In the 95 edition of the determination of Cimetidine Tablets, the non-aqueous titration method was used for content determination. However, the endpoint judgment is susceptible to the effects of the type and dosage of tablet excipients, as well as human error. Cimetidine is easily soluble in methanol. In this paper, methanol is used as a diluent, and the UV spectrophotometric method is applied for the determination of Cimetidine Tablets, rather than using 0.1 mol/L hydrochloric acid solution as the diluent. The absorption peak shape is good, and the quantitative accuracy is high. The report is as follows:
1. Instruments and Reagents
1.1 Instruments: Shimadzu UV-2201 Spectrophotometer (Japan).
1.2 Reagents: Cimetidine controlled goods (China Institute for Drug Control, 99.8%), Cimetidine Tablets (Nanchang Five-Star Jiangxi Pharmaceutical Factory, Batch No. 980501).
2. Methods and Results
2.1 Selection of Test Conditions: Controlled goods of cimetidine and film powder were dissolved and diluted to a certain concentration with methanol (the film powder was filtered), using methanol as blank. Scanning was conducted within the wavelength range of 200-400nm. The results showed that cimetidine has a maximum absorption at a wavelength of 221nm. There was no absorption from excipients at this wavelength, so 221nm was selected as the measurement wavelength (see Figure 1).
Figure 1: UV Absorption Spectrum of Cimetidine Tablets (A), Cimetidine Controlled Goods (B), and Excipients (C).
2.2 Standard Curve Equation and System Precision: Weigh accurately about 50mg of dried-to-constant-weight cimetidine control at 105°C, place it in a 500ml volumetric flask, dissolve and dilute to the mark with methanol. Precisely measure 1, 3, 5, 7, and 0ml into a 100ml volumetric flask, dilute to the mark with methanol. Shake well, use methanol as blank, and determine absorbance at 221nm wavelength. A standard curve regression equation is obtained: A = 0.0854C + 0.002, R = 0.9998. Recovery experiments showed an average yield of 101.4%, RSD = 1.05%.
2.3 Sample Content Determination: Take 20 tablets of Cimetidine Tablets, weigh accurately, grind finely. Precisely weigh an appropriate amount (equivalent to about 50mg of cimetidine) into a 500ml volumetric flask, dissolve and dilute to the mark with methanol, shake well, filter. Precisely measure 5ml of the filtrate into a 100ml volumetric flask, dilute to the mark with methanol according to the 2.2 operation, substitute into the standard curve equation for calculation. The result is 94.2% of the labeled amount (non-aqueous determination result is 93% of the labeled amount).
3. Discussion
This method has no interference from excipients, good stability, simple operation, and accurate quantification.