A stability study was performed to evaluate the degradation rate of the aspirin-cysteine conjugate in phosphate-buffered saline (PBS) at 37°C over time. A 1 mg/mL solution of the conjugate in PBS was prepared and incubated at 37°C. Samples were taken at different time points (0, 1, 2, 4, 6, 8, 12, and 24 hours) and analyzed by HPLC to determine the concentration of the conjugate. To prepare the samples for HPLC analysis, 500 µL of each sample was mixed with 500 µL of acetonitrile to precipitate any proteins or other interfering substances. The mixture was vortexed for 30 seconds and then centrifuged at 14,000 rpm for 10 minutes. The supernatant was collected and filtered through a 0.2 µm syringe filter to remove any particulate matter. Cartridge-based HPLC analysis was performed through Sep-Pak C18 cartridges. The mobile phase consisted of acetonitrile and water containing 0.1% trifluoroacetic acid. Each fraction was analyzed at 280 nm using a UV-5100B spectrophotometer. The stability of the conjugate was determined by plotting the concentration of the conjugate versus time and calculating the half-life of the conjugate using a first-order decay model. The stability of the conjugate was defined as the time required for the conjugate to degrade to 50% of its initial concentration.