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A microanalyzer prototype for copper(II) ion monitoring in mining industrial processes is presented. The microanalyzer is designed as an assembly of different modules, each module being responsible for a unit operation. In order to optimize the industrial processes, the microanalyzer can automate all sample management, signal processing, and mathematical calculations and wirelessly transfer data to a control room. The determination of copper(II) ion is done using a colorimetric reaction and the microanalyser performs autocalibration by in situ dilution of a stock solution, matching the higher analyte concentration of the working range defined for the sample to be determined, using a multicommutation approach. The performance of the microanalyzer for monitoring copper(II) ion in water effluents of mining facilities was optimized in the working range from 1 to 10 mg/L to match Mexican environmental law regulations, which allow a maximum concentration of 4 mg/L of copper(II) ion in these circumstances.

The progress made in recent years in the area of micro total analysis system (μ-TAS) has allowed the development of analytical tools for determination and measurement of elements and compounds that previously required bench laboratory equipment for such purposes. μ-TAS provides a high degree of sensitivity and they are simple and affordable. This work details a process by which classical colorimetric methodologies used in analysis have been adapted from discontinuous to continuous flow systems, for determination of cobalt in aqueous solutions in real time. The purpose of this adaptation is the subsequent system miniaturization using low temperature co-fired ceramics (LTCC). The adapted methodology for the colorimetric determination of cobalt uses 3-Hydroxy-4-nitroso-2,7-naphtalene disulfonic acid disodium salt or nitroso-R salt (NRS) as the main reagent, in an environment of acetate and sodium citrate which favors the reaction. The carrier solution is prepared with sulfuric acid. The system encompasses a microfluidic structure in LTCC, a peristaltic pump to maintain the continuous flow, a six-way valve for sample injection, and an issuer of light of 540 nm based on a multiled. Using the integrated circuit TCS3414, the signal is sent to the computer wirelessly through zigbee protocol, and at the end a LabVIEW-based application shows the absorbance for a range of concentrations between 0.5 and 10 mg/L.

The successful integration of sample pretreatment stages, sensors, actuators and electronics in microfluidic devices enables the attainment of complete micro total analysis systems, also known as lab-on-a-chip devices. In this work, we present a novel monolithic autonomous microanalyzer that integrates microfluidics, electronics, a highly sensitive photometric detection system and a sample pretreatment stage consisting on an embedded microcolumn, all in the same device, for on-line determination of relevant environmental parameters. The microcolumn can be filled/emptied with any resin or powder substrate whenever required, paving the way for its application to several analytical processes: separation, pre-concentration or ionic-exchange. To promote its autonomous operation, avoiding issues caused by bubbles in photometric detection systems, an efficient monolithic bubble removal structure was also integrated. To demonstrate its feasibility, the microanalyzer was successfully used to determine nitrate and nitrite in continuous flow conditions, providing real time and continuous information.

Ultrasmooth gold/silver/gold trilayer nanostructured plasmonic sensors were obtained using commercial Blu-ray optical discs as nanoslits-based flexible polymer substrates. A thin gold film was used as an adhesion and nucleation layer to improve the chemical stability and reduce the surface roughness of the overlying silver film, without increasing ohmic plasmon losses. The structures were physically and optically characterized and compared with nanostructures of single gold layer. Ultrasmooth and chemically stable trilayer nanostructures with a surface roughness, Departament d'Universitats, Recerca i Societat de la Informació, Grant/Award Number: 2014 SGR 624; Ministerio de Economía y Competitividad, Grant/Award Number: SEV-2013-0295; Programa Estatal de investigación, desarrollo e innovación orientada a los Retos de la Sociedad, Grant/Award Number: TEC2016-78515-R; Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant/Award Number: SEV2013-0295; CERCA programme/Generalitat de Catalunya; Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya, Grant/Award Number: 2014 SGR 624; PreDICT project, Grant/Award Number: TEC2016-78515-R; CONACYT, Grant/Award Number: 225362

This work is focused on the design and implementation of a microsystem for continuous colorimetric determination of cobalt in aqueous solutions in real time. The main goal is the colorimetric determination of cobalt by adapting colorimetric methodologies used in discontinuous analysis systems to a continuous flow system and its subsequent miniaturization using the LTCC (Low Temperature Co-fired Ceramics) technology. The measure absorbance was recorded using an optical detection system based on a LED (Light Emitting Diode) with a wavelength of 540 nm.

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 present paper describes the use of a microfluidic system to synthesize carbon dots (Cdots) and their use as optical pH sensors. The synthesis is based on the thermal decomposition of ascorbic acid in dimethyl sulfoxide. The proposed microsystem is composed of a fluidic and a thermal platform, which enable proper control of synthesis variables. Uniform and monodispersed 3.3 nm-sized Cdots have been synthesized, the optical characterization of which showed their down/upconversion luminescence and colorimetric properties. The obtained Cdots have been used for pH detection with down and upconverison fluorescent properties as excitation sources. The naked eye or a photographic digital camera has also been implemented as detection systems with the hue parameter showing a linear pH range from 3.5 to 10.2. On the other hand, experiments on the cytotoxicity and permeability of the Cdots on human embryonic kidney cells revealed their adsorption on cells without causing any impact on the cellular morphology. This work was supported by Projects SGR 2009-0323 from Catalonia Government and P10-FQM-5974 from the Junta de Andalucía (Spain). These projects were partially supported by European Regional Development Funds (ERDF). Our thanks to “Reincorporacion de Doctores UGR” programs and Greib startup

This work describes the development of a fully integrated Low Temperature Co-fired Ceramic (LTCC) microreactor for the synthesis of carbon dots (CDots). The microreactor integrates fluidics, a heating resistor and an optical window for fluorescence imaging of the reaction progress in a monolithic, all ceramic device, ensuring homogeneous surface chemistry and physical properties. A pool of different CDots was synthesized at high temperature and pressure using a hydrothermal method, demonstrating the robustness of the microreactor. The synthesis was monitored by following the photoluminescence of the produced CDots, and the reaction conditions were optimized according to their Quantum Yield (QY) and the flow pattern inside the microchannel. The obtained CDots exhibited blue photoluminescence upon irradiation with UV light with QYs of up to 0.77. The CDots were screened as metal nanoprobes and bioimaging contrast agents.

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 general procedure is presented for the fabrication of miniaturized continuous flow analytical microsystems based on photometric detection using the low temperature co-fired ceramics technology. Optical elements such as light emitting diodes and photodiodes (all in the size of a few hundred micrometers) are integrated by means of an off-chip approach. A simple procedure is demonstrated to integrate a glass window after the ceramic sintering in order to minimize the decrease in sensitivity due to the reduction of the optical path length when scaling down. A flow cell with a shape of a bubble has been used to increase the area of the light beam. The device is robust, affordable, and small-sized. It enables absorbance measurements to be performed in-situ or for continuous monitoring of environmental samples. Specifically, a microsystem is introduced for colorimetric determination of chromium (VI) ion in waters based on the diphenylcarbazide reagent as a model. Under the optimized conditions, a linear response is obtained for the concentration range from 0.1 to 20 mg L-1, with a detection limit of 50 μg L-1.

The construction and evaluation of a Low Temperature Co-fired Ceramics (LTCC)-based microsystem prototype as a possible on-site microanalyzer to monitor the presence of two ions in water simultaneously is presented. The approach has been assayed to detect nitrate and chloride ions as model analytes by means of integrating in the same single substrate an ion selective polymeric membrane to nitrate and two screen-printed Ag/AgCl electrodes. One supplies the chloride ion concentration and the other is to complete the potentiometric detection system as the reference electrode. The results obtained by the full characterization of the microanalyzer prove the relevance of the proposal and the possibility to be transferred to real-world samples and environmental monitoring.

A novel fluorescence dip-probe POF (Polymer Optical Fiber) sensor that allows performing in situ chemical determinations has been fabricated. The dip-probe sensor design has been optimized by simulations in order to improve the fluorescence collection. To demonstrate its possibilities, it has been chemically activated with a lead-selective plasticized PVC (polyvinylchloride) membrane containing a new synthesized suitable fluoroionophore and a commercial lead ionophore. The analytical response of the dip-probe sensor has been characterized and it shows a fully reversible response with a sensitivity of −35.10 mV/dec C and a Pb2+ detection limit of 7 × 10−6 M, which can be appropriate for monitoring contamination episodes. No significant interferences with other metal ions have been found. The device has been finally tested to determine the lead content in contaminated natural samples with promising results.

A novel compact dual-wavelength measurement system for absorbance chemical sensing incorporating digital lock-in amplifiers is reported. Its main innovation is the introduction of a reference wavelength to correct the possible non-specific optical changes of the system. The performance of the instrumentation has been tested on a laboratory setup and with integrated optical absorbance sensors.

The present report describes the development of a thick-film sensor with intended applications for soil analysis. A probe incorporates three sensors, each at a different depth and featuring a copper plate as the reference electrode. In addition, the probe also contains all necessary instrumentation required for processing the sensor signal and to transmit it via radio. The developed sensors were calibrated in situ using two different soil compositions by adding standard solutions. Results show a quasi-Nernstian response in soil, in response to the addition of fertilisers. Extracts of soil samples analysed by the Kjeldahl method were compared with results from the probe. This comparison confirms that the sensors are capable or measuring chemical parameters in situ in an automated fashion.

Proceeding of: 2013 Asia-Pacific Microwave Conference Proceedings (APMC), Seoul, Korea (South), 5-8 Nov. 2013 A novel design combining standard microstrip technology with single ring resonator and high dielectric constant resonator for design of low and band pass filtering electromagnetic band gap(EBG) structures, operating in the range from 1 to 20 GHz is presented in this paper. The design is based on a high dielectric constant resonator embedded in a microstrip structure substrate. The dielectric resonator is fabricated by using commercial high dielectric constant EPOXY paste in a process compatible with serigraphy and screen printing technology. This work has been supported by Ministerio de Ciencia y Educación of the Spanish government under the project TEC2010-16060.

In this work, an analytical microsystem based on LTCC (low-temperature co-fired ceramic) technology with monolithic incorporation of an optical flow cell for determination of dipyrone in pharmaceuticals is described. The detection system is based on the formation of a blue chromophore between dipyrone and Fe(III) photometrically monitored at 630 nm using a lab-made LED mini-photometer constructed with a light emitting diode as a radiation source and a Si photodiode as a detector. The lab-made mini-photometer elaborated presented a good performance in regard to high signal/noise ratio, low drift and good sensitivity. The analytical curve was linear in the dipyrone concentration range from 1.0 × 10-4 to 3.5 × 10-3 mol L-1, limit of detection of 4.5 × 10-5 mol L-1 and total time of analyses of 20 s yielding an analytical frequency of 195 h-1 with a low waste generation per analysis (480 µL). Neste trabalho, a aplicação de um microssistema analítico construído com tecnologia LTCC (cerâmica cossinterizada a baixa temperatura) com incorporação monolítica de uma cela óptica de fluxo para determinação de dipirona em formulações farmacêuticas é descrita. O sistema de detecção baseou-se na formação de um cromóforo azul entre a dipirona e Fe(III) monitorado fotometricamente em 630 nm usando um minifotômetro de LED lab-made construído com um diodo emissor de luz como fonte de radiação e um fotodiodo de Si como detector. O minifotômetro elaborado apresentou um bom desempenho com respeito à elevada relação sinal ruído, baixo ruído e sensibilidade satisfatória. A curva analítica foi linear na região de concentração de dipirona de 1,0 × 10-4 a 3,5 × 10-3 mol L-1 tendo sido obtido um limite de detecção de 4,5 × 10-5 mol L-1 e um tempo total de análise de 20 s equivalente à uma frequência analítica de 195 h-1 com pouca geração de resíduos por análise (480 µL).

In this paper, a computer controlled microreactor to synthesize water soluble CdS and CdS/ZnS nanocrystals with in situ monitoring of the reaction progress is developed. It is based on ceramic tapes and the Low-Temperature Co-fired Ceramics technology (LTCC). As well the microsystem set-up, the microreactor fluidic design has also been thoroughly optimized. The final device is based on a hydrodynamic focusing of the reagents followed by a three-dimensional micromixer. This generates monodispersed and stable CdS and core–shell CdS/ZnS nanocrystals of 4.5 and 4.2 nm, respectively, with reproducible optical properties in terms of fluorescence emission wavelengths, bandwidth, and quantum yields, which is a key requirement for their future analytical applications. The synthetic process is also controlled in real time with the integration of an optical detection system for absorbance and fluorescence measurements based on commercial miniaturized optical components. This makes possible the efficient managing of the hydrodynamic variables to obtain the desired colloidal suspension. As a result, a simple, economic, robust and portable microsystem for the well controlled synthesis of CdS and CdS/ZnS nanocrystals is presented. Moreover, the reaction takes place in aqueous medium, thus allowing the direct modular integration of this microreactor in specific analytical microsystems, which require the use of such quantum dots as labels.

Microfluidic reactors offer many potential advantages in several research and industrial fields such as processes intensification, which includes a better reaction control (kinetics and thermodynamics), a high throughput and a safer operational environment (reduced manipulation of dangerous reagents and low sub-products generation). Nevertheless, scaling-down limitations appear concerning the materials used in the fabrication of microreactors for most of the liquid-phase reactions, since they usually require high temperatures (up to 300 °C), solvents and organic reagents. In this work, the development of a set of modular and monolithic microreactors based on the integration of microfluidics and a thermal platform (sensor/high-temperature heater) is proposed to perform high temperature reactions. The reliability and performance of both configurations were evaluated through an exhaustive characterization process regarding their thermal and microfluidic performance. Obtained results make the devices viable for their application in controlled and reproducible synthetic processes occurring at high temperatures such as the synthesis of quantum dots. The proposed microfluidic approach emerge as an engaging tool for processes intensification, since it provides better mass and temperature transfer than conventional methods with a reduction not only of the size and energy consumption, but also of by-products and reagents consumption. 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 Government through SGR 2009 -0323.

This work proposes a new dielectric resonator type characterized by an extreme topology that confines the electromagnetic fields in such a way that only superficial modes are allowed. The technique can be potentially utilized to combine dielectric resonators with multilayer planar technologies.

The Electrical Discharge Machining (EDM) is used to drill and mechanize a variety of rigid materials that cannot be cut or shaped by typical tools because of their high hardness or complex shape. The EDM operating principle is based on the interaction between solid matter and the electronic arc discharge. The severe physical conditions around the spark are be used to mill and drill all kind of materials [1]. The electro-perforation is a particular case of the EMD which allows to make holes in permeable materials such as paper or biological membranes to generate a drilling pattern with controlled porosity for different applications[2].

Proceeding of: 13th International Conference on Electrostatics (Electrostatics 2011), 10–14 April 2011, Bangor, Wales (UK). The aims of this work are to show the influence of adding a series resistance at the output of a discharge generator circuit and to point out that this component can be used to control the spark energy in electrostatic perforation systems. Analysis of the experimental results reveals that there exists a close connection between the resistor value and the obtained perforation pattern both in hole density and size. The use of a series resistor has a strong influence on the material porosity, which is an important industrial parameter for assessing the pattern perforation quality. Publicado

Several methods to enhance the efficiency of paper electroperforation processes are presented in this work. In all the cases, the discharge confinement effect is used for obtaining higher perforation densities than those found in the standard industrial processes. To quantify the efficiency of the proposed methods, statistical tools are used to characterize the 2-D perforation pattern. Publicado

Proceeding of: Electrostatics 2011 The electroperforation distribution in thin porous materials is investigated using the quadrat counts method (QCM), a classical statistical technique aimed to evaluate the deviation from complete spatial randomness (CSR). Perforations are created by means of electrical discharges generated by needle-like tungsten electrodes. The objective of perforating a thin porous material is to enhance its air permeability, a critical issue in many industrial applications involving paper, plastics, textiles, etc. Using image analysis techniques and specialized statistical software it is shown that the perforation locations follow, beyond a certain length scale, a homogeneous 2D Poisson distribution. The authors acknowledge the TRACE project from Ministerio de Ciencia e Innovación, Spain. Publicado

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.

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.

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 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.

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.

Altres ajuts: CICYT/TIC93-0525 A new approach for developing optochemical absorbance sensors is presented. The method is based on a planar micro-optic circuit in which an optochemically active membrane that responds to selective compounds is deposited in the device, yielding a part of the guiding planar structure. In this way the optical field is confined in the direction transverse to the substrate and controlled in the lateral direction by means of planar micro-optics components. High sensitivity of the device can be easily obtained because of the relatively long light paths through the membrane, and the response time is low because the analyte has to diffuse through a several-micrometer-thin membrane. Experimental results of measurements of the concentration of potassium are also presented to verify the possibilities of these devices as specific absorbance sensors.

A novel compact dual-wavelength analyser for Integrated Waveguide Absorbance Optodes (IWAOs) is reported. The main innovation is the introduction of a reference wavelength to correct possible unspecific optical changes of the system.

A flow injection system for the simultaneous determination of total Fe and CrVI based on the sandwich technique is described. Both metals were determined spectrophotometrically at 526 nm with a single detector over the range 0.2–10 p.p.m. The sampling frequency achieved was 60 samples h–1 and the standard deviations were 0.09 and 0.08 p.p.m. for total Fe and CrVI, respectively.