Determination Of Sulfite Research Articles

Determination of Sulfite in Botanical Medicine Using Headspace Thin-Film Microextraction and Surface Enhanced Raman Spectrometry

A facile method using headspace thin-film microextraction (HS-TFME) coupled with surface enhanced Raman spectrometry (SERS) has been developed for the determination of sulfite in traditional Chinese herbal medicine. The extraction substrate was synthesized by depositing urchin-like ZnO micron particles on glass sheets using chemical liquid phase deposition. Under the optimal conditions, the intensity of the SERS signal at 630–640 cm−1 provided a good linear relationship with the concentration of sulfite from 25 to 400 mg/kg, and the linear correlation coefficient (R) was 0.996 with a detection limit of 6 mg/kg. The method was employed for the determination of sulfite in herbal medicines, and the results were confirmed by a traditional distillation-titration method. Therefore, this developed HS-TFME-SERS method may play an important role in the rapid, simple, and selective determination of sulfite residues in Chinese herbal medicine and become a potentially universal method for this analyte in various solid samples.

A simple field method for the determination of sulfite in natural waters: Based on automated dispersive liquid-liquid microextraction coupled with ultraviolet-visible spectrophotometry

Sulfite is known to be harmful to human health and associated to sulfur related environmental effects and ideally should be analyzed onsite owing to its instability. Here we describe an automated, miniaturized, and highly efficient dispersive liquid-liquid microextraction (DLLME) system that seamlessly coupled to a UV–vis spectrophotometer for the trace analysis of sulfite in natural waters. The automated DLLME system was constructed by a single syringe pump that is coupled with a multiposition valve. Nanomolar levels of sulfite could be extracted from natural water samples and injected into the hyphenated spectrophotometer for quantification. The whole analytical procedures, including chromogenic reactions, DLLME, collecting and transferring of microvolume of extracts, and spectrophotometric quantification, were automatically carried out. Key parameters that affect the performance of the method were investigated. The method allows the determination of trace levels of sulfite in the range of 15–1500 nM with a detection limit of 1.2 nM. Good reproducibility and recoveries were obtained by analyzing a series of natural water samples that were spiked with different concentration levels. The method was successfully applied to real natural water samples with satisfactory results. The proposed analytical system is light (3.9 kg), simple to use, able to be applied in the field, and sensitive enough for fresh and saline waters analysis.

Determination of Sulfite in Real Sample by an Electrochemical Sensor Based on Ni/Poly(4-Aminobenzoic Acid)/Sodium Dodecylsulfate/Carbon Paste Electrode

In this research, a modified electrode has been produced during the electropolymerization of 4-Aminobenzoic acid in the presence of sodium dodecylsulfate (SDS) and then Ni(II) ions were incorporated to the polymer by immersion of the modified electrode in a 0.1 M Ni(II) ions solution. The electrochemical behavior of Ni/poly(4-aminobenzoic acid)/sodium dodecylsulfate/carbon paste electrode (Ni/poly(4-AB)/SDS/CPE) was investigated by using cyclic voltammetry. The experimental results exhibited the stable redox behavior of the Ni(III)/Ni(II) couple immobilized at the polymeric electrode. This polymeric modified electrode has a very good activity toward the sulfite electrooxidation in a phosphate buffer solution (pH 11). By comparison of the different responses to sulfite oxidation using electrodes Ni/poly(4-AB)/SDS/CPE, poly(4-AB)/SDS/CPE and CPE, we observed that the former electrode is a more effective catalyst for the electrooxidation of sulfite. Under optimal experimental conditions, the peak current response increased linearly with sulfite concentration over the range of 0.1–1 and 1–10 mM. The detection limit of the method was 0.063 mM. Finally, the method was applied to the determination of sulfite in weak liquor sample.

A mitochondria-targeted near infrared ratiometric fluorescent probe for the detection of sulfite in aqueous and in living cells

A near infrared fluorescent probe YSP for sulfite was synthesized, in which a julolidine fused with a pyran-2-one was employed as the fluorophore and the vinyl activated by an indole salt as the receptor. The introduction of julolidine and indole salt strengthens the electron push-pull effect of the probe and allows it to absorb (597 nm) and emit (681 nm) in red wavelength region. The addition of sulfite to the C˭C bond led to prominent blue-shifts in both absorption (171 nm) and emission (165 nm) spectra, which made it possible for colorimetric and ratiometric fluorescent detection of sulfite. NMR titration results illustrated that the determination of sulfite is a two-step process: nucleophilic addition of sulfite to the unsaturated carbon of C˭N in indole ring followed by intramolecular rearrangement through a four-membered ring to form adduct-B with shorter absorption wavelength. In addition, the cationic feature of YSP enables the probe to be specifically localized in mitochondria, and it could ratiometric bioimaging sulfite in living HepG-2 and L929 cells.

Spectrophotometric Determination of Sulphite in Various Water Samples Via Chromium-1,5-Diphenylcarbazide Complex

A simple and rapid spectrophotometric method for the determination of sulphite SO3-2 is described. The method is based on the rapid reduction of known amount of chromate CrO4-2 in the presence of sulphite in acidic medium of 2N H2SO4. The amount of excess of chromate was measured after it reactions with 1,5-diphenylcarbazide which finally gives a pink-violet, water soluble and stable complex, which exhibit a maximum absorption at 542 nm. Beer's law was obeyed in the concentration range from 0.004-6.0 µg of sulphite in a final volume of 25 ml with a molar absorbtivity of 4.64×104 l.mol-1.cm-1, Sandal's sensitivity index of 0.001724 ?g .cm-2 and relative standard deviation of ±0.55 - ±0.83 depending on the concentration level. The present method has been developed for the determination of sulphite in the presence of thiosulphate. Good recoveries of sulphite from various water samples are achieved using the proposed method.

Simultaneous electrochemical sensing of sulphite and nitrite on acid-functionalized multi-walled carbon nanotubes modified electrodes

Detection of anions like sulphite and nitrite, which are environmental pollutants, by utilizing conducting substrates like multiwall carbon nanotubes with metal oxides and others are highly desired to monitor pollution. Herein, we report construction of COOH-functionalized, multiwall carbon nanotubes (HOOC-MWCNT) modified GCE for simultaneous estimation of sulphite and nitrite under neutral condition. The physiochemical characterizations of HOOC-MWCNT were carried out by using advanced characterization techniques to probe the thermal stability, morphology and functional groups present in the HOOC-MWCNT. From morphological studies, it was confirmed that HOOC-MWCNT has discrete tube like morphology with more active surface area which enhanced the sensor response of sulphite and nitrite anions. The modified GCE was used to detect sulphite and nitrite by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The peak separation between sulphite and nitrite are comparatively higher to probe the sensing of anions in nanomolar concentrations, it was found to be around 420 mV by CV technique. This potential difference is highly attractive to determine the sulphite and nitrite simultaneously. The sensitivity for the simultaneous determination of SO32− and NO2− were 25.29 μA cm-2 mM-1 and 209.9 μA cm-2 mM-1 and it had low limit of detection (LOD) of 215 nM and 565 nM, respectively, for SO32− and NO2−. To demonstrate the practical applicability, the proposed sensor was utilized for the determination of sulphite and nitrite anions in low concentration levels in different water real samples by the well-known recovery method.

Spectrophotometric Determination of Sulphite in Various Water Samples Via Chromium-1,5-Diphenylcarbazide Complex

A simple and rapid spectrophotometric method for the determination of sulphite SO3-2 is described. The method is based on the rapid reduction of known amount of chromate CrO4-2 in the presence of sulphite in acidic medium of 2N H2SO4. The amount of excess of chromate was measured after it reactions with 1,5-diphenylcarbazide which finally gives a pink-violet, water soluble and stable complex, which exhibit a maximum absorption at 542 nm. Beer's law was obeyed in the concentration range from 0.004-6.0 µg of sulphite in a final volume of 25 ml with a molar absorbtivity of 4.64×104 l.mol-1.cm-1, Sandal's sensitivity index of 0.001724 ?g .cm-2 and relative standard deviation of ±0.55 - ±0.83 depending on the concentration level. The present method has been developed for the determination of sulphite in the presence of thiosulphate. Good recoveries of sulphite from various water samples are achieved using the proposed method.

Quantitative analysis and stability of p-hydroxybenzyl hydrogen sulfite in sulfur-fumigated Gastrodiae Rhizoma

Studies on the characteristic chemical markers of sulfur fumigation have become an effective auxiliary way for quality control of traditional Chinese medicine. This study established a quantitative analysis method for the determination of p-hydroxybenzyl hydrogen sulfite (p-HS) in Gastrodiae Rhizoma (GR) based on UPLC-MS/MS. Then, 37 batches of GR were screened, and the results showed that 27 batches of them were sulfur-fumigated. Especially, the GR samples in Yunnan producing areas were sulfur-fumigated more seriously. Based on the stability of p-HS after different storage time and heat treatment methods, it was found that the content of p-HS was stable and reliable in the storage period of 8 months and under normal heat treatment (50, 60, 70, 80 °C) conditions. In conclusion, this study shows a high sensitivity, good selectivity and good stability of p-HS, which can provide reference for the quality control and sulfur fumigation screening of GR.

A Fast, Low-Cost, and Environmental Friendly Micro-Flow-Batch Analyzer for Photometric Determination of Sulfites in Beverages

An automated microsystem for sulfite determination in beverages was developed. It presents higher sampling throughput, lower chemical consumption and less waste generation than previous flow methods, while using the same p-rosaniline-formaldehyde-sulfite reaction. The sampling rate, limit of detection (LOD), and relative standard deviation (RSD) were estimated at 130 h-1, 80.0 µg L–1, and < 1.3% (n = 5), respectively. Recoveries ranged from 96.8 to 102.6%.

A rapid, sensitive and green analytical method for the determination of sulfite in vinegars using pararosaniline reaction with image detection

A green, rapid and sensitive automated analytical method with imaging detection for the determination of sulfite in vinegars using the pararosaniline (PRA)–formaldehyde–sulfite reaction is demonstrated.

Determination of free and total sulfur(IV) compounds in coconut water using high-resolution continuum source molecular absorption spectrometry in gas phase

This work proposes a method for the determination of free and total sulfur(IV) compounds in coconut water samples, using the high-resolution continuum source molecular absorption spectrometry. It is based on the measurement of the absorbance signal of the SO2 gas generate, which is resultant of the addition of hydrochloric acid solution on the sample containing the sulfating agent. The sulfite bound to the organic compounds is released by the addition of sodium hydroxide solution, before the generation of the SO2 gas.The optimization step was performed using multivariate methodology involving volume, concentration and flow rate of hydrochloric acid. This method was established by the sum of the absorbances obtained in the three lines of molecular absorption of the SO2 gas. This strategy allowed a procedure for the determination of sulfite with limits of detection and quantification of 0.36 and 1.21mgL−1 (for a sample volume of 10mL) and precision expressed as relative standard deviation of 5.4% and 6.4% for a coconut water sample containing 38.13 and 54.58mgL−1 of free and total sulfite, respectively.The method was applied for analyzing five coconut water samples from Salvador city, Brazil. The average contents varied from 13.0 to 55.4mgL−1 for free sulfite and from 24.7 to 66.9mgL−1 for total sulfur(IV) compounds. The samples were also analyzed employing the Ripper´s procedure, which is a reference method for the quantification of this additive. A statistical test at 95% confidence level demonstrated that there is no significant difference between the results obtained by the two methods.

Groundwater-based water wells characterization from Guinea Bissau (Western Africa): A risk evaluation for the local population

The study conducted in two regions of Guinea Bissau, Oio and Cacheu, focusing on the characterization of the groundwater supplies sampled during the dry season and their associated risks for human health. Twenty samples were collected in wells located nearby pit latrines. In situ analyses were conducted with Semi-quantitative test strips for the determination of turbidity, pH, chloride, carbonate, sulfites, ammonium, nitrite and nitrate. The analysis of metals was performed by an ICP-MS Elan DRC-e and an ICP-OES Optima 8000. The Target Hazard Quotient (THQ) was applied to evaluate the risk of developing chronic systemic effects derived from exposure to metals. Values of concern of turbidity ammonium, and pH values were lower than the normal range for drinking water in most samples. From both regions, Fe and Al were occasionally found with values higher than the international thresholds fixed by the World Health Organization and by the European Commission for drinking water, while, only in one sample from Cacheu region Pb was found significantly above these limits. THQs resulted next to the level of risk (1) for the highest values found of Al, As, Fe and Mn. Of great concern is the resident risk obtained from a well water of Cacheu for the highest value of Pb (96.8μg/L), because the values of the resident risk found of 1 and 0.7 for child and adults respectively. The results obtained highlighted a close correlation between the chemistry of water and sediment and a correlation with the proximity of the water supplies with the latrines. This study evidenced the potential toxicity of the water supplies for the local populations and the risk of developing chronic systemic effects due to some physico-chemical parameters, the importance of functioning water pipeline system, the importance of maintaining adequate distance between latrines and drinking water access.

Determination of Sulfite in Food by Liquid Chromatography Tandem Mass Spectrometry: Collaborative Study.

Sulfites are added to a wide range of food and beverage products to prevent browning or oxidation. Although most of the population do not experience side effects from consuming sulfites, a small subset has been shown to experience an "allergic-like" response. For this reason, the U.S. Food and Drug Administration requires that sulfites be labeled on all products that contain more than 10 mg/kg (parts per million) sulfur dioxide. The current regulatory method, optimized Monier-Williams (OMW) Official Method 990.28, has been successful in quantifying sulfites in most matrixes, but is time-consuming and has a method detection limit at the regulatory-labeling threshold. Recently, an LC-tandem MS (MS/MS) method was published that was applicable to a wide range of sulfite-containing matrixes. This method converts free and reversibly bound sulfite to the formaldehyde adduct hydroxymethylsulfonate, which could then be separated from matrix constituents using a hydrophilic interaction LC analytical column and subsequently be detected with tandem MS (MS/MS). In this study, multilaboratory validation was conducted with 11 laboratories in the United States and Canada. Four matrixes were spiked at varying concentrations and three additional commercially sulfited matrixes were included. An abbreviated comparison study between the LC-MS/MS and OMW methods was conducted for select samples. Average recoveries for all matrixes ranged from 86 to 114% with RSDr and RSDR values of 4.5-17.5 and 8.6-22.5%, respectively. Further comparisons will be necessary to draw comparisons between the two methods. This method proved to be a faster and more sensitive way to determine sulfites in food and beverages, showing promise for the continuing improvement of enforcement of sulfite labeling requirements to protect individuals who have sulfite sensitivity.

Ion-selective electrodes based on long-chain quaternary ammonium salts with enhanced steric accessibility, and their application for determination of hydrophilic double-charged inorganic anion

The effect of long-chain quaternary ammonium salts’ exchange center steric accessibility and presence of a neutral anion carrier, 4-(trifluoroacetyl)benzoic acid heptyl ester, upon analytical characteristics of ion-selective electrodes reversible to molybdate, tungstate, sulfate, hydrogen phosphate, sulfite, carbonate and thiosulfate anions, has been studied. When the most sterically hindered quaternary ammonium salts, trinonyl octadecyl ammonium bromide, is replaced by one of the salts with the accessible exchange center, the selectivity is altered, the magnitude of the selectivity coefficient change being determined by the nature of the interfering ion. Thus, for carbonate- and sulfate-selective ISEs with hydrophobic thiocyanate ions as interference, the effect achieved is 6–8 orders of magnitude, while with nitrate ions as interference it is 3.4–5.7 orders, and for such hydrophilic interference ions as sulfate, chloride and oxalate, it is even less. Replacing trinonyl octadecyl ammonium bromide with a sterically accessible ammonium salt improves lower detection limit generally by 1–2 orders, while for sulfite and thiosulfate ISEs the effect is only 0.3–0.95 orders. The procedures for determination of sulfate, sulfite and carbonate ions in real objects (mineral water, dried fruits) have been proposed. They are simple, reasonably accurate, require only widely available equipment and can be recommended for use in chemical and food industries.

Flow injection analysis–flame atomic absorption spectrometry system for indirect determination of sulfite after on-line reduction of solid-phase manganese (IV) dioxide reactor

A new and simple flow injection method followed by atomic absorption spectrometry was developed for indirect determination of sulfite. The proposed method is based on the oxidation of sulfite to sulphate ion using solid-phase manganese dioxide (30% W/W suspended on silica gel beads) reactor. MnO2 will be reduced to Mn(II) by sample injection in to the column under acidic carrier stream of HNO3 (pH 2) with flow rate of 3.5mLmin−1 at room temperature. Absorption measurement of Mn(II) which is proportional to the concentration of sulfite in the sample was carried out by atomic absorption spectrometry. The calibration curve was linear up to 25mgL−1 with a detection limit (DL) of 0.08mgL−1 for 400µL injection sample volume. The presented method is efficient toward sulfite determination in sugar and water samples with a relative standard deviation (RSD) less than 1.2% and a sampling rate of about 60h−1.

A highly sensitive determination of sulfite using a glassy carbon electrode modified with gold nanoparticles-reduced graphene oxide nano-composites

A gold nanoparticles-reduced graphene oxide composite (AuNPs-rGO) was synthesized by chemical co-reduction strategy using ethylene glycol (EG) as a reducing agent. The structure and composition of this AuNPs-rGO composite were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), as well as the transmission electron microscope (TEM) techniques. Moreover, a glassy carbon electrode (GCE) was modified with this AuNPs-rGO composite by dropping method. The electrochemical behavior and the electrocatalytic activity of this AuNPs-rGO/GCE electrode for the oxidation of sulfite were also investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results showed that this AuNPs-rGO/GCE exhibited high electrochemical activity for the oxidation of sulfite under the synergistic action of AuNPs and rGO. In 0.10molL−1 H2SO4, the linear range for the determination of sulfite by amperometry at 0.40V vs SCE was 2.0×10−7−2.3×10−3molL−1 (r2=0.995 6) with a detection limit of 4.5×10−8molL−1 (S/N=3). The sensitivity for the determination of sulfite is 1026.5μA (mmolL−1)−1cm−2. At last, the as-prepared modified electrode was successfully used for the determination of sulfite in red wines with satisfactory results.

Sulphur dioxide in meat products: 3-year control results of an accredited Italian laboratory

ABSTRACTSulphiting agents are well-known food preservatives. The European legislation does not allow their addition in fresh meat preparations. Therefore this type of food products has often been verified. To high sulphite levels in food is a health safety risk, due to toxic effects that these compounds may exercise on humans. In this study the control activity as performed by an Italian accredited laboratory from 2013 to 2015, relating to determination of sulphites in meat products, is described. Six hundred and sixty-nine meat product samples were analysed. Both applied techniques, a screening method (malachite green test) and a confirmatory method (ion chromatography), were accredited. Forty-three samples resulted positive at screening test and nineteen of these samples showed high-sulphite concentrations, in the range 67.6–1437 mg kg−1. The non-negligible percentage of positives (6.4%) and the high concentrations verified confirmed that the control of sulphuring treatment of fresh meat preparations is an important task for organisations in charge of food inspections and control.

Determination of Enzymes Associated with Sulfite Toxicity in Plants: Kinetic Assays for SO, APR, SiR, and In-Gel SiR Activity.

The amino acid cysteine plays a major role in plant response to abiotic stress by being the donor of elemental sulfur for the sulfuration of the molybdenum cofactor, otherwise the last step of ABA biosynthesis, the oxidation of abscisic aldehyde, is inactivated. Additionally, cysteine serves as a precursor for the biosynthesis of glutathione, the reactive oxygen species scavenger essential for redox status homeostasis during stress. Cysteine is generated by the sulfate reductive pathway where sulfite oxidase (SO; EC 1.8.3.1) is an important enzyme in the homeostasis of sulfite levels (present either as a toxic intermediate in the pathway or as a toxic air pollutant that has penetrated the plant tissue via the stomata). SO is localized to the peroxisomes and detoxifies excess sulfite by catalyzing its oxidation to sulfate. Here we show a kinetic assay that relies on fuchsin colorimetric detection of sulfite, a substrate of SO activity. This SO assay is highly specific, technically simple, and readily performed in any laboratory.5'-adenylylsulfate (APS) reductase (APR, E.C. 1.8.4.9) enzyme regulates a crucial step of sulfate assimilation in plants, algae and some human pathogens. The enzyme is upregulated in response to oxidative stress induced by abiotic stresses, such as salinity and hydrogen peroxide, to generate sulfite an intermediate for cysteine generation essential for the biosynthesis of glutathione, the hydrogen peroxide scavenger. Here we present two robust, sensitive, and simple colorimetric methods of APR activity based on sulfite determination by fuchsin.Sulfite reductase (SiR) is one of the key enzymes in the primary sulfur assimilation pathway. It has been shown that SiR is an important plant enzyme for protection plant against sulfite toxicity and premature senescence. Here we describe two methods for SiR activity determination: a kinetic assay using desalted extract and an in-gel assay using crude extract.Due to the energetically favorable equilibrium, sulfurtransferase (ST) activity measured as sulfite generation or consumption. Sulfite-generating ST activity is determined by colorimetric detection of SCN- formation at 460 nm as the red Fe(SCN)3 complex from cyanide and thiosulfate using acidic iron reagent. Sulfite-consuming (MST) activity is detected as sulfite disappearance in the presence of thiocyanate (SCN-) or as SCN- disappearance. To abrogate interfering SO activity, total ST activities is detected by inhibiting SO activity with tungstate.

Green analytical flow method for the determination of total sulfite in wine using membraneless gas–liquid separation with contactless conductivity detection

New and green automated flow-method based on membraneless vaporization technique suitable for monitoring of total sulfite in wine.

Electrochemical sensing of total sulphites in beer using non-modified screen-printed carbon electrodes

An analytical method that combines gas-diffusion microextraction with square-wave voltammetric detection using commercial non-modified screen-printed carbon electrodes was employed in the determination of total sulphites in beer. The developed methodology showed low limits of detection (0.050 mg L−1) and quantification (0.17 mg L−1) and an intraday precision of 4.8%. The proposed method was also compared with a reference methodology used in the beer industry (EBC method 9.25.3) showing no significant differences in the obtained results. This is a simple, cheap and notably portable alternative for brewers that wish to quantify sulphites in their products. Copyright © 2017 The Institute of Brewing & Distilling