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- Construction and use of a tubular picrate ion-selective electrode for reducing sugar determination in Port wine by flow-injection analysisPublication . Lopes, Teresa I. M. S.; Rangel, António O. S. S.; Lima, José L. F. C.; Montenegro, M. Conceição B. S. M.A picrate ion-selective electrode without inner reference solution and based on bis(triphenylphosphoranylidene)ammonium picrate dissolved in 2-nitrophenyloctyl ether was constructed and its characteristics assessed. With respect to reducing sugar determination in Port wine, a tubular electrode based on the same sensor system was developed and incorporated into a flow-injection manifold devised for this determination. The methodology involves a reaction between the reducing sugar and picric acid, the decrease in the picrate concentration being monitored with the tubular electrode. A linear dependence between peak width, at a fixed potential and the logarithm of sugar concentration in the range 25–200 g l−1 was obtained. The proposed system allows wine samples to be injected with no previous treatment and allows a sample throughput of 50 determinations per hour, a relative standard deviation less than 4%, and the results are comparable to the reference procedures.
- Sequential determination of titratable acidity and tartaric acid in wines by flow injection spectrophotometryPublication . Rangel, António O. S. S.; Tóth, Ildikó V.A flow injection manifold is proposed for the sequential determination of titratable (total) acidity based on a pseudotitration and of tartaric acid based on the formation of a coloured vanadate complex. The method involves in-line dialysis prior to injection to avoid interference from the sample background absorption in the spectrophotometric detection. The changes in the colour of both reactions were monitored using two flow cells aligned in the optical path of a single spectrophotometer. Wine samples were analysed without any sample pre-treatment; table wines in the range 1–10 g l21 (total acidity) and 0.5–4 g l21 (tartaric acid) and port wines in the range 1–8 g l21 (total acidity) and 0.5–5 g l21 (tartaric acid). Sixteen samples can be measured per hour, and the results were comparable to those obtained by reference procedures for both determinations. RSDs (n = 10) generally lower than 3% were obtained
- Sequential injection system for the spectrophotometric determination of reducing sugars in winesPublication . Araújo, Alberto N.; Lima, José L. F. C.; Rangel, António O. S. S.A sequential injection system for the spectrophotometric determination of reducing sugars in wines is described. The methodology is based on the formation of a coloured complex produced by the reaction of copper (I) with 2,9-dimethyl-1,10-phenanthroline (neocuproine), after reduction of copper (II) to copper (I) by reducing sugars. In the present SI system, a dialysis unit was incorporated not only to allow the sample dilution, but also to minimise the interference of some coloured compounds. In this way, direct sample introduction into the system was possible, without any previous treatment of the wine samples. The proposed method can be applied to the determination of reducing sugars in two concentration ranges: from 2 to 25 g l 1 (table wines) and from 20 to 140 g l 1 (Port wines). To perform determinations in these two ranges, the manifold configuration remained the same; just a few operational parameters were changed in the controlling software. A sampling-rate of 14–18 samples per hour was obtained with good repeatability for ten consecutive injections of wine samples (relative standard deviations (RSD) B2.1%). The results obtained from 19 wine samples were comparable to those obtained by the reference method.
- Sequential injection system for the enzymatic determination of ethanol in alcoholic beverages with in-line dilutionPublication . Pais, Teresa F. M.; Vidigal, Susana S. M. P.; Tóth, Ildikó V.; Rangel, António O. S. S.A sequential injection system for the enzymatic determination of ethanol in wines with spectrophotometric detection was developed. The determination was based on the enzymatic reaction involving ethanol and NAD(+) in the presence of alcohol dehydrogenase. A gas-diffusion unit was introduced in the system to perform an in-line dilution. It was possible to operate the system with a reagent consumption of 1.3 mg of NAD(+), 0.45 U of ADH, and 32 mu L of sample, per assay with a determination rate of 21 h(-1). The results obtained from the analysis of wine samples were statistically equivalent to those obtained by the reference method, with good repeatability; the relative standard deviation (n = 10) was <1% with a LOQ of 0.3% (v/v). (C) 2012 Elsevier Ltd. All rights reserved.
- A gas diffusion sequential injection system for the determination of sulphur dioxide in winesPublication . Segundo, Marcela A.; Rangel, António O. S. S.In the present work, a sequential injection system with spectrophotometric detection was developed for the determination of free and total sulphur dioxide in wines. It was based on the formation of a coloured product from the reaction among SO2, formaldehyde and pararosaniline. A gas diffusion unit (GDU) was incorporated into the manifold to prevent the wine matrix interference in the spectrophotometric measurement. An acid solution was added to the sample prior to its passage through the donor channel of the GDU to promote gaseous SO2 formation. For the free SO2 determination, the sample was directly aspirated into the holding coil; for the total SO2 determination, the sample was processed after previous in-line hydrolysis of bound SO2 with an alkali solution. Two second-order calibration curves were established, defining two concentration ranges: 2–40 mg l−1 for the free SO2 determination and 25–250 mg l−1 for the total SO2 determination. Relative standard deviations (n=10) were lower than 1.2% for the determination of free SO2 and lower than 2.3% for the determination of total SO2. The sample frequency was about 16 h−1. This methodology was applied to the determination of free and total sulphur dioxide in 10 table wines and the results were statistically comparable with those furnished by the recommended procedure.
- Enzymatic determination of L(-)malic and L(+)lactic acids in wine by flow injection analysisPublication . Lima, José L. F. C.; Rangel, António O. S. S.The enzymatic determination of L(-)malic and L(+)lactic acids in several types of wines by flow injection analysis (FIA) with spectrophotometric detection is described. This flow injection system, which incorporates a dialysis unit for adjusting the composition of the injected solutions to the requirements of the measuring system, enables determinations of these two organic acids without the need for any prior treatment of the wine samples, with a concentration interval of between 0.02 and 4 g/L, and a sampling rate of approximately 20 determinations per hour. The results obtained with this FIA method for various types of Portuguese wines are in good agreement with those of the batch method which uses the same enzymatic technique and are quite precise as they present a coefficient of variation below 2.5%.
- Sequential injection system for the enzymatic determination of ethanol in winePublication . Páscoa, Ricardo N. M. J.; Vidigal, Susana S. M. P.; Tóth, Ildikó Varga; Rangel, António O. S. S.A sequential injection system was developed for the enzymatic determination of ethanol in wine. The spectrophotometric determination is based on the enzymatic reaction catalyzed by alcohol dehydrogenase in the presence of NAD+. The system was applied to the determination of ethanol in a range of 0.008-0.024% (v/v) with good repeatability; RSDn)10 < 2.3%. The results obtained with the developed system showed good agreement with those obtained by using the reference method. The determination rate was 25 h-1; 1 ímol of NAD+, 1.1 units of enzyme, and 50 íL of sample were consumed per determination; and the waste produced was 2.2 mL per assay.
- Exploiting the bead injection LOV approach to carry out spectrophotometric assays in wine: application to the iron determinationPublication . Vidigal, Susana S. M. P.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Cell membrane damage induced by phenolic acids on wine lactic acid bacteriaPublication . Campos, F.M.; Couto, J.A.; Figueiredo, A.R.; Tóth, I.V.; Rangel, António O. S. S.; Hogg, TimThe aim of this work was to investigate the effect of phenolic acids on cell membrane permeability of lactic acid bacteria from wine. Several phenolic acids were tested for their effects on the cell membrane of Oenococcus oeni and Lactobacillus hilgardii by measuring potassium and phosphate efflux, proton influx and by assessing culture viability employing a fluorescence technique based on membrane integrity. The experimental results indicate that hydroxycinnamic acids (p-coumaric, caffeic and ferulic acids) induce greater ion leakages and higher proton influx than hydroxybenzoic acids (p-hydroxibenzoic, protocatechuic, gallic, vanillic, and syringic acids). Among the hydroxycinnamic acids, p-coumaric acid showed the strongest effect. Moreover, the exposure of cells to phenolic acids caused a significant decrease in cell culture viability, as measured by the fluorescence assay, in both tested strains. The results agree with previous results obtained in growth experiments with the same strains. Generally, phenolic acids increased the cell membrane permeability in lactic acid bacteria from wine. The different effects of phenolic acids on membrane permeability could be related to differences in their structure and lipophilic character.
- Use of a Mixing Chamber for Sample Preparation and Multiple Collection in Sequential Injection Analysis: Determination of Sulfate in WinesPublication . Silva, Helena R.; Segundo, Marcela A.; Rangel, António O. S. S.A sequential injection system for determination of sulfate in wines was developed. It was based on the formation of BaSO4, measured turbidimetrically at 420 nm. As sample dilution and acidification were required, both sample and acid were sent to a mixing chamber placed in a lateral port of the selection valve; after thorough mixing, up to six aliquots could be drawn and analyzed. A linear calibration curve was established using 10% v/v ethanol standards with concentrations between 300 and 1500 mg L-1 of K2SO4. The results obtained by the present methodology were statistically comparable with those furnished by the reference procedure, with relative deviations < 3.5%. The sample frequency was about 5 samples per h with relative standard deviations (RSD) < 10%.