Levothyroxine sodium (LS, L-T4) is a sodium salt of natural thyroid hormone thyroxine (T4), commonly used in treatment of hypothyroidism. In this work a new voltammetric method of levothyroxine sodium (LS) determination using renewable mercury film electrode is presented. A linear voltammetric response was obtained for analyte in the concentration range from 0.025·10−6 mol L−1 (1.99·10−5 g L−1) to 4.0·10−6 mol L−1 (3.19·10−3 g L−1), with a detection limit of 1.8·10−8 mol L−1 for preconcentration time of 30 s. Repeatability of method was determined as RSD % for levothyroxine sodium concentration of 0.2·10−6 mol L−1 as 1.4% (n = 9). The proposed method was successfully applied and validated by studying the recovery of levothyroxine sodium in different pharmaceutical products.

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A glassy carbon electrode modified with a Nafion/MWCNTs composite is shown to enable the determination of codeine using differential pulse voltammetry in phosphate buffer of pH 3.0. At a preconcentration time of 15 s, the calibration graph is linear in the 0.5 µM (0.15 mg·L−1) to 15 µM (4.5 mg·L−1) concentration range with a correlation coefficient of 0.998. The detection limit at a preconcentration time of 120 s is as low as 4.5 μg·L−1. The repeatability of the method at a 0.6 μg·L−1 concentration level, expressed as the RSD, is 3.7% (for n = 5). The method was successfully applied and validated by analyzing codeine in drug, human plasma, and urine samples.

Novel, rapid and high sensitive voltametric methods and flow injection analysis were proposed for the determination of sodium metamizole on glassy carbon electrode modified with single-walled carbon nanotube with Nafion composite film. The results showed that SWCNT/Nafion remarkably enhanced the oxidation of metamizole which improved the anodic peak current of metamizole significantly. Under the optimized conditions peak current was proportional to sodium metamizole concentration in the range from 0.15 to 5 μM (DPV method) and from 20 to 100 μM (FIA method). The detection limit was 13 nM for DPV and 0.4 μM for FIA determination. The RSD for proposed methods were equal to 4.1% (n = 9) and 2.4% (n = 7) for voltammetry and FIA measurement respectively. Proposed methods were successfully validated by studying the recovery of metamizole in drugs and urine.

Application of cyclic renewable amalgam silver-based electrode (Hg(Ag)FE) for sensitive metronidazole detection by the differential pulse voltammetry (DPV) is described. The unique properties of the Hg(Ag)FE such as the relative large surface area and its fast and very simple renewal were fully utilized for sensitive measurements. Compared with the classical hanging mercury drop electrode (HMDE), the renewable Hg(Ag)FE significantly increases the reduction peak current of metronidazole because of its large surface area. The effects of various factors for the metronidazole determination such as: pulse height and width, step potential, surface area of the working electrode, and basic electrolyte composition are optimized. The obtained calibration graph is linear from 0.1 (17 μg L -1 ) to 2 µM (342 μg L -1 ) with correlation coefficient 0.999. For the Hg(Ag)FE with the surface area of 10.1 mm 2 the limit of detection (LOD) is 20 nM (3.4 μg L -1 ). The repeatability of the method at a concentration of the analyte of 0.5 µM (5.6 μg L −1 ), expressed as relative standard deviation (RSD) is 2.1 % (n = 7). The proposed method was successfully applied and confirmed by studying recovery of metronidazole from spiked samples.