Stability-Indicating Method Development and Validation of Gabapentin and Nortriptyline in Bulk And Pharmaceutical Dosage Forms Using LC–MS And HPTLC

Abstract

Background: Gabapentin and nortriptyline are used in combination-oriented therapeutic strategies for neuropathic pain, but their markedly different physicochemical properties create analytical challenges for simultaneous estimation and stability assessment. This study developed and evaluated complementary LC–MS and HPTLC approaches for identification, quantitative analysis, method validation, and forced-degradation assessment of gabapentin (GAB) and nortriptyline (NOR) in bulk materials and pharmaceutical dosage forms.

Methods: LC–MS method development was investigated through systematic mobile-phase and column trials, followed by optimization using a Sciex API 4000 mass detector with a Turbo IonSpray source. The optimized LC–MS conditions used water:methanol (5:95, v/v) containing 1 mL ammonia solution, a flow rate of 1.0 mL/min with 50:50 splitter configuration, and a CHIRALCEL OZ-3R column (4.6 × 150 mm, 3 µm). HPTLC was performed on silica gel 60 GF254 plates using chloroform:methanol:formic acid (8.2:1.5:1, v/v/v), with 15 min chamber saturation and approximately 15 min development. Validation included selectivity/specificity, linearity, accuracy, precision, sensitivity, robustness, and assay of formulations. Forced-degradation studies included oxidative, thermal and photolytic conditions for gabapentin and acid, alkaline, wet/thermal and photolytic conditions for nortriptyline, as documented in the thesis.

Results: The thesis data demonstrated satisfactory precision and accuracy for the validated procedures. For gabapentin, the reported LOQ was 0.509 ng/mL, with 97.5% accuracy and 4.2% precision at the LOQ. For nortriptyline, the reported LOQ was approximately 49.10 pg/mL, with 95.6% accuracy and 6.3% precision. Gabapentin showed intraday precision of 0.9–2.0% CV and interday precision of approximately 0.9–3.8% CV, with intraday accuracy of 100.0–105.2% and interday accuracy of 98.0–105.2% for the reported quality-control levels. Robustness testing by wavelength variation showed minimal changes in retention factor and peak area. In oxidative stress testing, gabapentin showed three additional degradation peaks and an approximately 35.66% reduction in parent peak intensity. Under dry-heat stress, no detectable degradation was reported for gabapentin under the tested conditions. The HPTLC assay of three formulations produced gabapentin and nortriptyline contents within the ranges reported in the thesis.

Conclusion: The combined LC–MS/HPTLC strategy provides complementary capabilities for sensitive analytical characterization and routine stability-indicating quality assessment of gabapentin and nortriptyline. LC–MS is particularly useful for sensitive detection and degradation-product investigation, whereas HPTLC offers a comparatively rapid and practical platform for simultaneous assay and stability screening. The analytical procedures described in the thesis provide a foundation for further journal-level validation and independent confirmation using complete chromatographic, statistical and degradation-product datasets.