Fluorospectrophotometric Determination of Free Salicylic Acid in Aspirin After Its Separation by Extraction with Bi-aqueous Extraction System of PEG 1500-OP-(NH₄)₂SO₄-H₂O

A bi-aqueous extraction system composed of polyethylene glycol (PEG) 1500,non-ionic surfactant OP,solid ammonium sulfate and a little amount of water was proposed and applied to the extraction of free salicylic acid from the aspirin matrix. The experimental conditions for the extraction were studied and optimized with the following parameters: ① ratio of volumes of PEG 1500 (500 g·L-1) to OP (500 g·L-1) VPEG∶VOP=2.50 mL∶1.50 mL;② amount of (NH4)2SO4 2.0 g;③ addition of pH 6.0 B-R buffer to a volume of about 10 mL. Rate of extraction of salicylic acid obtained was 98.6%. After extraction,the upper layer (i.e. the surfactant phase) was separated and diluted to 10.0 mL with the B-R buffer solution in a volumetric flask. Its fluorescence intensity was measured at the wavelengths (λex) 305 nm and (λem) 392 nm. The proposed method was applied to the determination of free salicylic acid in 3 aspirin samples,each for 10 determinations. Values of RSD′s (n=10) obtained were in the range of 1.7%-2.1%. Test for recovery was made by addition of standard salicylic acid to these samples,values of recovery were found in the range of 93.3%-103.3% with RSD (n=5)≤2.5%.