Determination of quinine in tonic water at the miniaturized and polarized liquid-liquid interface

Determination of hordenine in beer samples and bodybuilding supplement at the electrified liquid-liquid interface

This paper presents an electrochemical approach to quantitative and qualitative determination of hordenine (HODE) at the electrified liquid-liquid interface (eLLI). In this regard, we have employed ion transfer voltammetry (ITV) as an electroanalytical detection technique. The response of peak current values (positive or negative currents) increased linearly with HODE concentration in the studied concentration range from 28.49 to 1250 μM. Furthermore, the effect of pH (2-12) of the aqueous phase on recorded HODE signals was studied. Based on the obtained results a number of significant physicochemical parameters, such as the formal Galvani potential of the ion transfer reaction (∆orgaqΦ'), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (∆G'aq→org) and water-1,2-dichloroethane partition coefficient (logPDCE') were determined. Finally, we have also showed that the elaborated method can be successfully used in the electroanalysis of complex matrixes, especially: beer and bodybuilding supplement samples.

Ready-to-use polymeric films used as the electrified liquid-liquid interface supports

In this work, we have tested two commercially available polymeric films: one with natural porosity (polyvinylidene difluoride - PVDF) and the other modified to include micropores (ethylene-vinyl acetate - EVA) created through needle puncturing. Subsequently, these films were successfully employed for the miniaturization of the electrified liquid-liquid interface formed between water and 1,2-dichloroethane solutions. The geometry of the membranes was assessed with confocal microscopy, the aqueous phase wettability was evaluated with a drop-shape analyzer whereas their ability to support the electrified liquid-liquid interfaces was followed with ion transfer voltammetry. Finally, the resulting platforms were applied to the electroanalytical detection of 2-phenylethylamine.

A dual-functional monomer-based molecularly imprinted fluorescent aptasensor employing near-infrared carbon dots for selective detection of quinine in food

A molecularly imprinted fluorescent aptasensor was designed for selective detection of quinine (Qn) based on dual functional monomers. In the sol-gel polymerization of molecularly imprinted polymers (MIPs), 3-aminopropyltriethoxysilane (APTES) and quinine aptamer (Apt) were employed as dual functional monomers, and Qn was the template molecule. Near-infrared carbon dots (RCDs) were used as fluorescence signal probe, and effectively avoided the interference of fluorescence emitted by Qn. Due to the diverse interaction among APTES, Apt and Qn, the near-infrared fluorescent molecularly imprinted aptasensor (RCDs-Apt@MIPs) exhibited higher specificity towards Qn than the sensor with APTES or Apt as a single functional monomer. The sensor had a wide linear range of 5.0-110.0 μM with a low detection limit of 1.7 μM. Satisfactory recovery between 93.4% and 104.0% with relative standard deviation from 1.30% to 3.60% in drinks, which showed great potential that this method can be used to detect Qn in food.

Electrified liquid - liquid interface strategy for sensing lactic acid in buttermilk extract

Lactic acid (LA) serves as a freshness marker in certain foods. In the present work, electrified interfaces of different nature (i.e., liquid-liquid and liquid-organogel) have been developed for the quantification of LA. Electrochemical sensing of LA at the liquid-organogel interface revealed that adsorptive stripping voltammetry, with a preconcentration time of 500 s offered better sensitivity. Electroanalytical ability of LA under optimized conditions displayed a detection limit of 0.97 μM and 0.71 μM with sensitivity of 2.84 nA μM-1 and 3.59 nA μM-1 for liquid-liquid and liquid-organogel interfaces respectively. Quantification of LA using the developed methodology has been demonstrated in buttermilk as the real matrix. Analysis demonstrate that electrified liquid-liquid and liquid-organogel interfaces are promising approach for sensing LA in buttermilk extract.

Electroanalytical applications of ITIES - A review

Over the last decades, the interface between two immiscible electrolyte solutions (ITIES) attracted considerable attention of the scientific community due to their vast applications, such as extraction, catalysis, partition studies and sensing. The aim of this Review is to highlight the potential of electrochemistry at the ITIES for analytical purposes, focusing on ITIES-based sensors for detection and quantification of chemically and biologically relevant (bio)molecules. We start by addressing the evolution of ITIES in terms of number of publications over the years along with an overview of their main applications (Chapter 1). Then, we provide a general historical perspective about pioneer voltammetric studies at water/oil systems (Chapter 2). After that, we discuss the most impacting improvements on ITIES sensing systems from both perspectives, set-up design (interface stabilization and miniaturization, selection of the organic solvent, etc.) and optimization of experimental conditions to improve selectivity and sensitivity (Chapter 3). In Chapter 4, we discuss the analytical applications of ITIES for electrochemical sensing of several types of analytes, including drugs, pesticides, proteins, among others. Finally, we highlight the present achievements of ITIES as analytical tool and provide future challenges and perspectives for this technology (Chapter 5).

The Protective Action of Coutarea hexandra (Rubiaceae) on the Neuromuscular Blockade Induced by Lachesis muta muta (Viperidae: Crotalinae) Venom

Envenomations by snakes represent a neglected health problem in tropical and subtropical countries. In South America, Lachesis muta occasionally causes severe human envenomation, with treatment being conditioned to an unspecific antivenom. In this work, we examined the neutralizing ability of Coutarea hexandra stem bark hydroalcoholic extract (Ch-E), including the commercial phytochemicals coumarin and quinine, on the neuromuscular blockade induced by L. m. muta venom in mouse phrenic nerve-diaphragm preparation. Biological assays were performed following conventional myographic technique ex vivo. Ch-E was phytochemically characterized to detect the presence of coumarin and quinine using analytical methods. Ch-E and commercial phytochemicals were tested separately or combined under pre- and post-venom incubation protocols. Ch-E attenuated the venom-induced neuromuscular blockade only under the pre-venom incubation protocol. Quinine was not detected in Ch-E. Commercial coumarin and quinine exhibited a concentration-dependent counteracting effect on the venom-induced neuromuscular blockade. The pre-venom incubation protocol showed to be efficient in attenuating the L. m. muta venom-induced neuromuscular blockade, most likely due to the presence of coumarin derivatives and unknown alkaloids in this extract.

Testing adulterated liquid-egg: developing rapid detection techniques based on colorimetry, electrochemistry, and interfacial fingerprinting

To develop rapid detection techniques for liquid eggs' adulteration, three types of adulterations were considered: water dilution, manipulation of yolk ratio in whole egg, and blending different varieties of egg white or yolk. Objective: Establish detection techniques utilizing colorimetry, electrochemistry, and interfacial fingerprinting for these adulterations, respectively. Results: Colorimetry allows for detection (1 min·sample-1) of water dilution through linear (R2 ≥ 0.984) and exponential fitting (R2 ≥ 0.992); Electrochemistry enables detection (6 min·sample-1, R2 ≥ 0.979) of the adulteration of yolk ratio in whole egg; Interfacial fingerprinting technique effectively detects (detection duration: 10 min·sample-1, detection limit: 1.0-10.0 wt%) the adulteration of different varieties of egg white. Subsequently, through 3D-fluorescence microscopy (interface height variation: 22.49-573.45 μm), interfacial tension variation (65.54-35.48 mN·m-1), contact angle variation (89.7°-32.9°), particle size range (free water: 0.94-14.29 μm; protein aggregation: 6.57-10.76 μm), and etc., interfacial fingerprinting mechanism was elucidated. This research contributes novel insights into the detection of adulteration in liquid eggs.

Comparative electrochemical study of veterinary drug danofloxacin at glassy carbon electrode and electrified liquid-liquid interface

This work compares the electroanalytical performance of two electroanalytical systems based on (1) the glassy carbon electrode (GCE), and (2) the electrified liquid-liquid interface (eLLI), for the detection of fluoroquinolone antibiotic-danofloxacin (DANO). Our aim was to define the optimal conditions to detect the chosen analyte with two employed systems, extract a number of electroanalytical parameters, study the mechanism of the charge transfer reactions (oxidation at GCE and ion transfer across the eLLI), and to provide physicochemical constants for DANO. Detection of the chosen analyte was also performed in the spiked milk samples. To the best of our knowledge, this is the first work that directly compares the electroanalytical parameters obtained with solid electrode (in this case GCE) and eLLI. We have found that for DANO the latter provides better electroanalytical parameters (lower LOD and LOQ) as well as good selectivity when the milk was analyzed.

Phenylethylamine sensing at the electrified liquid-liquid interface. Can electrochemistry be used to follow the UHT milk spoilage process?

This study involved an investigation into the electrochemical characteristic of a few biogenic amines (BAs) occurring at the polarized interface between two immiscible electrolyte solutions (ITIES) with ion transfer voltammetry (ITV). The main focus of this research was the comprehensive electroanalytical and physicochemical analysis of phenylethylamine (PEA), allowing the determined of the formal Galvani potential of the ion transfer reaction (ΔorgaqΦ'), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (ΔG'aq→org) and water-1,2-dichloroethane partition coefficient (logPwater/DCEPEA). Furthermore, the collected data were employed to calculate analytical parameters, including voltametric detection sensitivity, limits of detection and the target analyte quantification. Moreover, the influence of the presence of 7 other BAs (histamine, spermine, spermidine, putrescine, cadaverine, tyramine and tryptamine) on the recorded signals originating from the PEA ion transfer was checked. The feasibility of the developed method was corroborated through experimentation with milk samples. Additionally, utilizing the devised methodology, an electrochemical assessment of the spoilage progression in milk samples was undertaken.

Electrochemical screening of selected β-blockers at a polarized liquid-liquid interface

This paper describes the electrochemical behavior of five β-blockers at the polarized liquid-liquid interface formed between aqueous solution (sodium chloride solution or Britton-Robinson buffers) and bis(triphenylphosphoranylidene)ammonium tetrakis(4-chlorophenyl)borate (BTPPATPBCl) dissolved in 1,2-dichloroethane (the organic phase). All measurements reported in this work were conducted using cyclic voltammetry (CV). The effects of the concentration of analytes, the pH of the aqueous phase, and applied electrochemical parameters on the analytical performance of the studied system are studied and discussed. The linear dynamic ranges (LDRs) of the studied β-blockers were in the range of 5-200 μmol L-1 and the lowest limit of detection (LOD) value was determined for pindolol (LOD = 1.96 μM μmol L-1). The highest LOD value was 4.96 μmol L-1 found for nebivolol. In addition, physicochemical parameters such as the formal Galvani potential difference (Δaqorgϕ), formal Gibbs free energies of the ion transfer reaction (ΔaqorgG') and partition coefficients (log P'aq/org) for all studied molecules were determined. The latter were compared and correlated with the available literature values of log Poctanol. Finally, a standard addition method was used to determine the concentration of nebivolol in pharmaceutical preparations using a platform based on the electrified liquid-liquid interface.

Electroanalytical characterization of clozapine at the electrified liquid-liquid interface and its detection in soft and hard drinks

Clozapine (CZ) is a prescribed benzodiazepine psychiatric drug that is often possessed as an illicit drug and is associated with drug-facilitated sexual assaults (DFSA) due to its strong sedative capabilities. Hence, we propose an electrified liquid-liquid interface (eLLI) based transducing element as an alternative electroanalytical platform for rapid screening of CZ in soft and hard drinks which is habitually associated with DFSA crimes. First, molecular partitioning and the effect of chemical composition, pH, and the presence of ethanol in the biphasic configuration of the aqueous phase on the interfacial behaviour and analytical performance of the CZ at the eLLI have been investigated with voltammetry. Next, the electrochemical profiles of various soft and hard drinks were studied at the eLLI. The eLLI-based CZ sensor has shown a broad dynamic range (15-150 μM), lower detection limits (1μM), and adequate reliability towards rapid CZ screening in spiked soft and hard drink samples with reference to the standard chromatographic analysis.

A Novel Equipment-Free Paper-Based Fluorometric Method for the Analytical Determination of Quinine in Soft Drink Samples

A simple, equipment-free, direct fluorometric method, employing paper-based analytical devices (PADs) as sensors, for the selective determination of quinine (QN) is described herein. The suggested analytical method exploits the fluorescence emission of QN without any chemical reaction after the appropriate pH adjustment with nitric acid, at room temperature, on the surface of a paper device with the application of a UV lamp at 365 nm. The devices crafted had a low cost and were manufactured with chromatographic paper and wax barriers, and the analytical protocol followed was extremely easy for the analyst and required no laboratory instrumentation. According to the methodology, the user must place the sample on the detection area of the paper and read with a smartphone the fluorescence emitted by the QN molecules. Many chemical parameters were optimized, and a study of interfering ions present in soft drink samples was carried out. Additionally, the chemical stability of these paper devices was considered in various maintenance conditions with good results. The detection limit calculated as 3.3 S/N was 3.6 mg L^-1, and the precision of the method was satisfactory, being from 3.1% (intra-day) to 8.8% (inter-day). Soft drink samples were successfully analyzed and compared with a fluorescence method.

Nitrazepam and 7-aminonitrazepam studied at the macroscopic and microscopic electrified liquid-liquid interface

Two benzodiazepine type drugs, that is, nitrazepam and 7-aminonitrazepam, were studied at the electrified liquid-liquid interface (eLLI). Both drugs are illicit and act sedative in the human body and moreover are used as date rape drugs. Existence of the diazepine ring in the concerned chemicals structure and one additional amine group (for 7-aminonitrazepam) allows for the molecular charging below their pKa values, and hence, both drugs can cross the eLLI interface upon application of the appropriate value of the Galvani potential difference. Chosen molecules were studied at the macroscopic eLLI formed in the four electrode cell and microscopic eLLI formed within a microtip defined as the single pore having 25 μm in diameter. Microscopic eLLI was formed using only a few μL of the organic and the aqueous phase with the help of a 3D printed cell. Parameters such as limit of detection and voltammetric detection sensitivity are derived from the experimental data. Developed methodology was used to detect nitrazepam in pharmaceutical formulation and both drugs (nitrazepam and 7-aminonitrazepam) in spiked biological fluids (urine and blood).

Heroin detection in a droplet hosted in a 3D printed support at the miniaturized electrified liquid-liquid interface

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.

Voltammetric study of cefotaxime at the macroscopic and miniaturized interface between two immiscible electrolyte solutions

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 (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta }_{org}^{aq}{\varPhi}^{\prime }$$\end{document}ΔorgaqΦ′), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (∆G^{′aq → org}), and water-1,2-dichloroethane partition coefficient (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\log}{P}_{water/ DCE}^{CTX+}$$\end{document}logPwater/DCECTX+). 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.