Mcdonoughfields5399

An improved step-by-step colorimetric method for determination of halides has been developed. The method is based on successive selective oxidation of iodide, bromide and chloride into corresponding free halogens, their extraction by airflow and colorimetric detection with different paper test-strips. This procedure can be performed in a single analyzed solution and possesses high selectivity and good sensitivity due to the extraction step. Three types of paper test-strips were examined paper modified with tetramethylammonium iodide and starch, paper modified with methyl orange and paper modified with silver triangular nanoplates. Limits of detection for iodide, bromide and chloride are 0.01, 0.02, and 0.04 mg L-1 respectively in case of the last mentioned paper. The method was applied to the analysis of samples having complex matrices, such as various seafood, preserves, bread, and natural waters, showing good accuracy of the analysis with recoveries of 95-105% and relative standard deviations not higher than 6%.The application of a voltammetric electronic tongue (ET) towards the classification and authentication of vinegar is reported. AZ191 Vinegar samples of different varieties were analysed with a three-sensor array, without performing any sample pre-treatment, but only an electrochemical cleaning stage between sample measurements to avoid fouling onto the electrode surfaces. Next, the use of discrete cosine transform (DCT) for the compression and reduction of signal complexity in voltammetric measurements was explored, and the number of coefficients was optimized through its inverse transform. Finally, the obtained coefficients were analysed by principal component analysis (PCA) to attempt the discrimination of the different vinegars and by linear discriminant analysis (LDA) to build a model that allows its categorization. Satisfactory results were obtained overall, with a classification rate of 100% for the external test subset (n = 15).An analytical apparatus is described, based on on-line connection of electrophoresis in a short capillary with a dialysis unit enabling dialysis in micro-litre sample volumes into submicro-litre volumes of an acceptor solution in a dialysing fibre. After a defined dialysis time, the dialysate from the dialysing fibre is injected into a separation capillary through an air-assisted flow-gating interface cast from PDMS. In the flow-gating injection space, the exit from the delivery capillary bringing the dialysate is placed directly opposite the entrance into the separation capillary at a distance of 380 μm. In order to enable injection of a very small volume of dialysate, the background electrolyte is forced out of the injection space with air before the injection, so that a drop of dialysate with a volume of about 0.1 μL is formed between the exit from the delivery and the entrance into the separation capillary; the dialysate is injected hydrodynamically from this dialysate drop. Then the injection space is filled with the background electrolyte and the separation is commenced. The basic properties of the apparatus were tested on model mixtures of inorganic cations (K+, Ba2+ and Na+) and organic molecules (creatinine, histidine and arginine). The applicability to real samples was tested on the determination of basic amino acids (histidine, lysine and arginine) in a blood serum sample.A pH colorimetric sensor array (CSA) with fast response time ( less then 1 min) using only one acid-base indicator, Bromothymol Blue (BB), was prepared and characterized by modulating the amount, C, of the surfactant Hexadecyltrimethylammonium p-toluenesulfonate between 0 and 0.3725 gCTApTs/gprecursor with a constant amount of the OrMoSil precursors. The effect of the C increase is a continuous acidic shift of the calibration position, i.e. a huge variation of the pKa value of BB in the pH range 5.80-13.50. The precision error decreased with increasing C from 0.096 pH units (lower C values) to 0.023 pH units (larger C values). This result led to the development of a model to determine the number of spots with suitable C values required for having a similar value of precision in the entire working interval of the CSA. By selecting only 4 spots the precision error is less then 0.100 pH units in the pH range 5.80-13.50. With 256 spots (diameter of each spot ≈ 3 mm), the model predicted an error almost constant (≈0.010) in the entire pH range.Cannabidiol (CBD), a major non-psychoactive cannabinoid, has received a lot of attention due to its potential anti-inflammatory, pain-relieving, and anti-anxiety properties. This has led to a recent boom in CBD-rich commercial products, which are sold without prescription in the form of oils, candies, and cosmetics. Since these products are derived from cannabis, the presence of the psychoactive tetrahydrocannabinol (THC) has to be tested before they enter the market. Here, we present a high-throughput approach based on liquid chromatography coupled to UV and tandem mass spectrometric detection for the determination of CBD, THC, and six other minor cannabinoids (cannabigerolic acid, cannabidivarin, cannabinol, cannabigerol, cannabidiolic acid, and tetrahydrocannabinolic acid) in a wide range of concentrations and in a variety of matrices, including oils, hydrophobic ointments, water-soluble liquids, plant material and gelatinous gummies. Each product was dissolved in a suitable solvent and further diluted to t material. The developed method was used for the analysis of thirteen real products with a wide range of CBD content, with positive THC findings in twelve of them.Quantification of endogenous hormones in plants is essential to understand their growth, development and response to biotic and abiotic stresses. However, it is challenging to develop high-throughput sample treatments from complex plant tissues containing low amounts of structurally unrelated and labile phytohormones while delivering clean and analyte-enriched extracts. In this paper we propose the use of supramolecular solvents (SUPRASs) made up or inverted hexagonal nanostructures of alkanols to address this challenge. The strategy was applied, as a proof of concept, to the quantification of stress-related phytohormones belonging to different categories (abscisic acid, salicylic acid, jasmonic acid, methyl jasmonate and 3-indoleacetic acid) in melon and pepper leaves. Sample treatment consisted in a single extraction-cleanup step involving the use of a low volume of SUPRAS (244 μL), the stirring (5 min) and centrifugation (15 min) of the sample at room temperature, and the direct analysis of the extract by liquid chromatography tandem mass spectrometry (LC-MS/MS). This high-throughput sample treatment method delivered excellent results for the target phytohormones regarding absolute recoveries (80-92%), method quantification limits (0.05-2 ng g-1), reproducibility (1-7%) and matrix effects (+13 to -31%), in both melon and pepper leaves, compared to reported methods based on repetitive solvent extraction, purification and solvent evaporation steps. The method was successfully applied to determine target hormones in melon and pepper plants for the evaluation of the effect of thermal stress. It was found that their concentration increased in the ranges 1.2-1.9 and 1.3-3.8 times in melon and pepper leaves, respectively, compared with control samples.Here we report membrane capacitive sensors based on anodic aluminum oxide (AAO) Au/AAO/Au structures fabricated by aluminum anodization, followed by gold electrodes sputtering on the countersides of porous ceramic membrane. Electrochemical impedance spectroscopy with AC amplitude 5-100 mV in the frequency range of 1-1000 Hz was utilized for sensor characterization in the presence of water and organic vapors in a full range of P/P0. The sensors illustrate ultimate sensitivity to ambient environment with exponential-scale capacitance relation to vapors content resulting in typical 4-6 orders of magnitude response signal change for 15-85% P/P0 range at a single AC frequency, and up to 7 orders of magnitude response range for 0-100% P/P0 pressure range with using two different AC frequencies. In case of water vapors, the sensitivity increases from ~0.5 nF/RH% at ~20 RH% to over ~1.0 μF/RH% at ~80 RH%. The sensors are capable for highly accurate sensing of gas humidity as well as any dissociative vapors with pKa less then 30. They are also sensible to polar components with high enough dipole moment or polarizability. The capacitance is affected by any adsorbed molecules, including those having zero dipole moment. The data for sensor response to CH3OH, C2H5OH, CH2ClCHF2, i-C4H10 depending on partial pressures is provided. Due to high porosity (10-30%) and gaseous permeance (up to 200 m3(STP) m-2 bar-1 h-1) the sensors offer fast response rate and a possibility for flow-through measurements, providing also a mass-flow response option, which was tested with SF6, CO2, N2 and He. The basic principles of dielectric loss sensor and the equivalent scheme were proposed for sensor operation in different environment, allowing estimating sensor response.This paper describes the first biosensor reported to date for the determination of mustard seed traces. The biosensor consists of an amperometric immunosensing platform able to sensitively and selectively determine Sin a 1 content, the major allergen of yellow mustard and the most abundant protein of these seeds. The immunosensing platform exploits the coupling of magnetic microbeads (MBs) modified with sandwich-type immune complexes, comprising polyclonal and monoclonal antibodies, selective to the target protein for its capturing and detection, respectively. In addition, a HRP-conjugated secondary antibody was used for enzymatic labelling of the monoclonal antibody, and amperometric transduction was made at screen-printed carbon electrodes (SPCEs) using the hydroquinone (HQ)/H2O2 system. The electrochemical immunosensor allows the simple and fast detection (a single 1-h incubation step) of Sin a 1 with a limit of detection of 0.82 ng mL-1 (20.5 pg of protein in 25 μL of sample) with high selectivity against structurally similar non-target allergenic proteins (such as Pin p 1 from pine nut). The developed immunoplatform was successfully used for the analysis of peanut, rapeseed, cashew, pine nut and yellow mustard extracts, giving only positive response for the yellow mustard extract with a Sin a 1 content, in full agreement with that provided by conventional ELISA methodology.This work describes a novel, simple and inexpensive pen-on-paper (PoP) method for patterning hydrophobic structures in paper substrates aiming the production of paper-based analytical devices (PADs). This fabrication protocol uses a commercially available plastic welding kit that can be easily acquired and is sold as a repair tool. It consists of an acrylate-based resin which is deposited on the paper and then cured using a UV led, or even the sunlight, for creation of the hydrophobic barriers. The protocol is instrument-free and can be easily implemented in any laboratory. To the best of our knowledge, this is the first report of the use of this material for production of analytical devices. The developed PADs were fully characterized and exhibited better chemical resistance than other recently reported PoP approaches regarding organic media and surfactants. Moreover, the fabrication method demonstrated good analytical versatility since it allowed the production of flexible devices, flow-based devices and pencil-drawn electrochemical devices.