Sulfide measurements by flow injection analysis and ion chromatography with electrochemical detection

Ratiometric fluorescent platform for on-site monitoring of sodium pyrosulfite in preserved fruits

The rapid detection of pyrosulfites in food chemistry is crucial to food safety and health. Here, a coumarin-type ratiometric fluorescent probe was developed based on the Michael addition reaction to detect sodium pyrosulfite (Na2S2O5). The probe exhibited high selectivity and fast response (t1/2 = 6 s) to Na2S2O5 and a low detection limit (26 nM). Because of its excellent ratiometric response performance, the probe was successfully applied to measure the amount of Na2S2O5 in preserved fruits. Colour information analysis and formula calculations were performed to quickly determine the sodium pyrosulfite amount in an actual sample by using a smartphone. Therefore, the intelligent strategy of combining the sensing process and smartphone provides a convenient and efficient method for the fast monitoring of sodium metabisulfite in actual food.

Polydopamine-Coated Co3O4 Nanoparticles as an Efficient Catalase Mimic for Fluorescent Detection of Sulfide Ion

Surface engineering of nanozymes has been recognized as a potent strategy to improve their catalytic activity and specificity. We synthesized polydopamine-coated Co₃O₄ nanoparticles (PDA@Co₃O₄ NPs) through simple dopamine-induced self-assembly and demonstrated that these NPs exhibit catalase-like activity by decomposing H₂O₂ into oxygen and water. The activity of PDA@Co₃O₄ NPs was approximately fourfold higher than that of Co₃O₄ NPs without PDA, possibly due to the additional radical scavenging activity of the PDA shell. In addition, PDA@Co₃O₄ NPs were more stable than natural catalase under a wide range of pH, temperature, and storage time conditions. Upon the addition of a sample containing sulfide ion, the activity of PDA@Co₃O₄ NPs was significantly inhibited, possibly because of increased mass transfer limitations via the absorption of the sulfide ion on the PDA@Co₃O₄ NP surface, along with NP aggregation which reduced their surface area. The reduced catalase-like activity was used to determine the levels of sulfide ion by measuring the increased fluorescence of the oxidized terephthalic acid, generated from the added H₂O₂. Using this strategy, the target sulfide ion was sensitively determined to a lower limit of 4.3 µM and dynamic linear range of up to 200 µM. The fluorescence-based sulfide ion assay based on PDA@Co₃O₄ NPs was highly precise when applied to real tap water samples, validating its potential for conveniently monitoring toxic elements in the environment.

Synthesis and Properties of a Water-soluble Fluorescent Probe Based on ICT System for Detection of Ultra-trace SO2 Derivatives

SO2 and its derivatives are widely present in the environment and living organisms, endangering the environment and human health. Therefore, it is of great significance for the effective detection of sulfur dioxide (SO2) and its hydrated derivatives (HSO3- /SO32-). In this study, based on the mechanism of intramolecular charge transfer (ICT), a water-soluble colorimetric fluorescent probe (E)-2-(4-acetamidostyryl)-3-(5-carboxypentyl)-1, 1-dimethyl-1H-benzo[e]indol-3-ium (ABI) for the detection of SO2 derivatives was successfully synthesized from p-acetaminobenzaldehyde by connecting the benzo[e]indoles cationic fluorophore containing highly activated methyl via C = C double bond, and the ABI structure was characterized by HRMS and 1H NMR, 13 C NMR. Studies have shown that the ABI probe has some advantages such as good selectivity for SO2 derivatives, high sensitivity (detection limit LOD = 14.9 nM), and fast reaction rate. After adding HSO3-, the color of the probe solution changed from light yellow to colorless within 10 s, which provides a simple way to identify bisulfite with the naked eye. Studies on the effect of pH on the fluorescence performance of ABI showed that fluorescence performance of ABI was stable in the range of pH (7.0-10.26). Therefore, ABI is expected to become an effective tool for detecting SO2 derivatives in cells and organisms in the future.

Preparation and characterization of γ-Fe2O3 nanoparticles and investigation of its adsorption performance for sulfide, sulfite and thiosulfate from aqueous solutions using ultrasonic assisted method: Modeling and optimization

Maghemite nanoparticles, as an adsorbent, was used for the removal of sulfur species including sulfide, sulfite and thiosulfate from waste water samples by ultrasonic-assisted adsorption method. The characterization of the prepared nanoparticles was carried out by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and BET technique. The nanoparticles well dispersed in the water. The adsorbent was easily separated magnetically from the solution after loading with adsorbate. According to central composite design, the best experimental conditions including initial pH, the dosage of adsorbent and sonication time were obtained for sulfide, sulfite and thiosulfate. After optimization of the parameters, the removal of analytes in these conditions lead to the highest analytes removal efficiency (above 98%). The adsorption capacity was evaluated using different adsorption isotherm models. The maximum predicted adsorption capacities for sulfide, sulfite and thiosulfate were obtained as 148.5, 122.5 and 119.6mgg^-1, respectively. Then, desorption process of the adsorbed thiosulfate was also investigated using sodium hydroxide solution as the solvent and the other conditions affect to desorption were optimized.

A new fluorescent enhanced probe based on (E)-9-(2-nitrovinyl)-anthracene for the detection of bisulfite anions and its practical application

A new fluorescent enhanced probe based on (E)-9-(2-nitrovinyl)-anthracene is developed, which shows high selectivity and sensitivity for the detection of bisulfite anions at Na2HPO4 citric acid buffer solutions (pH 5.0). When addition of HSO3(-), the fluorescence intensity is significantly enhanced and the probe displays apparent fluorescence color changes from non-fluorescence to blue under a UV lamp illumination, the solution color also changes from yellow to colorless. The detection limit is determined to be as low as 6.30 μM. This offers another specific colorimetric and fluorescent probe for bisulfite anions detection, furthermore it is applied in detecting the level of bisulfite in sugar samples.

A comparison between determination of trace amounts of sulfide in the presence and absence of micelle particles in natural waters (Qazvin, Iran): a kinetic spectrophotometric approach

A new sensitive kinetic spectrophotometric method described for the determination of trace amounts of sulfides based on the addition reaction of sulfide ions with malachite green has been investigated in aqueous and micellar media at 25 °C. The variables affecting the rate of the reaction were investigated, and the optimum conditions were established. Under the optimum experimental conditions, decreases in the absorbance of malachite green at 615 nm in the absence and 630 nm in the presence of micelle particles, their λ max, were proportional to the concentrations of sulfide ions at the first 15 and 25 s from initiation of the reaction. The working curve was linear over the concentration range 50-1200 ng mL(-1) of sulfide ions with a fixed time method at the first 15 and 25 s from initiation of the reaction in aqueous medium and 25-1750 ng mL(-1) with a fixed time method at the first 15 s and 25-1500 ng mL(-1) for primitive 25 s in micellar medium. For the proposed kinetic method, the experimental and theoretical limit of detection (LOD) and limit of quantification (LOQ) in the presence and absence of micelle particles were obtained and tabulated at Δt = 15 and 25 s. The effective range concentration was achieved from the plot of Ringbom in both media and reported. Different surfactants, such as nonionic surfactant (Triton-X100), anionic surfactant sodium dodecyl sulfate (SDS), and cationic surfactant cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC), were investigated and Triton X-100 selected as a suitable surfactant. To valuable vision into the reaction pathways, pseudo-first-order condition was applied and different kinetic parameters like ΔG (≠), ΔE (≠), ΔS (≠), and ΔH (≠) computed. The 2:1 stoichiometry of malachite green to sulfide ions was indicated by the results of mole ratio and Job's method of continuous variation. The effect of different environments on the interfering of various ions on sulfide determination with the suggested method was studied, and final results have been presented. To investigate the usefulness of the different media of the proposed method, sulfide ions were determined in natural waters such as river and spring samples without any purification or using masking reagents.

Carbamodithioate-based dual functional fluorescent probe for Hg(2+) and S(2-)

Carbamodithioate-based compound T1 was designed and synthesized as a dual-functional probe for Hg(2+) ions and S(2-) anions. The underlying signaling mechanism was intramolecular charge transfer (ICT). It could serve as a direct probe towards Hg(2+) ions through "on-off" fluorescence changes and an indirect probe towards S(2-) anions through "on-off-on" fluorescence changes.

Selective spectrofluorimetric determination of sulfide ion using manganese doped ZnS quantum dots as luminescent probe

This work reports a spectrofluorimetric method for selective and sensitive determination of sulfide ion in aqueous solution. The ultra-small zinc sulfide quantum dots (QDs) doped with manganese (ZnS:Mn) were synthesized by using a simple and fast procedure based on the co-precipitation of nanoparticles in aqueous solution in the presence of 2-mercaptoethanol, as capping agent. The nanoparticles have exhibited two strong fluorescent emissions at about 424 and 594 nm. Luminescent surface-capped ZnS:Mn QDs, with particle size below 5 nm, have been applied for determination of sulfide anions in water samples. Under the optimum conditions, the fluorescence intensity of ZnS:Mn QDs is linearly proportional to the sulfide ion concentration in the range 1.2×10(-6) to 2.6×10(-5) mol L(-1) with a detection limit as 3.3×10(-7) mol L(-1). The relative standard deviation for five replicate measurements (for 8.0×10(-6) mol L(-1) of S(2-)) was obtained to be 2.6%. It was founded that the interference of the other anions was negligible on the quantitive determination of sulfide ion.

On-site measurement of trace-level sulfide in natural waters by vapor generation and microchannel collection

Aqueous sulfide plays an important role in the environment even at low concentrations. However, it is unstable, which means field samples cannot be transported to the laboratory for analysis without fixation. In this work, a novel method was developed to determine trace levels of sulfide on site. This method is based on vapor generation and collection in a special microchannel device followed by fluorescence measurement (VG-μGAS). The microchannel scrubber gave a high enrichment factor, and a high sensitivity was achieved, which allowed measurement of nanomolar (nM) levels of sulfide. The theoretical approach to vapor generation for several compounds is discussed to evaluate the applicability of the method to these analytes, and compounds having a low Henry's law constant (<1 M atm(-1)) are suitable to measure by VG-μGAS. Under optimized conditions, concentrations of 1.0-100 nM of sulfide could be measured. The sulfide contents of hot spring, aquarium, pond, and seawater were successfully measured by this method. Nanomolar levels of sulfide could be measured on site without loss of analyte, and results were obtained instantly in the field, both of which are advantageous for effective field surveys. The method was also applied to field measurements of aqueous sulfide in the Ariake Sea and Lake Baikal.

Direct introduction of water sample in multisegmented flow-injection analysis for sulfide determination

The present paper describes an inline flow-injection analysis system for the determination of sulfide in water samples, exploiting the Fischer reaction. Water samples were collected and introduced into a reactor of the FIA system. The sulfide released, after sample acidification, was carried out with a nitrogen gas flow and mixed with N,N diethyl-p-phenylenediamine (DEPD) solution in the presence of Fe(III). The blue dye formed was measured in the wavelength range between 672-679 nm. An evaluation of the effects of chemical and flow factors was performed using the factorial design of two levels, while optimization was accomplished by a Doehlert matrix. The system presented two linear-response ranges: the first of 0.433 to 400 µg L(-1) and the second of 400 to 3500 µg L(-1). The detection and quantification limit were found to be 0.130 and 0.433 µg L(-1), respectively, while the sample throughput was 12 h(-1). The precision was evaluated as the relative standard deviation (n = 10); for 50 and 100 µg L(-1) sulfide it was found to be 1.9 and 2.3%, respectively. The method showed satisfactory selectivity regarding the main interference present in environmental samples. The accuracy of the method was successfully evaluated in environmental water samples after a comparison with a literature reference method.

Chemical redox-regulated mesoporous silica-coated gold nanorods for colorimetric probing of Hg2+ and S2-

The past a few years have witnessed the wide use of metallic nanoparticles as ideal reporters for colorimetric detection, which generally involves an analyte-triggered alteration of aggregation degree of applied nanoparticles, and thus the change of colloidal color. However, these aggregation-based colorimetric probe are associated with a number of drawbacks, including poor stability of nanoaggregates, requirement of complicated functionalization and non-linearity of output signals. To address these problems, we herein employ mesoporous silica-coated gold nanorods (MS AuNRs) as novel nanocomposites for non-aggregation-based label-free colorimetric sensing relying on their chemical redox-modulated surface chemistry. In our sensing system, Hg(2+) ions are reduced to Hg(0) depositing on the surface of MS AuNPs and result in a great color change of MS AuNRs, while the subsequent introduction of S(2-) leads to a reverse process owing to the extraction of Hg(0) by S(2-). The experimental results for colorimetric sensing of Hg(2+) and S(2-) imply considerable sensitivity and specificity, suggesting the high potential of our approach for rapid environmental monitoring and bioanalysis in the future.

Single-drop and nanogram level determination of sulfite (SO3(2-)) in alcoholic and nonalcoholic beverage samples based on diffuse reflectance fourier transform infrared spectroscopic (DRS-FTIR) analysis on KBr matrix

The diffuse reflectance Fourier transform spectroscopic (DRS-FTIR) method, using potassium bromide matrix, has been developed for the one-drop microdetermination of sulfite in beverage samples. The present method is very simple, rapid, and precise for the determination of sulfite. The nanogram level of sulfite determination is based on the selection of a quantitative analytical peak at 495 cm (-1) among the three observed vibrational peaks obtained by diffuse reflectance Fourier transform infrared spectroscopy (DRS-FTIR). As little as a single drop of sample is sufficient for quantitative analysis of sulfite. The limit of detection (LOD) and the limit of quantification (LOQ) of the method are found to be 8 and 40 ng of SO 3 (2-) 0.1 g (-1) of KBr matrix, respectively. The linear range of the method (LR) as well as the LOD based on the concentration of sulfite in the solution are 5-500 and 0.8 microg/mL, respectively. The precision in terms of standard deviation and relative standard deviation value at a level of 100 ng of SO 3 (2-) 0.1 g (-1) of KBr for n = 10 are found to be 2 ng of SO 3 (2-) and 2.3%, respectively. The relative standard deviation ( n = 10) for the determination of sulfite in beverage samples available in the local market was observed to be in the range of 2.4-7.8%. The method is free from interionic effects of foreign species. No sample pretreatment is required in this method. The proposed method avoids the requirement of large numbers and bulk amounts of reagents. The method is well-suited to the need of green chemistry.

A highly stable and sensitive chemically modified screen-printed electrode for sulfide analysis

We report here a highly stable and sensitive chemically modified screen-printed carbon electrode (CMSPE) for sulfide analysis. The CMSPE was prepared by first ion-exchanging ferricyanide into a Tosflex anion-exchange polymer and then sealing with a tetraethyl orthosilicate sol-gel layer. The sol-gel overlayer coating was crucial to stabilize the electron mediator (i.e., Fe(CN)6(3-)) from leaching. The strong interaction between the oxy-hydroxy functional group of sol-gel and the hydrophilic sites of Tosflex makes the composite highly rigid to trap the ferricyanide mediator. An obvious electrocatalytic sulfide oxidation current signal at approximately 0.20 V versus Ag/AgCl in pH 7 phosphate buffer solution was observed at the CMSPE. A linear calibration plot over a wide range of 0.1 microM to 1mM with a slope of 5.6 nA/muM was obtained by flow injection analysis. The detection limit (S/N=3) was 8.9 nM (i.e., 25.6 ppt). Practical utility of the system was applied to the determination of sulfide trapped from cigarette smoke and sulfide content in hot spring water.