Search

A very simple flow injection analysis system for direct determination of glucose in blood serum based on Trinder's reaction is described. The sera samples (15 μl) can be injected directly to the system without the deproteinization or the use of a dialyzer. Calibration curves are linear in the range 50–400 mg/dl. The sampling frequency is 60 samples per hour. Results obtained by the proposed procedure are compared with those acquired at a local hospital using their routine glucose procedure also based on Trinder's reaction. It is shown that a better mix between sample and reagents is achieved using the single bead string reactor (SBSR).

A simply constructed, tubular, all-solid-state, flow-through silver electrode for flow-injection analysis (F.I.A.) is described. Use of a single line manifold accommodating the silver electrode, with a low level of silver ion (5 × 10 −4 M) in the carrier stream, is a useful method to determine chloride in serum, by means of a precipitation pseudotitration F.I.A. technique. The sampling frequency is about 60/h.

A microwave digestion procedure has been evaluated for use in the determination of chemical oxygen demand (COD) by the dichromate method, using small volumes of sample and reagents. Different organic substances with COD values between 50 and 500 mg O2‐1−1 were analyzed by both the proposed procedure and the standard method, obtaining satisfactory results (mean recoveries 91–102%) with digestion times lower than 5 min. Samples of river water and wastewater were also analyzed, obtaining results showing good agreement with the standard 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.

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.

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.

This paper describes the application of the Powell algorithm to the optimization of a flow injection system configuration. The performance of this algorithm has been compared with the modified simplex method. The system studied is the determination of ammonia, based on the indophenol blue reaction. A linear combination of sensitivity and sample throughput is used as the objective function because of its simultaneous optimization capability. Results obtained show that the proposed method may reach the optimal conditions with a lower number of experimental evaluations.

A linear response function RF=C H R H +C T (1−R T ) (R H =peak height, used as a measure of «sensitivity», and R T =analysis time, 1−R T used as a measure of sampling rate) was used to optimize a FIA system for the determination of nitrite in water with respect to four experimental parameters (two tube lengths and two flow rates) by a Simplex procedure

Potentiometric detectors based on ion-selective electrodes are specially suited to flow measurements because of their low cost and high selectivity. Simultaneously in flow analysis the use of tubular-electrode configuration seems ideal as the flow characteristics can be kept constant throughout the system. The design of very simple manifolds, which increases the robustness and the system reliability, is constrained by the knowledge of the influence of hydrodynamic parameters in the detector response. With the aim to optimize the design of this kind of systems a mathematical model, that simulates the response of tubular potentiometric detectors in flow-injection systems, has been developed and tested. Results provided by simulation are compared with experimental ones, and the model capabilities are discussed.

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.

The Powell algorithm is adapted for the optimization of a flow-injection system for the spectrophotometric determination of ammonia based on the indophenol blue reaction. Its performance is compared with that of the modified simplex method in experimental optimization, and in simulation of the course along the experimental response surface, which can be modelled conveniently for this analytical system. The Powell algorithm needed fewer evaluations of the objective function (maximal sensitivity and sample throughput), thus minimizing experimental work, particularly in the initial optimization.

A methodology to design a flow- injection system with optimized performance characteristics for different experimental requirements is presented which requires minimal experimental effort. Departing from basic experimental knowledge of the hydrodynamic parameters and rates of the reactions involved, the coupling of a mathematical model describing the flow system with the Powell's optimization algorithm allows the automated generation of a complete set of flow- injection configurations, each of them being optimal with respect to its objective function. From this set of configurations, the performance of the flow- injection system is easily visualized, allowing the user to select the system that better suits the requirements of his particular application and exploiting the potentiality of multiple flow- injection optimal configurations.

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 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.

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.