Julián Alonso-Chamarro

Determination of probable alcohol yield in musts by means of an SPR optical sensor

Abstract 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.

Continuous flow synthesis of nanoparticles using ceramic microfluidic devices

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.

Sequential determination of calcium and nitrate ions in waters by potentiometric flow injection

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.

Sandwich techniques in flow-injection analysis: Part 3. Simultaneous determination of Cr(VI) in two concentration ranges

A flow-injection system based on the sandwich technique is proposed for the determination of Cr(VI). Two simultaneous working ranges of concentration are achieved by appropriate selection of the reagent composition at the two reagent—sample interfaces. The optimized system allows the determination of CR(VI) at levels up to 1 μg ml−1 with a detection limit of 0.01 μg ml−1 for one of the interfaces. for the other, determinations up to 30 μg ml−1 with a detection limit of 0.5 μg ml−1 are possible. The sample throughput achieved was about 45 h−1 with a relative standard deviation <1% in the middle of both ranges.

Microreactor with integrated temperature control for the synthesis of CdSe nanocrystals

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 with 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 continuous synthesis of CdSe quantum dots. Since temperature can be accurately regulated as required, size-controlled 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 fluorescence spectrophotometry. 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 method to produce quantum dots in organic media, enhancing its application from laboratory-scale to pilot-line scale processes.

A Monolithic Continuous-Flow Microanalyzer with Amperometric Detection Based on the Green Tape Technology

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 microA) to do precise determinations at different levels of current intensity.

Aroylthioureas: new organic ionophores for heavy-metal ion selective electrodes

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.

Biparametric potentiometric analytical microsystem for nitrate and potassium monitoring in water recycling processes for manned space missions.

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.

Colorimetric determination of copper in aqueous samples using a flow injection system with a pre-concentration poly(ethylenimine) column

A colorimetric flow injection-system for the determination of Cu(II) in waters based on complexation reaction with 4-(2-pyridylazo)-resorcinol, usually termed PAR, is described. Performing measurements in 0.25 mol l(-1) HNO(3) medium allowed improved selectivity of the analytical method. The lack of sensitivity deriving from the low complex absorption under acidic conditions was balanced by the insertion of an immobilised poly(ethylenimine) (PEI) column where Cu(II) pre-concentration in neutral media occurs. Using sample volumes ranging from 2 to 4 ml, sampling rates of 24 and 12 samples h(-1) within a detection limit of 25 and 13 mug l(-1), respectively, were accomplished. Accuracy of the developed methodology was assessed by comparison with atomic absorption spectrometry being the relationship [FIA] mg l(-1)=1.00 (+/-0.03)x[AAS] mg l(-1)+0.00 (+/-0.02) obtained after analysing 15 samples. Precision was also evaluated using two samples of 0.05 and 0.5 mg l(-1) copper, and a relative standard deviation (R.S.D.) better than 3% was attained for both.

Potentiometric analytical microsystem based on the integration of a gas-diffusion step for on-line ammonium determination in water recycling processes in manned space missions.

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.