HPLC Assay Validation
The stability-indicating nature of both assay methods was proven by monitoring forcibly degraded samples for interfering peaks. The epinephrine method was previously validated as stability indicating. Three 10-mL samples of epinephrine (1 mg/mL) were prepared. The pH of one sample was adjusted to 1, the pH of the second sample was adjusted to 12, and 1 mL of 30% hydrogen peroxide was added to 9 mL of the third sample. A sample obtained at time 0 was analyzed, and the degradation samples were followed over several days to identify interfering peaks. Peak purity was assessed using ultraviolet (UV) spectral overlays (200-350 nm) and multiwavelength analysis (230 and 280 nm) of the parent peaks in the degradation chromatograms.
Forced degradation samples of lidocaine were created by adjusting the pH of 10 mL of a commercial solution (1%) of lidocaine (AstraZeneca Canada Inc; lot 9923075-2, expiry November 2009) to an approximate pH of 1.1 with concentrated hydrochloric acid (BDH Inc, Toronto, Ontario; lot 120834-78180) or 7.6 with 1 N sodium hydroxide solution (Fisher Scientific Inc, Nepean, Ontario; lot SC6252970, expiry September 30, 2008) or by adding 0.5 mL of 30% hydrogen peroxide (Fisher Scientific Inc; lot 073191). The pH of 7.6 was chosen for the alkaline degradation because the lidocaine precipitated out of solution at higher pH values (as indicated by cloudiness at pH of about 8.2 or above). All of the degradation samples were monitored 6 times over a 9-day period. Acidic and alkaline samples were incubated at 50°C in a hot water bath, and the oxidized sample was stored at 22°C. A known degradation product of lidocaine, 2,6-dimethylaniline, was also tested for interference with the parent peak. The HPLC method was further validated by preparing a 5-point standard curve and by determining the precision of the method. Precision was determined by calculating the coefficient of variance for intraday comparisons (over 25 h) and interday comparisons (5 separate days). The accuracy of the method was based on sample recovery, and the sensitivity was also determined. Multiwavelength (220 and 270 nm) and UV spectral analysis (200-350 nm) were used to test the peak purity of the lidocaine. cheap cialis canadian pharmacy
Stability StudyOn the day of analysis, all samples were removed from the -70°C freezer and allowed to thaw to room temperature (minimum of 2 h, maximum of 3 h). The internal standard was added to the samples after further dilution with mobile phase. Once the samples had been prepared for final analysis, they were immediately loaded into the sample cooler until analysis. Therefore, the thawing process had little but equal effect on all samples. Samples were prepared in triplicate and assayed in duplicate after visual inspection for any precipitation that might have occurred because of freezing.
Data are reported as percentage of the initial drug concentration remaining on each study day for samples stored at 5°C with protection from light. The final expiry dates assigned were based on the standard acceptable pharmaceutical end point of maintaining no less than 90% of the initial drug concentration. Apcalis Oral Jelly