Determination Of Sulfite Research Articles

A novel spectrophotometric method for batch and flow injection determination of sulfite in beverages

A novel spectrophotometric assay method for batch and flow injection determination of sulfite in beverages is described. The method involves a reaction with diaquacobyrinic acid heptamethyl ester (diaquacobester, DACbs) in acetate buffer of pH 3 to form a highly stable sulfite cobester complex (SO 3Cbs). In the absence of sulfite, the reagent displays three absorption maxima at 349, 409 and 525 nm. Addition of sulfite is associated with the development of a new absorption band at 313 nm, an increase in the intensity of the band at 425 nm and a decrease in the absorbance of the bands at 349 and 525 nm. Variations of the absorptions at 313, 349, 425 and 525 nm are linearly proportional to sulfite concentrations over the range of 0.05–25 μg ml −1with a detection limit of 0.01–0.2 μg ml −1. Negligible interferences are caused by most common ions. Validation of the method according to the quality assurance standards shows suitability for quality control assessment of sulfite in complex matrices without prior treatment. The method has the advantages of high selectivity, good sensitivity, fast reaction, high stability of the reagent and reaction product and absorbance measurements at four different wavelengths in the same run. The method is successfully applied to determine the sulfite contents of some beverages. The results compare fairly well with data obtained using the standard method.

Sulfite determination using sulfite oxidase biosensor based glassy carbon electrode coated with thin mercury film

The preparation of sulfite biosensor by immobilization of sulfite oxidase on a glassy carbon electrode coated with mercury thin film is described. Dissolved oxygen can be readily reduced at the glassy carbon electrode coated with mercury thin film. The working principle of the biosensor was based on monitoring decrease in the peak current due to the depletion in dissolved oxygen concentration according to the reaction of sulfite oxidase. The biosensor allowed a low working potential of −0.24 V vs. Ag/AgCl. Immobilization parameters such as sulfite oxidase activity, gelatin amount, and glutaraldehyde percentage were investigated. The pH optimum of 7.0 was found when using phosphate buffer. Appropriate buffer concentration was found to be 0.05 M. Working temperature was accepted as 40 °C. The biosensor was stable at 40 °C for 3 h without loss of its initial activity. The calibration graph for the biosensor was linear between the concentration ranges of 2 × 10 −4–2.8 × 10 −3 M sulfite. The results of sample analyses obtained with the biosensor agreed well with the enzymatic-spectrophotometric reference method.

Sulfite Determination at In Situ Plated Copper Modified Gold Ultramicroelectrode Arrays

AbstractThe electroanalytical detection of sulfite has been explored at an in situ formed copper ultramicroelectrode array. The protocol is based upon the in situ deposition of copper at a gold ultramicroelectrode array of cubic geometry which consists of 256 ultramicroelectrodes which are 5 microns in radius and are separated from their nearest neighbor by 100 microns. The immobilized copper array is electrocatalytic for the electrochemical reduction of sulfur dioxide which is formed after protonation of sulfite at low pH values (<pH 2). A sensitivity and detection limit of 0.35 nA μM−1 and 6 μM respectively is shown to be possible in pH 2.5 using linear sweep voltammetry with a linear range observed from 20–500 μM.

Chemiluminescence of ClO3−‐SO32−‐Rh6G‐SDBS System and Its Application to the Determination of Sulfite

AbstractBased on the micelle synergism mechanism, a chemiluminescence (CL) flow system for the determination of sulfite was described. The CL signal generated from the reaction of chlorate with sulfite in acidic solution was very weak, while the interfusion of sodium dodecylbenzenesulfonate (SDBS) resulted in a highly chemiluminescent intensity. The major goal of this work was to investigate and develop the SDBS micelle synergetic CL system. The mechanism was proposed and proved by spectrometry. The results indicated that the unique structure of SDBS micelles promoted the aggregation of rhodamine 6G (Rh6G) and a much easier energy transfer, leading to a marked shift to red in the CL emission. This CL system was developed for the determination of sulfite and the concentration of sulfite was proportional to the CL intensity in the range of 5.0×10−8–1.0×10−5 mol/L with the detection limit of 1.7×10−8 mol/L (S/N=3). The relative standard deviation was 3.3% for 1.0×10−6 mol/L sulfite solution with eleven repeated measurements. This method was successfully applied to the determination of sulfite in powder sugar.

Simultaneous kinetic-spectrophotometric determination of sulfide and sulfite and genetic algorithim variable selection using partial least squares calibration

Simultaneous multicomponent analysis is usually carried out using multivariate calibration models, such as the partial least squares (PLS) one, that utilize the full spectrum. It has been shown by both experimental and theoretical considerations that better results can by obtained by proper selection of the spectral range to be included in calculations. A genetic algorithm (GA) is one of the most popular methods for selecting variables for PLS calibration of mixtures with almost identical spectra without loss of predictive capability. In this work, a simple and precise method for rapid and accurate simultaneous determination of sulfide and sulfite ions based on the addition reaction of these ions with new fuchsin at pH 8 and 25°C using PLS regression and GA for variable selection is proposed. The concentrations of sulfide ions varied between 0.05–2.50 and 0.15–2.00 μg/mL, respectively. A series of model solutions containing different concentrations of sulfide and sulfite were used to check the predictive ability of GA-PLS models. The root mean square error of prediction with PLS on the whole data set was 0.19 μg/mL for sulfide and 0.09 μg/mL for sulfite. After the application of GA, these values reduced to 0.04 and 0.03 μg/mL, respectively.

Exploiting Sulphide Generation and Gas Diffusion Separation in a Flow System for Indirect Sulphite Determination in Wines and Fruit Juices

A flow system for sulphite determination in wines and fruit juice samples has been developed exploiting H2S generation and gas diffusion separation. The composed sandwich gas diffusion cell was coupled in the flow manifold to permit sulphite reduction to H2S and H2S diffusion through a microporous PTFE membrane to produce methylene blue resulting from the reaction with N,N-dimethylphenylene diamine (DMPD) and Fe3+. The flow parameters were optimized, and the best results were obtained by using NaOH solution for H2S collection. Interferences of H2S, CO2 and ascorbic acid were evaluated. Limits of detection (3σ) for the free and total sulfite were calculated at 0.12 and 0.25 mg L−1, respectively. The results obtained by the proposed process were in agreement with the reference methods for a 95% confidence level.

Simple methods for rapid determination of sulfite in food products

Two simple methods for sulfite determination in food products were proposed. The modified para-rosaniline (PRA)-formaldehyde method showed a much broader linear range (0.05–5.0 mg l −1 as SO 2) than the commonly used procedure for the sulfur dioxide detection in the atmosphere (0.05–1.0 mg l −1 as SO 2). By using a standard reference color card, this method only needed 5 min to complete a test. The 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) method was another good alternative for rapid determination of sulfite since it only needed one main reagent and the method was robust and easy to operate with the linear range of 0.10–4.3 mg l −1 as SO 2. When applying to real food samples, the DTNB method had good recoveries for all the tested samples and the results agreed well with those obtained by the official iodometric titration. The modified PRA-formaldehyde method worked well with all the tested dried food products, though matrix effect of sulfite binding was observed for the beer samples. Thus, the modified PRA-formaldehyde method has advantages of sensitivity and rapidity, but the DTNB method offers a wider range of applications. Both methods provided practical ways for in situ determination of sulfite by non-professional operators with the modified PRA-formaldehyde method suited for food samples with less sulfite binding problems.

An optoelectronic instrument for the determination of sulphite in beverages

The paper describes an optoelectronic device that has been designed and developed to measure the sulphite concentration in beverages for quality evaluation. A selective and sensitive method for determination of sulphite is based on the reaction with pararosaniline acid bleached dye and formaldehyde solution, which gives violet colored complex having absorption maxima at 560 nm. Lambert–Beer’s law is obeyed in the concentration range up to 25 μg/ml (25 ppm) of test solution within an accuracy of ±0.05μg/ml (0.05 ppm). The instrument involves the use of high intensity green light emitting diode (LED) of wavelength 565 nm as light source. BPW21 photodiode having the relative spectral sensitivity above 90% in the range of 500–600 nm has been used as a detector, for the determination of sulphite concentration.

Determination of sulfite in beer samples using an amperometric fill and flow channel biosensor employing sulfite oxidase

A simple method is described to determine sulfite in beer samples using a fill and flow channel biosensor. A droplet of sample is placed into the inlet of a rectangular flow cell and begins to flow through the channel by capillarity. The flow is maintained and controlled by a porous outlet plug of defined porosity. In a rectangular flow cell, the sample solution flows through three consecutive zones: over a predictor electrode, an enzyme layer and a detector electrode. Together these three zones enable the differentiation between current due to sulfite and current due to other electroactive species in the sample. The predictor electrode is located upstream, and on the opposite channel wall to the enzyme layer and detector electrode, and is poised at the same potential (+0.65 V versus Ag/AgCl) as the detector electrode. On this electrode, the current contribution from all species in the sample solution that are oxidized at that potential is determined. The enzyme layer contains sulfite oxidase, which, in the process of oxidizing sulfite, produces hydrogen peroxide, which itself is reduced by excess sulfite. The current at the downstream detector electrode is therefore different from that at the predictor electrode as a result of the enzyme reaction and the difference of the currents, corrected for the dimensions of the electrodes, is proportional to the concentration of sulfite. The method enables a straightforward correction of the interfering current at the detector electrode and a determination of the analyte concentration. The effect of interferences from ascorbic acid, ethanol, sorbic acid and tartaric acid in the detection of sulfite is efficiently removed. The concentration of sulfite in a sample of beer measured by the biosensor is equivalent to that measured using a reference method based on the AOAC-recommended Monier–Williams method.

Determination of total sulfite in wine: Zone electrophoresis–isotachophoresis quantitation of sulfate on a chip after an in-sample oxidation of total sulfite

This work deals with the determination of total sulfite in wine. The determination combines an in-sample hydrogen peroxide oxidation of total sulfite in alkalized wine to sulfate with the separation and quantitation of the latter anion by zone electrophoresis (ZE) on-line coupled with isotachophoresis (ITP) on a column-coupling chip. Sample clean up, integrated into the ITP–ZE separation, eliminated wine matrix in an extent comparable to that provided by a highly selective distillation isolation of sulfite. At the same time, conductivity detection, employed to the detection of sulfate in the ZE stage of the ITP–ZE combination, provided for sulfate the concentration limit of detection corresponding to a 90 μg/l concentration of sulfite in the loaded sample (0.9 μl). Such a detectability allowed a reproducible quantitation of total sulfite when its concentration in wine was 15 mg/l. Formaldehyde binding of free sulfite in wine, included into the pre-column sample preparation, prevented an uncontrolled oxidation of this sulfite form. This step contributed to an unbiased determination of sulfate present in the original wine sample (this determination corrected for the concentration of sulfate determined in the sample after the peroxide oxidation of sulfite to the value equivalent to the total sulfite). The 99–101% recoveries of sulfite, determined for appropriately spiked wine samples, indicate a very good accuracy of the present method. Such a statement also supports excellent agreements of the results of quantitation based on the in-sample peroxide oxidation of the total sulfite (bound sulfite released at a high pH) with those in which this analyte was isolated from wine by distillation (bound sulfite released at a very low pH).

Chemiluminescence Microflow Injection Analysis System on a Chip for the Determination of Sulfite in Food

Based on the chemiluminescence (CL) reaction between Ce (IV) and sulfite sensed by Rh6G and Tween 80 in acid medium, a new microflow injection analysis (µFIA) system on a chip for the determination of sulfite with chemiluminescence method was described in this paper. The channels of the µFIA system etched by CO2 laser were 200 µm wide and 150 µm deep and the volume of reaction area was 1.80 µL. All reagents, including sample, were monitored by the injection pump with the rate of 50 µL/min. The linear range of sulfite concentration was 1.0–60 µg/mL with the detection limit of 0.5 µg/mL. The proposed method had good reproducibility with the relative standard deviation 3.0% (n = 7) for 20 µg/mL of sulfite and was very sensitive and simple. It had been successfully applied to the determination of sulfite in food. Supported by a grant from the Science and Technique Ministry of China (2003BA310A05).

A novel electroreduction strategy for the determination of sulfite

The reduction of sulfite in acidic medium was found to lead to the production of a radical anion that provides a versatile, sensitive and readily accessible diagnostic alternative to current electrochemical detection methodologies.

Determination of sulphite and acetic acid in foods by gas permeation flow injection analysis

Two simple, rapid and sensitive gas-diffusion conductimetric methods were used for the determination of acetic acid and sulphite, separately. For sulphite, the method was based on formation of sulphur dioxide in acid medium (1.5 mol L −1 HCl). The sulphur dioxide formed diffuses through an hydrophobic permeable membrane into an acceptor stream (de-ionised water). The change in the conductivity of the de-ionised water was measured and referred to sulphite content in the samples. The method is applicable in the range of 1.0–50.0 mg L −1 sulphite and the limit of detection is 0.03 μg mL −1. The relative standard deviation for 10 replicate determinations of 10.0 μg mL −1 of sulphite is 0.2%. Sulphite was determined by the method of standard addition. Recovery of sulphite from wine samples ranged from 97.3% to 99.3%. The method was successfully applied to the determination of sulphite in wines and compares well with the standard iodometric method. For acetic acid determination, the method was based on the change of the conductivity of acceptor solution (de-ionised water) when acetic acid from the matrix, diffuses via a permeable membrane into the receptor solution. The increase in conductivity of the de-ionised water was proportional to the acid content. A linear calibration graph in the range of 0.010–0.100 mol L −1 of acetic acid with a relative standard deviation of 0.8% (0.010 mol L −1 acetic acid, N − 10) was obtained. Sample throughputs of 120 h −1 for sulphite and 80 h −1 for acetic acid were achieved. The systems were successfully applied for the assays of sulphite in wines and fruit juices and acetic acid content in vinegar, respectively.

Specific features of iodometric methods for determining the content of sodium sulfite in fixing-bleaching photographic solutions

The conditions of oxidation of thiocyanate ions and thiocarbamide with iodine in aqueous solutions are discussed. The range of the pH values of the solutions, in which thiocyanate ions do not interfere with the iodometric determination of sodium sulfite in fixing-bleaching photographic solutions and the expenditure of iodine for oxidation of thiocarbamide can be taken into account correctly, is revealed.

Usefulness of Ytterbium(III) as Analytical Reagent for Total Sulfite Determination in White Wine Samples

Ytterbium(III) is used as reagent for the determination of sulfite by measuring the formation of the Yb(III)-sulfite complex through the variation of the light scattering intensity with time. The low solubility of this complex causes an efficient dispersion of the radiation at 490 nm, which is measured at 980 nm. Each kinetic datum is automatically obtained in only 0.5 s by stopped-flow mixing technique. The application of the initial rate method using a long emission wavelength minimizes the potential interference of fluorescent background signals from the sample matrix. The dynamic range of the calibration graph is 1-250 microg/mL, and the calculated detection limit is 0.35 microg/mL. The precision, expressed as relative standard deviation, is <6%. The method has been applied to the determination of total sulfites in white wine samples, which requires only the sample dilution and the use of two aliquots to improve selectivity. However, the matrix effect found for red wines precludes the application of the method to the direct analysis of these samples. Analytical recoveries ranged from 96.0 to 106.7%. The results obtained with the proposed method agreed with those provided by the p-rosaniline method. Unlike this method, in which toxic reagents are required, the use of ytterbium(III) as analytical reagent shows the advantage of its low acute toxic rating.

Electrochemical sensor for sulfite determination based on iron hexacyanoferrate film modified electrodes

The development of a sulfite sensor and its application to wine analysis is described. The method for the determination of sulfite is based on the use of glassy carbon electrodes modified with films of Prussian Blue [iron(III,II) hexacyanoferrate(II,III)]. The resulting modified electrodes exhibit a reversible redox response ascribed to the oxidation/reduction of iron atoms present in the electrodeposited film. These films have a potent and persistent electrocatalytic activity towards the oxidation of sulfite with a detection limit of 80 μM and a good linear relationship (0.999) between the catalytic current and sulfite concentrations. According to these results, the described modified electrodes have been used as sensors for the determination of sulfite in various types of wine samples and the results obtained are in agreement with those obtained by the standard iodometric method.

Direct determination of sulfite in food samples by a biosensor based on plant tissue homogenate

In the work described here, a biosensor was developed for the determination of sulfite in food. Malva vulgaris tissue homogenate containing sulfite oxidase enzyme was used as the biological material. M. vulgaris tissue homogenate was crosslinked with gelatin using glutaraldehyde and fixed on a pretreated Teflon membrane. Sulfite was enzymatically converted to sulfate in the presence of the dissolved oxygen, which was monitored amperometrically. Sulfite determination was carried out by standard curves, which were obtained by the measurement of consumed oxygen level related to sulfite concentration. Several operational parameters had been investigated: the amounts of plant tissue homogenate and gelatin, percentage of glutaraldehyde, optimum pH and temperature. Also, some characterization studies were done. There was linearity in the range between 0.2 and 1.8 mM at 35 °C and pH 7.5. The results of real sample analysis obtained with the biosensor agreed well with the enzymatic reference method using spectrophotometric detection.

Chemiluminescent determination of sulfite traces based on the induced oxidation of Ni(II)/tetraglycine complex by oxygen in the presence of luminol: mechanistic considerations

The emission produced by sulfite induced autoxidation of Ni(II)/tetraglycine complex in the presence of luminol can be used to determine sulfite in the range of (0.0500–5.00)×10 −6 mol l −1. The limit of detection is 2.8×10 −8 mol l −1 and the relative standard deviation is 4.6% for 1×10 −7 mol l −1 sulfite in five repeated measurements. This method has been successfully used for the determination of sulfite in wine, juices, white sugar and rainwater. The sulfite was extracted from the sample by using one gas-diffusion unit. Results for various samples of wine and juices were compared with those obtained by using a recommended procedure (correlation coefficient=0.9998, n=10), and recovery range for white sugar was between 99 and 104%. The mechanism involves a chain reaction with Ni(II) and radicals formations, which can then oxidize luminol.

Analysis of hydroxide, inorganic sulphur species and organic anions in kraft pulping liquors by capillary electrophoresis

A new method has been developed for the determination of hydroxide, sulphide, thiosulphate, sulphate, sulphite, chloride, oxalate and formate in kraft green, white and black liquors by capillary electrophoresis. The method provides baseline resolution of all analytes of interest using an electrolyte composed of 10 mM sodium chromate and 2 mM tetradecyltrimethylammonium hydroxide. Separations are conducted under constant current conditions at 25 °C and analytes are quantified by indirect UV-detection at 275 nm. A brief, post run wash of the capillary with 0.5 M NaOH and water gave improved inter- and intra-run repeatability of both migration times and peak areas. Sulphide and other oxysulphur species were relatively stable in white and green liquors diluted in helium-sparged water. However, sulphide present in black liquor samples diluted in the same solvent underwent rapid oxidation to form sulphite and thiosulphate, thereby precluding the measurement of all three anions. We discovered that quinone-type compounds present in black liquor catalyze the oxidation of sulphide and that the addition of reduced glutathione at a concentration of 1 mg/mL during black liquor dilution completely stabilized sulphide, sulphite and thiosulphate for at least one hour, thus allowing for quantitative analysis of the analytes. A mechanism is proposed to explain the action of both quinones and that of glutathione. Results obtained by the new method compared well with those obtained by ion chromatography, titrimetry, and from spike-recovery experiments.

Analysis of hydroxide, inorganic sulphur species and organic anions in kraft pulping liquors by capillary electrophoresis

A new method has been developed for the determination of hydroxide, sulphide, thiosulphate, sulphate, sulphite, chloride, oxalate and formate in kraft green, white and black liquors by capillary electrophoresis. The method provides baseline resolution of all analytes of interest using an electrolyte composed of 10 mM sodium chromate and 2 mM tetradecyltrimethylammonium hydroxide. Separations are conducted under constant current conditions at 25 °C and analytes are quantified by indirect UV-detection at 275 nm. A brief, post run wash of the capillary with 0.5 M NaOH and water gave improved inter- and intra-run repeatability of both migration times and peak areas. Sulphide and other oxysulphur species were relatively stable in white and green liquors diluted in helium-sparged water. However, sulphide present in black liquor samples diluted in the same solvent underwent rapid oxidation to form sulphite and thiosulphate, thereby precluding the measurement of all three anions. We discovered that quinone-type compounds present in black liquor catalyze the oxidation of sulphide and that the addition of reduced glutathione at a concentration of 1 mg/mL during black liquor dilution completely stabilized sulphide, sulphite and thiosulphate for at least one hour, thus allowing for quantitative analysis of the analytes. A mechanism is proposed to explain the action of both quinones and that of glutathione. Results obtained by the new method compared well with those obtained by ion chromatography, titrimetry, and from spike-recovery experiments.