Solid phase extraction of thionine on agar as an adsorbent and spectrophotometric determination

A new sensitive solid phase extraction procedure has been developed for the separation and determination of thionine by spectrophotometry. In this method thionine is retained by agar as an adsorbent in a mini-column, eluted by sulfuric acid-acetone mixture and its absorbance is measured at 600 nm. The effect of different parameters such as pH, eluent type and volume, flow rate, amount of adsorbent and volume of sample on the adsorption was investigated and optimum conditions were established. The calibration graph was linear in the range of 3-100 ng/mL of thionine in the initial solution with r = 0.9984. Limit of detection (LOD) based on 3s (b) was 0.9 ng/mL and the relative standard deviation (RSD) for 20 ng/mL of thionine was 2.9%. The method was applied to the determination of thionine in water samples.