SORPTION BEHAVIOR IN THE “CLONIDINE–CHITOSAN” SYSTEM AND ITS APPLICATION TO SAMPLE PREPARATION FOR THIN-LAYER CHROMATOGRAPHIC DETERMINATION OF CLONIDINE

The possibility of improving the thin-layer chromatographic determination of clonidine in biological samples by using chitosan as a functional sorption material at the sample preparation stage was investigated. The chromatographic mobility of clonidine in seven solvent systems was studied, and the dependence of the Rf value on the mobile-phase composition was established. The methanol–25% ammonium hydroxide (98:2) and methanol–water–hydrochloric acid (49.5:49.5:1) systems were found to be the most promising for analytical applications, providing satisfactory chromatographic mobility and close Rf values for the standard solution and clonidine isolated from biological matrices. A set of chemical visualization reagents and UV detection at 254 nm were investigated for visualization of clonidine zones. The efficiency of clonidine sorption by chitosan was found to depend significantly on the pH of the medium. The maximum sorption efficiency of 84.7% and equilibrium sorption capacity of 169.4 μg/g were achieved at pH 9.0. The efficiency of clonidine desorption from the chitosan sorbent was investigated; the highest desorption efficiency of 91.2% was achieved using acidified methanol. Comparative evaluation of conventional extraction and chitosan-assisted sample preparation showed an increase in clonidine recovery from 74.8 to 86.5% and a decrease in the relative standard deviation from 6.2 to 4.7%. Sorption preconcentration using chitosan reduced the limit of detection of clonidine by TLC from 3.0 to 1.6 μg/sample without any significant change in its chromatographic mobility. The results demonstrate the potential of chitosan for the extraction, clean-up, and preconcentration of clonidine from biological samples prior to TLC analysis. The proposed approach may be useful for the further development of accessible screening procedures for the chemical-toxicological and forensic-toxicological analysis of clonidine.