Coated Wire Potentiometric Detection for Capillary Electrophoresis Studied Using Organic Amines, Drugs, and Biogenic Amines

Influence of Brewing Process on the Profile of Biogenic Amines in Craft Beers

The evaluation of the biogenic amines (BAs) profile of different types of craft beers is herein presented. A previously developed and validated analytical method based on ion-pair chromatography coupled with potentiometric detection was used to determine the presence of 10 BAs. Good analytical features were obtained for all amines regarding linearity (R² values from 0.9873 ± 0.0015 to 0.9973 ± 0.0015), intra- and inter-day precision (RSD lower than 6.9% and 9.7% for beer samples, respectively), and accuracy (recovery between 83.2-108.9%). Detection and quantification limits range from 9.3 to 60.5 and from 31.1 to 202.3 µg L^-1, respectively. The validated method was applied to the analysis of four ale beers and one lager craft beer. Ethylamine, spermidine, spermine, and tyramine were detected in all analyzed samples while methylamine and phenylethylamine were not detected. Overall, pale ale beers had a significantly higher total content of BAs than those found in wheat pale and dark samples. A general least square regression model showed a good correlation between the total content of BAs and the brewing process, especially for Plato degree, mashing, and fermentation temperatures. Knowledge about the type of ingredients and manufacturing processes that contribute to higher concentrations of these compounds is crucial to ensuring consumer safety.

HPLC-potentiometric method for determination of biogenic amines in alcoholic beverages: A reliable approach for food quality control

Determination of ten biogenic amines in alcoholic beverages by HPLC coupled to a potentiometric detector for food quality control is herein presented. Biogenic amines were separated by ion-pair chromatography on a C18 column using a gradient mobile phase of acetic acid, acetonitrile, and butane-sulfonic acid. Detection was accomplished by a miniaturized amine-selective electrode. The method was validated following ICH and Eurachem guidelines. Linear regression models provided R² values from 0.9870 ± 0.0019 to 0.9991 ± 0.0014 for tyramine and cadaverine, respectively. Detection and quantification limits depend on the molecular weight of BAs, ranging from 9.3 to 60.5 and from 31.1 to 202.3 µg L^-1 for methylamine and spermine, respectively. Repeatability and intermediate precision showed RSD values lower than 5.8 and 8.3%, respectively. Accuracy of assays yielded recovery values from 86.4 to 109.9%. The biogenic amines content in red wine, white wine, and beer samples were 7.54, 5.24, and 4.58 mg L^-1, respectively.

Cucurbit[8]uril-Based Potentiometric Sensor Coupled to HPLC for Determination of Tetracycline Residues in Milk Samples

The determination of chlortetracycline, doxycycline, oxytetracycline, and tetracycline in milk samples by HPLC coupled to a cucurbit[8]uril-based potentiometric sensor is herein presented. The new tetracycline-selective electrode is based on a polymeric membrane incorporating cucurbit[8]uril as a macrocyclic host, potassium tetrakis(p-chlorophenyl) borate as an ionic additive, 2-fluorophenyl 2-nitrophenyl ether as a plasticizer, and multi-walled carbon nanotubes as nanostructured materials. A microfluidic wall-jet flow-cell is implemented as a potentiometric detector after chromatographic separation by a C8 column using a gradient mobile phase of sulphuric acid and acetonitrile. The proposed methodology was validated following International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) and European Union (EU) guidelines. Linear regression models provided R2 in the range from 0.9973 ± 0.0026 to 0.9987 ± 0.0012 for all tetracycline antibiotics. The limits of detection and quantification ranged from 13.3 to 46.0 μg L−1 and 44.4 to 92.1 μg L−1, respectively. Precision intra-day, inter-day, and inter-electrode showed relative standard deviation values lower than 12.5%, 13.5%, and 12.9%, respectively. Accuracy was assessed by analysis of spiked milk samples around the maximum residue limit, yielding recovery values in the range from 81.3 to 108.5%. The simple, sensitive, cost-effective, and reliable HPLC-ion-selective electrode method justifies its use as a competitive alternative for the analysis of tetracycline residues in the food quality control sector.

A reaction-based sensing scheme for volatile organic amine reagents with the chromophoric-fluorogenic dual mode

In this study, we present the classical Michael's addition reaction-based sensing scheme for volatile organic amine reagents such as ethylenediamine, N, N-dimethylethylenediamine and diethylenetriamine using a near-infrared fluorescent dye TCF1. Obvious spectral changes in the UV-vis absorption and fluorescence spectra of TCF1 were observed upon addition of these amine reagents with an effective catalyst DBU, resulting in significant and fast color changes detectable by the naked-eye. TCF1 showed an efficient response to these amine reagents with a low detection limit, especially for diethylenetriamine. NMR and MS spectral analysis proved that the mechanism of the detection was based on the classical Michael addition, which was also verified by the theoretical calculations. In addition, a portable test paper incorporated with TCF1 had also successfully realized the detection of a low concentration of these amine reagents.

Computational optimization of a novel solid-state sensor for stable assay of isoxsuprine hydrochloride in the presence of its nephrotoxic/hepatotoxic photothermal degradation products: application in different sampling matrices

The DOE optimization of a solid-state potentiometric sensor for isoxsuprine assay in the presence of its photothermal degradation products within complex matrices.

ISE-potentiometric sensor for the determination of zolmitriptan: applications in plasma, pharmaceutical formulation and in vitro release profile

Six different sensors were fabricated and compared for the potentiometric determination of a widely used serotonin receptor agonist zolmitriptan (ZT), which is mainly used for the treatment of acute migraine attacks.

Concentration-related response potentiometric titrations to study the interaction of small molecules with large biomolecules

In the present paper, the utility of a special potentiometric titration approach for recognition and calculation of biomolecule/small-molecule interactions is reported. This approach is fast, sensitive, reproducible, and inexpensive in comparison to the other methods for the determination of the association constant values (Ka) and the interaction energies (ΔG). The potentiometric titration measurement is based on the use of a classical polymeric membrane indicator electrode in a solution of the small-molecule ligand. The biomolecule is used as a titrant. The potential is measured versus a reference electrode and transformed into a concentration-related signal over the entire concentration interval, also at low concentrations, where the millivolt (y-axis) versus log canalyte (x-axis) potentiometric calibration curve is not linear. In the procedure, Ka is calculated for the interaction of cocaine with a cocaine binding aptamer and with an anticocaine antibody. To study the selectivity and cross-reactivity, other oligonucleotides and aptamers are tested, as well as other small ligand molecules such as tetrakis(4-chlorophenyl)borate, metergoline, lidocaine, and bromhexine. The calculated Ka compared favorably to the value reported in the literature using surface plasmon resonance. The potentiometric titration approach called "concentration-related response potentiometry" is used to study molecular interaction for seven macromolecular target molecules and four small-molecule ligands.

Potentiometric sensors doped with biomolecules as a new approach to small molecule/biomolecule binding kinetics analysis

The most successful binding kinetics analysis systems at this moment include surface plasmon resonance (SPR), quartz microcrystal balance (QMB) and surface acoustic wave (SAW). Although these are powerful methods, they generally are complex, expensive and require the use of monolayers. Here, we report on potentiometric sensors as an inexpensive and simple alternative to do binding kinetics analysis between small molecules in solution and biomolecules (covalently) attached in a biopolymer sensor coating layer. As an example, dopamine and an anti-dopamine aptamer were used as the small molecule and the biomolecule respectively. Binding between both follows a Langmuir adsorption type model and creates a surface potential. The system operates in Flow Injection Analysis mode (FIA). Besides being an interesting new binding kinetics tool, the approach allows systematic design of potentiometric biosensors (in the present study a dopamine sensor), and gives new insights into the functioning of ion-selective electrodes (ISE's).

Use of potentiometric sensors to study (bio)molecular interactions

Potentiometric sensors were used to study molecular interactions in liquid environments with sensorgram methodology. This is demonstrated with a lipophilic rubber-based and a collagen-based hydrogel sensor coating. The investigated molecules were promazine and tartaric acid, respectively. The sensors were placed in a hydrodynamic wall-jet system for the recording of sensorgrams. Millivolt sensor responses were first converted to a signal, expressing the concentration of adsorbed organic ions. Using a linearization method, a pseudo-first order-kinetic model of adsorption was shown to fit the experimental results perfectly. K(assoc), k(on), and k(off) values were calculated. The technique can be used over 4 decades of concentration, and it is very sensitive to low-MW compounds as well as to multiply charged large biomolecules. This study is the first to demonstrate the application of potentiometric sensors as an alternative and complement to surface plasmon resonance methods.

Fundamentals of electrochemical detection techniques for CE and MCE

The electroanalytical techniques of amperometry, conductometry and potentiometry match well with the instrumental simplicity of CE. Indeed, all three detection approaches have been reported for electrophoretic separations. However, the characteristics of the three methods are quite distinct and these are not related to the optical methods more commonly employed. A detailed discussion of the underlying principles of each is given. The issue of possible effects of the separation voltage on the electrochemical detection techniques is considered in depth, and approaches to the elimination of such interferences are also discussed for each case.

Polymerized Nile Blue derivatives for plasticizer-free fluorescent ion optode microsphere sensors

Lipophilic H+-selective fluorophores such as Nile Blue derivatives are widely used in ISE-based pH sensors and bulk optodes, and are commonly dissolved in a plasticized matrix such as PVC. Unfortunately, leaching of the active sensing ingredients and plasticizer from the matrix dictates the lifetime of the sensors and hampers their applications in vivo, especially with miniaturized particle based sensors. We find that classical copolymerization of Nile Blue derivatives containing an acrylic side group gives rise to multiple reaction products with different spectral and H+-binding properties, making this approach unsuitable for the development of reliable sensor materials. This limitation was overcome by grafting Nile Blue to a self-plasticized poly(n-butyl acrylate) matrix via an urea or amide linkage between the Nile Blue base structure and the polymer. Optode leaching experiments into methanol confirmed the successful covalent attachment of the two chromoionophores to the polymer matrix. Both polymerized Nile Blue derivatives have satisfactory pH response and appropriate optical properties that are suitable for use in ion-selective electrodes and optodes. Plasticizer-free Na+-selective microsphere sensors using the polymerized chromoionophores were fabricated under mild conditions with an in-house sonic microparticle generator for the measurement of sodium activities at physiological pH. The measuring range for sodium was found as 10(-1)-10(-4) M and 1-10(-3) M, for Nile Blue derivatives linked via urea and amide functionalities, respectively, at physiological pH. The observed ion-exchange constants of the plasticizer-free microsphere were log K(exch) = -5.6 and log K(exch) = -6.5 for the same two systems, respectively. Compared with earlier Na+-selective bulk optodes, the fabricated optical sensing microbeads reported here have agreeable selectivity patterns, reasonably fast response times, and more appropriate measuring ranges for determination of Na+ activity at physiological pH in undiluted blood samples.

Capillary electrophoresis and microchip capillary electrophoresis with electrochemical and electrochemiluminescence detection

Recent advances and key strategies in capillary electrophoresis and microchip CE with electrochemical detection (ECD) and electrochemiluminescence (ECL) detection are reviewed. This article consists of four main parts: CE-ECD; microchip CE-ECD; CE-ECL; and microchip CE-ECL. It is expected that ECD and ECL will become powerful tools for CE microchip systems and will lead to the creation of truly disposable devices. The focus is on papers published in the last two years (from 2005 to 2006).

Development of in situ ion selective sensors for dissolution

The dissolution of formulations of the drugs dapoxetine, paliperidone, cinnarizine, tetrazepam, mebeverine, loperamide, galantamine and ibuprofen was studied by an in-line potentiometric measurement system. The transpose of a Nikolskii-Eisenman type function performed the conversion of potential to percentage of dissolution. A novel gradient membrane electrode was developed especially for dissolution, varying continuously in composition from an ionically conducting rubber phase to an electronically conducting solid state PVC/graphite composite. The gradient part had a thickness of 200 microm. The electrodes life span exceeded 6 months. An ion exchange procedure was used to prepare them for one specific drug. This enabled us to use one universal electrode built to measure a wide array of drugs. The system parameters such as accuracy, reproducibility and linearity were presented with the data obtained for the drug dapoxetine. In dissolution, accurate measurements were possible from 10(-9) to 10(-3) M concentrations, for high log P drugs. The effect of t(90) response times on the measurement error was estimated. The t(90) response times of the electrodes were concentration dependent, and varied between 50 and 10 s for, respectively, 10(-6) and 10(-3) M concentrations. Potential drift was studied in detail. The measurements performed with these electrodes showed an accuracy of 1%, and inter- and intra electrode variabilities of 0.6 and 1.7%, respectively. The electrodes were successfully applied in colloidal media containing suspended matter, typically formed during dissolution of tablets. The advantages and pitfalls of potentiometry over the presently used techniques for dissolution testing are discussed.