Development of a flow injection analytical system for short chain amide determination based on a tubular bioreactor and an ammonium sensor.

Pseudomonas aeruginosa (P. aeruginosa) possesses intracellular amidase activity, which catalyses the hydrolysis of short aliphatic amides producing NH4+, and has already been used along with an ammonium ion selective electrode for amide quantification. However, the incorporation of a biological membrane turned to be a challenging process and either the final arrangement was prone to amidase losses or the recovery of the sensor coating after the interaction took too long. In this article a flow injection system with an ammonium acoustic wave sensor is proposed, and after testing several different arrangements for the biological element, the ultimate choice consisted of the immobilization of a P. aeruginosa cell-free extract in the inner wall of a tubular glass reactor, which resulted in a reliable analytical system. Response times less than one minute and complete recovery in less than two minutes assured conveniently fast analysis. The analytical system, as long as the column was properly stored in HEPES buffer containing 2 mM ß-mercaptoethanol and 1 mM benzamidine and refrigerated when not in use, could be used at least for 20 working days, along a period of one month, maintaining the initial sensitivity.

N-Confused Porphyrin Immobilized on Solid Supports: Synthesis and Metal Ions Sensing Efficacy.

In this work, the N-confused porphyrin 5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrin (NCTPP) was immobilized on neutral or cationic supports based on silica and on Merrifield resin. The new materials were characterized by appropriate techniques (UV-Vis spectroscopy, SEM, and zeta potential analysis). Piezoelectric quartz crystal gold electrodes were coated with the different hybrids and their ability to interact with heavy metals was evaluated. The preliminary results obtained showed that the new materials can be explored for metal cations detection and the modification of the material surface is a key factor in tuning the metal selectivity.

Surface coupling of molecularly imprinted polymers as strategy to improve sulfamethoxazole removal from water by carbons produced from spent brewery grain.

This work aims to assess the surface coupling of molecularly imprinted polymers (MIP) on carbon adsorbents produced from spent brewery grain, namely biochar (BC) and activated carbon (AC), as a strategy to improve selectivity and the adsorptive removal of the antibiotic sulfamethoxazole (SMX) from water. BC and AC were produced by microwave-assisted pyrolysis, and MIP was obtained by fast bulk polymerization. Two different methodologies were used for the molecular imprinting of BC and AC, the resulting materials being tested for SMX adsorption. Then, after selecting the most favourable molecular imprinting methodology, different mass ratios of MIP:BC or MIP:AC were used to produce and evaluate eight different materials. Molecular imprinting was shown to significantly improve the performance of BC for the target application, and one of the produced composites (MIP1-BC-s(1:3)) was selected for further kinetic and equilibrium studies and comparison with individual MIP and BC. The kinetic behaviour was properly described by both the pseudo-first and pseudo-second order models. Regarding equilibrium isotherms, they fitted the Freundlich and Langmuir models, with MIP1-BC-s(1:3) reaching a maximum adsorption capacity (qm) of 25 ± 1 µmol g-1, 19 % higher than BC. In comparison with other seven pharmaceuticals, the adsorption of SMX onto MIP1-BC-s(1:3) was remarkably higher, as for the specific recognition of this antibiotic by the coupled MIP. The pH study evidenced that SMX removal was higher under acidic conditions. Regeneration experiments showed that MIP1-BC-s(1:3) provided good adsorption performance, which was stable during five regeneration-reutilization cycles. Overall, this study has demonstrated that coupling with MIP may be a suitable strategy to improve the adsorption properties and performance of biochar for antibiotics removal from water, increasing its suitability for practical applications.

Polyoxometalate Functionalized Sensors: A Review.

Polyoxometalates (POMs) are a class of metal oxide complexes with a large structural diversity. Effective control of the final chemical and physical properties of POMs could be provided by fine-tuning chemical modifications, such as the inclusion of other metals or non-metal ions. In addition, the nature and type of the counterion can also impact POM properties, like solubility. Besides, POMs may combine with carbon materials as graphene oxide, reduced graphene oxide or carbon nanotubes to enhance electronic conductivity, with noble metal nanoparticles to increase catalytic and functional sites, be introduced into metal-organic frameworks to increase surface area and expose more active sites, and embedded into conducting polymers. The possibility to design POMs to match properties adequate for specific sensing applications turns them into highly desirable chemicals for sensor sensitive layers. This review intends to provide an overview of POM structures used in sensors (electrochemical, optical, and piezoelectric), highlighting their main functional features. Furthermore, this review aims to summarize the reported applications of POMs in sensors for detecting and determining analytes in different matrices, many of them with biochemical and clinical relevance, along with analytical figures of merit and main virtues and problems of such devices. Special emphasis is given to the stability of POMs sensitive layers, detection limits, selectivity, the pH working range and throughput.

A new formaldehyde optical sensor: Detecting milk adulteration.

A sensor consisting of an optical fibre with the exposed tip coated with the polyoxometalate salt [(C4H9)4N]4H[PMo10V2O40], specially designed to be insoluble in water, which UV-Vis spectrum changed in contact with formaldehyde, is presented. The sensor limit of detection for formaldehyde was 0.2 mg L-1, and the limit of quantification was 0.6 mg L-1, which were close to the conventional spectrophotometric method values of 0.2 mg L-1 and 0.5 mg L-1, respectively, and lower than the tolerable limit for ingested food. The sensor was tested for formaldehyde quantification in milk, as its deliberate addition is a matter of concern. The results obtained analysing formaldehyde in milk samples by the optical sensor and by the conventional method were not statistically different (α = 0.05).

Preserve Your Books through the Smell.

The identification of paper composition, pH, early signs of paper degradation, and emitting volatile organic compounds (VOCs) are mandatory for effective preventive conservation of paper/books. Sampling restrictions in the analysis of cultural heritage materials limit the choice of appropriate analytical methods. Solvent-free analytical techniques with nondestructive sampling are needed. Addressing this challenge, an electronic nose based on six-coated piezoelectric quartz crystals was assembled and used to analyze VOCs emitted from books. Careful selection of sensor coatings and cluster analysis allowed us to achieve a clear distinction between cotton/linen rag and wood pulp paper, and among the letter group, the discrimination between papers manufactured from alkaline and acidic stocks. This six-element sensor array was therefore able to replace destructive tests as the ones ordinarily used for paper pH measurements. The same electronic nose was able to separate aged pale-yellow paper, a visible initial sign of paper degradation, from well-preserved still white papers, even when made from the same raw material. One of the used sensors detected furfural, often seen as a marker of cellulose degradation, at lower levels than the detection limit found in the literature with gas chromatography-mass spectrometry, a much more complex bulky and expensive instrument.

Aluminium migration into beverages: are dented cans safe?

Aluminium (Al) migration from cans to beer and tea was studied along time. Analyses of Al in the canned drinks were performed till the sell-by date, and, in seven months, aluminium migration was found to increase 0.14 mg L(-1) in beer, and 0.6 mg L(-1) in tea. This study included dented cans from which aluminium migration into tea was found to be particularly severe. Al concentration in dented canned tea increased 9.6 mg L(-1) in seven months.

Determination of 5-hydroxymethylfurfural in honey, using headspace-solid-phase microextraction coupled with a polyoxometalate-coated piezoelectric quartz crystal.

High concentrations of 5-hydroxymethylfurfural (HMF) in honey provide an indication of overheating under inappropriate storage conditions or aging. Conventional methods for determining HMF are cumbersome and require expensive equipment or hazardous reagents. Hence the aim of this study was to propose a new analytical tool for HMF determination in honey, using a low cost acoustic wave sensor. Volatile organic compounds (VOCs) of honey samples were extracted, using the solid phase microextraction (SPME) technique, and HMF was quantified, using a piezoelectric quartz crystal with gold electrodes coated with a layer of decamolybdodivanado phosphoric acid, sensitive to HMF. The reliability of the proposed method was confirmed after comparing the results of HMF quantification with those obtained by the conventional spectrophotometric White method, and no statistical differences were found (α=0.05).

The quality of our drinking water: aluminium determination with an acoustic wave sensor.

A new methodology based on an inexpensive aluminium acoustic wave sensor is presented. Although the aluminium sensor has already been reported, and the composition of the selective membrane is known, the low detection limits required for the analysis of drinking water, demanded the inclusion of a preconcentration stage, as well as an optimization of the sensor. The necessary coating amount was established, as well as the best preconcentration protocol, in terms of oxidation of organic matter and aluminium elution from the Chelex-100. The methodology developed with the acoustic wave sensor allowed aluminium quantitation above 0.07 mg L(-1). Several water samples from Portugal were analysed using the acoustic wave sensor, as well as by UV-vis spectrophotometry. Results obtained with both methodologies were not statistically different (alpha=0.05), both in terms of accuracy and precision. This new methodology proved to be adequate for aluminium quantitation in drinking water and showed to be faster and less reagent consuming than the UV spectrophotometric methodology.