A gas diffusion sequential injection system for the determination of sulphur dioxide in wines

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 ethanol and glycerol by flow injection parallel multi-site detection

A flow injection method was developed for the sequential enzymatic determination of ethanol and glycerol in wines, using immobilised ethanol dehydrogenase and glycerol dehydrogenase, respectively. The enzymes were immobilised separately on alkylaminated controlled pore glass. A multi-site spectrophotometric detection system was used in parallel configuration to monitor the absorbance change in the two independent analytical channels. A 50-fold dilution of the samples was necessary before injection. The working range was between 0.05 and 0.5% (v/v) for the ethanol and between 0.03 and 0.3 g l−1 for the glycerol determination, with corresponding detection limits of 2 10−3%(v/v) and 2 10−3 g l−1. Relative standard deviations (R.S.D.) (nD9) lower than 2.3% for the ethanol and 2.1% for the glycerol determination were found. For 13 samples of different types of table and Port wines, the results showed good agreement with the corresponding reference procedures; a two level recovery study also showed good accuracy for the developed methods. The sampling rate was 10 h−1, corresponding to 20 determinations per hou

Microfluidic paper-based devices as disposable, easy-to-use, real time quantification methods

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Exploiting flow-based separation techniques for sample handling in wine analysis

Wine is a fermented product consumed in a large scale all over the world that therefore has a large impact both economic and food safety terms. The analytical control of the final product is thus of high importance; it is not a simple task given that the chemical composition of wine is very variable and complex. Consequently, there is always the need for some sample pre-treatment prior to analysis. Flow-based analyses are known for their efficiency in sample manipulation and can be easily coupled to other techniques, such as separation techniques, namely membrane-based or extraction procedures. This possibility is an important step when dealing with complex matrices, such as wine samples. This review presents the state of the art of the methodologies that were developed using flow-based systems coupled to separation devices applied to wine analysis, namely membrane-based, solid, and liquid phase extraction and low pressure chromatography separations.info:eu-repo/semantics/acceptedVersio

Gas diffusion sequential injection system for the spectrophotometric determination of free chlorine with o-dianisidine

A gas diffusion sequential injection system for spectrophotometric determination of free chlorine is described. The detection is based in the colorimetric reaction between free chlorine and a low toxicity reagent o-dianisidine. A gas diffusion unit is used to isolate free chlorine from the sample in order to avoid possible interferences. This feature results from the conversion of free chlorine to molecular chlorine (gaseous) with sample acidification. With minor changes in the operating conditions, two different dynamic ranges were obtained enhancing the application both to water samples and bleaches. The results obtained with the developed system were compared to the reference method, iodometric titration and proved not to be statistically different. A detection limit of 0.6 mg ClO−/L was achieved. Repeatability was evaluated from 10 consecutive determinations being the results better than 2%. The two dynamic ranges presented different determination rates: 15 h−1 for 0.6–4.8 mg ClO−/L (water samples) and 30 h−1 for 0.047–0.188 g ClO−/L (bleaches).info:eu-repo/semantics/acceptedVersio

The State of the Art of Flow-Through Solid-Phase Spectrometry

Sample pretreatment is one of the bottlenecks in analytical chemistry, especially when dealing with complex matrices like environmental samples. When performed in a batch mode, sample handling methods are tedious and time consuming. Therefore, the hyphenation of these methods with flow-injection techniques yields many advantages. The possibility of automation not only increases the determination rate, but also decreases sample and reagent consumption. As a consequence, analyte separation, enrichment, and elimination of sample matrix becomes possible with an increase in selectivity and sensitivity. This is a significant contribution for the analysis of environmental samples because the analyte is usually present at trace levels in a complex matrix. In this scenario, the state of the art of solid-phase spectrometry (SPS) with a focus on the lab-on-valve (LOV) platform is discussed. LOV facilitates the manipulation of bead suspension for SPS with lower reagents consumption and waste production.info:eu-repo/semantics/publishedVersio

Usefulness of a detector inlet overpressure and stream splitting in FIA systems to deal with food sample pre-treatment requirements. Application to wine analysis

The use of stream splitting to obtain high sampling rate flow injection analysis (FIA) large dispersion manifolds to deal with pre-treatment requirements in the analysis of food components with a high concentration is described. This procedure is illustrated in the FIA determination of calcium using an atomic absorption detector and in the colorimetric determination of phosphate in wines. These manifolds proved to be an advantageous alternative to those including mixing chambers and diluters, as they are simpler and provide higher sampling rates (60–240 samples h−1 are achieved). Also described here is the use of an overpressure at the entrance to the atomic absorption nebulizer to minimize matrix physical interferences, by presenting the results obtained for the FIA—atomic absorption copper determination in wines. The results obtained for several wine samples by the developed FIA methodologies were in good agreement with those provided by the reference methods

In-line phosphate pre-concentration in a flow injection method platform for monitoring fertilizers excess in soil leachates

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