Electrochemical study of imipenem's primary metabolite at the mercury electrode. Voltammetric determination in urine.

Imipenem shows a fast chemical conversion to the more stable imin form (identical to that from biochemical dehydropeptidase degradation) in aqueous solutions that shows a wave at lower cathodic potential than the imipenem one. The aim of this work is the study of the electrochemical behaviour of the primary metabolite of imipenem (M1) and the proposal of electrochemical methods for the determination of M1 in human urine samples. Electrochemical studies were realized in phosphate buffer solutions over pH range 2.0-8.0 using differential pulse polarography, dc-tast polarography, cyclic voltammetry and linear sweep voltammetry (staircase). In acidic media, a non-reversible diffusion-controlled reduction involving two electrons and two protons occurs and the mechanism for the reduction was suggested. A differential pulse polarographic method for the determination of M1 in the concentration range 10(-6) to 10(-4)M with a detection limit of 4.5 x 10(-7)M was proposed. Also, a method based on controlled adsorptive pre-concentration of M1 on the hanging mercury drop electrode (HMDE) followed by linear sweep voltammetry allows its determination in the concentration range 2 x 10(-9) to 4 x 10(-8)M with a detection limit of 1.05 x 10(-9)M. The proposed methods have been used for the direct determination of M1 in spiked human urine and real human-derived urine with good results and should be appropriate for monitoring purposes.