Method for voltammetric determination of leucovorin, a drug frequently applied to decrease some unfavorable effects of anticancer drugs such as methotrexate or to increase the therapeutic effect of 5-fluorouracil, has been developed employing a bare boron-doped diamond electrode. It is the first method for leucovorin determination based on its electrochemical oxidation. Although at least three anodic and three cathodic voltammetric peaks could be recorded under the used conditions, only the anodic response situated at about ? 900 mV (vs. saturated Ag|AgCl electrode) was suitable, namely due to its shape and position, for analytical purposes. Using differential pulse voltammetry with optimized parameters and supporting electrolyte of pH 3, the linear dynamic range of leucovorin determination was recorded from 0.15 to 25 lmol dm-3. Under such conditions, low limit of quantification of 0.050 lmol dm-3 and limit of detection of 0.015 lmol dm-3 as well was reached. Relative standard deviation calculated from 11 repeated measurements amounted to 0.7% and calculated from five repeated determinations amounting less than 3.0%. Applicability of the developed method was verified by repeated analysis of the pharmaceutical preparation with excellent results (recovery 98.7-102.8%, relative standard deviation 1.81%).

Set of the lab-made boron-doped diamond electrodes (BDDEs) prepared with various B/C ratio (1000, 2000, 4000, 8000, 10 000, and 20 000 ppm) in the gas phase was subjected to the detailed characterization in the present paper. It was proved, that the B/C ratio influenced the electrochemical features of the working electrodes like a width of the potential window, which decreased with increasing B/C. Variations of reversibility of two redox systems (Fe(CN) 6 3−/4− and Ru(NH 3) 6 2+/3+) depending on B/C were observed as well. The best electrochemical properties were found for BDDE with B/C 10 000 ppm. Moreover, the working electrodes were tested for voltammetric analysis of leucovorin based on its oxidation. The lab-made BDDEs were applied for voltammetric analysis of the pharmaceutical preparation containing leucovorin with excellent results (recovery 97.7-103.3 %, RSD 5 ≤ 2.1 %).