Polyether ether ketone encased monolith frits made of polyether ether ketone tubing with a 0.25 mm opening resulting in an improved separation performance in liquid chromatography

Tiny polyether ether ketone encased monolith frits have been prepared by modified catalytic sulfonation of the inner surface of polyether ether tubing (1.6 mm od, 0.25 mm id) followed by modified formation of organic monolith and cutting of the tubing into slices. The frit was placed below the central hole of the column outlet union and supported by a combination of a silica capillary (0.365 mm od, 0.05 mm id) and a polyether ether ketone sleeve (1.6 mm od, 0.38 mm id) tightened with a nut and a ferrule when the column was packed to prevent sinking of the frit element into the union hole (0.25 mm opening) otherwise. The column packed this way with the frits investigated in this study has shown better separation performance owing to the reduced frit volume in comparison to the column packed with a commercial stainless‐steel screen frit. This study establishes the strategy of disposable microcolumns in which cheap disposable frits are used whenever the column is re‐packed to yield columns of even better chromatographic performance than the columns with commercial frits.     

Simple and fast near-infrared spectroscopic analysis of hydroxyl number of polyol using a disposable glass vial

Hydroxyl (OH) number of polyol was measured using near-infrared (NIR) spectroscopy with the use of a disposable glass vial as a sample container. Polyols are viscous, so disposable vials are advantageous when spectroscopic methods are employed. Due to the curvature of the vial walls, a narrow aperture was used to minimize the spectroscopic deviations. The narrow aperture attenuated the NIR radiation and increased the spectral noise in the collected polyol spectra. Wavelet transformation (WT) was employed to reduce this noise and partial least squares (PLS) calibration model was developed. The overall prediction results compare well with those from conventional wet analysis that requires time (1–3 h) and large amounts of chemical reagents. NIR spectroscopy with the use of disposable vials can be utilized for a simple and fast quality assurance of polyol in actual industrial settings.     

Multiresidue pesticides analysis in soils using modified QuEChERS with disposable pipette extraction and dispersive solid‐phase extraction

QuEChERS original method was modified into a new version for pesticides determination in soils. The QuEChERS method is based on liquid–liquid portioning with ACN and was followed by cleanup step using dispersive SPE and disposable pipette tips. Gas chromatographic separation with MS detection was carried out for pesticides quantification. The method was validated using recovery experiments for 36 multiclass pesticides. Mean reco‐veries of pesticides at each of the four spiking levels between 10–300 μg/kg of soil ranged from 70–120% for 26 pesticides with RSD values less than 15%. The method achieved low limit of detection less than 7.6 μg/kg. Matrix effects were observed for 13 pesticides. Matrix effects were compensated by using matrix‐matched calibration. The method was applied successfully using d‐SPE or DPX in the analysis of the pesticides in soils from organic farming and integrated pest management.     

Determination of trace cobalt(II) by adsorptive stripping voltammetry on disposable microfabricated electrochemical cells with integrated planar metal-film electrodes

This work reports the determination of trace Co(II) by adsorptive stripping voltammetry on disposable three-electrode cells with on-chip metal-film electrodes. The heart of the sensors was a bismuth-film electrode (BiFE) with Ag and Pt planar strips serving as the reference and counter electrodes, respectively. Metals were deposited on a silicon chip by sputtering while the areas of the electrodes were patterned via a metal mask. Co(II) was determined by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (the DMG concentration, the preconcentration potential, the accumulation time and the SW parameters), as well as potential interferences, were investigated. Using the selected conditions, the 3σ limit of detection was 0.09 μg l⁻¹ of Co(II) (for 90 s of preconcentration) and the relative standard deviation for Co(II) was 3.8% at the 2 μg l⁻¹ level (n = 8). The method was applied to the determination of Co(II) in a certified river water sample. These mercury-free electrochemical devices present increased scope for field analysis and μ-TAS applications.     

Disposable Glucose Sensors for Flow Injection Analysis Using Substituted 1,4‐Benzoquinone Mediators

The redox chemistry of several substituted benzoquinones was investigated by cyclic voltammetry at a glassy carbon electrode and candidates for inclusion in a mediated biosensor for use in flow analysis were selected on the basis of oxidation potential, electrochemical reversibility and solubility. Glucose sensors constructed by sequential deposition onto a carbon pellet of 2,6‐dimethyl‐1,4‐benzoquinone, 2,3,5,6‐tetramethyl‐1,4‐benzoquinone or phenyl‐1,4‐benzoquinone mediator solution, followed by glucose oxidase in polyvinylalcohol‐Nafion solution, were tested for response to glucose using flow injection analysis. Sensors prepared from 2,6‐dimethyl‐1,4‐benzoquinone gave highest sensitivity, with a linear range of response to glucose of 2.5–40 mM. The use of an enzyme‐free comparative electrode to eliminate the response from interferents was investigated.     

Feasibility of the use of disposable optical tongue based on neural networks for heavy metal identification and determination

This study presents the development and characterization of a disposable optical tongue for the simultaneous identification and determination of the heavy metals Zn(II), Cu(II) and Ni(II). The immobilization of two chromogenic reagents, 1-(2-pyridylazo)-2-naphthol and Zincon, and their arrangement forms an array of membranes that work by complexation through a co-extraction equilibrium, producing distinct changes in color in the presence of heavy metals. The color is measured from the image of the tongue acquired by a scanner working in transmission mode using the H parameter (hue) of the HSV color space, which affords robust and precise measurements. The use of artificial neural networks (ANNs) in a two-stage approach based on color parameters, the H feature of the array, makes it possible to identify and determine the analytes. In the first stage, the metals present above a threshold of 10⁻⁷ M are identified with 96% success, regardless of the number of metals present, using the H feature of the two membranes. The second stage reuses the H features in combination with the results of the classification procedure to estimate the concentration of each analyte in the solution with acceptable error. Statistical tests were applied to validate the model over real data, showing a high correlation between the reference and predicted heavy metal ion concentration.     

Colourimetric characterisation of disposable optical sensors from spectroradiometric measurements

Spectroradiometric measurements of reflectance and CIELAB hue-angle, were tested for K(I) determination using disposable optical sensors based on ion exchange mechanism. The linearisation of the sigmoidal response function, using a logistic regression, increases the linear range noticeably to 7.65 × 10⁻⁸–1.5 M and 1.22 × 10⁻⁷–1.5 M for CIELAB hue-angle and reflectance, respectively. The trueness of both procedures was demonstrated comparing it with results obtained by a DAD spectrophotometer used as a reference measurement procedure. The usefulness of the procedure was checked by analysing K(I) in different types of waters and beverages. Additionally, we studied the possible visual discrimination for the whole potassium range tested, obtaining the possibility of discriminating twelve groups of concentrations.     

Determination of cobalt in water samples by photoacoustic spectroscopy with a solid-phase spectrophotometry approach using 3-(2-pyridyl)-5,6-bis(4-sulfophenyl)-1,2,4-triazine

This work forms part of an investigation which seeks to determine metal complexes in a solid phase by photoacoustic spectrometry (PAS). Results of spectral determination of Co(II) complexes are introduced. The method is based on Co(II) colorimetric reaction with 3-(2-pyridyl)-5,6-bis(4-sulfophenyl)-1,2,4-triazine (FST, ferrozine) retained on an anion-exchange resin, DEAE Sephadex A-25. The immobilization of Co(II) on the solid phase is combined with PAS measurement. A numerical approach is applied to reduce noise in the spectral data. At λ = 477 nm, the calibration for Co(II) is linear over the range 14–300 μgL^{− 1}. The Co(II) concentration in water samples was determined by conventional photoacoustic measurement. The relative standard deviation (R.S.D.) of the method for the calibration is < 5%. Under optimized conditions, the obtained analytical features were LOD 14 μgL^{− 1} and LOQ 45 μgL^{− 1}.     

Organic monolith frits encased in polyether ether ketone tubing with improved durability for liquid chromatography

This study introduces a preparation method for polymer‐encased monolith frits with improved durability for liquid chromatography columns. The inner surface of the polyether ether ketone tubing is pretreated with sulfuric acid in the presence of catalysts (vanadium oxide and sodium sulfate). The tubing was rinsed with water and acetone, flushed with nitrogen, and treated with glycidyl methacrylate. After washing, the monolith reaction mixture composed of lauryl methacrylate, ethylene glycol dimethacrylate, initiator, and porogenic solvent was filled in the tubing and subjected to in situ polymerization. The tubing was cut into thin slices and used as frits for microcolumns. To check their durability, the frit slices were placed in a vial and a heavy impact was applied on the vial by a vortex mixer for various periods. The frits made in the presence of catalysts were found to be more durable than those made without catalysts. Furthermore, when the monolith‐incorporated tubing was used as a chromatography column, the column prepared in the presence of catalysts resulted in a better separation efficiency. The separation performance of the columns installed with the polyether ether ketone encased monolith frits was comparable to that of the columns installed with the commercial stainless‐steel screen frits.     

Modified screen printed electrode for development of a highly sensitive label-free impedimetric immunosensor to detect amyloid beta peptides

Alzheimer's disease (AD) is a fatal neurodegenerative disease affecting approximately 26 million people world-wide, and the number is increasing as life expectancy increases. Since the only reliable diagnosis for the pathology is histochemical post-mortem examination, there is a rather urgent need for reliable, sensitive and quick detection techniques. Amyloid beta, being one of the established and widely accepted biomarkers of AD is a target biomolecule.