Simultaneous spectrophotometric determination in solid phase of aspirin and its impurity salicylic acid in pharmaceutical formulations

Stability studies of aspirin-magaldrate double layer tablets

Accelerated stability testing was performed on aspirin-magaldrate double layer tablets as well as aspirin-maalox marketed double layer tablets (Ascriptin) in order to evaluate the effect of the presence of the alkaline moieties of the antacid (magaldrate and maalox) on the chemical stability of aspirin. The results were compared simultaneously with that obtained from the marketed Aspro plain tablets. The results revealed that the presence of the alkaline moieties in the tested tablets has increased the rate of aspirin decomposition and reduced its shelf-life. This effect was more pronounced for aspirin tablets containing magaldrate antacid. Determination of shelf-lives at 25 degrees C for the prepared and the marketed tablets was carried out using Arrhenius plots and the results showed that they were 35, 34.5 and 13.5 months for Aspro, Ascriptin and aspirin-magaldrate double layer tablets, respectively. The effect of storage for 50 days and at different temperatures, on the crushing strength and the disintegration time of the prepared and the marked tablets showed a slight decrease in the disintegration time and the crushing strength of the tablets as the storage temperature increased. Aspro tablets did not produce the same results. The in vitro release data of the prepared aspirin-magaldrate double layer tablets and the marketed Ascriptin tablets stored for 50 days and at different storage temperatures as well as Aspro tablets stored at 70 degrees C were best fitted to the first-order kinetics model. The release data of Aspro tablets stored at 50 and 60 degrees C for 50 days were best fitted to Higuchi's model.

A new salicylate ISFET for the determination of salicylic and acetylsalicylic acid in drugs

A salicylate ISFET for the analysis of salicylic and acetylsalicylic acid in drugs is described. It is based on a salicylate ion selective membrane coated on the surface of the Si3N4 gate of the FET. The sensitive membrane consists of tetra-dodecylammonium salicylate, polyvinyl chloride and a proper plasticizer. The linearity range of the sensor is 5 x 10(-5)-1.5 x 10(-2) M for the salicylic acid, and 7 x 10(-5)-1.5 x 10(-2) M for the acetylsalicylic acid, respectively. The detection limit for the two compounds is 5 x 10(-5) M while the response time is < or = 20 s. The effect of pH and different interfering ions was also studied. The sensor was used to analyse the content of acetylsalicylic and salicylic acid in some drugs, and the accuracy of the method was evaluated through recovery tests. The results obtained with this method are well correlated either with those obtained with a classical ISE employing the same sensitive membrane or with the classical volumetric method.

Comparison of three new spectrophotometric methods for simultaneous determination of aspirin and salicylic acid in tablets without separation of pharmaceutical excipients

Simultaneous analysis of aspirin (ASA) and salicylic acid (SA) in pharmaceutical tablet preparations was performed by two multicomponent UV-spectrophotometric methods utilizing principal component regression and classical least square algorithm. Additionally, an assay procedure based on second-derivative spectroscopy was developed. The analysis was performed in turbid solutions without separation of interfering excipients. The range, as determined by the second-derivative methods, was 0.2 to 103.2 micrograms/mL for ASA and 0.07 to 44.5 micrograms/mL for SA. Sensitivity for determination of SA was 0.004% of ASA content for the second-derivative method and 0.2% of ASA content for both multicomponent methods. The methods were applied to laboratory mixtures and commercial tablet formulations containing ASA and SA. The advantage of the second-derivative method in determining small amounts of SA in commercial tablet preparations is shown in comparison with a conventional HPLC method. All UV-spectrophotometric methods are rapid, accurate, and reproducible.

Fluorometric study of the molecular states of 2,5-diphenyloxazole in ground mixtures with gamma-cyclodextrin

Molecular states of 2,5-diphenyloxazole (PPO) were investigated in ground mixtures with gamma-cyclodextrin (gamma-CD). Crystalline PPO gradually became amorphous upon grinding in the presence of gamma-CD. Solid-state fluorescence spectra of the ground mixtures showed that the fluorescence emission peak due to PPO crystals was reduced in intensity with an increasing duration of grinding. A new fluorescence peak attributed to PPO excimer appeared at a longer wave-length. Results of the time-resolved fluorescence study indicated that the cogrinding caused an increase in the portion of PPO excimer in the gamma-CD ground mixture. On the other hand, only a small portion of excimer was formed in ground mixtures with beta-CD, which has a smaller cavity than gamma-CD. These results suggest that cogrinding of PPO with gamma-CD caused two PPO molecules to be included in the gamma-CD cavity, contributing to excimer formation.