Why Analyze Montelukast in Tablets?
Tablet formulations containing Montelukast must meet strict specifications for assay, dissolution, and impurity profile. Degradation can occur during storage, especially under high humidity and temperature, leading to loss of potency or formation of harmful byproducts. Routine assay testing confirms that each batch contains the label claim (typically 10mg per tablet) within the acceptable range of 95105%.
Principles of HPLC for Montelukast
HPLC separates Montelukast from excipients and potential degradation products on a reversedphase column. The method commonly employs a C18 stationary phase, a mobile phase consisting of a mixture of phosphate buffer (pH3.03.5) and acetonitrile, and detection at 254nm, where Montelukast exhibits a strong absorbance.
- Column: 250mm4.6mm, 5m particle size.
- Mobile Phase: 0.02M phosphate buffer (pH3.2) : acetonitrile (70:30, v/v).
- Flow Rate: 1.0mLmin.
- Injection Volume: 20L.
- Runtime: 8min per sample.
Retention time for Montelukast typically falls between 3.5 and 4.0min under the conditions above. The method is robust, showing minimal variation with changes in buffer concentration, acetonitrile proportion, or column temperature (252C).
Sample Preparation for HPLC
Accurate assay requires complete extraction of Montelukast from the tablet matrix. A typical protocol is:
- Weigh and finely powder 10 tablets (equivalent to 10mg each).
- Transfer an accurately weighed portion (equivalent to 10mg Montelukast) to a 100mL volumetric flask.
- Add 50mL of the mobile phase mixture and sonicate for 10min.
- Make up the volume to 100mL with mobile phase.
- Filter the solution through a 0.45m nylon filter before injection.
If the tablet contains a coating that interferes with extraction, a brief pretreatment with dilute methanol (10% v/v) can be employed, followed by the standard extraction steps.
Method Validation (HPLC)
Regulatory bodies such as the FDA and ICH require validation of the analytical method. Key parameters include:
| Parameter | Acceptance Criteria |
|---|---|
| Linearity | R0.999 over 50150% of the label claim. |
| Precision (intraday) | %RSD 1.5% (n=6). |
| Precision (interday) | %RSD 2.0% (n=18). |
| Accuracy | Recovery 98102% at three concentration levels. |
| Specificity | No interference at Montelukasts retention time. |
| Limit of Detection (LOD) | 0.02gmL. |
| Limit of Quantitation (LOQ) | 0.06gmL. |
| Robustness | 2% change in acetonitrile proportion does not shift retention time >0.2min. |
UVVisible Spectrophotometric Estimation
UVVis offers a rapid, costeffective alternative for routine assay when high precision is not required. Montelukast shows a max at 254nm in acidic aqueous media. The method typically employs a simple zeroorder calibration.
- Solvent: 0.1M phosphate buffer (pH3.0), adjusted with dilute HCl.
- Cuvette: 1cm quartz.
- Wavelength: 254nm (scan range 200350nm).
- Calibration Range: 212gmL (linear correlation coefficient >0.998).
Because many excipients are nonchromophoric at this wavelength, matrix effects are minimal. However, the presence of colored dyes or strong UVabsorbing binders may necessitate a blank correction using a placebo extract.
Sample Preparation for UV Analysis
A typical workflow is as follows:
- Weigh and powder 10 tablets; transfer a quantity equivalent to 10mg Montelukast to a 100mL volumetric flask.
- Add 50mL of the phosphate buffer and shake vigorously for 5min.
- Sonicate for 5min to aid dissolution.
- Make up the volume to 100mL with buffer.
- Filter the solution through a 0.45m filter; optionally, centrifuge to remove fine particulates.
- Measure absorbance of the filtrate at 254nm against a blank prepared with the same buffer.
The concentration of the final solution is typically 100gmL. Dilute appropriately (e.g., 1mL into 9mL buffer) to fall within the linear range.
Method Validation (UV)
Validation criteria mirror those of HPLC, albeit with slightly broader tolerance limits due to the lower selectivity of the technique.
| Parameter | Acceptance Criteria |
|---|---|
| Linearity | R0.998 over 10150% of the target concentration. |
| Precision (repeatability) | %RSD 2.0% (n=6). |
| Accuracy | Recovery 95105% at three levels. |
| Specificity | No absorbance from excipients at max. |
| LOD | 0.01gmL. |
| LOQ | 0.03gmL. |
| Robustness | 0.2pH unit change does not affect absorbance >1%. |
Comparative Advantages
HPLC provides high specificity, allowing simultaneous quantification of Montelukast and its impurities. It is the method of choice for stability studies, impurity profiling, and when regulatory submissions demand a validated chromatographic assay.
UVVis offers speed (analysis time <2min), low cost, and ease of operation. It is suitable for rapid routine checks, especially in largescale manufacturing where throughput is critical.
In practice, both methods can be employed in a complementary fashion: UV for quick batchtobatch assay, and HPLC for detailed verification, trend analysis, and investigation of outofspecification results.
Practical Tips for Reliable Results
- Always equilibrate the HPLC column for at least 30min before the first injection.
- Use freshly prepared buffer to avoid pH drift and microbial growth.
- Maintain the UV spectrophotometers wavelength accuracy with a standard reference material (e.g., holmium oxide).
- Validate the filtration step; membranes can adsorb Montelukast, leading to low recoveries.
- Document temperature of the laboratory; both techniques are temperaturesensitive.
References & Further Reading
1. ICH Q2(R1) Validation of Analytical Procedures.
2. United States Pharmacopeia (USP) Montelukast sodium tablets monograph.
3. S. J. Park, Development of a stabilityindicating HPLC method for Montelukast, J. Pharm. Anal., 2021.
4. M. A. Smith, UV spectrophotometric assay of leukotriene antagonists, Anal. Chem., 2019.
For detailed standard operating procedures, consult the manufacturers analytical handbook or the WHO Guidelines on Pharmaceutical Quality Assurance.
