Analysis for low molecular weight phenolic compounds in a red wine aged in oak chips

The evolution of low molecular weight polyphenols in a red wine aging in different systems (barrels, oak chips and oak staves) made of different oak species was studied. All were placed under the same aging conditions in a wine cellar participating the Cigales Appellation of Origin programme (Spain). The wine aged in contact with oak chips experienced a quicker aging and loss of certain compounds, and a greater number of polymerisations than the wine aged in barrels. The discriminant analysis showed that samples of the same source wine aged in barrels, oak chips and oak staves tended to group together according to the aging system when wood from different botanical species is used (American, French or Hungarian).     

Investigation and correction of the interference of ethanol,sugar and phenols on dissolved oxygen measurement in wine

The dissolved oxygen in wine is routinely measured to control and monitor various oenological processes. The availability of devices based on different technologies and features allows a user to select a device that best meets their needs. However, grape must and wine samples each exhibit a complex composition that varies with time, which, along with atmospheric conditions, makes it necessary to evaluate the effects of these factors on dissolved oxygen measurements. This work evaluates the effects that ethanol, sugar, and phenols have on dissolved oxygen measurements in a model and real wine. The results suggest that significant errors are made in all studied systems and that the response of each device is different. Therefore, a compensation value was developed to take into account the sample composition. A compensation value was proposed to minimise the error made by each device based on the ethanol and sugar contents of the measured liquid. The best results are those obtained after using the compensation value to correct the data from the Pyro-Mini device. In all cases, errors made in DO measurements by optical systems were reduced by 50–82% by applying the compensation value for synthetic wines and 45–100% for real wines.     

Estimation of uncertainty in electrochemical amperometric measurement of dissolved oxygen concentration

A procedure for the estimation of measurement uncertainty of dissolved oxygen (DO) concentration measurement based on the ISO approach is presented. It is based on a mathematical model that involves 14 input parameters. The uncertainty of DO concentration strongly depends on changes in experimental details (temperature difference between calibration and measurement, the time interval between calibration and measurement, etc.). The relative measurement uncertainty is, however, practically independent of the DO concentration itself. The uncertainty is the lowest if the calibration and the measurement are done at the same temperature and on the same day. A calculation tool is provided (in the form of a GUM Workbench file) for practitioners that can be used for uncertainty calculation of DO concentrations at very different experimental conditions.Electronic Supplementary Material The uncertainty calculation example is available as a GUM Workbench calculation file C_O2_meas.smu (GUM Workbench ver. 1.3.3, Metrodata GmbH) together with its data file Input_values.xls (MS Excel 97). For those users who do not have GUM Workbench, the full report of the GUM Workbench calculation is available as a PDF file C_O2_meas.pdf. This material is available via the Internet at .     

A highly accurate method for determination of dissolved oxygen: Gravimetric Winkler method

A high-accuracy Winkler titration method has been developed for determination of dissolved oxygen concentration. Careful analysis of uncertainty sources relevant to the Winkler method was carried out and the method was optimized for minimizing all uncertainty sources as far as practical. The most important improvements were: gravimetric measurement of all solutions, pre-titration to minimize the effect of iodine volatilization, accurate amperometric end point detection and careful accounting for dissolved oxygen in the reagents. As a result, the developed method is possibly the most accurate method of determination of dissolved oxygen available. Depending on measurement conditions and on the dissolved oxygen concentration the combined standard uncertainties of the method are in the range of 0.012–0.018 mg dm⁻³ corresponding to the k = 2 expanded uncertainty in the range of 0.023–0.035 mg dm⁻³ (0.27–0.38%, relative). This development enables more accurate calibration of electrochemical and optical dissolved oxygen sensors for routine analysis than has been possible before.     

Micro-Winkler titration method for dissolved oxygen concentration measurement

In this report a gravimetric micro-Winkler titration method for determination of dissolved oxygen concentration in water is presented. Mathematical model of the method taking into account all influence factors is derived and an uncertainty analysis is carried out to determine the uncertainty contributions of all influence factors. The method is highly accurate: the relative expanded uncertainties (k = 2) are around 1% in the case of small (9-10 g) water samples. The uncertainty analysis carried out in characterizing the uncertainty of the method is the most comprehensive published for a micro-Winkler method, resulting in experimentally obtained estimates for all uncertainty sources of practical significance (around 20 uncertainty sources altogether).     

Chromotropic acid-formaldehyde reaction in strongly acidic media. The role of dissolved oxygen and replacement of concentrated sulphuric acid

The procedure for formaldehyde analysis recommended by the National Institute for Occupational Safety and Health (NIOSH) is the Chromotropic acid spectrophotometric method, which is the one that uses concentrated sulphuric acid. In the present study the oxidation step associated with the aforementioned method for formaldehyde determination was investigated. Experimental evidence has been obtained indicating that when concentrated H₂SO₄ (18 mol l⁻¹) is used (as in the NIOSH procedure) that acid is the oxidizing agent. On the other hand, oxidation through dissolved oxygen takes place when concentrated H₂SO₄ is replaced by concentrated hydrochloric (12 mol l⁻¹) and phosphoric (14.7 mol l⁻¹) acids as well as by diluted H₂SO₄ (9.4 mol l⁻¹). Based on investigations concerning the oxidation step, a modified procedure was devised, in which the use of the potentially hazardous and corrosive concentrated H₂SO₄ was eliminated and advantageously replaced by a less harmful mixture of HCl and H₂O₂.     

A simple and rapid method for measuring dissolved oxygen in waters with gold microelectrode

Dissolved oxygen (DO) is an essential indicator in chemical, biological and biochemical processes and needs to be rapidly measured in many cases. In this work, a rapid, sensitive and simple electrochemical method, first derivative linear sweep voltammetry (FD-LSV), was established for the determination of DO. The peak height of FD-LSV was found to be influenced by scan rate and microelectrode surface area. An empirical formula was proposed to describe the relationship between the FD-LSV peak height and the influencing factors. Compared with other electrochemical methods for DO determination, the FD-LSV method needed lesser time and was more accurate. This method was successfully applied for the determination of the DO levels of various environmental water samples.     

Measurement of the dissolved oxygen concentration in acrylate monomers with a novel photochemical method

Because of the well‐known radical‐scavenging behavior, molecular oxygen is capable of inhibiting free‐radical chain polymerizations of unsaturated monomers. The deleterious effects of diffused oxygen in a polymerization system result in both a reduced polymerization rate and the loss of surface properties of a polymer film or coating. However, reliable data for oxygen concentration in organic monomers are relatively scarce because of the experimental and instrumental limitations of the commercially available techniques. In this study, a photochemical method was developed and was used to obtain the dissolved oxygen concentration in seven acrylate monomers. The principle of the method was to convert ground‐state molecular oxygen dissolved in monomer to the excited, singlet‐state oxygen and then react the singlet oxygen with a third compound (singlet oxygen trapper). By monitoring the concentration of this singlet oxygen trapper spectrophotometrically, the concentration of dissolved oxygen can be obtained with the established stoichiometry for the reaction between singlet oxygen and trapper. The singlet oxygen concentrations in the acrylate monomers varied from 0.59 to 2.07 × 10^?3 mol/L, depending on the monomer structure. The strategies and considerations for generalizing the method to other systems, including highly oxygenated organics, are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1285–1292, 2004     

in situ interlaboratory comparisons for dissolved oxygen concentration and pH

Organization, benefits, and possible drawbacks of in situ interlaboratory comparison are discussed using the example of dissolved oxygen concentration and pH measurements organized at the University of Tartu. In situ interlaboratory comparisons are intercomparison measurements, where all the participants (with their technical equipment and using their own competence) are measuring the same sample continuously at the same time, at the same site. In the field of proficiency testing–especially in chemical measurements–the in situ schemes are not yet widespread. Their main advantage emerges in the fields where, due to non-stability of samples, traditional comparison schemes can fail. Direct exchange of experience between the participants and presentations during measurements may add the value to in situ interlaboratory comparison. Dissolved oxygen concentration and pH measurements are among the most widespread chemical measurements. Both measurements are complex and less robust than often considered. In this paper, we describe in situ interlaboratory comparisons of dissolved oxygen concentration and pH organized at University of Tartu Testing Centre. Electronic Supplementary Material  Supplementary material is available for this article if you access the article at . The Final Report of the DO Concentration and pH Intercomparison is available in the electronic supplementary material.

A multisyringe flow injection Winkler-based spectrophotometric analyzer for in-line monitoring of dissolved oxygen in seawater

An integrated analyzer based on the multisyringe flow injection analysis approach is proposed for the automated determination of dissolved oxygen in seawater. The entire Winkler method including precipitation of manganese(II) hydroxide, fixation of dissolved oxygen, dissolution of the oxidized manganese hydroxide precipitate, and generation of iodine and tri-iodide ion are in-line effected within the flow network. Spectrophotometric quantification of iodine and tri-iodide at the isosbestic wavelength of 466 nm renders enhanced method reliability. The calibration function is linear up to 19 mg L⁻¹ dissolved oxygen and an injection frequency of 17 per hour is achieved. The multisyringe system features a highly satisfying signal stability with repeatabilities of 2.2% RSD that make it suitable for continuous determination of dissolved oxygen in seawater. Compared to the manual starch-end-point titrimetric Winkler method and early reported automated systems, concentrations and consumption of reagents and sample are reduced up to hundredfold. The versatility of the multisyringe assembly was exploited in the implementation of an ancillary automatic batch-wise Winkler titrator using a single syringe of the module for accurate titration of the released iodine/tri-iodide with thiosulfate.     

Aging markers from bottled red wine aged with chips, staves and barrels

This paper shows the results of the experiments carried on Spanish red wines aged through alternative as well as traditional oak barrel systems, i.e., chips stainless steel tanks and staves stainless steel tanks, at the same time and under the same conditions.Wine aging through wood pieces is not accepted as an enological practice by the European Union and, in fact, it is considered a fraud. It is, then, of a great interest to identify those parameters able to establish the aging technique that had been used in a wine ready to be consumed. With this idea in mind, the development of the same wine has been studied while aging for 3 years in three different systems.During the first six aging months wines stored with staves obtained characteristics that were halfway between wines treated with chips and those aged in barrels. However, as wood contact period length increased so did the differences between wines stored in traditional and alternative systems (either with staves or chips). These differences grew during the bottling period, so that after a 2-year bottling period wines from the three systems became different enough to tell them apart. Discriminant analysis of the variables studied made it possible to establish these differences. The most meaningful variables were yellow colour component, anthocyanins (cyanidin-3-glucoside, vitisin A and sum of pcoumaryl derivates), vanillin acid, protocachuic aldehyde and epicatechin.     

Flow injection system with in-line Winkler's procedure using 16-way valve and spectrofluorimetric determination of dissolved oxygen in environmental waters

Flow injection spectrofluorimetry with in-line Winklers procedure was developed for the dissolved oxygen (DO) determination. 2-Thionaphthol reacted with iodine produced by Winkler’s method to form fluorescence inactive disulfide compound. To automate the process completely, a 5-channel flow system with a newly designed 16-way valve was assembled. The system consisted of a dispersion coil (DC), a precipitate formation coil (PFC), a precipitate dissolving coil (PDC), and extraction coil (EC). A calibration can be constructed by using a standard iodine solution for dissolved oxygen. The calibration graph was linear over the range 1.2×10⁻⁴∼6.0×10⁻⁴ mol l⁻¹ iodine (1.96∼9.80 mg O l⁻¹)). The relative standard deviation (n=6) was below 0.3% for the 4×10⁻⁴ mol l⁻¹ iodine (6.27 mg O l⁻¹) determination. The sample throughput was 12/h.     

Flow-injection analysis for hypoxanthine in meat with dissolved oxygen detector and enzyme reactor

A low cost flow-injection analysis (FIA) with a dissolved oxygen (DO) detector and a xanthine oxidase immobilized column for the analysis of hypoxanthine as an index to determine degree of aging in meat was developed for quality control in the food industry. In this system, hypoxanthine is oxidized by an enzyme reaction with xanthine oxidase immobilized on the column to produce xanthine. Then the catalytic reaction between hypoxanthine and DO with xanthine oxidase proceeds with the DO concentration decreasing in the stream of the flow system. Decrease in the DO concentration was monitored by a DO detector located downstream of the flow system. This decrease in DO concentration was proportional to the hypoxanthine concentration. For detecting the decreased DO concentration efficiently a flow-through cell with a polarographic-type DO sensor was specially designed. As a result, a linear working curve was obtained from 3.68 × 10⁻⁵ to 1.84 × 10⁻³ M hypoxanthine concentrations with this FIA system. We applied the present system with a DO detector for the determination of hypoxanthine in meat samples and compared the results with those obtained by the conventional HPLC method. The data obtained with the present FIA method were in fairly good agreement with those obtained by the conventional HPLC method for the meat samples. Correlation factor and regression line between the two methods were 0.998 and Y= 1.51X-32.64 respectively. We concluded that the present FIA system with a DO detector was suitable as a simple, easy to handle and reliable instrument for quality control in the food industry.     

Feature characterization of microfabricated microfluidic chips by PDMS replication and CCD imaging

This paper presents a new approach for the metrological characterization of microfabricated features on microfluidic chips, based on a combination of poly(dimethylsiloxane) (PDMS) replication and charge-coupled device (CCD) imaging. A PDMS replicate was cast from the original chip sample, and a 2-mm thick sample slice was cut from the replica at the cross-section to be studied. The digital image of the revealed structural profile was captured by a CCD camera under a microscope, and the image was processed using specially-developed algorithms for CCD image calibration and edge detection. Depth and width measurements obtained using the method agreed well with those gained using a stylus profiler and universal measuring microscope, with a deviation of below 0.9 m, while profile distortions of deeper structures using stylus profilers were avoided. The method is reliable, non-destructive, and cheap and simple to implement in any analytical laboratory.     

Comparison of different alcohols in a caged lumophore for measuring supersaturated dissolved oxygen

Intense phosphorescence is observed when an alcohol is introduced to an aqueous solution containing 1-bromonaphthalene and a cyclodextrin complex. The enhancement of the phosphorescence intensity of 1-bromonaphalene is related closely with the alcohol’s effectiveness in shielding the photo-excited lumophore from dissolved oxygen. The phosphorescence intensity decreases and the phosphorescence decay rate increases as the dissolved oxygen concentration increases. In this paper, we measure the phosphorescence intensity and decay rate of the complex using different alcohols and explain their respective advantages. By relating the concentration of oxygen to the intensity and the lifetime of the phosphorescence, the dissolved oxygen concentration can be measured. The sensitivities and measurement ranges with the complexes containing different alcohols are compared. Currently, this technique can measure dissolved oxygen concentrations from 0 to 40.2 mM (31,400% saturation). The range of the measurement is 40 times larger than previous studies.     

Measurement of Dissolved Oxygen in Biological Fluids by Using a Modified Carbon Paste Electrode

A modified carbon paste electrode was constructed for the determination of dissolved oxygen using diamino‐o‐benzoquinone (DABQ) as the modifier. The electrochemical behavior of the electrode in citrate buffer (pH 2.0) was studied. In the presence of dissolved oxygen (DO) both cathodic and anodic peak currents decreased, indicating a chemical reaction between modifier and O₂. The decrease in peak current was linearly proportional to the amount of dissolved oxygen in the concentration range of 252–1260 μM of DO. The electrode was utilized in the determination of DO in urine samples. The relative error and RSD of the method were 1.6% and 4.1%, respectively. The electrode was applied more than two months for the determination of DO without any significant divergence in its voltammetric response.     

Study on liquid oxygen compatibility of bromine‐containing epoxy resins for the application in liquid oxygen tank

The liquid oxygen compatible epoxy resin was obtained by the polycondensation between tetrabromobisphenol A and neat epoxy resins. The results of liquid oxygen impact test indicated that the synthetic epoxy resins were compatible with liquid oxygen. The relationship between impact reaction sensitivity (IRS) and flame retardancy were studied by liquid oxygen impact test and limiting oxygen index test. The results showed that the flame‐retardant modification of epoxy resin was valuable to reduce the IRS. The thermal gravimetric analysis results indicated that the Br · radical was quickly released in relatively low temperature (approximately 370°C) for compatible epoxy resin. The Br · radical was a key factor to promote the epoxy resin compatible with the liquid oxygen. The X‐ray photoelectron spectroscopy was used to survey the distribution of functional groups on the surface of samples before and after impact. The results showed that the oxidation reaction and carbonization process may occur on the surface of samples after impact. The liquid oxygen compatibility mechanism is proposed in this paper. The bromine‐containing epoxy resin has the potential to be the material used in liquid oxygen tank. Copyright © 2015 John Wiley & Sons, Ltd.     

Application of manganese (II) phthalocyanine synthesized in situ in the SiO2/SnO2 mixed oxide matrix for determination of dissolved oxygen by electrochemical techniques

This work describes the in situ immobilization of Mn(II) phthalocyanine (MnPc) in a porous SiO₂/SnO₂ mixed oxide matrix obtained by the sol gel processing method. The chemically modified matrix SiO₂/SnO₂/MnPc, possessing an estimated amount of 8 × 10⁻¹⁰ mol cm⁻² of MnPc on the surface, was used to prepare an electrode to analyze dissolved oxygen in water by an electrochemical technique. The electrode was prepared by mixing the material with ultrapure graphite and evaluated using differential pulse voltammetry. Dissolved O₂ was reduced at −0.31 V with a limit of detection (LOD) equal to 7.0 × 10⁻⁴ mmol L⁻¹. A mechanism involving four electrons in O₂ reduction was determined by the rotating disk electrode technique.     

Study of interactions of concentrated marine dissolved organic matter with copper and zinc by pseudopolarography

The interaction of dissolved organic matter (DOM) with copper and zinc in a concentrated seawater sample was characterised by pseudopolarography. Measurements performed at increased concentrations of copper(II) ions showed successive saturation of active DOM sites which indicate possible partition of copper between (i) free or labile complexes, (ii) reduced and released within the potential window of the method, and (iii) electroinactive copper complexes. Pseudopolarograms measured at pH 4 indicate a release of copper which was bound to the active sites of DOM that formed non-labile complexes. Variation of the peak position and half-peak width along the scanned deposition potentials and with the increasing concentration of copper bear the information about the complex electrochemical processes at the electrode surface and in the bulk of the solution. Pseudopolarograms of zinc showed a strong dependence of the peak current and the peak position along the scanned deposition potentials on pH values, indicating preferentially complexation of zinc with carboxylic-like active sites of DOM in the measured sample. Pseudopolarography is a valuable method in the trace metal complexation and speciation studies, serving as a fingerprint of the analysed sample.