Determination of flavone C-glucosides in antioxidant of bamboo leaves (AOB) fortified foods by reversed-phase high-performance liquid chromatography with ultraviolet diode array detection

A sensitive solid-phase microextraction and gas chromatography-pulsed flame photometric detection technique was developed to quantify volatile sulfur compounds in wine. Eleven sulfur compounds, including hydrogen sulfide, methanethiol, ethanethiol, dimethyl sulfide, diethyl sulfide, methyl thioacetate, dimethyl disulfide, ethyl thioacetate, diethyl disulfide, dimethyl trisulfide and methionol, can be quantified simultaneously by employing three internal standards. Calibration curves were established in a synthetic wine, and linear correlation coefficients (R2) were greater than 0.99 for all target compounds. The quantification limits for most volatile sulfur compounds were 0.5 ppb or lower, except for methionol which had a detection limit of 60 ppb. The recovery was studied in synthetic wine as well as Pinot noir, Cabernet Sauvignon, Pinot Grigio, and Chardonnay wines. Although the sulfur compounds behaved differently depending on the wine matrix, recoveries of greater than 80% were achieved for all sulfur compounds. This technique was applied to analyze volatile sulfur compounds in several commercial wine samples; methionol concentrations were found at the ppm level, while the concentrations for hydrogen sulfide, methanethiol, and methyl thioacetate were at ppb levels. Only trace amounts of disulfides and trisulfides were detected, and ethanethiol was not detected.     

提高碘量法测定天然气中硫化氢效率的方法

碘量法是测定管道输送天然气中硫化氢的一种经典方法,而管道输送天然气中硫化氢含量较低,按照GB/T11060.1–2010方法测定,取样量较大,取样时间长,影响工作效率。针对此问题,从两方面对碘量法进行改进:减小天然气取样量进行试验,并与国标规定取样量时的实验结果进行比对,确定最佳取样量;增大取样流量进行试验,并与国标规定取样流量时的实验结果进行比对,确定最佳取样流量。对硫化氢质量浓度为7.2~14.3,14.3~28.7 mg/m~3的天然气样品进行试验测定,结果表明,将天然气取样量减少为20 L,取样时间分别由200,100 min缩短为40 min;将天然气取样流量设定为750 m L/min,取样时间分别由200,100 min缩短为133,67 min。减少取样量或者提高取样流量,均能缩短管输天然气的取样时间,提高检测效率。     

GC–MS Analysis of Hydrogen Sulfide,Carbonyl Sulfide,Methanethiol, Carbon Disulfide,Methyl Thiocyanate and Methyl Disulfide in Mainstream Vapor Phase Cigarette Smoke

A method is described for the simultaneous analysis of hydrogen sulfide, carbonyl sulfide, methanethiol, carbon disulfide, methyl thiocyanate and methyl disulfide in mainstream vapor phase (MVP) cigarette smoke by gas chromatography–mass spectrometry. The fresh MVP smoke was collected in a gas bag, followed by injection of a 50 μL gas sample into the GC inlet via an automatic six-port valve. The separation was on a CP-PoraPLOT Q column and MS was operated in SIM mode. It was found that while carbonyl sulfide and carbon disulfide are very stable in the gas bag, hydrogen sulfide, methanethiol, methyl disulfide and methyl thiocyanate are extremely reactive and their levels increase or decrease drastically with the storage time in the gas bag. These results suggest that there is an absolute need to analyze the smoke sample as quickly as possible. Maintaining a precise time after the smoke collection is a key factor in order to obtain reproducible results. In this study, all the samples are injected within 2 min after MVP smoke was collected in the bag. Under smoke conditions of 60 mL puff of 2 s duration every 30 s, 12 brands of commercial cigarettes and Kentucky Reference 2R4F cigarettes were analyzed. Average values of three replicates of the 2R4F cigarettes were 31.6 μg cigt^?1 hydrogen sulfide, 40.7 μg cigt^?1 carbonyl sulfide, 25.6 μg cigt^?1 methanethiol, 2.2 μg cigt^?1 carbon disulfide, 23.7 μg cigt^?1 methyl thiocyanate and 17.6 μg cigt^?1 methyl disulfide. All other types of analyzed cigarettes show a similar quantitative distribution for these analytes.     

Trace determination of volatile sulfur compounds by solid-phase microextraction and GC-MS

A method was developed for the simultaneous determination of the following nine volatile sulfur compounds in gas samples: carbon disulfide, carbonyl sulfide, ethyl sulfide, ethyl methyl sulfide, hydrogen sulfide, isopropanethiol, methanethiol, methyl disulfide and methyl sulfide. The target compounds were preconcentrated by solid-phase microextraction (SPME) and determined by gas chromatography combined with mass spectrometry. Experimental design was employed to optimize the extraction time and temperature and concurrent detection of the nine compounds was achieved by using an SPME fiber coated with Carboxen-polydimethylsiloxane (75 microns). Detection limits ranged from 1 ppt (v/v) for carbon disulfide to 350 ppt (v/v) for hydrogen sulfide and calibration functions were linear up to 20 ppb (v/v) for all the compounds investigated.     

Determination of Sulfur Compounds in Air by Chemiluminescence

Abstract

The present review is devoted to applications of chemiluminescence to the analysis of trace sulfur species in air. Determinations of oxidized (sulfur dioxide and sulfite), reduced (hydrogen sulfide, dimethyl sulfide, carbonyl sulfide, carbon disulfide and mercaptans) and/or sulfur compounds in general are described and some practical considerations are discussed. The development of detectors based on chemiluminescence in the aproximately last fifteen years is also reviewed.     

Determination of Sulfur in Trace Amounts

Abstract

An absolute method for the determination of trace amounts of sulfur in water and organic matrices is described. The method involves decomposition of organic samples in an oxygen bomb or oxidation of water samples with hydrogen peroxide. The resultant sulfates are reduced and distilled as hydrogen sulfide by the action of stannous phosphate in anhydrous phosphoric acid. The evolved hydrogen sulfide is absorbed in zinc acetate solution, converted to methylene blue and measured spectrophotometrically at 665 mm. The range is from 2 to 40 μg of sulfur using 1 cm cells.     

The fundamental properties of the direct injection method in the analysis of gaseous reduced sulfur by gas chromatography with a pulsed flame photometric detector

In this study, the fundamental aspects of gas chromatography with a pulsed flame photometric detector were investigated through the calibration of gaseous reduced sulfur compounds based on the direct injection method. Gaseous standards of five reduced sulfur compounds (hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide) were calibrated as a function of injection volume and concentration level. The results were evaluated by means of two contrasting calibration approaches: fixed standard concentration method (variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (injection of multiple standards with varying concentrations at a given volume). The optimum detection limit values of reduced sulfur compounds, when estimated at 100 μL of injection volume, ranged from 2.37 pg (carbon disulfide) to 4.89 pg (dimethyl sulfide). Although these detection limit values improved gradually with decreasing injection volume, the minimum detectable concentration (e.g., in nmol mol⁻¹ scale) remained constant due to a balance by the sample volume reduction. The linearity property of pulsed flame photometric detector also appeared to vary dynamically with changes in its sensitivity. According to this study, the performance of pulsed flame photometric detector, when tested by direct injection method, is highly reliable to precisely describe the behavior of reduced sulfur compounds above ∼20 nmol mol⁻¹.     

Conversion of dimethyl disulfide in the presence of zeolites

Dimethyl disulfide conversion in the presence of zeolites was studied at atmospheric pressure and T = 190–350°C. For all catalysts, the products of the reaction at T = 190°C—methanethiol, dimethyl sulfide, and hydrogen sulfide—result directly from dimethyl disulfide. The relative reaction rate and the dimethyl sulfide selectivity decreases in the order HZSM-5 ≥ CoHZSM-5 > HNaY > NaX, NaY. The methanethiol formation selectivity changes in the reverse order. The highest methanethiol selectivity at T = 190°C is shown by the sodium zeolites; the highest dimethyl sulfide selectivity, by the high-silicz zeolite HZSM-5. Raising the reaction temperature increases the reaction rate and changes the process route: at high temperatures, dimethyl disulfide decomposes to methanethiol, which then condenses to yield dimethyl sulfide and hydrogen sulfide. The observed regularities are explained in terms of the different acidic properties of the zeolite surfaces.     

DEHYDROCHLORINATION OF α-CHLORO SULFONES WITH KOH-T-BUOH: KINETIC VS EQUILIBRIUM CONTROL OF THE FORMATION OF α, β-UNSATURATED SULFONES AND THE β-T-BUTOXY AND β-HYDROXY MICHAEL ADDUCTS

Abstract

Inorganic sulfur compounds are used by microorganisms (bacteria, fungi, algae) and plants for assimilation, i.e. biosynthesis of sulfur-containing cell constituents.

Quantitatively, within the biogeochemical cycle of sulfur the utilization of inorganic sulfur compounds in bacterial energy metabolism, i.e. dissimilatory sulfur utilization, is of far higher importance. Reduced sulfur compounds serve as electron donors for photosynthesis and respiration, whereas inorganic sulfur compounds of oxidation levels above sulfide serve as electron donors in anaerobic respiration as well as in fermentation. In still other bacteria reduced sulfur compounds act as protective agents against hydrogen peroxide.     

Development of novel and sensitive methods for the determination of sulfide in aqueous samples by hydrogen sulfide generation-inductively coupled plasma-atomic emission spectroscopy

Two new, simple and accurate methods for the determination of sulfide (S²⁻) at low levels (μg L⁻¹) in aqueous samples were developed. The generation of hydrogen sulfide (H₂S) took place in a coil where sulfide reacted with hydrochloric acid. The resulting H₂S was then introduced as a vapor into an inductively coupled plasma-atomic emission spectrometer (ICP-AES) and sulfur emission intensity was measured at 180.669 nm. In comparison to when aqueous sulfide was introduced, the introduction of sulfur as H₂S enhanced the sulfur signal emission. By setting a gas separator at the end of the reaction coil, reduced sulfur species in the form of H₂S were removed from the water matrix, thus, interferences could be avoided. Alternatively, the gas separator was replaced by a nebulizer/spray chamber combination to introduce the sample matrix and reagents into the plasma. This methodology allowed the determination of both sulfide and sulfate in aqueous samples. For both methods the linear response was found to range from 5 μg L⁻¹ to 25 mg L⁻¹ of sulfide. Detection limits of 5 μg L⁻¹ and 6 μg L⁻¹ were obtained with and without the gas separator, respectively. These new methods were evaluated by comparison to the standard potentiometric method and were successfully applied to the analysis of reduced sulfur species in environmental waters.     

The properties of calibration errors in the analysis of reduced sulfur compounds by the combination of a loop injection system and gas chromatography with pulsed flame photometric detection

In order to evaluate the extent of analytical biases involved in the GC calibration, we conducted a series of experiments to examine the calibration methods of trace gas components. For the purpose of this comparative study, gaseous standards of reduced sulfur compounds (RSC) including hydrogen sulfide (H₂S), methanethiol (CH₃SH), dimethyl sulfide (DMS), carbon disulfide (CS₂), and dimethyl disulfide (DMDS) were calibrated by the combination of a GC/PFPD technique and a loop-injection method. In the course of this study, two different types of calibration methods were tested and compared: incremental-injection of a given standard with the fixed standard concentration (FSC) versus injection of multiple standards (with different concentrations) at the fixed standard volume (FSV). In the case of the FSV calibration, a notable increase in the GC sensitivity is apparent with decreasing loop size (or injection volume). For instance, the calibration slope for RSC obtained using a 10 μl loop system was approximately three times higher than that for a 250 μl one. However, the results obtained by the FSC method exhibit much poorer sensitivity than its counterpart with slight differences in their sensitivities across different standard concentrations (due to such factors as the matrix effect from varying injection volumes). Thus, the overall results of this study confirm that the detailed characterization of the selected calibration method (e.g., the use of FSV approach relative to FSC) is of primary significance to perform an accurate quantification of trace gases.     

The Photochemistry of Diazomethane-Hydrogen Sulfide Mixtures. The Decomposition Rate of Chemically Activated Methanethiol

The photochemistry of diazomethane in presence of hydrogen sulfide gas has been studied at 4358 and 3660-Å. Singlet methylene radicals react with hydrogen sulfide to from methanethiol which decomposes at lower pressures. The measured decomposition rate constants are 5.5×10¹⁰ and 9.6×10¹⁰ s^?1 in 4358 and 3660-Å systems, respectively. Singlet methylene inserts into a S-H bond as 200 times fast as into a C-H bond.     

Activity of cobalt sulfide catalysts in the hydrogenolysis of dimethyl disulfide to methanethiol: Effects of the nature of a support and the procedure of supporting a cobalt precursor

The conversion of dimethyl disulfide to methanethiol on various catalysts containing supported cobalt sulfide in an atmosphere of hydrogen was studied at atmospheric pressure and T = 190°C. On CoS introduced into the channels of zeolite HSZM-5, the process occurred at a high rate but with a low selectivity for methanethiol because the proton centers of the support participated in a side reaction with the formation of dimethyl sulfide and hydrogen sulfide. Under the action of sulfide catalysts supported onto a carbon support, aluminum oxide, silicon dioxide, and an amorphous aluminosilicate, the decomposition of dimethyl disulfide to methanethiol occurred with 95–100% selectivity. The CoS/Al₂O₃ catalysts were found to be most efficient. The specific activity of alumina-cobalt sulfide catalysts only slightly depended on the phase composition and specific surface area of Al₂O₃. The conditions of the thermal treatment and sulfurization of catalysts and, particularly, the procedure of supporting a cobalt precursor onto the support were of key importance. Catalysts prepared through the stage of supporting nanodispersed cobalt hydroxide were much more active than the catalysts based on supported cobalt salts.     

Low-temperature catalytic decomposition of hydrogen sulfide into hydrogen and diatomic gaseous sulfur

The thermodynamics of three pathways of the hydrogen sulfide decomposition reaction is considered. In the thermal process, the gas-phase dissociation of hydrogen sulfide yields hydrogen and diatomic singlet sulfur. Over sulfide catalysts, the reaction proceeds via the formation of disulfane (H₂S₂) as the key surface intermediate. This intermediate then decomposes to release hydrogen into the gas phase, and adsorbed singlet sulfur recombines into cyclooctasulfur. Over metal catalysts, H₂S decomposes via dissociation into surface atoms followed by the formation of gaseous hydrogen and gaseous triplet disulfur. The last two pathways are thermodynamically forbidden in the gas phase and can take place at room temperature only on the surface of a catalyst. An alternative mechanism is suggested for hydrogen sulfide assimilation in the chemosynthesis process involving sulfur bacteria. To shift the hydrogen sulfide decomposition equilibrium toward the target product (hydrogen), it is suggested that the reaction should be conducted at room temperature as a three-phase process over a solid catalyst under a layer of a solvent that can dissolve hydrogen sulfide and sulfur. In this case, it is possible to attain an H₂S conversion close to 100%. Therefore, hydrogen sulfide can be considered as an inexhaustible source of hydrogen, a valuable chemical and an environmentally friendly energetic product.     

Density Functional Investigation of Methanethiol and Dimethyl Sulfide Adsorption on Zeolite

The density functional theory and cluster model methods have been employed to investigate the interactions between methanethiol, dimethyl sulfide and zeolites. The molecular complexes formed by adsorption of methanethiol or dimethyl sulfide on silanol H3SiOSi(OH)2OSiH3 with five coordination forms or four coordination forms, and complexes formed by interactions of Bronsted acid sites of bridging hydroxyl H3Si(OH)Al(OH)2OSiH3 with methanethiol or dimethyl sulfide have been investigated. Full optimization and frequency analysis of all cluster models have been carried out using the B3LYP hybrid method at 6-31 G (d,p) basis set level for hydrogen, silicon, aluminum, oxygen, carbon, and sulfur atoms. The structures and energy changes of different coordination forms between methanethiol and H3Si(OH)Al(OH)2OSiH3, dimethyl sulfide and H3Si(OH)Al(OH)2OSiH3, methanethiol and H3SiOSi(OH)2OSiH3, dimethyl sulfide and H3SiOSi(OH)2OSiH3 complexes have been comparatively studied. The calculated results showed the nature of interactions that led to the formation of all complexes was van der Waals force confirmed by an insignificant change of geometric structures and properties. The conclusions that methanethiol and dimethyl sulfide molecules were adsorbed on bridging hydroxyl group prior to silanol group were obtained on the basis of adsorption heat, the most stable adsorption models of a 6 ring structure for interaction between bridging hydroxyl and methanethiol, and a 7 ring structure for interaction between bridging hydroxyl and dimethyl sulfide.     

Decomposition of Gaseous Sulfide Compounds in Air by Pulsed Corona Discharge

The effectiveness of applying a pulsed corona discharge to the destruction of olfactory pollution in air was investigated. This paper presents a comparative study of the decomposition of three representative sulfide compounds in diluted concentrations: hydrogen sulfide (H₂S), dimethyl sulfide (DMS), and ethanethiol (C₂H₅SH), which could be completely removed when a sufficient but reasonable energy density was deposited in the gas. DMS showed the lowest energy cost (around 30 eV/molecules); C₂H₅SH and H₂S had an EC of respectively 45 eV and 115 eV. The efficiency of the non-thermal plasma process increased with decreasing the initial concentration of sulfide compounds, while the energy yield remained almost unchanged. SO₂ was the only identified byproduct of H₂S decomposition, but the sulfur balance suggests the formation of undetected SO₃. The byproducts analyzed during the degradation of DMS and C₂H₅SH enabled to propose a reaction mechanism, starting with radical attack and breaking of C–S bonds.     

Volatile sulfur compounds in Cheddar cheese determined by headspace solid-phase microextraction and gas chromatograph-pulsed flame photometric detection

The aim of this study was to develop a methodology for the analysis of volatile sulfur compounds (VSCs) in Cheddar cheese. Solid-phase microextraction (SPME) was employed to extract VSCs from the cheese matrix using a CAR-PDMS fiber. This extraction method was combined with gas chromatography-pulsed flame photometric detection (GC-PFPD) to achieve high sensitivity for sulfur compounds. The impact of extraction parameters, including time, temperature and sample size, was evaluated to determine the best conditions to analyze sulfur compounds in Cheddar cheese. Hydrogen sulfide, methanethiol, and dimethyl sulfide were found to constitute the majority of the overall sulfur profile while dimethyl disulfide and dimethyl trisulfide were present in lesser amounts. Artifact formation of volatile sulfur compounds was found to be minimal. Two commercial cheese samples were analyzed and differences in sulfur content were observed. Overall, SPME-GC-PFPD was found to be a highly sensitive technique for the analysis of sulfur compounds in Cheddar cheese.     

Dimethyl disulfide catalytic conversion into methanethiol in the presence of water

The processes of dimethyl disulfide conversion yielding methanethiol, ethylene and hydrogen sulfide, and the disproportionation of methanethiol formed in this reaction into hydrogen sulfide and dimethyl sulfide proceed on acid-base type catalysts at 350°C in the presence of water. Catalysts with weak proton sites exhibit low activity, which increases with the increasing surface acidity. Catalysts with weak Lewis acid sites and strong basic sites are most active and selective in the reaction of methanethiol formation. The presence of water inhibits the side reaction of disproportionation, thus enhancing the methanethiol formation selectivity. V. N. Yakovleva and L. G. Sakhaltueva participated in the experimental part of this work.     

Activity of catalysts in the synthesis of dimethyl sulfide from dimethyl disulfide

Dimethyl disulfide conversion at T = 190–350°C over catalysts containing acid and basic sites is reported. The products of this reaction are dimethyl sulfide, methanethiol, hydrogen sulfide, carbon disulfide, methane, and ethylene. At 190°C, these products form via parallel reactions. At higher temperature of up to 350°C, dimethyl sulfide can form by the condensation of the resulting methanethiol. The strong basic sites of the catalysts are uninvolved in dimethyl sulfide formation. Over catalysts whose surface has only strong protonic or strong Lewis acid sites, dimethyl sulfide formation does take place, but slowly and nonselectively. The highest dimethyl sulfide formation activity and selectivity are shown by catalysts having medium-strength basic sites along with strong protonic and strong Lewis acid sites.     

High-efficiency process for production of sulfur from metallurgical sulfur dioxide gases

Process in which sulfur is produced from a gas containing 25–55% SO₂ was studied in order to evaluate the real efficiency of the catalytic post-reduction of sulfur dioxide in a pilot unit with gas flow rate of up to 1.2 nm³ h^–1 at the following temperatures (°C): thermal stage 850–1100, catalytic conversion 350–570, and Claus reactor 219–279. It was found that the conversion at 400–550°C and space velocity of 1600 h^–1 on AOK-78-57 promoted aluminum oxide catalyst provides full processing of organosulfur compounds (CS₂ and COS). The temperature dependence of the conversion/generation of hydrogen sulfide on AOK-78-57 catalyst corresponds to the equilibrium model. It was experimentally confirmed that the homogeneous reduction of sulfur dioxide gas with methane at T ≈ 1100°C, with catalytic post-reduction at 400–550°C and subsequent Claus-conversion of the reduced gas at 230–260°C, provide a sufficiently deep (by 92–95%) general processing of sulfur dioxide gas to sulfur.