Stripping voltammetric determination of silymarin in formulations and human blood utilizing bare and modified carbon paste electrodes

Silymarin is one of the most powerful natural substances that have the ability to protect and rebuild the liver cells damaged by alcohol and other toxic substances. Silymarin showed two irreversible anodic peaks in buffered solutions (pH 2.5–8.0) at either the bare carbon paste electrode or the montmorillonite-Ca modified carbon paste one. These two peaks have been attributed to oxidation of the two phenolic OH groups at positions C-20 and C-7 of silymarin molecule. A square-wave adsorptive anodic stripping voltammetry method was optimized for determination of silymarin utilizing the bare and the modified carbon paste electrodes. The method was fully validated and successfully applied for the determination of silymarin in commercial formulations and human serum without prior extraction utilizing both carbon paste electrodes. Limits of quantitation of 1 × 10−7 and 7 × 10−9 mol L−1 silymarin have been achieved in bulk form or in formulations while 2 × 10−7 and 8 × 10−9 mol L−1 silymarin were achieved in spiked human serum utilizing the bare carbon paste electrode and the modified one, respectively. The two electrodes exhibited excellent selectivity towards silymarin even in the presence of 102to 103-fold excess of its co-formulated drugs, common excipients, and common metal ions. The pharmacokinetic parameters of silymarin in plasma of healthy human volunteers were estimated following the administration of a single oral dose of 120 mg silymarin utilizing the modified carbon paste electrode. The estimated pharmacokinetic parameters were favorably compared with those reported in literature.