Organic-resistant screen-printed graphitic electrodes: Application to on-site monitoring of liquid fuels

This work presents the potential application of organic-resistant screen-printed graphitic electrodes (SPGEs) for fuel analysis. The required analysis of the antioxidant 2,6-di-tert-butylphenol (2,6-DTBP) in biodiesel and jet fuel is demonstrated as a proof-of-concept. The screen-printing of graphite, Ag/AgCl and insulator inks on a polyester substrate (250 μm thickness) resulted in SPGEs highly compatible with liquid fuels. SPGEs were placed on a batch-injection analysis (BIA) cell, which was filled with a hydroethanolic solution containing 99% v/v ethanol and 0.1 mol L⁻¹ HClO₄ (electrolyte). An electronic micropipette was connected to the cell to perform injections (100 μL) of sample or standard solutions. Over 200 injections can be injected continuously without replacing electrolyte and SPGE strip. Amperometric detection (+1.1 V vs. Ag/AgCl) of 2,6-DTBP provided fast (around 8 s) and precise (RSD = 0.7%, n = 12) determinations using an external calibration curve. The method was applied for the analysis of biodiesel and aviation jet fuel samples and comparable results with liquid and gas chromatographic analyses, typically required for biodiesel and jet fuel samples, were obtained. Hence, these SPGE strips are completely compatible with organic samples and their combination with the BIA cell shows great promise for routine and portable analysis of fuels and other organic liquid samples without requiring sophisticated sample treatments.     

Development of a microfluidic paper-based analytical device for the determination of salivary aldehydes

A low cost, disposable and easy to use microfluidic paper-based analytical device (μPAD) was developed for simple and non-invasive determination of total aldehydes in saliva with a potential to be used in epidemiological studies to assess oral cancer risk. The μPAD is based on the colour reaction between aldehydes (e.g. acetaldehyde, formaldehyde), 3-methyl-2-benzothiazolinone hydrazone (MBTH) and iron(III) to form an intense blue coloured formazan dye. The newly developed μPAD has a 3D design with two overlapping paper layers. The first layer comprises 15 circular detection zones (8 mm in diameter), each impregnated with 8 μL of MBTH, while the second layer contains 15 reagent zones (4 mm in diameter). Two μL of iron(III) chloride are added to each one of the second layer zones after the addition of sample to the detection zones in the first layer. All hydrophilic zones of the μPAD are defined by wax printing using a commercial wax printer.     

Use of a programmed temperature vaporizer and an in situ derivatization reaction to improve sensitivity in headspace-gas chromatography. Application to the analysis of chlorophenols in water

In the present work we propose the combined use of a derivatization reaction within the vial of a headspace sampler with a programmed temperature vaporizer (PTV) inlet in the solvent vent mode as a new methodology for obtaining an increase in sensitivity in headspace-gas chromatography (HS-GC) for the analysis of sparingly volatile compounds. As test analytes the following chlorophenols were used: 2-chlorophenol (2CP), 2,4-dichlorophenol (24DCP), 4-chloro-3-methylphenol (4C3MP) and 2,4,6-trichlorophenol (246TCP). The derivatization reaction was carried out with acetic anhydride because it can be carried out in situ in aqueous medium. In the programmed temperature vaporizer inlet, three different liners, one of them empty and the others with materials of different trapping strengths (glass wool and Tenax-TA), were compared. The best results were obtained when an empty liner was used, with better repeatability and S/N ratios. In the case of the liner filled with Tenax-TA, a considerable lack of repeatability was observed, this being attributed to interactions between the derivatized compounds and the adsorbent. The proposed methodology affords very low limits of detection, in the range of a few ng/L for all the compounds, with good precision and accuracy values.     

A novel monolithic silicon sensor for measuring acceleration,pressure and temperature on a shock absorber

A fabricated micro-mechanical sensor to assess the condition of automotive shock absorbers is presented. The monolithic sensor, measures the oil temperature, acceleration and internal pressure of the shock absorber. A dual mass accelerometer with optimized beam geometry is used for acceleration readout. In addition, a 23.1 μm thickness square membrane and two buried resistors are used for pressure and temperature sensing respectively. The proposed miniaturized sensor can be effectively integrated with standard single- and dual-tube shock absorbers. The data acquired during normal vehicle operation can be continuously used to monitor the condition of the shock absorbers, allowing shock absorbers to be replaced before their degradation significantly reduce the comfort, performance and safety of the vehicle.     

Complexes based on asymmetrically substituted pyridine–dithiolene ligands [M(4-pedt)2] (M = Au,Cu, Ni; 4-pedt = 1-(pyridin-4-yl)-ethylene-1,2-dithiolate): Synthesis,structure and physical properties

The monoanionic Ni, Au and Cu bisdithiolene complexes based on the 1-(pyridin-4-yl)-ethylene-1,2-dithiolate were prepared and isolated as [PPh₄]⁺, [n-Bu₄N]⁺ and [Na(18C6)]⁺ salts which were characterised by single-crystal X-ray diffraction, cyclic voltammetry, EPR and magnetic susceptibility measurements. All the complexes adopt a square planar coordination geometry with a trans arrangement of the substituent pyridine rings whose planes are rotated from 13° to 33° relatively to the central MS₄ core. The C–C and C–S bond lengths are consistent with ene-1,2-dithiolate form of the ligand and M^III oxidation state. The Ni complexes are paramagnetic with an effective magnetic moment of ～1.7 BM.     

Extraction by reversed micelles of the intrecellular enzyme xylose reductase

Applied Biochemistry and Biotechnology - Xylose reductase enzyme (EC 1.1.1.21) produced by Candidaguilliermondii in sugarcane bagasse was extracted by reversed micelles of N-benzyl-N-dodecyl-N-bis...     

Superelectrophilic bromination of deactivated aromatic rings with tribromoisocyanuric acid—an experimental and DFT study

The reaction of deactivated arenes with tribromoisocyanuric acid (TBCA) in 98% H₂SO₄ produced bromoarenes in good yields. The acidity of the medium controls the strength of the brominating agent and the amount of polybrominated products. DFT calculations at B3LYP/6-311++G^∗∗ level showed that the protonated TBCA (a superelectrophilic species) can easily transfer Br⁺ to deactivated arenes, in order to decrease internal charge-charge repulsion.     

Triclosan

The title compound [systematic name: 5‐chloro‐2‐(2,4‐dichlorophenoxy)phenol], C₁₂H₇Cl₃O₂, is a biologically relevant molecule with biocide activity. It crystallizes in the chiral trigonal space group P3₁ with one molecule in the asymmetric unit. As in biological adducts, the two aromatic rings are almost mutually perpendicular, with this structural feature leading to a distribution of the pendant –OH groups to maximize the formation of O—H...O hydrogen bonds. This arrangement leads to a chain of molecules running parallel to the c axis and having a C(2) graph‐set motif at its core.