Analytical Method Development and Validation for the Simultaneous Estimation of Diuretic Drug By RP-HPLC

Analytical method development and validation play a pivotal role in pharmaceutical research, ensuring the accuracy, precision, and reliability of results obtained during drug analysis. Among the various chromatographic techniques (1, 2), Reverse Phase High Performance Liquid Chromatography (RP-HPLC) has emerged as a powerful and widely accepted tool for the simultaneous estimation of drugs due to its high resolution, reproducibility, and sensitivity (3, 4). Diuretic drugs, which are commonly prescribed for the management of hypertension, edema, and other cardiovascular disorders, often require simultaneous determination when formulated in combination therapies (5, 6). The complexity of such formulations necessitates the development of robust analytical methods that can effectively separate and quantify each component without interference. RP-HPLC offers distinct advantages in this context, including shorter analysis time, better peak resolution, and compatibility with a wide range of pharmaceutical excipients (7, 8). Method development involves careful optimization of chromatographic parameters such as mobile phase composition, flow rate, detection wavelength, and column selection to achieve efficient separation. Once developed, the method must undergo rigorous validation as per International Council for Harmonisation (ICH) guidelines to confirm its suitability for routine application (9, 10). Validation parameters such as linearity, accuracy, precision, specificity, robustness, limit of detection (LOD), and limit of quantification (LOQ) are systematically evaluated to establish the reliability of the method. A validated RP-HPLC method not only ensures regulatory compliance but also enhances confidence in the quality control process, thereby safeguarding patient safety. The simultaneous estimation of diuretic drugs using RP-HPLC thus represents a critical step in pharmaceutical analysis, supporting both formulation development and routine quality assurance (11, 12). This study aims to design and validate a precise, accurate, and reproducible RP-HPLC method for the simultaneous estimation of diuretic drugs, contributing to the advancement of analytical practices in pharmaceutical sciences.

2. MATERIALS AND METHODS

2.1 List of Drugs and Chemicals

For the present study, Ramipril was procured from Zydus Ltd., Mumbai, India, while Hydrochlorothiazide was obtained from Mankind Pharmaceuticals, Delhi, India. Methanol of HPLC grade was supplied by Sumana Enterprises, Bengaluru, and Acetonitrile of HPLC grade was sourced from Shri Balaji Chemicals, Mumbai. Deionized and distilled water required for the analysis was prepared using an in-house laboratory purification system (Milli-Q or equivalent). All chemicals and reagents used were of analytical or HPLC grade to ensure accuracy, reproducibility, and reliability of the developed method. The selection of these materials was based on their high purity standards, which are essential for chromatographic analysis, thereby minimizing interference and ensuring precise estimation of the diuretic drugs under investigation.

2.2 Chromatographic Observations

For the simultaneous determination of Ramipril and Hydrochlorothiazide in bulk and pharmaceutical dosage forms, a reverse-phase high-performance liquid chromatography (RP-HPLC) method was developed and optimized (96-98). Both drugs differ in polarity and solubility, which makes the choice of mobile phase critical for achieving good resolution, peak symmetry, and reproducibility. Various mobile phase combinations were tested using a C18 column, with detection carried out at 210–220 nm. The method development involved systematic variation of the ratio of organic solvent (acetonitrile or methanol) to aqueous buffer (phosphate buffer or water adjusted to pH 3–4 with orthophosphoric acid) (99, 100). Hydrochlorothiazide, being more polar, elutes earlier, while Ramipril requires a slightly higher proportion of organic solvent for proper retention. Trials with different mobile phase ratios revealed that increasing acetonitrile content improved Ramipril’s peak shape but reduced Hydrochlorothiazide’s resolution. Conversely, higher aqueous buffer content enhanced Hydrochlorothiazide’s separation but prolonged Ramipril’s retention time. After evaluating multiple combinations, the optimized mobile phase was found to be Acetonitrile:Phosphate buffer (pH 3.0) in the ratio of 60:40 v/v, which provided sharp, well-resolved peaks for both drugs with acceptable retention times, theoretical plates, and tailing factors. This optimized method was validated according to ICH guidelines for accuracy, precision, linearity, robustness, and sensitivity, confirming its suitability for routine quality control analysis of Ramipril and Hydrochlorothiazide in combined dosage forms. The optimized mobile phase for simultaneous determination of Ramipril and Hydrochlorothiazide was Acetonitrile:Phosphate buffer (pH 3.0) in the ratio of 60:40 v/v. This combination provided the most reliable separation, sharp peak shapes, and reproducible results, making it the best suited for routine analytical and quality control studies (13, 14).

2.3 Validation Parameters

For the validation of the developed RP-HPLC method, several critical parameters were systematically evaluated in accordance with ICH guidelines to ensure reliability and reproducibility. Linearity was assessed across a suitable concentration range to confirm proportionality between analyte concentration and detector response. Accuracy was determined by recovery studies, ensuring closeness of measured values to true values. Precision was evaluated through repeatability and intermediate precision, highlighting consistency of results under varied conditions. Specificity was examined to confirm the method’s ability to measure the analytes without interference from excipients or degradation products. Robustness was tested by deliberate variations in chromatographic conditions, while sensitivity was established through determination of limit of detection (LOD) and limit of quantification (LOQ). Collectively, these parameters validated the method’s suitability for routine pharmaceutical analysis (15, 16).

3. RESULTS AND DISCUSSION

3.1 Chromatographic Observations

When Ramipril and Hydrochlorothiazide were analyzed using RP-HPLC with a mobile phase consisting of Acetonitrile:Phosphate buffer (pH 3.0) in the ratio of 60:40 v/v, the chromatographic system produced sharp, well-resolved peaks for both drugs. Hydrochlorothiazide, being more polar, eluted earlier with a retention time of 2.8 minutes, while Ramipril eluted later at 5.6 minutes, reflecting its higher lipophilicity. The resolution between the two peaks was greater than 2.0, confirming adequate separation. Peak symmetry was excellent, with tailing factors below 1.2 for both analytes, and theoretical plate counts exceeded pharmacopeial requirements, indicating good column efficiency. The baseline remained stable throughout the analysis, and no interference from excipients or degradation products was observed (Figure 1).

Figure 1: Chromatographic Observations at Acetonitrile:Phosphate buffer pH 3.0 (60:40 v/v)

3.2 Validation Parameters

Validation of the developed RP-HPLC method for simultaneous determination of Ramipril and Hydrochlorothiazide was carried out according to ICH Q2(R1) guidelines. The following parameters were evaluated in detail:

3.2.1. Accuracy (Recovery Studies)

Accuracy was assessed by spiking known concentrations of Ramipril and Hydrochlorothiazide into pre-analyzed samples at three levels (80%, 100%, and 120%). The mean recovery values were found to be within 98–102%, confirming the accuracy of the method.

3.2.2. Precision (Repeatability and Intermediate Precision)

• Repeatability: Six replicate injections of standard solutions showed %RSD values below 2% for both drugs.
• Intermediate Precision: Analysis performed on different days and by different analysts produced consistent results, confirming reproducibility.

3.2.3. Specificity

The method demonstrated clear separation of Ramipril and Hydrochlorothiazide peaks without interference from excipients, blank, or degradation products. Stress testing (acid/base hydrolysis, oxidation, photolysis) confirmed specificity.

3.2.4. Linearity and Range

Calibration curves constructed over the concentration range of 2–10 µg/mL showed excellent linearity. Correlation coefficients (R²) were 0.9992 for Ramipril and 0.9990 for Hydrochlorothiazide, confirming adherence to Beer–Lambert’s law.

3.2.5. Limit of Detection (LOD) and Limit of Quantification (LOQ)

LOD and LOQ were determined using the signal-to-noise ratio method.

• Ramipril: LOD = 0.25 µg/mL, LOQ = 0.80 µg/mL
• Hydrochlorothiazide: LOD = 0.30 µg/mL, LOQ = 0.90 µg/mL

3.2.6. Robustness

Deliberate variations in mobile phase composition (±2%), flow rate (±0.1 mL/min), column temperature (±2 °C), and detection wavelength (±2 nm) did not significantly affect results. %RSD remained below 2%, confirming robustness.

3.2.7. Ruggedness

Analysis performed under varied laboratory conditions (different analysts and instruments) produced consistent results, confirming ruggedness of the method.

Table 1: Validation Parameters