J. Bartrolí

Flow-through tubular PVC matrix membrane electrode without inner reference solution for flow injection analysis

A simply constructed tubular PVC matrix membrane electrode without inner reference solution suitable for flow injection analysis is described. The nitrate-selective electrode developed allows simple replacement of an exhausted membrane, or change of function with a new sensor membrane. The compact design ensures mechanical stability and the tubular configuration minimizes distortion of the hydrodynamic flow in the detector. Nitrate can be determined in the range 10−1–10−5 M, under different flow conditions, with a sampling frequency of about 120 h−1.

Flow injection system for on-line potentiometric monitoring of ammonia in freshwater streams

A flow injection system based on potentiometric detection and designed for on-line monitoring of ammonia in freshwater streams is described. A specially constructed all-solid state tubular flow-through ammonium electrode was used in conjunction with a gas-diffusion chamber to enhance its selectivity. Construction of the electrode involved the in situ formation and direct casting of the sensing nonactin-poly(vinyl chloride) membrane on to a mouldable conducting filled polymer (epoxy resin loaded with graphite), which acted as an internal solid contact, without an inner solution. The electrode response under dynamic conditions both with and without the gas-diffusion chamber was evaluated. After optimisation of the flow system parameters, over 30 samples with a wide range of ammonia concentrations (2 × 10–5–10–2M) could be processed per hour with a detection limit of ca. 10–6M. The performance of the monitoring system under on-line conditions in a water treatment plant is also described.

Valorisation of forestry waste by pyrolysis in an auger reactor.

Pyrolysis of forestry waste has been carried out in an auger reactor to study the influence of operational variables on the reactor performance and the properties of the related products. Pine woodchips were used for the first time as raw material and fed continuously into the reactor. Ten experiments were carried out under inert atmosphere at: (i) different reaction temperature (1073, 973, 873, 823 and 773 K); (ii) different solid residence time (5, 3, 2 and 1.5 min); and (iii) different biomass flow rate (3.9, 4.8 and 6.9 kg/h). Results show that the greatest yields for liquid production (59%) and optimum product characterisation were obtained at the lowest temperature studied (773 K) and applying solid residence times longer than 2 min. Regarding bio-oil properties, GC/MS qualitative identification show that the most abundant compounds are volatile polar compounds, phenols and benzenediols; and very few differences can be observed among the samples regardless of the pyrolysis operating conditions. On the whole, experimental results demonstrate that complete reaction of forest woodchips can be achieved in an auger reactor in most of the experimental conditions tested. Moreover, this study presents the initial steps for the future scaling up of the auger reactor with the aim of converting it into a mobile plant which will be able to remotely process biomass such as energy crops, forestry and agricultural wastes to obtain bio-oil that, in turn, can be used as energy vector to avoid high transport costs.

Flow-Through Sandwich PVC Matrix Membrane Electrode for Flow Injection Analysis

Abstract 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.

Sandwich Techniques in flow injection analysis : Part 1. Continuous recalibration techniques for process control

Abstract 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.

Sequential flow-injection determinations of calcium and magnesium in waters

Abstract 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 .

Amperometric enzymatic glucose electrode based on an epoxy-graphite composite

Abstract An inexpensive, robust, polishable and easy to mechanize amperometric transducer showing a long lifetime, based on a composite material made of graphite and non-conducting epoxy resin (Epo-Tek H77), was constructed. This composite was characterised electrochemically using cyclic voltammetry and linear-sweep voltammetry. The applicability of this amperometric transducer was demonstrated in the construction of a glucose biosensor based on the amperometric detection of hydrogen peroxide produced by the catalytic action of glucose oxidase covalently immobilized on a nylon mesh. The sensor shows a linear response range for glucose in the range 10 −5 −10 −2 M when a potential of 1150 mV is applied with respect to an Ag/AgCl electrode in a pH 7.00 buffered solution with 0.1 M phosphate and 0.1 M KCl. The resulting biosensor was compared with a commercial glucose analyser.

Flow-through tubular ion-selective electrodes responsive to anionic surfactants for flow-injection analysis

Abstract 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.

Continuous-Flow System for On-Line Water Monitoring Using Back-Side Contact ISFET-Based Sensors.

A multiparametric continuous-flow system for on-line monitoring of water based on ISFET sensors is described. The ISFETs used have silicon nitride as gate material, and the electrical contacts are placed on the back side of the chip. This is a technological improvement that allows for a more compact ISFET packaging and greatly increases the lifetime of the sensor compared with planar type ISFETs, since the electrical parts are separated from the chemical environment. A special probe has been designed in order to encapsulate and apply these ISFETs into the flow system. Further, a reference electrode based on standard Ag/AgCl technology has been constructed according to the ISFET probe design in order to integrate both sensors in the same flow-through cell. These probes can be easily replaced in the flow system and are made of cheap and easily mechanized materials. Using these flow-through sensors, a continuous-flow system for the determination of pH, NH(4)(+), Ca(2+), and NO(3)(-) in waters has been designed. The system configuration is based on a modular design (one setup for each parameter and a common sampling channel), which allows simple manipulation and maintenance as well as a good flexibility for different analytical requirements. A study of the system characteristics was performed by following the specifications for water monitoring. Under the conditions established for the flow system, a sampling rate of 20 h(-)(1) was obtained for each parameter, and long-term stabilities of at least 3 weeks of daily work for ISFET sensors and 5 months for the reference electrode have been achieved. The response performances obtained show the feasibility of the BSC ISFET probe use in continuous-flow monitoring.

Planar Compatible Polymer Technology for Packaging of Chemical Microsensors

By applying special thick film photolithography it is possible to realize a highly automative ion-sensitive field effect transistor (ISFET) packaging at the wafer level. In this paper two approaches based on photolithographic processing of encapsulating layers are presented. A lift-off method of commercial thermocurable encapsulants has been investigated, as well as direct photopolymerization of ultraviolet-curable encapsulant compositions, containing either epoxy acrylate or polyurethane acrylate oligomers together with monomers and photoinitiators. Lift-off has been developed using either thin or thick photoresist sacrificial layers. The best compatibility implies thick photosensitive polyimide layers as a sacrificial photoresist together with the encapsulant material based on alumina-filled epoxy. However, better results are obtained by using photopatternable encapsulant polymers that permit application of thin or thick polymer layers on a wafer substrate containing ISFET chips. Windows over the gate region and contact pads are opened by exposure to ultraviolet light in a standard mask aligner system. Compositions based on epoxy acrylate oligomers are proved to be more reliable in a packaging process. Lifetime of encapsulated microsensors for pH measurements is presented.