Solid‐phase Extraction Coupled Simple On‐line Derivatization Gas Chromatography – Tandem Mass Spectrometry for the Determination of Benzophenone‐type UV Filters in Aqueous Samples

The rapid determination of three benzophenone‐type UV filters: 2‐hydroxy‐4‐methoxy‐benzophenone (BP‐3), 2,4‐dihydroxybenzophenone (BP‐1) and 2,2′‐dihydroxy‐4‐methoxy‐benzophenone (BP‐8), in aqueous samples is described. The method involved the extraction of an aqueous sample using an Oasis HLB solid‐phase extraction (SPE) cartridge, followed by on‐line derivatization gas chromatography ‐ tandem mass spectrometry (GC‐MS/MS) with a trimethylsilylating (TMS) reagent. This eco‐friendly, injection‐port derivatization method, is sensitive, rapid, and provides reproducible results for these hydroxylated benzophenones in aqueous samples. The limits of quantitation (LOQs) were determined to be 1.0 to 2.5 ng/L for samples in 100 mL of water. The precision for these analytes, as indicated by relative standard deviations (RSDs), proved to be less than 11% for both intra‐ and inter‐day analysis. Accuracy, expressed as the mean extraction yield, was between 80 and 106%. The method was then applied to some environmental water samples, river water and samples of effluents from a wastewater treatment plant (WWTP), having the potential to contain BP‐3 and BP‐1.     

Separation of Enantiomers by On‐Line Capillary Isotachophoresis‐Capillary Zone Electrophoresis

The ability of capillary zone electrophoresis (CZE) coupled on‐line with capillary isotachophoresis (ITP) sample pretreatment in the column‐coupling capillary electrophoresis equipment to separate trace enantiomers present in samples of complex ionic matrices and enantiomers present in their mixtures at significantly differing concentrations has been studied. Enantiomers of 2,4‐dinitrophenyl labeled norleucine (DNP‐Nleu) and tryptophan enantiomers were employed as model analytes in this work while urine and mixtures of tryptophan enantiomers of differing concentrations served as model samples. Experiments performed with urine samples spiked with the DNP‐Nleu racemate at sub‐μmol/L concentrations demonstrated excellent sample pretreatment capabilities of ITP (concentration of the analytes, in‐column and post‐column sample clean up) when coupled on‐line with chiral CZE separations. In the CZE separations of enantiomers present in the samples at trace concentrations the sample pretreatment could be performed in both achiral and chiral ITP electrolyte systems. The use of a chiral electrolyte system was found to be essential in the ITP pretreatment of the samples containing the enantiomers at very differing concentrations. For example, a 2×10^–7 mol/L concentration of L‐tryptophan could be detected in the CZE separation stage of the ITP‐CZE combination in samples containing about a 10⁴ excess of D‐tryptophan only when the ITP pretreatment was carried out in the electrolyte system providing the resolution of enantiomers (α‐cyclodextrin served for this purpose in the present work). A post‐column ITP sample clean up was found effective in enhancing the destacking rate of the trace enantiomer in the CZE stage when the migration configuration of the enantiomers was less favorable (the trace constituent migrating behind the major enantiomer).     

Ionic Liquid Modified Single‐use Electrode Developed for Voltammetric Detection of miRNA‐34a and its Application to Real Samples

The ionic liquid (IL) modified chemically activated (CA) pencil graphite electrodes (PGEs) were developed for label‐free voltammetric detection of miRNA‐34a, and implemented to the real samples. Firstly, the electrochemical characterization of unmodified PGE, CA‐PGE, IL‐PGE and IL‐CA‐PGE was performed by cyclic voltammetry (CV) as well as their DNA binding capacity was studied by electrochemical impedance spectroscopy (EIS) technique. The microscopic characterization of the surface of each electrodes was investigated by scanning electron microscopy (SEM). Differential pulse voltammetry (DPV) technique was used for measuring the oxidation signal of guanine in order to perform a label‐free voltammetric monitoring of a full‐match hybridization specific to miRNA‐34a. The selectivity of biosensor was tested against to miRNA‐155, miRNA‐660 as well as to the mismatch sequence of miRNA‐34a. The further selectivity of this proposed biosensor was studied in the mixture of samples containing miRNA‐34a with other miRNAs (1 : 1). The voltammetric detection of miRNA‐34a was also explored in the artificial serum medium as fetal bovine serum (FBS) and also in total RNA samples isolated from HUH‐7 human hepatocellular carcinoma cell line.     

Stereoselective On‐Surface Cyclodehydrofluorization of a Tetraphenylporphyrin and Homochiral Self‐Assembly

The thermally induced cyclodehydrofluorization of iron tetrakis(pentafluorophenyl)porphyrin proceeded highly stereoselectively to give a prochiral product on a gold surface in an ultrahigh vacuum, whereas dehydrocyclization of the respective iron tetrakisphenylporphyrin did not show such selectivity. Stereoselectivity was predominantly observed for closely packed layers, which is an indication of intermolecular cooperativity and steric constraints induced by adjacent species. Density functional theory identified intermolecular packing constraints as the origin of such selectivity during the reaction. Scanning tunneling microscopy revealed the formation of an enantiomerically pure two‐dimensional self‐assembly as a conglomerate of mirror domains. On‐surface two‐dimensional topochemistry, as reported herein, may open new routes for stereoselective synthesis.     

Selective Voltammetric Detection of Uric Acid in the Presence of Ascorbic Acid at Well‐Aligned Carbon Nanotube Electrode

The voltammetric behaviors of uric acid (UA) and L ‐ascorbic acid (L ‐AA) were studied at well‐aligned carbon nanotube electrode. Compared to glassy carbon, carbon nanotube electrode catalyzes oxidation of UA and L ‐AA, reducing the overpotentials by about 0.028 V and 0.416 V, respectively. Based on its differential catalytic function toward the oxidation of UA and L ‐AA, the carbon nanotube electrode resolved the overlapping voltammetric response of UA and L ‐AA into two well‐defined voltammetric peaks in applying both cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which can be used for a selective determination of UA in the presence of L ‐AA. The peak current obtained from DPV was linearly dependent on the UA concentration in the range of 0.2 μM to 80 μM with a correlation coefficient of 0.997. The detection limit (3δ) for UA was found to be 0.1 μM. Finally, the carbon nanotube electrode was successfully demonstrated as a electrochemical sensor to the determination of UA in human urine samples by simple dilution without further pretreatment.     

Biomimetic Peptide‐Gated Nanoporous Membrane for On‐Demand Molecule Transport

The controllable molecule transport is crucial to realize many highly valuable applications both in vivo and in vitro. Nanoporous membranes, with nanoscopic pores, high porosity, uniform pore dimensions, and controllable surface chemical properties, hold tremendous potential to achieve this function. Herein, we report a nano‐gating system for on‐demand molecule transport based on a peptide‐gated nanoporous membrane. Acting as gatekeeper, the peptides introduced to the nanoporous membrane provide an opportunity to realize on‐demand on–off states via reversible conformational switching of the peptides. This nano‐gating system offers sustained release and can be used as a sophisticated molecule transport platform for localized drug delivery with a feedback function.     

On‐Surface Reactions

On‐surface synthesis constitutes a rapidly growing field of research due to its promising application for creating stable molecular structures on surfaces. While self‐assembled structures rely on reversible interactions, on‐surface synthesis provides the potential for creating long‐term stable structures with well‐controlled properties, for example superior electron transport for future molecular electronic devices. On‐surface synthesis holds the promise for preparing insoluble compounds that cannot be produced in solution. Another highly exciting aspect of on‐surface synthesis is the chance to discover new reaction pathways due to the two‐dimensional confinement of the reaction educts. In this review, we discuss the current state‐of‐the‐art and classify the reactions that have been successfully performed so far. Special emphasis is put on electrically insulating surfaces, as these substrates pose particular challenges for on‐surface synthesis while at the same time bearing high potential for future use, for example, in molecular electronics.     

Ability to determine the desferrioxamine‐chelatable iron fractions of nontransferrin‐bound iron using HPLC

Iron is an essential element in human development. It is imperative for oxygen and electron transport and also for DNA and neurotransmitters synthesis. On the other hand, this metal is able to participate in Fenton's reaction that in turn leads to free radical damage. The most toxic fraction of iron – nontransferrin‐bound iron and its part desferrioxamine‐chelatable iron – can serve as an exquisite biomarker in the identification of iron imbalance. The goal of the present study was to devise a simple, repeatable, and inexpensive method for the determination of desferrioxamine‐chelatable iron in serum blood samples. The assay procedure is based on desferrioxamine complex formation with iron ions followed to ferrioxamine and its quantitative measurement using RP‐HPLC method. The desferrioxamine‐chelatable iron was extracted from blood by centrifugation and SPE method. Chromatographic separation was performed at 40°C by step‐form gradient elution using Cadenza CD‐C18 column (150 × 4.6 mm id, particle size of 3.0 μm) connected with precolumn for contaminants removal. Gradient HPLC elution has been carried out with solvent A (10 mM Tris‐HCl, pH 5.5) and solvent B (ACN). The flow rate was 1.2 mL/min, and the total separation time was 5 min. The linear quantitation range was 2.5–500 μM (r = 0.9973), and the LOD and LOQ were 0.42 and 1.29 μM, respectively. Proposed HPLC method allowed for the determination of desferrioxamine‐chelatable iron fraction's of nontransferrin‐bound iron, both in the buffer and the serum supplemented with iron ions as well as in the patients’ serum samples with good results of precision and recovery. The developed method found to be sufficiently precise and reproducible for established conditions and after validation and may be used for routine assay of desferrioxamine‐chelatable iron in biological samples.     

Determination of Se(IV) in On‐Line System by Cathodic Stripping Voltammetry

A sensitive and selective on‐line voltammetric procedure for determination of traces of Se(IV) is presented. The pulsed potential accumulation was proposed for minimization of interferences of surface active substances and foreign ions. The calibration plot was linear from 1×10^?9 mol L^?1 to 4×10^?8 mol L^?1 for accumulation time of 180 s. The relative standard deviation was 6.1% (n=5) for a Se(IV) concentration of 1×10^?8 mol L^?1. The detection limit estimated from (3 σ) for an accumulation time of 180 s was about 4×10^?10 mol L^?1. The validation of the procedure proposed was made by a recovery tests for tap and river water samples.     

Gold Electrode Modified with Self‐Assembled Monolayer of Cysteamine‐Functionalized MWCNT and Its Application in Simultaneous Determination of Dopamine and Uric Acid

The voltammetric behavior of dopamine (DA) and uric acid (UA) on a gold electrode modified with self‐assembled monolayer (SAM) of cysteamine (CA) conjugated with functionalized multiwalled carbon nanotubes (MWCNTs) was investigated. The film modifier of functionalized SAM was characterized by means of scanning electron microscopy (SEM) and also, electrochemical impedance spectroscopy (EIS) using para‐hydroquinone (PHQ) as a redox probe. For the binary mixture of DA and UA, the voltammetric signals of these two compounds can be well separated from each other, allowing simultaneous determination of DA and UA. The effect of various experimental parameters on the voltammetric responses of DA and UA was investigated. The detection limit in differential pulse voltammetric determinations was obtained as 0.02 µM and 0.1 µM for DA and UA, respectively. The prepared modified electrode indicated a stable behavior and the presence of surface COOH groups of the functionalized MWCNT avoided the passivation of the electrode surface during the electrode processes. The proposed method was successfully applied for the determination of DA and UA in urine samples with satisfactory results. The response of the gold electrode modified with MWCNT‐functionalized SAM method toward DA, UA, and ascorbic acid (AA) oxidation was compared with the response of the modified electrode prepared by the direct casting of MWCNT.     

On‐chip electromembrane extraction of acidic drugs

In the present work, a new supported liquid membrane (SLM) has been developed for on‐chip electromembrane extraction of acidic drugs combined with HPLC or CE, providing significantly higher stability than those reported up to date. The target analytes are five widely used non‐steroidal anti‐inflammatory drugs (NSAIDs): ibuprofen (IBU), diclofenac (DIC), naproxen (NAX), ketoprofen (KTP) and salicylic acid (SAL). Two different microchip devices were used, both consisted basically of two poly(methyl methacrylate) (PMMA) plates with individual channels for acceptor and sample solutions, respectively, and a 25 µm thick porous polypropylene membrane impregnated with the organic solvent in between. The SLM consisting of a mixture of 1‐undecanol and 2‐nitrophenyl octyl ether (NPOE) in a ratio 1:3 was found to be the most suitable liquid membrane for the extraction of these acidic drugs under dynamic conditions. It showed a long‐term stability of at least 8 hours, a low system current around 20 µA, and recoveries over 94% for the target analytes. NPOE was included in the SLM to significantly decrease the extraction current compared to pure 1‐undecanol, while the extraction properties was almost unaffected. Moreover, it has been successfully applied to the determination of the target analytes in human urine samples, providing high extraction efficiency.     

Electrochemical Properties of Electrode Modified with Langmuir‐Blodgett Film of p‐tert‐Butylcalix[4]arene Derivatives and Its Application in Determining of Silver

A new type of voltammetric sensor, Langmuir‐Blodgett (LB) film of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐di(3‐thiadiazole‐propanoxy)‐26,28‐dihydroxycalix[4]arene modified glassy carbon electrode (LB_TZCA–GCE), was prepared. The electrochemical properties of LB_TZCA–GCE were researched in detail and its recognizing mechanism for silver ion in aqueous solution was discussed. Using this voltammetric sensor, a new stripping voltammetric method for determining of Ag⁺ was erected with good sensitivity, selectivity, reproducibility and recovery. The detection limit was 8×10^?9 M at accumulation time of 180 s. By this method, real samples (lake water, tap water and synthesis sample) were analyzed and the results obtained were well satisfactory.     

Construction of a New Flow‐through Cell for Screen Printed Electrodes

In this paper a new flow‐through cell for voltammetric determinations using screen printed electrodes is described. This cell is much simpler than one with similar performances described in a previous work. This new flow‐through cell has been coupled to a multisyringe flow injection system (MSFIA) and to a multiport selection valve allowing the online calibration using the standard addition method. The uses of the MSFIA, together with the small volume of the flow cell and the reduced surface area of the solid phase electrode (SPE) have considerably reduced the volume of reagents and samples to be used. This system has allowed obtaining similar or better detection limits than those obtained using other techniques and flow analysis devices such as SIA, FIA, LOV and microfluidic channels. Graphite ink has been used for the development of screen‐printed electrodes. The determination of Cd and Pb with ASV has been made through its co‐deposition with Bi. For this, Bi(III) solution and the sample were mixed in line. Due to the creation of a new Bi film in each voltammetric cycle, very well defined and reproducible peaks corresponding to Cd and Pb have been obtained. The use of Bi is one of the most important advantages of this system, since it is a recognized substitute for Hg, and its impact on the environment is much lower due to its reduced toxicity. The fact of being an automatic system, the low cost of its components, its simplicity and ease of handling, make it a system that could be useful for monitoring tasks in fieldwork, or measurements on board.     

Ultrasound Assisted Emulsification Microextraction Based on dimetyl (E)‐2‐[(Z)‐1‐acetyl)‐2‐hydroxy‐1‐propenyl]‐2‐butenedioate for Determination of Total Amount of Iron in Water and Tea Samples

An ultrasound assisted emulsification microextraction (USAEME) is successfully used for extraction and determination of trace amount of iron in water and tea samples, followed by flame atomic absorption spectroscopy (FAAS). In this approach, a new synthetic ligand dimetyl (E)‐2‐[(Z)‐1‐acetyl)‐2‐hydroxy‐1‐propenyl]‐2‐butenedioate (DAHPB) is used as chelating agent and chloroform is selected as an extraction solvent. The factors influencing the complex formation and extraction by USAEME method are optimized. These factors are extraction solvent type as well as extraction volume, time, temperature, pH, and the amount of chelating agent. Under optimum conditions, an enrichment factor of 202.9 is obtained from only 7.1 mL of aqueous phase. The calibration graph using the preconcentration system for iron is linear between 40.0 and 800.0 μg L^?1 with a detection limit of 7.4 μg L^?1. The relative standard deviation (R.S.D) for ten replicate measurements of 500.0 μg L^?1 of iron is 2.5%.     

Voltammetric Determination of α‐Tocopheryl Acetate in Pharmaceutical Dosage Forms

A simple and rapid voltammetric method has been developed for the quantitative determination of α‐tocopheryl acetate (α‐TOAc) in pharmaceutical preparations. Studies with linear scan (LSV), square‐wave (SQWV) and differential pulse voltammetry (DPV) were carried out using platinum microelectrodes. A well‐defined, irreversible oxidation wave/peak was obtained at 1.30 V (vs. Ag/AgCl reference electrode.) The use of SQWV or DPV technique provides a precise determination of α‐tocopheryl acetate using the multiple standard addition method. The statistical parameters and the recovery study data clearly indicate good reproducibility and accuracy of the method. Accuracy of the results assessed by recovery trials was found within the 99.3% to 103.5%, and 99.1% to 101.4%, for SQWV and DPV, respectively. The quantification limits for the both voltammetric techniques were found to be 6×10^?5 M (SQWV) and 7×10^?5 M (DPV). Analysis of the authentic samples containing α‐TOAc showed no interference with common additives and excipients, such as unsaturated fatty acids (co‐formulated as glycerine esters) and vitamin A (as retinol or β‐carotene). The method proposed does not require any pretreatment of the pharmaceutical dosage forms. A gas chromatography determination of α‐TOAc in real samples was also performed for comparison.     

Genomics‐Driven Discovery of NO‐Donating Diazeniumdiolate Siderophores in Diverse Plant‐Associated Bacteria

Siderophores are key players in bacteria–host interactions, with the main function to provide soluble iron for their producers. Gramibactin from rhizosphere bacteria expands siderophore function and diversity as it delivers iron to the host plant and features an unusual diazeniumdiolate moiety for iron chelation. By mutational analysis of the grb gene cluster, we identified genes (grbD and grbE) necessary for diazeniumdiolate formation. Genome mining using a GrbD‐based network revealed a broad range of orthologous gene clusters in mainly plant‐associated Burkholderia/Paraburkholderia species. Two new types of diazeniumdiolate siderophores, megapolibactins and plantaribactin were fully characterized. In vitro assays and in vivo monitoring experiments revealed that the iron chelators also liberate nitric oxide (NO) in plant roots. This finding is important since NO donors are considered as biofertilizers that maintain iron homeostasis and increase overall plant fitness.     

Electrochemical Behavior and Determination of Hyoscine‐N‐Butylbromide from Pharmaceutical Preparations

The electrooxidation of hyoscine N‐butylbromide (HBB) was investigated by rotating disk electrode voltammetry, cyclic voltammetry and controlled potential coulometry in 0.1 M HNO₃ and in 0.1 M tetrabutylammonium perchlorate (TBAP) solutions of acetonitrile at a platinum (Pt) electrode. Based on the results obtained, it is suggested that a bromide ion of HBB was oxidized in one reversible step in aqueous solutions and in two reversible steps in acetonitrile. A differential pulse voltammetric (DPV) method at a Pt electrode was developed for the determination of HBB in the concentration range of 1.0 × 10^?6‐1.0 × 10^?3 M. The procedure was applied to the determination of HBB in its formulations as well as its recovery from blood serum and urine samples.     

Voltammetry of a Novel Antimycobacterial Agent 1‐Hydroxy‐N‐(4‐nitrophenyl)naphthalene‐2‐carboxamide in a Single Drop of a Solution

The aim of this study is the development of a miniaturized voltammetric method for the determination of an antimycobacterial agent 1‐hydroxy‐N‐(4‐nitrophenyl)naphthalene‐2‐carboxamide (HNN) in a single drop (20 μL) of a solution by cathodic and anodic voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate its redox properties followed by the optimization of differential pulse voltammetric determination in a regular 10 mL volume. The optimal medium for the analytical application of both cathodic and anodic voltammetry was found to be Britton‐Robinson buffer pH 7.0 and dimethyl sulfoxide (9 : 1, v/v). HNN gave one cathodic peak at around −0.6 V and one anodic peak at around +0.2 V vs. Ag|AgCl (3 mol L⁻¹ KCl) reference electrode. Determination of HNN in a 10 mL volume gave the limit of quantification around 10 nmol L⁻¹ by both adsorptive stripping anodic and cathodic voltammetry. Afterwards, miniaturized voltammetric methods in a single drop of solution (20 μL) were investigated. This approach requested some modifications of the cell design and voltammetric procedures. A novel method of removing dissolved oxygen in a single drop had to be developed and tested. Developed miniaturized voltammetric methods gave parameters comparable to the determination of HNN in 10 mL. The applicability of the miniaturized method was verified by the determination of HNN in a drop of a bacterial growth medium.     

N‐(3,4‐Dihydroxyphenethyl)‐3,5‐dinitrobenzamide‐Modified Multiwall Carbon Nanotubes Paste Electrode as a Novel Sensor for Simultaneous Determination of Penicillamine,Uric acid,and Tryptophan

N‐(3,4‐dihydroxyphenethyl)‐3,5‐dinitrobenzamide modified multiwall carbon nanotubes paste electrode was used as a voltammetric sensor for oxidation of penicillamine (PA), uric acid (UA) and tryptophan (TP). In a mixture of PA, UA and TP, those voltammograms were well separated from each other with potential differences of 300, 610, and 310 mV, respectively. The peak currents were linearly dependent on PA, UA and TP concentrations in the range of 0.05–300, 5–420, and 1.0–400 µmol L^?1, with detection limits of 0.021, 2.0, and 0.82 µmol L^?1, respectively. The modified electrode was used for the determination of those compounds in real samples.     

Tagging of Model Amphetamines with Sodium 1,2‐Naphthoquinone‐4‐sulfonate: Application to the Indirect Electrochemical Detection of Amphetamines in Oral (Saliva) Fluid

Proof‐of‐concept is shown for the indirect electrochemical detection of model amphetamines, D ‐amphetamine sulfate and pseudoephedrine, based on the labeling of the amphetamine models with sodium 1,2‐naphthoquinone‐4‐sulfonate (NQS). The presence of the amphetamine models is monitored via either the reduction in the magnitude of the voltammetric peak corresponding to the electrochemical reduction of the quinone functionality of the sodium 1,2‐naphthoquinone‐4‐sulfonate or via growth of a new voltammetric peak related to reaction between the amphetamine model and NQS, both of which are well resolved from one another. The protocol is shown to be successful in artificial saliva and authentic human oral (saliva) fluid. Such a protocol may be particularly attractive for roadside testing of amphetamines in drug drivers.