In this work we report an electrochemical approach to quantitative and qualitative analysis of quinine (QN) at the interface between two immiscible electrolyte solutions (ITIES). This was done at the macroscopic (macroITIES) and microscopic (µITIES) systems using ion transfer voltammetry (ITV). The linear response of the peak current vs. increasing concentrations of QN at the µITIES was from 2.50 µM to 29.13 µM and the corresponding calculated limit of detection (LOD) for the current signals originating from QN transfer from the aqueous to the organic phase was equal to 0.49 µM. Additionally, the influence of pH (2-12) of the aqueous phase on the recorded QN signals was investigated. We have found that our method is fully applicable for QN direct determination in non-treated tonic water, as confirmed on three different real samples from three different manufacturers. Finally, a number of validation parameters for the developed method are provided and discussed.

Short pieces of fused silica capillary tubing were used to support an electrified liquid – liquid interface. A methyl deactivated silica capillary having a diameter of 25 µm was filled with 1,2-dichloroethane solution and served as the organic part of the liquid – liquid interface. A non-deactivated fused silica capillary having a diameter of 5, 10 or 25 µm were filled with an aqueous HCl solution and served as the aqueous part of the electrochemical cell. For the latter, silanization of the capillary interior with chlorotrimethylsilane allowed for a successful phase reversal. All capillaries were characterized by ion transfer voltammetry using tetramethylammonium cation as a model ion. This simple, fast and low-cost miniaturisation technique was successfully applied for detection of the antibiotic ofloxacin.

In this work, the use of square-wave adsorptive stripping voltammetry (SWAdSV) in combination with boron-doped diamond electrode modified with multiwalled carbon nanotubes (MWCNTs-BDDE) and β-cyclodextrin (β-CD, β-CD-MWCNTs-BDDE) for the determination of the fungicide carbendazim (Cbz) is described for the first time. Cbz oxidation response was observed in the Britton-Robinson buffer supporting electrolyte in a pH range from 2.3 to 6.0 in potential range from + 1.0 to + 1.3 V vs SCE. The SWAdSV peak current of Cbz oxidation response on β-CD-MWCNTs-BDDE with peak maxima close to + 1.2 V vs SCE at pH 4.0 was linear over the wide linear dynamic range of 6.72 × 10⁻⁷–1.12 × 10⁻⁵ mol L⁻¹ with a detection limit (LOD) of 1.96 × 10⁻⁷ mol L⁻¹. The obtained results demonstrated the viability of the proposed methodology for determination of Cbz in river water samples containing low concentrations of Cbz. Moreover, the effect of Cbz on the corrosion properties of an AISI type 316 L stainless steel used to fabricate farming equipment and tools was tested by means of the potentiodynamic method. The characterization and evaluation of the corrosion inhibition effect raised from the use of Cbz was performed using optical microscope.

Simple sensing protocols for the detection of illicit drugs are needed. Electrochemical sensing is especially attractive in this respect, as its cost together with the analytical accuracy aspires to replace still frequently used colorimetric tests. In this work, we have shown that the interfacial transfer of protonated heroin can be followed at the electrified water-1,2-dichloroethane interface. We have comprehensively studied the interfacial behavior of heroin alone and in the presence of its major and abundant cutting agents, caffeine and paracetamol. To maximally increase developed sensing protocol applicability we have designed and 3D printed a platform requiring only a few microliters of the aqueous and the organic phase. The proposed sensing platform was equipped with a cavity hosting a short section of Ag/AgCl electrode, up to 20 µL of the aqueous phase and the end of the micropipette tip being used as a casing of a fused silica capillary having 25 µm as the internal pore diameter. The volume of the organic phase was equal to around 5 µL and was present inside the micropipette tip. We have shown that under optimized conditions heroin can be detected in the presence of caffeine and paracetamol existing in a sample with 10,000 times excess over the analyte of interest. The calculated limit of detection equal to 1.3 µM, linear dynamic range spanning to at least 50 µM, good reproducibility, and very low volume of needed sample is fully in line with forensic demands.

The electrochemical behavior of cefotaxime (CTX⁺) was investigated at the polarized macro- and micro-interface between two immiscible electrolyte solutions (ITIES) by cyclic voltammetry and alternating current voltammetry. Miniaturization was achieved with fused silica microcapillary tubing entrapped in a polymeric casing. Scanning electron microscopy (SEM) was employed for the fabricated LLI support characterization. Voltammetric investigation of CTX⁺ at macro- and μ-ITIES allowed the determination of many physicochemical parameters, such as formal Galvani potential of the ion transfer reaction ( $${\Delta }_{org}^{aq}{\varPhi}^{\prime }$$Δ org aq Φ ′ ), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (∆G^{′aq → org}), and water-1,2-dichloroethane partition coefficient ( $${\log}{P}_{water/ DCE}^{CTX+}$$log P w a t e r / D C E C T X + ). Additionally, based on the results obtained the analytical parameters including voltammetric sensitivity, limits of detection and the limits of quantification (in micromolar range) were calculated. The applicability of the developed procedures was verified in spiked still mineral and tap water samples. Graphical abstract