P. Linares

Simultaneous determination of carbon dioxide and sulphur dioxide in wine by gas-diffusion/flow-injection analysis

Abstract A method is proposed for the simultaneous determiantion of carbon dioxide and sulphur dioxide in complex matrices. The method involves preseparation of the analysis with a flow-through gas-diffusion unit. The analytes are sensed by two detectors in series, a potentiometric detector responsive to both analytes and a photometric detector for SO2 (p-rosaniline—formadehyde method). The usefulness of the method was tested by applying it to samples of fruity wines and the results were compared with those obtained with the standard EEC recommended method. The reproducibility was generally 7% or better, with a sampling frequency of about 25 h-1.

Fluorimetric differential-kinetic determination of silicate and phosphate in waters by flow-injection analysis.

A flow-injection analysis (FIA) method for simultaneous determination of silicate and phosphate, based on the different rates of formation of their molybdate heteropoly acids is suggested. The fluorimetrically monitored product is thiochrome, formed by oxidation of thiamine by the heteropoly acid. The FIA configurations designed allow performance of two measurements at different times on each sample injected. The method permits the determination of these anions in the range 30-600 ng ml in ratios from 1:10 to 10:1 and can be applied to samples of running and bottled water with good results. The sampling frequency achievable is 60 hr .

Direct automatic determination of polyphenols in olive oils in the aqueous phase of a flow-injection liquid-liquid extraction system without phase separation

A method for the determination of polyphenols in olive in which the analytes are extracted into the aqueous phase by a liquid-liquid extraction system based on the use of a flow-injection configuration with iterative change of the flow direction is proposed. None of the typical units for this continuous separation technique are required by the proposed configuration. The analytes can be determined in the range over which polyphenols normally occur in these samples (100–900 μg ml−1) with better precision (2.8–4.0% vs. 6%) and sampling frequency (28 h−1 vs. 0.5 h−1) and sample (< 1 g vs. 30 g) and reagent consumption than by the conventional method.

Effects of ultrasonic irradiation in flow-injection systems

Abstract The effects of ultrasonic irradiation on transport and reactions in several flow-injection manifolds are described. The influences of ultrasound on the physical dispersion of the injected plug is considered. Its effects on systems involving homogeneous (catalytic and non-catalytic) and heterogeneous (liquid/liquid extraction, precipitation) reactions are critically evaluated. In general, greater sensitivity is obtained, especially for heterogeneous systems, slow reactions and low analyte concentrations. Finally, practical considerations and potential uses of the combination of ultrasonic irradiation with flow-injection analysis are discussed.

Integrated reaction and photometric detection with enzymes immobilized in the flow cell of a flow-injection system

Abstract A biosensor based on the integration of reaction and detection with a conventional photometric detector is proposed. An enzyme is immobilized on the walls of the flow cell and reaction-rate measurements of the enzymatic reaction are made by halting the flow when the sample-coenzyme plug is in the flow cell and monitoring the increase in the reduced form of the coenzyme (λ max = 340 nm).

Sequential determination of glucose and fructose in foods by flow-injection analysis with immobilized enzymes

Abstract A sequential method for determination of glucose and fructose involving the use of enzymes (hexokinase and glucose-6-phosphate dehydrogenase) immobilized on controlled-pore glass is proposed. The flow is selected so as to determine glucose or both sugars by fluorimetric determination of the NADH formed. The method is applied to the determination of these compounds in fruit juices, yoghourt and dessert powder with good results.

Direct automatic determination of free acidity in oils by flow-injection analysis

An automatic method is proposed for the determination of free acidity. It uses the same reagents as the manual standard method (potassium hydroxide and phenolphthalein as indicator) and is based on peak-height measurements in the low concentration range (0.15–0.81%) and peak-width measurements or flow-injection titrations for higher concentrations. The sampling frequency is 60 h-1. The results obtained by the proposed method are in good agreement with those obtained by the conventional standard method.

Simultaneous determination of ammonia and urea with an asymmetric merging zones/flow-injection configuration

Abstract A method is proposed for the simultaneous determination of urea and ammonia using a reagent-injection configuration that includes a dual injection valve (for insertion of Nesslers reagent and for accommodating the enzyme reactor). The resolution of the two peaks obtained on each injection allows the determination of both analytes in mixtures. The determination range is 1–5 μg ml−1 for ammonia and 1–6 μg ml−1 for urea, with relative standard deviations of 1.13% and 2.31% for ammonia (first and second peaks) and 1.86% for urea.

Determination of benzocaine, dextromethorphan and cetylpyridinium ion by high-performance liquid chromatography with UV detection

Abstract A high-performance liquid chromatographic method for the determination of benzocaine, cetylpyridinium ion and dextromethorphan based on the use of an end-capped Ultrabase C18 column and an ion-pair formation reaction in a water-chloroform-methanol (10:50:40, v/v/v) mobile phase containing dioctyl sulphosuccinate is proposed. The use of a conventional or diode-array spectrophotometer resulted in calibration graphs with very different features. The determination ranges for benzocaine, cetylpyridinium and dextromethorphan provided by the diode-array detector were 10–100, 250–2000 and 250–2000 μg/ml, respectively, with relative standard deviations smaller than 3.0% for peak-height measurements and less than 1.40% for peak-area measurements. The conventional detector provided poorer results as a compromise wavelength must be chosen for measurements. The method was applied to the resolution of mixtures of the three analytes in pharmaceutical tablets. No interferences from other components of the tablets such as sorbitol, mint flavour and magnesium stearate were observed.

Spectrofluorimetric flow-injection determination of cyanide

Abstract The spectrofluorimetric determination of cyanide (0.1–20 μg ml−1) with pyridoxal and pyridoxal-5-phosphate by a normal flow-injection method and a stopped-flow procedure is reported. The large number of interfering species in the normal method is significantly decreased by the use of the stopped-flow method. The relative standard deviation is