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meso-Bromosubstituted indodicarbocyanine dyes produce dimeric molecules, together with the debrominated species, under acid catalysis. The relationship between the dimerization and hydrodebromination routes depends on the aryl substitution of the dyes. A possible reaction mechanism is also proposed.

The design, construction and evaluation of a low-cost cyclic olefin copolymer (COC)-based continuous flow microanalyzer with optical detection to determine the titratable acidity content of wine is here presented. The analysis method is based on the monitoring of the blue coloration decrease of a buffered bromothymol blue (BTB) solution in the presence of the acidic compounds of wine. The microanalyzer monolithically integrates the required microfluidic motifs as well as an optical flow cell where the measurements are performed by using a miniaturized and versatile photometric detection system. Fluid management is totally automated by the use of computer-controlled microvalves, permitting the automatic calibration of the system as well as the automatic sampling, including in-line dilution and analysis. The reduced size of the whole system along with its high simplicity and automation make it suitable for its application to the on-line monitoring of titratable acidity during wine-making processes. With the optimal conditions, a linear range up to 0.50 g L−1 tartaric acid, a quantification limit (LOQ) of 0.01 g L−1 and a detection limit (LOD) of 0.004 g L−1 were obtained, covering the most common acidity content of musts and wines. A sampling rate up to 26 h−1 could be achieved, consuming less than 3 mL of inexpensive reagents per analysis and requiring no pretreatment of the sample. The microsystem has been successfully applied to the quantification of the titratable acidity content of several wine samples, being the results in excellent agreement with the ones obtained by the reference method.

The analysis of soluble reactive phosphate (SRP) in water is key to control water quality. In order to continuous monitor orthophosphate content in water during treatment processes and in the effluents of wastewater treatment plants, conventional procedures, usually performed in a laboratory, must be adapted. This means pursuing efforts on miniaturizing systems to operate in situ and automating analytical methods to work on-line. The design, construction and evaluation of an automatic and low cost cyclic olefin copolymer (COC)-based spectrophotometric microanalyzer, capable of operating in unattended conditions, is presented to monitor soluble reactive phosphorous, as orthophosphate ion, in wastewater samples coming from sewage treatment plants. The microsystem, constructed by CNC micromilling and using a multilayer approach, integrates microfluidics to carry out the phosphomolybdenum blue (PMB) reaction and an optical flow-cell for the spectrophotometric orthophosphate determination in a single polymeric substrate smaller than a credit card. It is connected to a compact optical detection system composed by a LED emitting at 660 nm and a PIN-photodiode, both integrated in a PCB. Flow management is automatically performed by programmed microvalves and micropumps, which control autocalibration processes and allow unattended operation. Analytical features after the optimization of the microfluidic platform and the chemical and the hydrodynamic variables, were a linear range from 0.09 to 32 mg L−1 P and a detection limit of 0.03 mg L−1 P with a sampling rate of 24 samples h−1, demonstrating the microanalyzer suitability for SRP monitoring in water. Moreover, real samples were analyzed obtaining promising results.

The design, construction and evaluation of a low cost, cyclic olefin copolymer (COC)-based continuous flow microanalyzer, with optical detection, to monitor carbon dioxide in bottled wines and beers as well as in fermentation processes, is presented. The microsystem, constructed by computer numerically controlled (CNC) micromilling and using a multilayer approach, integrates microfluidics, gas-diffusion module and an optical flow-cell in a single polymeric substrate. Its size is slightly bigger than a credit card, exactly 45 × 60 × 4 mm in the microfluidic and diffusion module zone and 22.5 × 40 × 3 mm in the flow-cell zone. The gas-diffusion module is based on a hydrophobic polyvinylidene fluoride (PVDF) membrane, which allows the transfer of the carbon dioxide present in the sample to a bromothymol blue (BTB) pH-sensitive acceptor solution, where the color change is measured optically. The detection system consisted of a LED with an emission peak at 607 nm and a photodiode integrated in a printed circuit board (PCB). The obtained analytical features after the optimization of the microfluidic platform and hydrodynamic variables are a linear range from 255 to 10000 mg L−1 of CO2 and a detection limit of 83 mg L−1 with a sampling rate of 30 samples h−1.

A boron trifluoride–methanol complex demonstrated remarkable deprotection selectivity against commonly used amino-protecting groups in the deacetylation of acetanilides and high sensitivity to the steric hindrance of substrates. The scope and limitations of the reaction were explored.

Assisted reproductive technology (ART) can benefit from the features of microfluidic technologies, such as the automation of time-consuming labor-intensive procedures, the possibility to mimic in vivo environments, and the miniaturization of the required equipment. To date, most of the proposed approaches are based on polydimethylsiloxane (PDMS) as platform substrate material due to its widespread use in academia, despite certain disadvantages, such as the elevated cost of mass production. Herein, we present a rapid fabrication process for a cyclic olefin copolymer (COC) monolithic microfluidic device combining hot embossing—using a low-temperature cofired ceramic (LTCC) master—and micromilling. The microfluidic device was suitable for trapping and maturation of bovine oocytes, which were further studied to determine their ability to be fertilized. Furthermore, another COC microfluidic device was fabricated to store sperm and assess its quality parameters over time. The study herein presented demonstrates a good biocompatibility of the COC when working with gametes, and it exhibits certain advantages, such as the nonabsorption of small molecules, gas impermeability, and low fabrication costs, all at the prototyping and mass production scale, thus taking a step further toward fully automated microfluidic devices in ART.

The synthesis of a set of open-chain bis-aminosubstituted cyanine dyes as well as others with cyclic fragments in the polymethine chain is presented. These dyes are suitable for the development of polymeric compositions with variable optical characteristics as they can be covalently incorporated into the polymer.

An optical microfluidic system based on the use of modified gold nanoparticles for monitoring Hg(II) is presented. The system is based on the specific recognition of the heavy metal by a new synthesized ionophore based on a modified thiourea, which is attached to the gold nanoparticles. This interaction generates a change on the gold Surface Plasmon Resonance (SPR) band. The sensitivity and selectivity of the procedure is firstly studied in batch. The obtained results demonstrate the mercury selective response over the different tested ions that can be found in environmental water samples. Due to the remarkable unusual rapid signal change observed during the interaction of the metal and the modified gold nanoparticles, the reaction can be easily performed in a microfluidic system. Results obtained by using the microfluidic system revealed improved analytical features compared to batch experiments such as a lower detection limit (11 ppb), higher sensitivity and faster analysis time, all this with an easy and automated procedure. Therefore, the approach has shown great potential for designing low cost instrumentation for automatic in-field discrete or continuous measurements of Hg(II).

The construction and evaluation of a Low Temperature Co-fired Ceramics (LTCC)-based continuous flow potentiometric microanalyzer prototype to simultaneously monitor the presence of two ions (potassium and nitrate) in samples from the water recycling process for future manned space missions is presented. The microsystem integrates microfluidics and the detection system in a single substrate and it is smaller than a credit card. The detection system is based on two ion-selective electrodes (ISEs), which are built using all-solid state nitrate and potassium polymeric membranes, and a screen-printed Ag/AgCl reference electrode. The obtained analytical features after the optimization of the microfluidic design and hydrodynamics are a linear range from 10 to 1000 mg L−1 and from 1.9 to 155 mg L−1 and a detection limit of 9.56 mg L−1 and 0.81 mg L−1 for nitrate and potassium ions respectively.

A boron trifluoride–methanol complex demonstrated remarkable deprotection selectivity against commonly used amino-protecting groups in the deacetylation of acetanilides and high sensitivity to the steric hindrance of substrates. The scope and limitations of the reaction were explored.

Monitoring organic environmental contaminants is of crucial importance to ensure public health. This requires simple, portable and robust devices to carry out on-site analysis. For this purpose, a low-temperature co-fired ceramics (LTCC) microfluidic potentiometric device (LTCC/ POT) was developed for the first time for an organic compound: sulfamethoxazole (SMX). Sensory materials relied on newly designed plastic antibodies. Sol–gel, self-assembling monolayer and molecular-imprinting techniques were merged for this purpose. Silica beads were amine-modified and linked to SMX via glutaraldehyde modification. Condensation polymerization was conducted around SMX to fill the vacant spaces. SMX was removed after, leaving behind imprinted sites of complementary shape. The obtained particles were used as ionophores in plasticized PVC membranes. The most suitable membrane composition was selected in steady-state assays. Its suitability to flow analysis was verified in flow-injection studies with regular tubular electrodes. The LTCC/ POT device integrated a bidimensional mixer, an embedded reference electrode based on Ag/AgCl and an Ag-based contact screen-printed under a micromachined cavity of 600 m depth. The sensing membranes were deposited over this contact and acted as indicating electrodes. Under optimum conditions, the SMX sensor displayed slopes of about −58.7 mV/decade in a range from 12.7 to 250 g/mL, providing a detection limit of 3.85 g/mL and a sampling throughput of 36 samples/h with a reagent consumption of 3.3 mL per sample. The system was adjusted later to multiple analyte detection by including a second potentiomet-ric cell on the LTCC/ POT device. No additional reference electrode was required. This concept was applied to Trimethoprim (TMP), always administered concomitantly with sulphonamide drugs, and tested in fish-farming waters. The biparametric microanalyzer displayed Nernstian behaviour, with aver-age slopes −54.7 (SMX) and +57.8 (TMP) mV/ decade. To demonstrate the microanalyzer capabilities for real applications, it was successfully applied to single and simultaneous determination of SMX and TMP in aquaculture waters. The authors acknowledge the financial support from FCT, Fundacão para a Ciência e Tecnologia/FEDER (project PTDC/AGR-AAM/68359/2006). Oneofus (Almeida SAA) is grateful to FCT for the PhD Grant (SFRH/BD/42509/2007). Publicado

A multicommutation-based flow system with photometric detection was developed, employing an analytical microsystem constructed with low temperature co-fired ceramics (LTCC) technology, a solid-phase reactor containing particles of Canavalia ensiformis DC (urease source) immobilized with glutaraldehyde, and a mini-photometer coupled directly to the microsystem which monolithically integrates a continuous flow cell. The determination of urea in milk was based on the hydrolysis of urea in the solid-phase reactor and the ammonium ions produced were monitored using the Berthelot reaction. The analytical curve was linear in the urea concentration range from 1.0 x 10(-4) to 5.0 x 10(-3) mol L(-1) with a limit of detection of 8.0 x 10(-6) mol L(-1). The relative standard deviation (RSD) for a 2.0 x 10(-3) mol L(-1) urea solution was lower than 0.4% (n = 10) and the sample throughput was 13 h(-1). To check the reproducibility of the flow system, calibration curves were obtained with freshly prepared solutions on different days and the RSD obtained was 4.7% (n = 6). Accuracy was assessed by comparing the results of the proposed method with those from the official procedure and the data are in close agreement, at a 95% confidence level.

Low-temperature cofired ceramics (LTCC) technology is a versatile fabrication technique used to construct microflow systems. It permits the integration of several unitary operations (pretreatment, separation, (bio)chemical reaction, and detection stage) of an analytical process in a modular or monolithic way. Moreover, because of its compatibility with biological material, LTCC is adequate for analytical applications based on enzymatic reactions. Here we present the design, construction, and evaluation of a LTCC microfluidic system that integrates a microreactor (internal volume, 24.28 microL) with an immobilized beta-galactosidase from Escherichia coli (0.479 activity units) and an optical flow cell to measure the product of the enzymatic reaction. The enzyme was immobilized on a glyoxal-agarose support, maintaining its activity along the time of the study. As a proof of concept, the LTCC-beta-galactosidase system was tested by measuring the conversion of ortho-nitrophenyl beta-D-galactopyranoside, the substrate usually employed for activity determinations. Once packed in a monolithically integrated microcolumn, the miniaturized flow system was characterized, the operational conditions optimized (flow rate and injection volume), and its performance successfully evaluated by determining the beta-galactosidase substrate concentration at the millimolar level.

A miniaturized and robust optical fluorosensor, designed as a portable instrumentation for the in situ analysis of ions in water samples by using optodes has been constructed with low cost discrete optical components. The chemical recognition element of the device consists of a plasticized PVC-based fluorescent optode, which includes a new hexamethine–hemicyanine dye as a fluorophore. The signal can be attributed to a certain analyte depending on the ionophore employed. In this work, a commercial potassium ionophore (valinomycin) has been used to formulate a model membrane selective to potassium. The sensor has been fully characterized using a simple flow injection analysis (FIA) system and analytical parameters such as sensitivity (0.71 mV dec −1 ), limit of detection (2.2 × 10 −5 M K + ), repeatability (R.S.D. = 4.2%), reproducibility, lifetime and ionic interferences have been determined. The developed miniaturized system has been applied to the potassium concentration determination in spiked tap water samples. The obtained results have been compared to those acquired by the ICP-OES reference method and the suitability of the experimental setup for the determination of ions in water samples by the miniaturized fluorescence proposal has been demonstrated.

New nor-based cyanine dyes have been characterised for their use as long wavelength chromoionophores in optochemical sensors. Since common quaternary cyanine dyes present optimum spectroscopic characteristics but with high basicities, three kinds of molecules (nortricarbocyanine dyes, norindosquarocyanine dyes and norindocrococyanine dyes), based on an acid–base equilibrium, where the proton attached to the indolic nitrogen is involved, have been designed, expecting to obtain lower p K a values. For comparison purposes, every type of dye has been synthesised with a different central group and molecules with the same heterocyclic substituents have been proposed. The acid forms of the norcyanine dyes present sharp and intense absorption bands from the far visible to the NIR region, with absorption maxima between 648 and 821 nm, allowing the use of non-expensive semiconductor based optical sources and detectors. Relationships between the optical properties, the basicity and the molecular structure are discussed.

This paper describes the development of a new flow system by substituting the injection valve of a FIA system with an automatic microburette controlled by a PC via an RS-232 interface to introduce flexibility into the system. Initially, the response of the system was characterized without a chemical reaction by using a reference system (6-port valve) and a modified system (automatic microburette). The response vs. flow rate and injected volume were studied. The statistic analysis and comparison of the dispersion coefficients obtained for both systems showed no significant difference between them. Comparative studies with chemical reactions were also performed using a reverse Flow Injection Analysis (r-FIA) technique and the Griess-Ilosvay model reaction for nitrite ions. Finally, the system based on the automatic microburette was validated for the analysis of nitrite in two complementary concentration ranges (0.0–0.1 and 0.0–3.0 mg · L−1) using 25 and 350 µL of reactant, respectively. The detection limits obtained were 0.009 and 0.024 mg · L−1, respectively. High repeatability was obtained for both concentration ranges (RSD: 0.52 and 1.35%, respectively).

Some new symmetrical and unsymmetrical near-infrared absorbing acidochromic dyes are synthesised by a simple one-step reaction. Such indicators belong to the ketocyanine dyes type and as well as their full characterisation as the relationship between their structure and optical properties are discussed. They are mainly tested for their future application as pH or solvent polarity sensors. The absorption maxima of the long-wavelength absorbing acidic form span the region from 715 to 750 nm, nearly matching the emission wavelength of the 780 nm laser diode. p K a values in ethanol cover the range between 1.7 and 4.3, and reversible absorption spectra are observed while pH is changed forth and back. As merocyanine dyes, the synthesised ketocyanine dyes show a positive solvatochromism. Since one of the requirements for a solvatochromic molecule to be useful to establish a solvent polarity scale is its stability, the photostability of the dyes is tested in ethanolic solution as well.

In this paper, the universal determination of non-ionic surfactants (NIS) of the polyethoxylate type is attempted using flow-injection potentiometry. Two systems are proposed which use specifically developed tubular flow-through ion selective electrodes (ISEs). These are sensitive to NIS with an hydrophilic chain between 6 and 18 ethoxylate units, which are predominant species in the environment. An on-line pre-concentration system is designed with the aim of a possible application for the unattended monitoring of NIS in surface waters. This on-line pre-concentration is achieved by employing a column packed with a commercial solid phase extraction (SPE) sorbent for the enrichment and purification of the target analytes. The procedure outlined improves the detection limit of a direct system, decreasing it from 1×10 −4 to 3×10 −6 M by use of a pre-concentration volume of 40.0 ml and 200 μl of 75% acetonitrile in water as the eluent. Precision was estimated as 4% relative standard deviation (R.S.D.) ( n =25) for a 1×10 −6 M (0.7 ppm) nonylphenol polyethoxylate with 12 ethoxylate units when 10.0 ml of sample are pre-concentrated. Finally, the on-line pre-concentration system is applied for the total NIS determination in environmental samples from Llobregat river basin of Barcelona area (NE Spain).

The design, construction and evaluation of a versatile cyclic olefin copolymer (COC)-based continuous flow potentiometric microanalyzer to monitor the presence of ammonium ion in recycling water processes for future manned space missions is presented. The microsystem integrates microfluidics, a gas-diffusion module and a detection system in a single substrate. The gas-diffusion module was integrated by a hydrophobic polyvinylidene fluoride (PVDF) membrane. The potentiometric detection system is based on an all-solid state ammonium selective electrode and a screen-printed Ag/AgCl reference electrode. The analytical features provided by the analytical microsystem after the optimization process were a linear range from 0.15 to 500 mg L−1 and a detection limit of 0.07 ± 0.01 mg L−1. Nevertheless, the operational features can be easily adapted to other applications through the modification of the hydrodynamic variables of the microfluidic platform.

A flow injection system for the determination of polyethoxylated nonionic surfactants is described. Potentiometric detection based on tubular flow-through ion-selective electrodes (ISEs) sensitive to this type of surfactants was used. As ion-exchanger, the plasticised PVC membrane incorporates the ion pair between the adduct of a nonionic surfactant with barium and tetraphenylborate. Two different membrane compositions were studied. They differed in the nonionic surfactant used in the ion-exchanger preparation: either nonylphenoxypolyethoxylate with 5 (Ig5) or 12 (Ig12) ethylene oxide units were used. Experimental results showed that the use of Ig5 membrane with a barium salt adjusting solution allowed lower detection limits, while Ig12 ISE with potassium salt solution presented enhanced sensitivity. Both FI systems were evaluated employing three different polyethoxylate standards, which could be determined down to ca. 10 −5 M. Precision was 3% R.S.D. for n = 50 using repetitive injections of a 3 × 10 −4 M Ig12 standard. Preliminary tests of an on-line preconcentration flow system employing the developed sensing devices are also shown. © 2001 Elsevier Science B.V. All rights reserved.

The development of a new electrochemical microsensor based on silicon technology with a photocurable enzyme membrane based on polyurethane acrylate is described. The use of photocurable polymers as the entrapping matrix for enzymes fulfils all the requirements expected for these materials without damaging the biological material. Additionally, the preparation of biosensor devices following this methodology is fast and simple, and this entails the main improvement shown by the new immobilisation method proposed here. The polymer used for enzyme immobilisation enhances the adhesion of the membrane to the previously silanised ion-sensitive field effect transistor (ISFET) gate and assures a long-term stability of more than one month. Additionally, this material provides a membrane deposition methodology compatible with photolithographic techniques allowing mass-production of low cost biosensors. The membrane has been optimised taking into account a good entrapment of the biological material and the effective transport of the substrate and the products through the membrane. After mixing the components of the prepolymer solution, a short exposure (30 s) to 365 nm UV-radiation produced a polymeric membrane without damaging the enzyme. The calibration parameters for the sensors prepared compared well with other methods yielding a slope of 58 mV/dec and a linear range of 0.04–36.0 mM urea in a NH4Cl pH 5.6 solution. The response time (t 95%) was approximately 2 min.

A flow-injection system based on potentiometric detection and designed for the monitoring of anionic surfactant content of printing plates washing solutions is described. Two new PVC membrane ion-selective electrodes, constructed with an all-solid-state tubular flow-through design, are used. The sample, with high ionic strength and extremely alkaline pH, is conditioned in a two-channel flow-injection system, allowing for surfactant determination in the 1 × 10 −4 to 1 × 10 −3 M range, with NaOH contents up to 0.3 M.

A set of amino-group possessing cyanine dyes is obtained from their N-acetyl derivatives via deprotection with boron trifluoride–methanol complex in good yields.

Ion-selective electrodes with poly(vinyl chloride) membranes cast directly on conductive composite substrates are easy to build and have shown their usefulness both in quiescent and flow analysis applications. Matching PVC-composite technology to that of ion-sensitive field-effect transistors (ISFETs) has produced a new type of hybrid chemical sensor. In this novel configuration, a graphite-loaded araldite layer is used to cover the gate opening of encapsulated ISFETs. A poly(vinyl chloride) membrane featuring a plasticiser and an ionophore is cast on top of the conductive composite, rendering the device sensitive to the ion of choice. The resulting hybrid devices show similar electrochemical features when compared to traditional sensors (ISFET + PVC membrane). They also display increased longevity and reduced optical sensitivity when compared with ISFETs featuring transparent PVC membranes.

Synthesis of new acidochromic-based dyes is presented. The dyes obtained have acid absorbance maxima at 640–700 nm and expose spectral changes in the pH-range from 8 to 12.

A simple flow-injection metod for the determination of ammonium ions in water, based on a flow-through pH-ISFET, is described. Ammonium is converted to ammonia, which diffuses through a microporous hydrophic membrane into an ammonium chloride recipient stream, forming a pH buffer which is monitored by the semiconductor detector. The linear working range extends from 0.1 to 10 mmol l−1 with a relative standard deviation of ca. 1% at the 0.7 mmol l−1 level.

In this work a microflow structure, suitable for micro-FIA (micro flow injection analysis), will be described, evaluated and applied to real samples. Microchannels, the detector flow cell and input/output ports have been micromachined in silicon and sealed with anodically bonded Pyrex glass. The channels are defined by etching approximately 200 microm depth in silicon using a dry reactive ion etching (RIE) process. Optical windows integrated in the chip structure allow simple absorbance/transmission measurements to be made. The optical measurements were made using an LED as emitter (lambda=525 nm) and a photodiode as a detector. A Visual-Basic program has been developed to control an automatic burette, three-way solenoid valves and the data acquisition system. The micro-FIA for nitrite determination using the Griess-Ilosvay reaction has been implemented for the on-line monitoring of wastewater treatment plants (WWTPs). The multicommutation concept has been applied in order to enhance the mixing process inside the microsystem. Tandem streams of reagent and sample were generated and evaluated at different commutation frequencies. Two optimal frequencies, 400/200 ms and 150/450 ms, were found to be the most suitable ones. The first commutation ratio gave rise to wide linear working range (0-250 ppm), in spite of a high detection limit (0.35 ppm) and a low sensitivity (0.0041+/-0.0004 AU ppm-1). With the second ratio, the working linear range was smaller (0-50 ppm) but the detection limit (0.17 ppm) and the sensitivity (0.0091+/-0.0003 AU ppm-1) improved remarkably. Finally, real samples with a high nitrite concentration (0-1500 ppm) coming from a study of kinetic inhibition in the nitrification process at a WWTP has been analysed with the proposed micro-FIA system. The obtained results have allowed the corroboration of the model of inhibition by the nitrite ion with great exactitude.

A novel autoadaptative sequential injection system for the analysis of nitrite is described. The automatic determination uses a direct spectrophotometric method, based on the Griess–Ilosvay reaction. In this method the absorbance of the purple azo dye formed is measured at 555 nm. In the sequential injection operation, the sample and the reagent are aspirated and mixed by reverse flow. The sequencing and overlapping of stacked (reagent) zones as well as selection of volumes have been studied in detail. The proposed analytical system is intelligent, simple and robust, allowing for nitrite determination in a double concentration range, by a simple and automatic programmable operation change. These two ranges are 0.0–3.0 and 0.0–20.0 ppm with detection limits being 0.048 and 0.4 ppm, respectively. Next surroundings have been developed allowing autocalibration and independent monitoring of nitrite concentration. The experimental set-up has been evaluated applying it to real samples analysis of very diverse concentration samples coming from a WWTP. The throughput of the method was 12 samples per hour.

A novel system based on reverse flow injection analysis with a gaseous diffusion step (GD-r-FIA) has been developed for the analysis of ozone. It includes an automatic microburet injection system. The ozone diffuses through a microporous membrane of polyvinylidene difluoride (PVDF) from the donor stream to the acceptor stream containing nitrite ions. The nitrite concentration in the acceptor solution decreases due to the ozone reduction reaction. In this way, a simple indirect measurement of the ozone concentration can be performed using the Griess-Ilosvay reaction for the nitrite ion. This correlates with the decrease in absorbance of the azoic dye formed with the ozone concentration in the donor stream. The system has been optimised by investigating the effect of the nitrite concentration in the acceptor stream on the diffusion flow. The optimum nitrite concentration was set at 0.250 ppm with a flow rate of 1.5 ml/min. The efficiency of the ozone diffusion through the membrane was only 4.4%. This affects the average sensitivity, which is low (0.0092+/-0.0012 AU/ppm), although the detection limit is similar to that obtained with other reported methods (0.03 ppm). The main advantage of the system reported here is that it has a linear range that is an order of magnitude broader than those observed for other GD-FIA systems. This is especially useful for continuous monitoring systems, since the residual ozone concentration is normally between 0.05 and 5.0 ppm. Additionally, using the reverse flow injection analysis (FIA) technique minimises chemical consumption and residue generation. Finally, the stability of the ozone solution and the repeatability and reproducibility of the method have been studied.

Earlier work of potentiometric Ion-selective electrodes (ISEs) sensitive to nonionic surfactants of the polyethoxylate type is further extended. The ISEs constructed were all-solid-state sensors with plasticized PVC membranes. The sensing material was a tetraphenylborate salt of the barium complex with a polyethoxylate nonionic surfactant. As membrane component, the combinations of two polyethoxylates of the nonylphenoxy type, which differed in the number of oxyethylene units (5 or 12), and two different plasticizers, (o-nitrophenyloctyl ether and o-nitrophenylphenyl ether), were tested. The response of these electrodes to different nonionic surfactants and the interference effect of several species has been evaluated. For all the types of tested electrodes, the sensitivities shown were ca. 30.0 mV dec−1 and the limit of detection, ca. 10−5 M, when a nonylphenoxyde with 12 oxyethylene units was used as standard. The membrane with the best response characteristics was then applied in potentiometric titrations of this kind of surfactants in the presence of Ba2+ ion and using tetraphenylborate as the titrant.

In this work, we have studied the immobilisation of the haemoglobin/glucose oxidase coupled enzymatic system in poly(vinyl alcohol) membranes. These are to be used as a reagent phase either in the development of an optical sensor or as an efficient bilirubin (BR) removal reactor. Poly(vinyl alcohol) (PVA) was chosen as the support for this purpose, due to its good biocompatibility, hydrophilicity and non-thrombogenic effects. A hydrogel containing the enzymatic system, consisting of PVA crosslinked with glutaraldehyde, was prepared and characterised by DSC, enzyme activity measurements and release tests. Investigating protein conformational changes as a function of temperature and the enzymatic system activity we have found that, in spite of the destabilizing effect of the glutaraldehyde in the acidic medium, the PVA insolubilisation conditions seem do not perturb either the conformation of the [`]native state' nor the enzymatic system activity. Moreover, it was found that PVA/glutaraldehyde membranes offer a simple way to hold enzymatic system, with the possibility of controlling the conditions to obtain either the effective prevention of leaching of the entrapped proteins or the in situ delivery of the haemoglobin. http://www.sciencedirect.com/science/article/B6TWB-3WN7BVW-6/1/e0eaa7d95e2a3cd559b85f445644c387

As part of the development of disposable urea bioselective probes, the covalent binding of urease on ammonium-selective potentiometric membranes has been assessed. Nonactin/bis(1-butylpentyl)adipate/poly(vinylchloride) (PVC) membranes, directly applied to an internal solid contact (conductive epoxy-graphite composite), has been used as a support for covalent immobilization of urease. Two types of all-solid-state construction process have been assayed: thin layers of cellulose acetate (CA) were coated on the PVC ammonium-selective membranes (type 1) and blends of PVC and CA at various ratios were used as ammonium-selective membrane matrices (type 2). Urease was covalently attached to CA via aldehyde groups. These groups were created on the polysaccharide with sodium periodate to which the enzyme was immobilized through a spacer (hexamethylenediamine). The viability of both types of probe for the determination of ammonium ions was assessed after each step of the activation process. Results indicated that type 2 potentiometric probes are altered after the treatment with sodium periodate. Good results were obtained with type 1 probes. Their dynamic concentration range of response to urea was from 2 x 10(-5) to 0.01 M with a sensibility of 50 mV/decade.

Synthesis of new acidochromic-based dyes is presented. The dyes obtained have acid absorbance maxima at 640–700 nm and expose spectral changes in the pH-range from 8 to 12.

Novel nitrate-sensitive membranes have been developed using an aliphatic urethane diacrylate photocurable polymer. This polymer has been chosen due to its easy and fast deposition procedure compared with PVC membranes and its compatibility with microelectronic techniques. These membranes were obtained after UV irradiation during no more than 60 seconds. To optimize their composition and evaluate the chemical response ion selective electrodes (ISEs) with solid inner reference were used. Studies of different plasticizers for nitrate PVC membranes and compositions increasing the ratio between oligomer and diluting agent were performed. ISEs developed presented a sensitivity of −56 mV/dec and a lifetime up to one year. Membrane compositions containing dibutyl phthalate and trioctyl phosphate as plasticizers were deposited onto ISFETs. Studies to elongate ISFETs lifetime were carried out modifying the encapsulation methodology, by using the same polymer family. ISFETs showed a sensitivity between 65–69 mV/decade, depending on the plasticizer, and a linear range of 2.4×10−5−0.06 M. The long-term stability of ISFET sensors with trioctyl phosphate plasticizer was up to 10 months, being superior to that described in the literature for PVC membranes and even for other kind of polymers.

Thiourea derivatives (46 aroylthioureas) having different substituents close to the sulfur atom were synthesized and their ionophore potential in ion selective electrodes (ISEs) was examined. Structural considerations were taken into account based on the corresponding heavy-metal ISE parameters. As ionophores, some 1-furoyl-3-substituted thioureas (series 2) gave the best results in Pb(II), Hg(II) and Cd(II) ISEs. The strong intramolecular hydrogen bond in series 2 allows ligand interaction only through the CS group. Substituents on the furan and phenyl rings give rise to low solubility in the membrane plasticizer. 3-Alkyl substituted furoylthioureas improve solubility but enhance oxidative processes with chain length. New X-ray diffraction (XRD) structures and theoretical DFT calculations were considered in the analysis of the substituent influence on the selectivity of ISEs. These new ionophores have advantages because of their stability, simple synthesis and easy modification of the sulfur binding ability resulting from substitution.

An approach to automation, in routine control, for the determination of anionic surfactants in river water and treatment plant water in the concentration range 0.04–3.5 µg ml–1 using a continuous solvent extraction process with flow injection analysis, is described. The method is based on an ion-pair extraction reaction with Methylene Blue in chloroform. The separation of both phases is accomplished by means of a membrane phase separator and detection is based on injection of the coloured organic phase into a chloroform stream which passes to the detector. Methanol was added to the organic phase in order to enhance the extraction process and to ensure efficient extraction of the various anionic surfactants. A number of anionic species and non-ionic surfactants have been tested as possible interferents. The results obtained for samples of river water show good agreement with those obtained with the Methylene Blue batch method.

The construction, assessment and pharmaceutical appalications of a tubular potentiometric detector sensitive to the 5,5-diethylbarbiturate anion based on quaternary ammonium salt (tetraoctylammonium5,5-diethylbarbiturate) dissolved in o-nitrophenyl octyl ether immobilized in PVC are described. The intrinsic characteristics of the tubular electrode were determined in a low-dispersion manifold and compared with those of a conventional-shaped electrode with no internal reference solution and incorporating the same sensor. The behaviour of a double-channel flow-injection manifold with the same potentiometric detector was evaluated to assess its applicability to the determination of 5,5-diethylbarbiturate in pharmaceutical preparations. Data obtained in the determination of the anion in the latter matrices are presented and compared with those obtained by the conventional British Pharmacopoeia method.

The design of a compact and reliable surface plasmon resonance (SPR) sensor is described and its use in industrial process control is reported. Its application for probable alcoholic degree (PAD) determination in must samples, integrated in a flow-injection system, is described. The sensor response is first evaluated and optimized under dynamic conditions in order to match its working range to that shown by must samples. The performance of the overall system has been tested during harvest time at a wine production plant. Results are compared with those obtained using the conventional refractometric procedure and show adequate agreement.

An automated spectrophotometric method for the determination of titanium(IV) is described based on the reaction between titanium(IV) and hydrogen peroxide in a flow injection system. The system was optimised by a suitable numerical treatment of the different variables using the simplex algorithm. A wide linear range up to 1000 p.p.m. can be achieved at a sampling rate of 240 samples h–1. The method was applied to the determination of low titanium(IV) concentrations in the presence of high concentrations of salts. Under these conditions, the calibration is linear up to 30 p.p.m. and a sampling rate of up to 120 samples h–1 can be achieved. A study of possible interferences demonstrated that the method has good selectivity, but vanadium(V) and molybdenum(VI) interfere.

A compact and robust flow injection system for the simultaneous determination of calcium and nitrate in waters, with sequential detection by potentiometric sensors, is described. The effects of silver ionic strength adjuster (ISA) or lead ISA carrier solutions on the response of the tubular electrodes used and on the ability of the system to control interferences were studied in detail. Under the selected experimental conditions, the response slope and lower limit of linear response were 53.4 mV per decade and 10–4.3 mol l–1 for the nitrate sensor and 31.3 mV per decade and 10–4.75 mol l–1 for the calcium sensor. The reproducibility (relative standard deviation) was better than 1% and the sample throughput was approximately 145 h–1. The results provided by the flow system were shown to be accurate, reproducible and free from interferences. The results obtained for calcium and nitrate in 23 samples with the flow injection system and with a reference method were in good agreement with each other. No significant interferences from other ions, especially chloride and hydrogencarbonate, were observed in surface waters, excluding those with a high saline content. The sequential method described was shown to be useful in routine determinations with a high sampling rate at a low cost.