Abstract
The solid phase spectrophotometry technique, in which the absorbance of the species of interest sorbed on a solid support is measured directly, was applied to the determination of salicylic acid using flow injection-analysis. Salicylic acid was determined by monitoring of its intrinsic absorbance at 297 nm sorbed on Sephadex QAE A-25 resin placed in an appropriate flow-through cell. The method proposed improves the selectivity compared with the corresponding solution-phase method and the sensitivity is increased by a factor of 30 or more. The flow-through sensor proposed allows working with several calibration lines simply by varying the sample volume injected. Thus, linear dynamic ranges from 1 to 20 and from 2 to 40 μg ml −1 can be obtained by using 1000 and 300 μl, respectively, with detection limits being 0.064 and 0.135 μg ml −1. Relative Standard Deviations (RSDs) of 0.52 and 0.38%, and sampling frequencies of 18 and 25 h −1, respectively, were also achieved. The sensor also allows the indirect determination of acetylsalicylic acid previous hydrolysis on-line to salicylic acid. For acetylsalicylic acid, a linear dynamic range from 5 to 120 μg ml −1 and 25 h −1 of sampling frequency (300 μl of sample volume) were obtained. The proposed flow-through sensor has been successfully applied to the determination of both analytes in pharmaceutical preparations.
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