Development of method for the speciation of inorganic iron in wine samples

Novel approach to determination of Fe(II) using a flow system with direct-injection detector

Abstract

This paper presents a novel, automatic, simple approach to stop-flow photometric determination of Fe(II) in wastewater and wine samples using a multi-pumping flow system with a direct-injection detector. The basis for the determination was the reaction of Fe(II) with 1,10-phenanthroline, which was carried out in the reaction chamber of the direct-injection detector. The research included a selection of appropriate parameters of the proposed analytical procedure and method validation. Under optimized conditions, linear calibration curves were obtained in two concentration ranges of Fe(II) 0.07–1.00 and 1.00–7.00 mg/dm3, with the quantification limit of 0.07 mg/dm3. The procedure was validated by studying the accuracy (8.2%, RE) and precision (9.6 and 14.8%, RSD, for higher and lower concentration range, respectively). The proposed method was successfully employed in Fe(II) determination in spiked wastewater and wine samples with recovery of 95.8–104.5%. Using the procedure, time of a single analysis (for three independently measured signals) was about 300 s and sample and reagent consumptions were 240 and 60 mm3, respectively.

Graphic abstract

A Production-Accessible Method: Spectrophotometric Iron Speciation in Wine Using Ferrozine and Ethylenediaminetetraacetic Acid

Wine oxidation is reported to be linked to the iron species present in the wine, but spectrophotometric speciation is plagued by unstable measurements due to alterations to the reduction potential of iron by complexing agents. Ferrozine raises the reduction potential of iron by complexing preferentially to iron(II), inducing the reduction of iron(III) during analysis; here, EDTA is added to chelate iron(III) and to stabilize the forms of iron. Bisulfite addition allows the use of ferrozine for red wine analysis by mitigating color interference. Measurements agree with values from a previous method for iron(II) and from FAAS for total iron. Spike recoveries were in the range of 103.5-110.1%. The method is linear for iron concentrations in the range of 0.10-6.00 mg L^-1 and offers good precision (CV 0.4-10.1%) and low limits of detection (0.02 mg L^-1) and quantification (0.06 mg L^-1). The method demonstrated changes to iron speciation during the oxygenation of red wines.

Speciation analysis based on digital image colorimetry: Iron (II/III) in white wine

This work proposes an analytical strategy utilizing digital images (DI) for the iron inorganic speciation in white wine. The method was established by the reaction of iron(II) ions with 1,2 ortho-phenanthroline as a chromogenic reagent. Total iron was determined using the same reagent after the addition of hydroxyl ammonium chloride as a reducing agent. In both cases, digital images of the standards/chromogenic reagent and samples were acquired and stored in JPEG format. The region of interest (ROI) was determined with a constant square shape for all images. The ROI was submitted to decomposition in color values according to the RGB additive color model. However, the data obtained by the blue channel was the one used in the construction of the analytical curves because it presented the highest sensitivity. The optimization of the experimental conditions of the procedure was performed by employing multivariate techniques. The precision was evaluated using a wine sample with iron (II) and total iron contents of 0.41 and 0.69 mg L^-1, respectively. The results expressed as relative standard deviations were 3.57% for iron (II) and 4.76% for total iron contents. A comparison between the results obtained for total iron by the DI method with the results found using flame atomic absorption spectrometry confirmed the method accuracy. The DI procedure was applied for speciation analysis in six white wine samples and the contents found varied from 0.41 to 1.67 mg L^-1 for iron (II) and from 0.69 to 1.71 mg L^-1 for total iron. These results are in agreement with those found for speciation analysis of iron in wine samples. Iron (III) contents can be found by the difference between the total iron and iron (II) contents.

Determination of iron (III) in food, biological and environmental samples

The nanodrop spectrophotometric (NDS) determination of iron (III) in water samples has been established. The proposed method is simple, selective and highly sensitive. The extraction of Fe (III)-thiocyanate complex was done by novel organic reagents such as N-phenylacetamide, N-alkylacetamide, (alkyl=butyl, hexyl and octyl group) in chloroform. The Fe (III) extract was examined in the strong acidic (HCl+H₂SO₄) solution. The maximum value of molar absorptivity was found to be 1.8×10⁵Lmol^-1cm^-1 at λ_max, 477nm (⩾9 fold enrichments) for N-octylacetamide (N-OAA). The method obeys the Beers Law within the range of 0.05μgmL^-1-6.0μgmL^-1. The detection limit and RSD value of the method were found to be 5ppb and 0.5906% respectively. The correlation coefficient, slope and intercept were calculated and found to be 0.9989, 0.1112, and 0.0048, respectively. The proposed method was successfully applied to the determination of trace amount of iron (III) in food, biological and environmental samples.

Impact of wine production on the fractionation of copper and iron in Chardonnay wine: Implications for oxygen consumption

Copper and iron in wine can influence oxidative, reductive and colloidal stability. The current study utilises a solid phase extraction technique to fractionate these metals into hydrophobic, cationic and residual forms, with quantification by ICP-OES. The impact of aspects of wine production on the metal fractions was examined, along with the relationship between metal fractions and oxygen decay rates. Addition of copper and iron to juice, followed by fermentation, favoured an increase in all of their respective metal fractions in the wine, with the largest increase observed for the cationic form of iron. Bentonite fining of the protein-containing wines led to a significant reduction in the cationic fraction of copper and an increase in the cationic form of iron. Total copper correlated more closely with oxygen consumption in the wine compared to total iron, and the residual and cationic forms of copper provided the largest contribution to this impact.

Simplification of iron speciation in wine samples: a spectrophotometric approach

A simple direct spectrophotometric method was developed for the analysis of Fe(II) and total Fe in wine samples. This method is based on the formation of an Fe(II) complex with 2,2'-dipyridylketone picolinoylhydrazone (DPKPH), which shows a maximum green-blue absorption (λ = 700 nm) at pH 4.9. Operative conditions for the batch procedure were investigated including reagent concentration, buffer solutions, and wavelength. The tolerance limits of foreign ions and sample matrix have been also evaluated. Limits of detection and quantification were 0.005 and 0.017 mg L(-1) of Fe(II), respectively, allowing its determination in real wine samples. Finally, the proposed method was used in the analysis of white, rose, and red wines. Results were compared with a reference method of Commission Regulation (ECC) No. 2676/90 of September 1990 determining European Community methods for the analysis of wines for Fe analysis, showing the reliability of the proposed method in Fe analysis in wine samples.

An efficient and selective flourescent chemical sensor based on 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a new fluoroionophore for determination of iron(III) ions. A novel probe for iron speciation

A novel fluorescent chemical sensor for the highly sensitive and selective determination of Fe(3+) ions in aqueous solutions is prepared. The iron sensing system was prepared by incorporating 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a neutral Fe(3+)-selective fluoroionophore in the plasticized PVC membrane containing sodium tetraphenylborate as a liphophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Fe(3+) ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range from 6.0 × 10(-4) to 1.0 × 10(-7) M, with a relatively fast response time of less than 2 min. In addition to a high stability and reproducibility, the sensor shows a unique selectivity toward Fe(3+) ion with respect to common coexisting cations. The proposed fluorescence optode was applied to the determination of iron(III) content of straw of rice, spinach and different water samples. The fluorescent sensor was also used as a novel probe for Fe(3+)/Fe(2+) speciation in aqueous solution.

Iron(III) tartrate as a potential precursor of light-induced oxidative degradation of white wine: studies in a model wine system

The potential for iron(III) tartrate to act as a photoactivator in light-induced oxidative degradation of white wine is described. Using a tartaric-acid-based model wine system containing 5 mg/L iron, exposure to light from a xenon arc lamp led to the oxidative degradation of tartaric acid and the production of glyoxylic acid. The critical wavelength of light for the degradation process was found to be below 520 nm. No glyoxylic acid was formed in the absence of iron and/or light. Flint glass offered little protection from the light-induced photodegradation of tartaric acid. Antique Green glass offered more protection but did not stop the photodegradation process.

Development of a dispersive liquid-liquid microextraction method for iron speciation and determination in different water samples

A novel, simple and efficient method for the iron (Fe) speciation and determination in different water samples was developed using dispersive liquid-liquid microextraction (DLLME) technique followed by spectrophotometric analysis. The procedure is based on complexation of Fe(II) with O-phenanthroline (O-Phen), the subsequent ion-association formation with picrate anion, then extraction of the complex using DLLME technique. Some important parameters such as the type and volume of extraction and dispersive solvents as well as the extraction time were investigated and optimized in detail. Under the optimum conditions, the calibration graphs were linear over the range of 0.025-1.0 μg mL(-1) with limit of detection of 7.5 μg L(-1). Relative standard deviation for five replicate determinations of Fe at 0.2 μg mL(-1) concentration level was calculated to be 1.2%. Average recoveries for spiked samples were determined to be between 90% and 108%. The method was applied to water samples and parenteral solutions and the amounts of Fe found in these samples using the proposed method were similar with those obtained by a standard method.