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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.

New one-step synthesis of ketocyanine dyes is presented. The dyes obtained expose spectral changes in pH range from 1.7 to 4.3 and their protonated forms absorb at 715–750 nm.

A microfluidic system based on the low-temperature co-fired ceramics technology (LTCC) is proposed to reproducibly carry out a simple one-phase synthesis and functionalization of monodispersed gold nanoparticles. It takes advantage of the LTCC technology, offering a fast prototyping without the need to use sophisticated facilities, reducing significantly the cost and production time of microfluidic systems. Some other interesting advantages of the ceramic materials compared to glass, silicon or polymers are their versatility and chemical resistivity. The technology enables the construction of multilayered systems, which can integrate other mechanical, electronic and fluidic components in a single substrate. This approach allows rapid, easy, low cost and automated synthesis of the gold colloidal, thus it becomes a useful approach in the progression from laboratory scale to pilot-line scale processes, which is currently demanded.

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.

New one-step synthesis of ketocyanine dyes is presented. The dyes obtained expose spectral changes in pH range from 1.7 to 4.3 and their protonated forms absorb at 715–750 nm.

The development of micro total analysis systems (muTAS) has become a growing research field. Devices that include not only the fluidics and the detection system but also the associated electronics are reported scarcely in the literature because of the complexity and the cost involved for their monolithic integration. Frequently, dedicated devices aimed at solving specific analytical problems are needed. In these cases, low-volume production processes are a better alternative to mass production technologies such as silicon and glass. In this work, the design, fabrication, and evaluation of a continuous-flow amperometric microanalyzer based on the green tape technology is presented. The device includes the microfluidics, a complete amperometric detection system, and the associated electronics. The operational lifetime of the working electrode constitutes a major weak point in electrochemical detection systems, especially when it is integrated in monolithic analytical devices. To increase the overall system reliability and its versatility, it was integrated following an exchangeable configuration. Using this approach, working electrodes can be readily exchanged, according to the analyte to be determined or when their surfaces become passivated or poisoned. Furthermore, the electronics of the system allow applying different voltamperometric techniques and provide four operational working ranges (125, 12.5, 1.25, and 0.375 muA) to do precise determinations at different levels of current intensity. The authors would like to thank the Spanish MEC for its financial support through: Consolider-Ingenio 2010 (CSD2006-00012), TEC2006-13907-C04-04/MIC and CIT- 310200-2007-29.

Los hongos acumulan selenio, metal considerado nutricionalmente oligoelemento, pero nocivo para la salud del consumidor en dosis excesivas. Se estudió el contenido de selenio en setas silvestres comestibles, teniendo en cuenta los factores influyentes en su captación, y el riesgo toxicológico derivado de su consumo. 97 muestras de setas de 14 especies fueron recogidas en Lugo, Galicia (España). Separadamente, las porciones anatómicas: himenóforo y resto del carpóforo, fueron digeridas en medio ácido en un microondas, y analizadas mediante la técnica de inducción de plasma acoplado a espectrometría de emisión óptica. Boletus pinicola y Boletus edulis son las especies más acumuladoras de selenio en himenóforo con 74,93 y 52,7 mg/kg p.s., respectivamente. La materia orgánica del suelo entre 12–16% favoreció su absorción. Finalmente, considerando la dosis de toxicidad crónica del selenio, relativamente próxima a las recomendaciones dietéticas (OMS), y las concentraciones de las setas estudiadas, se aconseja el consumo moderado de algunas especies del género Boletus. Selenium is considered as a trace element metal, but in excessive doses it becomes toxic for the consumer's health. In this study, the goal was to determine the accumulation capacity of selenium in edible mushrooms in relation to some factors and their possible toxicological implications. Edible mushrooms (97 samples of 14 species) were collected in Lugo, Galicia (Spain). Anatomical parts, hymenophore and the rest of the fruiting body, were processed by digestion in acid medium in a microwave oven and analyzed by inductively coupled plasma-optical emission spectrometer. Boletus pinicola and Boletus edulis reached the highest mean selenium contents in hymenophore with values of 74.93 and 52.7 mg/kg dry weight, respectively. Organic matter in growth soil between 12–16% favoured its uptake. Finally, taking into account the dose of chronic toxicity of selenium, relatively close to the dietary recommendations (WHO), and the concentrations obtained in the studied mushrooms, a moderate consumption of some species of Boletus is recommended. La Xunta de Galicia subvencionó este trabajo a través del Proyecto INCITE08PXB261087PR SI

Results obtained in the evaluation of a mathematical model for flow-injection sandwich systems, in which the sample is inserted between two different carrier solutions with the aid of an eight-way injection valve, are presented. The model considers the system as a tubular reactor with axially dispersed plug flow, where chemical kinetics have been included. Only a minimum of parameters are needed for the model: the dispersion coefficients, which are obtained from experimental correlations for the different hydrodynamic conditions, and the rate constants, which are determined by univariate optimization. The behaviour of the model, when applied to the case of one analyte and one reagent, was evaluated for the enzymatic determinations of glucose or glycerol. The case of two analytes determined with two reagents was also studied in the combined determination of glucose and glycerol. Experimental profiles were compared with the simulated peaks and showed good agreement.

The present paper reports the modeling and characterization of the physical sample dispersion process observed in rectangular microchannels when pressure-driven pumping is used. To explain experimental results provided by the silicon fluidic device constructed, two different mathematical models were tested. The first one is based on the diffusion-convection model, and the second one is based on the combination of ideal reactors. The silicon designed and constructed chip includes a microfluidic manifold with four inlet-outlet ports and a monolithically integrated optical flow cell. The microchannels, the optical flow cell, and the input-output ports were micromachined on a silicon wafer and then sealed with Pyrex glass anodically bonded. Optical windows were integrated in the chip, allowing simple absorbance-transmission measurements. Pressure-driven flows through fluidic channels were controlled via three-way solenoid valves and provided by an automatic microburette operating in aspiration mode. Experimentally obtained results demonstrate that the physical sample dispersion process can be easily modeled as a combination of a continuous stirred tank reactor and a plug-flow reactor.

The miniaturization of analytical systems for different applications is currently a very active field of research. The inherent advantages of micro total analysis systems (muTASs) are well known. Although the fluidic platforms and the development of suitable miniaturized detection systems have been studied extensively, the integration in a single substrate of the electronics that is needed to manage the whole system using a single technology is still a sizeable challenge. In this overview, we discuss the role of the low-temperature co-fired ceramics (LTCC) as a potential alternative for miniaturizing analytical systems, since a single technology can easily combine fluidics and electronics to produce a number of novel chemical microanalyzers. The authors would like to thank the Spanish MEC for its financial support through: Consolider-Ingenio 2010 (CSD2006-00012), TEC2006-13907-C04-04/MIC and CIT-310200-2007-29. Publicado

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.

Recently, the low temperature co-fired ceramics technology has shown to be an excellent alternative to silicon-based microfabrication techniques for the production of three-dimensional structures using a multi-layer approach. This enables the integration of several unitary operations of a classical analytical process and also the integration of sensors, actuators and electronics in the same substrate. In this work, we show the integration of the actuators and the sensors needed for the control of temperature inside a miniaturized fluidic device. The proposed device presents enough thermal accuracy to be used in chemical systems where temperature control is a crucial factor, such as enzyme reactions or polymerase chain reaction systems. The authors would like to thank the Spanish MEC for its financial support through: Consolider-Ingenio 2010 (CSD2006-00012), TEC2006-13907-C04-04/MIC and CIT-310200-2007-29. CSM is also thankful to the Alban Program (High-level grants from the European Union to Latin America for its financial support (Grant number: E05D053315MX).

The advantages of microanalyzers, usually fabricated in silicon, glass, or polymers, are well-known. The design and construction of fluidic platforms are well-developed areas due to the perfectly established microfabrication technologies used. However, there is still the need to achieve devices that include not only the fluid management system but also the measurement electronics, so that real portable miniaturized analyzers can be obtained. Low-temperature co-fired ceramics technology permits the incorporation of actuators, such as micropumps and microvalves, controlled either magnetically, piezoelectrically, or thermally. Furthermore, electronic circuits can be also easily built exploiting the properties of these ceramics and the fact that they can be fabricated using a multilayer approach. In this work, taking advantage of the possibility of combining fluidics and electronics in a single substrate and using the same fabrication methodology, a chemical microanalyzer that integrates microfluidics, the detection system, and also the data acquisition and digital signal processing electronics is presented. To demonstrate the versatility of the technology, two alternative setups have been developed. In the first one, a modular configuration is proposed. In this case, the same electronic module can be used to determine different chemical parameters by simply exchanging the chemical module. In the second one, the monolithic integration of all the elements was accomplished, allowing the construction of compact and dedicated devices. Chloride ion microanalyzers have been constructed to demonstrate the operability of both device configurations. In all cases, the results obtained showed adequate analytical features. The authors thank the Spanish MEC for its financial support through: Consolider-Ingenio 2010 (CSD2006-00012), TEC2006-13907-C04-04/MIC, and CIT-310200-2007-29. C.S.M.-C. is also thankful to the Alban Program (High-level grants from the Eurepean Union to Latin America for its financial support: Grant E05D053315MX) and Conacyt, Mexico for further financial assistance. Publicado

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.

Optochemical sensors have had a huge expansion and in recent years interesting sorts of optical sensor have been developed which make use of the integrated circuit microelectronic technology and the optical technological advances achieved in the telecommunications industry. These devices are based on optical fibers, planar waveguides or the combination of both supports as light-guiding structures and offer an enhanced performance thanks to a miniaturized size, a feasible mass production at low cost, the possibility to measure at large distances and the capability of reaching places hard to access for the in situ monitoring of environmental or medical parameters. In this chapter, we provide an overall view of integrated chemical sensors based on absorbance measurements, describing their main characteristics, advantages and drawbacks. In order to focus on these types of devices, first of all, a brief classification is given, in terms of the interaction mechanisms and the reactive phases or membranes that are involved in the response, and the radiation transmission medium. Next, different waveguide configurations are briefly described because of to the relevancy of these structures as the main constituent of integrated optodes and, finally, some absorbance-based integrated sensors are detailed.

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.

A potentiometric sensor system based on potassium ion-selective electrodes was developed for agricultural purposes. Sensors were built using PVC ion-selective membranes over an inner solid contact prepared with graphite-epoxy composites. A copper plate was used as a reference electrode. A two-stage electronic circuit composed of current and voltage amplifiers was designed to interface the sensors to a distributed data acquisition system. Three ion-selective sensors and three off-the-shelf temperature sensors and their associated circuits were mounted in a PVC tube to set up a soil probe. The electronic controls were placed in an airtight box fixed at the upper part of the probe. The system was evaluated in the field, where the sensors presented sensibility within the range of 69-71 mV dec(-)(1). Extracts of soil samples were analyzed by a current flame photometry approach, and the results, compared with the probe measurements, showed a linear relationship (r (2) = 0.992 and 0.995, respectively, to 5 and 20 cm depths), which implies viability and instrumentation reliability for agricultural applications.

There are a number of variables that are useful to determine the optimal moment for the fruit collection such as starch content, sugar content, acidity and firmness. Other variables, including calcium and potassium concentrations, may establish better the state of ripeness of fruit and can help to optimise the collection process as well as augmenting the nutritional value of fruits. At present, these novel parameters cannot be used for the control of fruit collection due to the slow standard methods required. The need for in situ and in real-time ion measurements calls for fast response sensors and simpler and portable instrumentation. Solid-state sensors respond to these requirements. This work describes the application of ISFET sensors to analyse calcium, potassium and nitrates in several apple varieties, both in juice and in situ fruit. Results show that the analysis of potassium, calcium and nitrate permits to distinguish among apple varieties and can also be used to determine correctly the concentrations of these ions.

The optical and analytical characteristics of a series of neutral H+-selective chromoionophores in PVC membranes are described. Such indicators have been synthesized so that they can operate in bulk optode membranes as the chemically active region of integrated waveguide absorbance optodes (IWAOs), lambdamax near 780 nm. Their spectral characteristics, acid-base properties, chemical stability, and solubility in the membrane phase are given and discussed. The response characteristics are first tested in a conventional absorbance/transmittance flow cell. They offer a wide range of pKa's in PVC membranes, good sensitivity as a result of their high molar absortivities, excellent solubility in the plasticizer, and quick response times. They present good chemical stability in common laboratory conditions when stored in the dark, and the absence of leaching guarantees a long lifetime. Membranes have been finally applied as the sensing region of an integrated waveguide optode, demonstrating the extraordinary sensitivity improvement while preserving the remaining analytical features. Calibration curve slopes are multiplied by 3-28, and response times lower than 2 min are obtained.

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

Tesis (Economista)--Universidad Autónoma de Occidente, 1998 Pregrado Economista

Optical fiber chemical sensors are playing an important role in chemical detection because they combine the characteristics and advantages of optochemical detection with the possibility of developing miniaturized compact devices, able to be included in standard analytical chemical and medical labs as well as in control of industrial chemical processes.

The recent needs in the nanosciences field have promoted the interest towards the development of miniaturized and highly integrated devices able to improve and automate the current processes associated to the efficient nanomaterials production. Herein, a green tape based microfluidic system to perform high temperature controlled synthetic reactions of nanocrystals is presented. The device, which integrates both, the microfluidics and a thermally controlled platform, was applied to the automated and continuoussynthesis of CdSe quantum dots. Since temperature can be accurately regulated as required, sizecontrolled and reproducible quantum dots could be obtained by regulating this parameter and the molar ratio of precursors. The obtained nanocrystals were characterized by UV-Vis and fluorescencespectrophotometries. The band width of the emission peaks obtained indicates a narrow size distribution of the nanocrystals, which confirms the uniform temperature profile applied for each synthetic process, being the optimum temperature at 270° C (Full Width at Half Maximum = 40 nm). This approach allows a temperature controlled, easy, low cost and automated way to produce quantum dots in organic media, enhancing its application from laboratory-scale to pilot-line scale processes. This work has been supported by the Spanish Ministry of Science and Innovation (MICINN) through projects CTQ2009-12128 and the Consolider Ingenio 2010 project CSD2006 -12 and Catalonia 15 Government through SGR 2009 -0323.

O-3 graphite-epoxy composites have been developed and optimized as conducting plastic materials. These rigid and easily mechanized composites have been used in our laboratory to construct electrochemical sensors and biosensors in different sizes and shapes. All-solid-state Potentiometric sensors and biosensors have been developed using grahite-epoxy conducting substrates. The procedure has been extended to CHEMFET and ENFET sensors, rendering hybrid solid-state sensing devices with long lifetimes. It have been found out that enzymes retain their bioactivity within the graphite-epoxy matrices. Different biocomposites have been prepared and applied as amperometric transducers. Biologically bulk-modified graphite-epoxy materials offer several advantages for amperometric sensing.

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.

We report the application of a sandwich technique in flow injection systems which afford low consumption of expensive reagents and two reagent recirculation systems. The potential applicability of the technique thus developed was assessed by determining glucose in serum samples by the enzymatic glucosidase/peroxidase method. It was possible to perform up to 450 determinations with the same amount of reagent used to perform 50 determinations by batch procedures. The sampling rate was 80 determinations per hour with a 0.9% relative standard deviation.

An experimental comparison between the relative performances of the Powell and simplex methods for the optimization of a Flow Injection Analysis (FIA) system for the determination of nitrite in water is reported. An evaluation of the advantages of using a weighted linear combination of two variables (related to sensitivity and sample throughput rate) as the response function in the guidance of the optimization procedures towards different practical requirements is also included. Both methods proved to be effective for the optimization, none having shown definite advantages over the other. The use of a weighted response function in these optimization methods proved to be useful for assessing the versatility of FIA systems.

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.

A response function (RF) in order to simultaneously optimize different variables by the SIMPLEX method in FIA systems, with the possibility of applying weights, is proposed. The optimization program developed to use this RF is assayed in the optimization of two different flow injection procedures. The obtained results are discussed.

Flow injection methodology based on sample insertion between two different standard solutions used as carrier streams is described. This approach provides a simple system for continuous recalibration in process control; spectrophotometric and ion-selective electrode procedures are outlined.

A simply constructed flow-through pH-ISFET detector suitable for flow-injection analysis is described. Its response characteristics are presented and discussed. The calibration plot is linear in the pH range 2–12; the slope is 53 mV per decade.

A flow-through sandwich potentiometric detector for FIA in which a PVC membrane sensor is applied on a conductive epoxy support is described. It allows simple replacement of the membrane when exhausted or substituition of the sensor system and shows good mechanical and electric stability. The device can be easily included in a block with a location for the reference electrode. The detector was activated with a commercial sensor selective to nitrate and its behaviour in FIA was studied. A comparison of its perfomance with that of a nitrate selective electrode of classic shape constructed by the same technique is presented.

Samples (1500 μl) are inserted between zones of water and ascorbic acid solution with subsequent addition of 1,10-phenanthroline at pH 5.0. The signal provides a plateau region corresponding to Fe(Il) followed by a peak corresponding to total iron. The proposed system allows up to 90 injections per hour. Linear working ranges are 0.1–9 and 0.3–12 mg l−1 Fe(II) and total iron, with relative standard deviations of < 0.6 and 1.2%, respectively. Results obtained for various ground waters agree well with those obtained by a standard method.

A general construction procedure for conventional shape ion-selective electrodes based on a conductive support prepared with a mixture of a non-conductive epoxy and graphite was used in the preparation of a flow-through benzoate electrode to be used as potentiometric detector in flow injection analysis manifolds. The membranes were prepared from tetraoctylammonium benzoate in o -nitrophenyloctylether immobilized on PVC. The results of the assessment of the tubular electrodes behaviour in low dispersion manifolds against that of conventional electrodes with the same membrane are reported. Data obtained with a double-channel flow injection manifold incorporating these tubular detectors for benzoate determinations in several commercially available pharmaceutical preparations are also presented.

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.

A tubular PVC membrane electrode for calcium without inner reference solution and a device for location of the reference electrode are described. In the flow-injection system, calcium is determined potentiometrically and then magnesium is determined by atomic absorption spectrometry. The electrode provides linear response to calcium in the range 5 × 10 −5 /2-10 −1 M. On-line dilution of the sample allows magnesium determination in the range 0/2-10 mg l − . Flow rates between 3 and 6 ml min −1 are possible. The sampling frequency is 60/2-90 h −1 .