3,4-Methylenedioxypyrovalerone (MDPV) Sensing Based on Electropolymerized Molecularly Imprinted Polymers on Silver Nanoparticles and Carboxylated Multi-Walled Carbon Nanotubes.

3,4-methylenedioxypyrovalerone (MDPV) is a harmful and controlled synthetic cathinone used as a psychostimulant drug and as sport-enhancing substance. A sensor was developed for the direct analysis of MDPV by transducing its oxidation signal by means of an electropolymerized molecularly imprinted polymer (e-MIP) built in-situ on the screen-printed carbon electrode's (SPCE) surface previously covered with multi-walled carbon nanotubes (MWCNTs) and silver nanoparticles (AgNPs). Benzene-1,2-diamine was used as the functional monomer while the analyte was used as the template monomer. Each step of the sensor's development was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a solution containing ferricyanide, however no redox probe was required for the actual MDPV measurements. The interaction between the poly(o-phenylenediamine) imprinted polymer and MDPV was studied by density-functional theory (DFT) methods. The SPCE-MWCNT-AgNP-MIP sensor responded adequately to the variation of MDPV concentration. It was shown that AgNPs enhanced the electrochemical signal by around a 3-fold factor. Making use of square-wave voltammetry (SWV) the developed sensor provided a limit of detection (LOD) of 1.8 µmol L-1. The analytical performance of the proposed sensor paves the way to the development of a portable device for MDPV on-site sensing to be applied in forensic and doping analysis.

Electroanalytical profiling of cocaine samples by means of an electropolymerized molecularly imprinted polymer using benzocaine as the template molecule.

The analysis of 'cutting' or additive agents in cocaine, like benzocaine (BZC), allows police analysts to identify each component of the sample, thus obtaining information like the drugs' provenience. This kind of drug profiling is of great value in tackling drug trafficking. Electropolymerized molecularly imprinted polymers (e-MIPs) on portable screen-printed carbon electrodes (SPCEs) were developed in this study for BZC determination. The MIPs' electropolymerization was performed on a carbon surface using the anaesthetic BZC as the template molecule and 3-amino-4-hydroxybenzoic acid (3,4-AHBA) as the functional monomer. The build-up of this biomimetic sensor was carefully characterized by cyclic voltammetry (CV) and optimized. Cyclic voltammetric investigation demonstrated that BZC oxidation had a complex and pH-dependent mechanism, but at pH 7.4 a single, well-defined oxidation feature was observed. The BZC-MIP interactions were studied by computer-aided theoretical modeling by means of density functional theory (DFT) calculations. The electroanalytical methodology was effectively applied to artificial urine samples; BZC molecular recognition was achieved with a low limit of detection (LOD) of 2.9 nmol L-1 employing square-wave voltammetry (SWV). The e-MIPs were then used to 'fingerprint' genuine cocaine samples, assisted by principal component analysis (PCA), at the central forensic laboratory of the Brazilian Federal Police (BFP) with a portable potentiostat. This electroanalysis provided proof-of-concept that the drugs could be voltammetrically 'fingerprinted' using e-MIPs supported by chemometric analysis.

Organochlorine pesticide analysis in milk by gas-diffusion microextraction with gas chromatography-electron capture detection and confirmation by mass spectrometry.

Organochlorine pesticides (OCPs) are synthetic compounds less used nowadays due to their toxicity combined with slow degradation which leads to accumulation in the environment. Gas-diffusion microextraction (GDME) was employed prior to gas chromatography with electron capture detection (GC-ECD) and mass spectrometry (GC-MS). For the first time, the low-cost, eco-friendly GDME system was used to extract the OCPs directly from milk samples and associated with GC-ECD. Parameters that affect GDME's performance (extract volume, extraction time, and temperature) were optimized. The calibration curves of all OCPs (α- and ß-hexachlorocyclohexane, lindane, hexachlorobenzene, p,p'-DDE, aldrin, dieldrin, and α-endosulfan) had coefficients of determination (r2) ranging from 0.991 to 0.995, and limits of detection (LODs) values ranging from 3.7 to 4.8 µg L-1. This method also provided satisfactory values for precision with relative standard deviations (RSDs) lower than 10% and recoveries above 90%. As a proof-of-concept, several commercial milk samples were analyzed, aldrin was found in one of them but below the maximum residue limits.

Combining capillary electromigration with molecular imprinting techniques towards an optimal separation and determination.

Capillary electromigration is a well-established commercial group of analytical techniques, and, alike other column separation systems, it often benefits from a preceding sample preparation step. This step not only improves the analytical performance of many methods and prolongs the equipment's life span, but it also makes some determinations possible. A remarkable sample preparation technique is molecular imprinting technology: by creating tailored polymers able to 'select' the targeted analytes, matrix effects are severely diminished. This review aims to provide an overview of all the published works that combine capillary electrophoresis and molecularly imprinted polymers (MIP). Although a literature search produced around 130 published analytical methodologies and 5 patents, authors believe that there is still plenty of room for interesting developments. Works ranged from the analysis of pesticides to pharmaceuticals or hormones, being the most common instrumental detection spectrophotometric. The combination between MIP and electrophoresis can be divided into two main categories depending on where the MIPs are placed within the analytical 'pipeline': off-column and in-column. Off-column consisted of MIP batch application previous to capillary injection. In-column approaches are more complex, and can be divided into coating, monolith, packed (these three being considered capillary electrochromatography), and dispersed particles (affinity capillary electrophoresis).

Employing molecularly imprinted polymers in the development of electroanalytical methodologies for antibiotic determination.

Antibiotics, although being amazing compounds, need to be monitored in the environment and foodstuff. This is primarily to prevent the development of antibiotic resistance that may make them ineffective. Unsurprisingly, advances in analyticalsciences that can improve their determination are appreciated. Electrochemical techniques are known for their simplicity, sensitivity, portability and low-cost; however, they are often not selective enough without recurring to a discriminating element like an antibody. Molecular imprinting technology aims to create artificial tissues mimicking antibodies named molecularly imprinted polymers (MIPs), these retain the advantages of selectivity but without the typical disadvantages of biological material, like limited shelf-life and high cost. This manuscript aims to review all analytical methodologies for antibiotics, using MIPs, where the detection technique is electrochemical, like differential pulse voltammetry (DPV), square-wave voltammetry (SWV) or electrochemical impedance spectroscopy (EIS). MIPs developed by electropolymerization (e-MIPs) were applied in about 60 publications and patents found in the bibliographic search, while MIPs developed by other polymerization techniques, like temperature assisted ("bulk") or photopolymerization, were limited to around 40. Published works covered the electroanalysis of a wide range of different antibiotics (ß-lactams, tetracyclines, quinolones, macrolides, aminoglycosides, among other), in a wide range of matrices (food, environmental and biological).

Rational Design of an Ion-Imprinted Polymer for Aqueous Methylmercury Sorption.

Methylmercury (MeHg+) is a mercury species that is very toxic for humans, and its monitoring and sorption from environmental samples of water are a public health concern. In this work, a combination of theory and experiment was used to rationally synthesize an ion-imprinted polymer (IIP) with the aim of the extraction of MeHg+ from samples of water. Interactions among MeHg+ and possible reaction components in the pre-polymerization stage were studied by computational simulation using density functional theory. Accordingly, 2-mercaptobenzimidazole (MBI) and 2-mercaptobenzothiazole (MBT), acrylic acid (AA) and ethanol were predicted as excellent sulfhydryl ligands, a functional monomer and porogenic solvent, respectively. Characterization studies by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) revealed the obtention of porous materials with specific surface areas of 11 m2 g-1 (IIP-MBI-AA) and 5.3 m2 g-1 (IIP-MBT-AA). Under optimized conditions, the maximum adsorption capacities were 157 µg g-1 (for IIP-MBI-AA) and 457 µg g-1 (for IIP-MBT-AA). The IIP-MBT-AA was selected for further experiments and application, and the selectivity coefficients were MeHg+/Hg2+ (0.86), MeHg+/Cd2+ (260), MeHg+/Pb2+ (288) and MeHg+/Zn2+ (1510), highlighting the material's high affinity for MeHg+. The IIP was successfully applied to the sorption of MeHg+ in river and tap water samples at environmentally relevant concentrations.

Biosensing of D-dimer, making the transition from the central hospital laboratory to bedside determination.

Since the disclosure of the fibrinogen degradation mechanism, around half a century ago, a significant number of papers have been published related to the clinical relevance of D-dimer, a molecule immune to additional enzymatic decomposition by plasmin. Due to the obliquity of regulating blood coagulation in pathological events, the number of diseases and conditions associated with abnormal levels of D-dimer includes deep vein thrombosis, pulmonary embolism, sepsis, myocardial infarction, disseminated intravascular coagulation, among many others. D-dimer not only is an important player in medical diagnosis but also its role as a prognosis biomarker is being revealed. However, the number of analytical alternative methods has not accompanied this trend, even though novel simple point-of-care devices would certainly boost the relevance of D-dimer in emergency medicine. Some reasons for that could be related to the fact that D-dimer is a challenging analyte present in complex samples like blood. In this manuscript, subsequent to a fibrinogen degradation process introduction, it is provided a historical overview of the early D-dimer assays, followed by an extended focus on innovative solutions, with a spotlight on the electrochemical bioanalytical devices. The discussion is accompanied with a critical analysis and concluding thoughts concerning future perspectives.

Electrochemical sensing of the thyroid hormone thyronamine (T0AM) via molecular imprinted polymers (MIPs).

Recent studies have shown that besides the well-known T3 (triiodothyronine) and T4 (thyroxine) there might be other important thyroid hormones, in particular T0AM (thyronamine) and T1AM (3-iodothyronamine). The absence of a large number of studies showing their precise importance might be explained by the limited number of analytical methodologies available. This work aims to show an electroanalytical alternative making use of electropolymerized molecularly imprinted polymer (MIPs). The MIPs' polymerization is performed on the surface of screen-printed carbon electrodes (SPCEs), using 4-aminobenzoic acid (4-ABA) as the building and functional monomer and the analyte T0AM as the template. The step-by-step construction of the SPCE-MIP sensor was studied by cyclic voltammetry (CV) and by electrochemical impedance spectroscopy (EIS). After optimization, by means of square-wave voltammetry, the SPCE-MIP showed suitable selectivity (in comparison with other thyroid hormones and catechol amines), repeatability (intra-day of 3.9%), a linear range up to 10 µmol L-1 (0.23 × 103 µg dL-1) with an r2 of 0.998 and a limit of detection (LOD) and quantification (LOQ) of 0.081 and 0.27 µmol L-1 (1.9 and 6.2 µg dL-1), respectively.

4-hydrazinobenzoic acid as a derivatizing agent for aldehyde analysis by HPLC-UV and CE-DAD.

Aldehydes are relevant analytes in a wide range of samples, in particular, food and beverages but also body fluids. Hydrazines can undergo nucleophilic addition with aldehydes or ketones giving origin to hydrazones (a group of stable imines) that can be suitably used in the identification of aldehydes. Herein, 4-hydrazinobenzoic acid (HBA) was, for the first time, used as the derivatizing agent in analytical methodologies using liquid chromatography aiming the determination of low-molecular aldehydes. The derivatization reaction was simultaneously performed along with the extraction process, using gas-diffusion microextraction (GDME), which resulted in a clean extract containing the HBA-aldehyde derivates. The corresponding formed imines were determined by both high-performance liquid chromatography (LC) with UV spectrophotometric detection (HPLC-UV) and capillary electrophoresis with diode array detection (CE-DAD). HBA showed to be a rather advantageous derivatization reagent due to its stability, relatively high solubility in water and other solvents, high selectivity and sensibility, reduced impurities, simple preparation steps and applicability to different separation and/or different detection techniques. Limits of detections (LODs) of the optimized methodologies (in terms of time and pH among other experimental variables) were all below 0.5 mg L-1, using both instrumental techniques. Furthermore, for the first time, the HBA-aldehyde derivatives were analyzed by LC with mass spectrometry (LC-MS), demonstrating the possibility of identification by MS of each compound. The developed methodologies were also successfully applied in the analysis of formaldehyde and acetaldehyde in several alcoholic beverages. This was also the first time GDME was combined with CE, showing that it can be a valuable sample preparation tool for electrophoresis, in particular by eliminating the interference of ions and inorganic constituents present in the samples.

The Analytical Challenge in the Determination of Cathinones, Key-Players in the Worldwide Phenomenon of Novel Psychoactive Substances.

Since the turn of the century, the synthesis, availability, and use of new psychoactive substances (NPS) have been increasingly reported worldwide, being considered a complex global phenomenon. As most NPS are not detected in routine drug screening, extra efforts have been made to develop new analytical methods for the detection of these compounds, with several approaches being successfully applied and reported in the literature. The increased traffic of NPS is often related to the limited capacity for detecting and monitoring these compounds, which makes it essential to explore in detail both conventional and more recent approaches to prospect novel sensing strategies and develop in-the-field sensors that are able to detect NPS in a time-efficient manner, within a wide range of concentrations, and in a variety of sample matrices, such as biological samples, wastewater, powders, crystals, and post-mortem specimens. In this context, this review aims to provide an overview of the state of the art in the identification and analytical detection of cathinones, a considerable group within NPS, as well as a critical discussion of the most frequently described sample preparation techniques.

Electrochemical sensing using magnetic molecularly imprinted polymer particles previously captured by a magneto-sensor.

The determination of 1-chloro-2,4-dinitrobenzene (CDNB) was used as a proof-of-concept to a simple analytical practical configuration applying magnetic molecularly imprinted particles (mag-MIPs). Mag-MIPs were captured from an emulsion by a home-made magneto-sensor (where a small magnet was entrapped by a graphite-epoxy composite) and then, this sensor, was transferred to the solution containing the analyte, where, after binding to the mag-MIPs, the analyte was directly analysed using differential pulse voltammetry (DPV) since the magneto-sensor acted as the working electrode. After optimization, a detection limit of 6.0 µmol L-1 with a RSD of 2.7% was achieved along with suitable recoveries and selectivity. This methodology offers a different approach for electroanalytical methodologies using mag-MIPs.

Determination of Cephalosporins by UHPLC-DAD Using Molecularly Imprinted Polymers.

Molecularly imprinted polymers (MIPs) were synthesized for the determination of cephalosporins (cephazolin, ceftazidime, cefotaxime, ceftriaxone, cefepime and cephalexin) by ultra-high performance liquid chromatography with diode-array detection (UHPLC-DAD). After optimization, MIPs were synthesized using cephazolin as the template, methacrylic acid as the functional monomer, triethylenglycol dimethacrylate as the crosslinker, acetonitrile/dimethylsulfoxide as porogens and benzoyl peroxide as the radical initiator. Not only this is a novel route of MIP synthesis for cephalosporins, but also this choice of analytes is unique. Chromatographic separation was performed in a C8 column using a binary gradient with trifluoroacetic acid 0.1% in water and acetonitrile. Linearity was assessed up to 100 µg mL-1 and linear correlation coefficients (r) were all higher than 0.99, limits of detection were within the range of 3-12 ng mL-1, and recoveries from 86 to 102% were obtained for concentrations between 0.05 and 1.0 µg mL-1.

Derivatizing assay for the determination of aldehydes using micellar electrokinetic chromatography.

In this work, the use of a novel derivatization agent for the determination of aldehydes (in this particular case: formaldehyde, acetaldehyde, propionaldehyde, and valeraldehyde) using micellar electrokinetic chromatography is reported. The derivatization reaction is based on the reaction of aldehydes with benzhydrazide to form the corresponding derivates with maximum absorbance at 250 nm. The experimental conditions of the derivatization reaction as well of the separation were optimized. The adducts were separated with a +22 kV voltage at a temperature of 29°C. The adducts' separation was performed in less than 14 min using as the running buffer a mixture containing 110 mmol/L of sodium dodecyl sulfate and 27 mmol/L of sodium tetraborate at pH 9.45. Samples were injected using hydrodynamic mode (50 mbar × 5 s). The calibration curves were linear up to 15.0 mg/L with r2 above 0.99. Intra and inter-day precisions were in average 3 and 4%, respectively, and recoveries were in average of 95%. Limits of detection and quantification were around 0.5 and 1.5 mg/L, respectively. The developed method was successfully applied in the analysis of low molar weight aldehydes in yogurt and vinegar samples.

Can saliva testing replace blood measurements for health monitoring? Insights from a correlation study of salivary and whole blood glutathione in humans.

The feasibility of using saliva samples as diagnostic for health status is assessed. Although blood is regularly used for this purpose, an alternative non-invasive route which yields equivalent clinical information is desirable. The non-invasive saliva testing is validated by comparing its result to that of blood examination. In this investigation, we used glutathione as a paradigmatic example of a biomarker and diagnostic auxiliary. Correlation between the levels of total unbound glutathione, reduced and oxidized, in saliva and whole blood samples from healthy individuals is evaluated. Both salivary and blood glutathione were measured using an enzymatic kinetic assay which was improved to eliminate measurement errors arising from the variation in the enzyme activity from different batches.

Stochastic detection and characterisation of individual ferrocene derivative tagged graphene nanoplatelets.

Graphene nanoplatelets (GNPs) are 'tagged' with 1-(biphen-4-yl)ferrocene. Chronoamperometry is then utilised to observe single particle impacts when GNPs suspended in solution collide with a carbon fibre micro wire electrode held at an oxidising potential, resulting in current/time transient "spikes". The impacts are associated with two types of charge transfer: Faradaic due to oxidation of the 'tag' and capacitative due to disruption of the double layer. Analysis of the spikes suggests approximate monolayer coverage of 1-(biphen-4-yl)ferrocene on the GNP surfaces, with a surface coverage of (2.2 ± 0.3) × 10(-10) mol cm(-2). In contrast non-derivatised ferrocene does not exhibit any significant adsorption on the GNP material.

Application of gas-diffusion microextraction to solid samples using the chromatographic determination of α-diketones in bread as a case study.

Gas-diffusion microextraction (GDME) was applied to the extraction of vicinal diketones in bread samples aimed at the determination of these compounds by high-performance liquid chromatography with ultraviolet detection (HPLC-UV). For the first time, GDME was used for direct chemical determination in solid samples, i.e. avoiding any sample preparation prior to extraction. Different extraction parameters were studied and optimized, namely temperature, time and chemical composition of the acceptor solution where o-phenylenediamine was used as a derivatizing agent, originating quinoxalines that could be determined at 315 nm. GDME demonstrated to be a good tool for the sampling of volatile compounds in solid samples with suitable method features for butane-2,3-dione (diacetyl, DC), pentane-2,3-dione (PN) and hexane-2,3-dione (HX): low LODs (6.0, 8.6 and 12 µg kg(-1), for DC, PN and HX respectively) and LOQs (20, 29 and 38 µg kg(-1), for DC, PN and HX respectively), r(2) above 0.990, and CV around 5%. The developed methodology was applied to the determination of different bread samples and was used to reveal the decrease of α-diketones in bread during the timeframe of a week.

An overview on cardamonin.

Cardamonin, as shown by the increasing number of publications, has received growing attention from the scientific community due to the expectations toward its benefits to human health. In this study, research on cardamonin is reviewed, including its natural sources, health promoting aspects, and analytical methods for its determination. Therefore, this article hopes to aid current and future researchers on the search for reliable answers concerning cardamonin's value in medicine.

Another glimpse over the salting-out assisted liquid-liquid extraction in acetonitrile/water mixtures.

The use of the salting-out effect in analytical chemistry is very diverse and can be applied to increase the volatility of the analytes in headspace extractions, to cause the precipitation of proteins in biological samples or to improve the recoveries in liquid-liquid extractions. In the latter, the salting-out process can be used to create a phase separation between water-miscible organic solvents and water. Salting-out assisted liquid-liquid extraction (SALLE) is an advantageous sample preparation technique aiming HPLC-UV analysis when developing analytical methodologies. In fact, some new extraction methodologies like QuEChERS include the SALLE concept. This manuscript discusses another point of view over SALLE with particular emphasis over acetonitrile-water mixtures for HPLC-UV analysis; the influence of the salting-out agents, their concentration and the water-acetonitrile volume ratios were the studied parameters. α-dicarbonyl compounds and beer were used as test analytes and test samples, respectively. The influence of the studied parameters was characterized by the obtained phase separation volume ratio and the fraction of α-dicarbonyls extracted to the acetonitrile phase. Results allowed the distribution of salts within three groups according to the phase separation and their extractability: (1) chlorides and acetates, (2) carbonates and sulfates and (3) magnesium sulfate; of all tested salts, sodium chloride had the highest influence on the α-dicarbonyls fraction extracted.

Quartz crystal microbalance as a tool for kinetic enzymatic assays by variation of pH.

In this work, it is shown that the quartz crystal microbalance (QCM) can be a powerful and simple tool for quick and precise kinetic enzymatic assays. This is shown by measuring immobilized acetylcholinesterase (AChE) activity with variations of pH as a case study.