 µg/mL.The suggested method was successfully applied for the determination of MON in various commercial tablets; the results are shown in Table (4).

Results and Discussion
Absorption spectrum of blue color product of MON against the blank at room temperature (25 o C) at 592nm is shown in (Fig. 2), and the blank against distilled water is shown in (Fig. 3).4) that the best volume of the oxidizing agent is 0.75 ml which was used in subsequent studies.

Fig. (4):-Effect of oxidizing agent volume (KBr: KBrO 3 ) on absorption of the (MON) product Effect of the use of different acids
The acids used were (H 2 SO 4 , HCl, HNO 3 , CH 3 COOH), with a concentration of 1.0 M for each, and same volume of 0.5 ml for each, Table (1) shows that the best acid used to form the product is hydrochloric acid.5), the optimal added acid volume is 0.5 ml, after which, the color of the formed product disappears gradually.Abs.

Effect of the dye amount
Fig. (6) shows the effect of adding different volumes (0.5-3) ml of the CV dye on the absorption of the product.The best added volume was 1.0 ml.

Effect of time on product stability
The effect of time was followed using optimum conditions every ten minutes for three hours, the product absorption was then taken the next day.Table (2) shows the stability of the absorption values at λmax. with time, the absorption value of the product is fixed for 24 hours.

Effect of Interferences
The effect of interferences on the composition of the product was studied, and not observed any effect, as shown in the table (3).The stoichiometry of the product Under the optimum conditions, the stoichiometry of the reaction between MON and the dye was studied by mole-ratio and continuous variation methods.The equivalence between dye and this drug was 1:1 (Figs. 7, 8).Abs.

V[D]/[VD+VR]
Calibration curve Fig.( 9) shows the linearity of the calibration curve obtained at optimal conditions, where the linearity was within concentrations (5-50) µg/ml, which is equal to the volumes within (0.1-1.0) ml.

Characteristics of calibration curve
Calibration curve was constructed according to the optimum conditions in table (4).

Application of the proposed methods
The results of determination of MON in the pharmaceutical preparations are shown in table (5).

Table (4): Determination of MON in commercial tablets by the proposed spectrophotometric method
The suggested ractions The proposed reaction can be based on how the MON drug is oxidized, by connection three groups of bromine to the ring connected by the halogen group [20] , and how to convert the CV dye to Leuco form [21] as follows: BrO

Conclusion
This method described here is simple, rapid, convenient and do not requires special working conditions unlike many other reported methods.The procedure showed shorter reaction time, stable colored species with inexpensive reagent.The determination can be performed at room temperature and do not require heating step.The proposed method can be applied for the determination of MON in pharmaceutical preparations (Tablet).

Fig. ( 2
Fig. (2):-Absorption spectrum of "color product of MON"system against blank Effect of the acid amountDifferent volumes (0.2-2)ml of 0.1 M HCl were used, As shown in Fig.(