Pulsed Flame Photometric Detector Research Articles

Optimizing the identification of thiols in red wines using new oak-wood accelerated reductive treatment

This study proposes a new method for identifying thiols in red wines by mimicking specific chemical mechanisms that occur during bottle-aging. It involves the reaction of oak-wood extracts with hydrogen sulfide and the reduction of disulfides with DIBAL. After optimization of the reaction conditions, the aroma of fresh oak wood turned into intense “meaty” nuances reminiscent of the aging bouquet of red wines. Samples were analyzed by gas chromatography coupled with olfactometry (GC-O) and coupled with a pulsed flame photometric detector. This resulted in the identification of six odorant zones with meaty descriptors associated with sulfur compounds. One of the odorant zones was identified as 2-methoxybenzenethiol by using heart-cutting multidimensional GC coupled with olfactometry and time of flight mass spectrometer. Its identification in aged red wines was confirmed by GC coupled with tandem mass spectrometry analyses. Five other thiols associated with oak-wood precursors were also identified in red wines.

Efficient Oxidative Desulfurization of High-Sulfur Diesel via Peroxide Oxidation Using Citric, Pimelic, and α-Ketoglutaric Acids

The widespread use of diesel fuel for transportation, industry, and electricity generation causes several environmental issues via an increase in the amount of sulfur compound emissions. Commercial diesel fuel must be free of sulfur-containing compounds since they can cause several environmental problems. Considering the currently available processes to eliminate sulfur compounds, oxidative desulfurization (ODS) is one of the effective means for this purpose. This work presented a simple, low cost, and efficient ODS system of high-sulfur diesel fuels using peroxide oxidation with the aid of citric, pimelic, and α-ketoglutaric acids. The aim of the study was to investigate the potential of these acids as hydrogen peroxide (H2O2) activators for ODS and to optimize the reaction conditions for maximum sulfur removal. The results showed that citric, pimelic, and α-ketoglutaric acids were effective catalysts for the desulfurization of high-sulfur diesel with an initial sulfur content of 2568 mg L−1, achieving a sulfur removal efficiency of up to 95%. The optimized reaction conditions were found to be 0.6 g of carboxylic acid dosage and 10 mL of H2O2 at 95 °C. The desulfurization efficiency of the real diesel sample (2568 mg L−1) was shown to be 27, 34, and 84.57%, using citric acid, α-ketoglutaric acid, and pimelic acid after 1h, respectively. The effectiveness of the oxidation process was characterized by gas chromatographic pulsed flame photometric detector (GC-PFPD) and Fourier-transform infrared spectroscopy (FTIR) techniques. The experimental results demonstrated that the developed system exhibited high efficiency for desulfurization of real high-sulfur diesel fuels that could be a good alternative for commercial application with a promising desulfurization efficiency.

Determination of sarin and soman in industrial emissions by gas-chromatographic method using pulsating flame-photometric detector

Methods of gas chromatographic determination of trace amounts of sarin and soman in industrial emissions at a level of 1.0 × 10–6 mg/m3 have been developed. The capture and concentration of the target analyte was carried out using a specially designed sampling fluoroplastic cartridge filled with a pre-prepared sorbent Tenax TA with a grain size of 60/80 mesh and a volume of 8 cm3. The extraction of concentrated substances from the sampling cartridge was carried out using a modified and improved method of thermal desorption which consists in involving hot vapors of the solvent (resulted from the introduction of a liquid solvent into the cavity of the sampling cartridge with subsequent heating to 200°C) into desorption process in addition to the inert carrier gas. The substantially higher efficiency of the modified method of thermal desorption compared to the classical methods of extracting target substances from sorbents has been experimentally proved. Data on the quantitative content of sarin and soman were obtained by gas chromatographic method using a Varian CP-3800 gas chromatograph equipped with a pulsating flame-photometric detector, the mixture was separated on a VF-5ms capillary column. The sensitivity of a classical flame photometric detector and a pulsed flame photometric detector to sarin and soman has been studied. The developed methods have a relative error of determination about 27 %, and the duration of analysis of one sample is 3 h 30 min. The methods were tested on the real objects of control, appropriately certified and implemented in practice.

Identification and Categorization of Volatile Sulfur Flavor Compounds in Roasted Malts and Barley

We report for the first time the application of HS-SPME-GC coupled with sulfur-specific pulsed flame photometric detection to sensitively analyze the volatile sulfur compounds (VSC’s) present in drum roasted malt and barley samples typically used in brewing. Twenty-five VSC’s were identified across a range of 9 roasted products produced from barley/malt. Thiophenes (n = 10) were a major class of heterocyclic sulfur compounds identified, along with thiazoles (n = 4), and thiofurans (n = 2). Quantitative (n = 18) and semi-quantitative (n = 6) data are reported for VSC’s across this product range. Principal Component Analysis (PCA) of data clearly identified (PC1) that heterocyclic sulfur compounds were formed in products processed at high temperatures (>170 °C) under dry conditions (roasted barley, chocolate and black malts). Whereas compounds such as methyl dithiolane and methyl propyl sulfide were associated primarily with lower temperature finished products (crystal, amber and cara malts). Pathways for the generation of observed VSC’s are considered alongside typical roasting conditions employed in the manufacture of these products. Concentrations of VSC’s identified will certainly contribute characteristic aromas to the roasted products themselves. The transfer of VSC’s from the grist into finished beer, and their sensory impact in a range of beer styles, remains to be determined. Supplemental data for this article is available online at https://doi.org/10.1080/03610470.2021.2003669 .

Development and validation of a sampling and analysis method to determine biogenic sulfur in a desulfurization bioreactor by gas chromatography coupled with a pulsed flame photometric detector (GC-PFPD)

Suspended biomass bioreactors can be operated to remove H2S from biogas under anoxic conditions and produce elemental sulfur, the commercial value of which has been demonstrated. In the present paper, a novel methodology comprising the optimization of a determination method performed in a gas chromatograph equipped with a pulsed flame photometric detector (GC-PFPD), combined with a simple preparation based on filtration and extraction with toluene, is proposed. The injector temperature and carrier gas flow rate (QHe) values were optimized using a response surface methodology based on a face-centred composite central design. This optimization revealed that the optimum conditions were an injector temperature and carrier gas flow rate of 222 °C and 7 mL min−1, respectively. The chromatographic method shows an analysis time of 48 min, a detection limit of more than 5.9 mg L−1, a relative standard deviation of less than 3.71%, and a sulfur recovery percentage of more than 98%. These values provide excellent linearity and a reasonable concentration range (10–200 mg L−1). Finally, a measurement error of 4.45% was obtained when using the present method in a selectivity test.

Ecological and Human Health Risk Assessment of Pesticide Residues in Fish and Sediments from Vea Irrigation Reservoir

The low yield of food production ascribed to harm caused by pests has led to the application of pesticides to food crops. Pesticide residues from the application on crops are mostly found in foods that can cause diseases for consumers of such products. A total of 37 pesticide residues consisting of 15 organochlorines (OC), 13 organophosphorus (OP) and 9 synthetic pyrethroids (SP) were determined. The QuEChERS method was exploited for extraction and clean-up. Gas Chromatograph was used for detection and quantification which was equipped with an electron capture detector and pulse flame photometric detector. The results showed that the mean concentrations of pesticides in fish ranged from 0.007 mg·kg-1 to 1.026 mg·kg-1 for OCs, 0.002 mg·kg-1 to 0.190 mg·kg-1 for OPs and 0.004 mg·kg-1 to 0.032 mg·kg-1 for SP. Sediments have mean concentrations ranged from 0.005 mg·kg-1 to 1.207 mg·kg-1 for OCs. OP ranges from 0.002 mg·kg-1 to 0.399 mg·kg-1 and 0.003 mg·kg-1 to 0.202 mg·kg-1 for synthetic pyrethroids. Maximum Residue Limits were exceeded in both fish and sediment samples except for malathion, fenitrothion, profenofos, gamma-chlordane, and deltamethrin. Exposure in children ranged from 4.60 × 10-6 mg·kg-1·d-1 to 2.36 × 10-3 mg·kg-1·d-1 and in adults it is from 1.97 × 10-6 mg·kg-1·d-1 to 1.01 × 10-3 mg·kg-1·d-1. Health risk estimation revealed a non-cancer risk potential of β-HCH in sediment and aldrin and p,p'-DDE in fish. Carcinogenic risk assessed for organochlorine pesticide residues indicates cancer benchmark concentrations greater than 10-4 to 10-6 threshold for acceptance.

A multiresidue method for determining 136 pesticides and metabolites in fruits and vegetables: Application of macroporous diatomaceous earth column

A fast and easy multiresidue method using the macroporous diatomaceous earth (MDE) column for determining 136 pesticide an metabolite residues in fruits and vegetables was developed. The MDE column was used instead of the separation funnel for liquid/liquid partition in sample preparation. Through MDF columns, the preparation of test solution became easier and faster than traditional funnel liquid/liquid partition. The emulsion problem can also be avoided. Fifty one pesticides including acephate were determined by gas chromatography (GC) with a pulsed flame photometric detector (GC/PFPD) and 63 pesticides including aldrin were detected by GC with electron capture detection (GC/ ECD). Twenty carbamate peticides and metabolites including aldicarb were determined by high performance liquid chromatography with a post-column derivaization system and a fluorescence detector (HPLC/FLD) and two benzimidazole pesticides including carbendazim and thiabendazole were detected by HPLC with an ultraviolet detector (HPLC/UV). Recovery studies were performed by spiking pesticides (0.05-2.0 ppm) in fruit and vegetable samples, and the triplicate results showed satisfactory recoveries and repeatability. The detection limits ranged from 0.003 to 0.2 ppm. The developed multireside method can be employed to other pesticides or matrices with an easier and less solvent consumption way to prepare sample solution. It is an environment-friendly and useful method for routine pesticide analysis.

Methanethiol, an Off-Flavor Produced from the Thermal Treatment of Mandarin Juices: A Study of Citrus Sulfur Volatiles.

The off-flavor produced after thermal stabilization of mandarin (Citrus reticulata, Blanco) juices has limited the production of commercial juices. Methanethiol, a putrid-smelling sulfur volatile, has been identified for the first time in heated mandarin juices. Identification was achieved using a combination of capillary gas chromatography with two dissimilar columns and a dual sulfur-specific pulsed flame photometric detector and selected ion mass spectrometry detection. Static headspace solid-phase microextraction quantitation found that average odor activity values (OAVs) in heated juices were 25.5 for methanethiol compared to 10.8 for dimethyl sulfide. OAVs for methanethiol and dimethyl sulfide in fresh juices were ND (not detected) and 5.5, respectively. Hydrogen sulfide, carbonyl sulfide, carbon disulfide, and dimethyl disulfide were also identified and quantitated. Thermal decomposition studies of nonvolatile sulfur-containing potential precursors indicated that methionine was the major source of methanethiol. Additional heating studies with model juices demonstrated that ascorbic acid greatly accelerated the formation of methanethiol and methional, as well as dimethyl di and tri sulfides.

Occurrence of Ehrlich-Derived and Varietal Polyfunctional Thiols in Belgian White Wines Made from Chardonnay and Solaris Grapes.

Although almost disappeared at the end of the 20th century, Belgian wine production reached a million liters in 2017. The aim of the present work was to identify aroma markers for two white cultivars widespread in Belgium: Chardonnay (the most commercially grown cultivar worldwide) and Solaris (an interspecific fungus-resistant variety). Specific p-hydroxymercuribenzoic acid extraction followed by gas chromatography with a pulsed flame photometric detector was applied to single-varietal wine samples from 2015 to 2018 harvests. Among the Ehrlich-derived thiols, all found below their sensory thresholds, 3-sulfanylpropyl acetate usually outranged 3-sulfanylpropan-1-ol, while 2-sulfanylethan-1-ol concentrations always exceeded 2-sulfanylethyl acetate levels. The data confirm the occurrence, in both Chardonnay and Solaris wines, of 3-sulfanylhexan-1-ol and phenylmethanethiol (grapefruit and gunflint aroma, respectively), at concentrations far above their thresholds. This work also revealed, for the first time, the presence of 3-sulfanylheptan-1-ol, the branched alcohols 2-methyl-3-sulfanyl propan-1-ol, 2-methyl-3-sulfanylbutan-1-ol, and 3-sulfanyl-3-methylbutan-1-ol, and the carbonyls 3-sulfanylbutan-2-one (not in sparkling wines) and 3-sulfanylpentanal.

Effect of Ethanol on the Adsorption of Volatile Sulfur Compounds on Solid Phase Micro-Extraction Fiber Coatings and the Implication for Analysis in Wine

Complications in the analysis of volatile sulfur compounds (VSC) in wine using solid-phase microextraction (SPME) arise from sample variability. Constituents of the wine matrix, including ethanol, affect the volatility and adsorption of sulfur volatiles on SPME fiber coatings (Carboxen- polydimethylsiloxane(PDMS); DVB-Carboxen-PDMS and DVB-PDMS), which can impact sensitivity and accuracy. Here, several common wine sulfur volatiles, including hydrogen sulfide (H2S), methanethiol (MeSH), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS), methyl thioacetate (MeSOAc), and ethyl thioacetate (EtSOAc) are analyzed, using SPME followed by gas chromatography (GC), using a system equipped with a pulsed-flame photometric detection (PFPD) system, at various ethanol concentrations in a synthetic wine matrix. Ethyl methyl sulfide (EMS), diethyl sulfide (DES), methyl isopropyl sulfide (MIS), ethyl isopropyl sulfide (EIS), and diisopropyl disulfide (DIDS) are evaluated as internal standards. The absorption of volatile compounds on the SPME fiber is greatly affected by ethanol. All compounds exhibit a stark decrease in detectability with the addition of ethanol, especially between 0.0 and 0.5% v/v. However, the ratio of interested sulfur compounds to the internal standard becomes more stable when the total alcohol concentration exceeds 2%. EMS was found to best resemble DMS. EIS and DES were found to best resemble DMDS, MeSOAc, and EtSOAc. DIDS was found to best resemble DEDS, DMTS, H2S, and MeSH.

Effect of Wine Matrix Composition on the Quantification of Volatile Sulfur Compounds by Headspace Solid-Phase Microextraction-Gas Chromatography-Pulsed Flame Photometric Detection.

The analysis of volatile sulfur compounds using headspace solid-phase microextraction (HS-SPME) is heavily influenced by matrix effects. The effects of a wine matrix, both non-volatile and volatile components (other than ethanol) were studied on the analysis of several common sulfur volatiles found in wine, including hydrogen sulfide (H2S), methanethiol (MeSH), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS), methyl thioacetate (MeSOAc), and ethyl thioacetate (EtSOAc). Varying levels of devolatilized wine and common wine volatiles (acids, esters, alcohols) were added to synthetic wine samples to act as matrices. Sulfur standards were added and analyzed using gas chromatography with pulsed-flame photometric detection (GC-PFPD). Five internal standards were used to find best representatives of each compound despite matrix effects. Sensitivity remained stable with the addition of devolatilized wine, while addition of volatile components decreased sensitivity. DMS was found to be best measured against EMS; DMDS and the thioacetates were best measured against DES; H2S, MeSH, DEDS, and DMTS were best measured against DIDS. The method was used to quantitate the volatile sulfur compounds in 21 wines with various ethanol contents and volatile profiles.

Levels of tin and organotin compounds in human urine samples from Iowa, United States

Exposure to tin in the general US population is near ubiquitous, as determined using urinary tin levels measured by inductively coupled plasma mass spectrometry (ICP-MS). Urinary tin levels are associated with chronic health outcomes, such as diabetes; however, it is unclear if these associations are due to the presence of inorganic and organic forms of tin in urine. To address this knowledge gap, levels of total tin and several organotin compounds (OTCs) were measured in convenience urine samples from pregnant women and adults from Iowa, United States. Total tin and OTC levels in urine samples were quantified using ICP-MS and gas chromatography with pulsed flame photometric detection (GC-PFPD), respectively. ICP-MS detected tin in almost all urine samples from both study populations. Low levels of dibutyltin were detected in two out of fifty human urine samples. Importantly, storage of urine samples in plastic containers, but not HNO3-pretreated glass vials drastically reduced the recoveries of OTCs, in particular, tributyltin. Although their detection frequency is low, exposures to OTC should be considered when studying associations between human exposures to tin compounds and adverse health outcomes; however, urinary OTC levels measured in banked urine samples may not be suitable as biomarkers of OTC exposure.

Verification of <i>Aspergillus Niger</i> as a Myco-remediation Agent of Lambda-Cyhalothrin and Associated Heavy Metals in <i>Lactuca Sativa</i> (L.) Leaf

Pesticide residue constitutes a danger to soil micro and macro fauna and flora and to humans. This study assessed the impact of the application of Aspergillus niger as a pesticide remediating agent on Lambda-cyhalothrin and some of its associated heavy metals translocated to the leaves of Lactuca sativa . A Complete Randomized Design (CRD) experiment using three Treatments was conducted. Lambda-cyhalothrin was extracted from the Samples using the multiple residue technique and its residue determined using Gas Chromatography with Pulsed Flame Photometric Detector (PFPD). The associated heavy metals were determined using the Atomic Absorption Spectrophotometric method. Data so generated were means from five replicates, and were subjected to a one way analysis of variance - ANOVA with Tukey HSD Test for differences between means at 99% confidence interval (P≤0.01). The results show that the highest mean value of Lambda-cyhalotrhrin residue in L. sativa leaves was found in Treatment A (1.50 mg/kg), a value which was significantly higher (P≤0.01) than the residue found in Treatments B (1.0 mg/kg) and C(0.02 mg/kg). Mean Lambda-cyhalothrin residue in Treatment A alone was above the Maximum Residue Level (MRL) of 1.0 mg/kg in vegetable set in the legal EU regulation.The application of A. niger also precipitated a significant reduction (P≤0.01) in the level of all the heavy metals evaluated except Arsenic. All the heavy metals evaluated were however below the WHO/FAO safe limit. The result from this study posits A. niger as a promising mycoremediation agent of pesticide pollution.

Identification of Sulfur‐Containing Impurities in Biodiesel Produced From Brown Grease

AbstractFatty acid methyl esters (FAME) from waste grease usually contain higher concentrations of sulfur (S) than allowed to meet the specified quality standard for biodiesel (<15 ppm). Brown grease lipid‐derived FAME was produced and fractionated by two passes through a wiped‐film evaporator (WFE) to produce three fractions: (1) a 120 °C pass distillate, (2) a 170 °C pass distillate, and (3) a heavy residue. Solid phase extraction (SPE) was used to concentrate the S species from the distillate fractions so that they could be detected by a gas chromatography–pulsed flame photometric detector (GC–PFPD) and GC–mass spectrometry (MS). The ethyl acetate and methanol (MeOH) fractions obtained by SPE of the 120 °C WFE distillate and methyl tert‐butyl ether and acetone fractions obtained by SPE of the 170 °C WFE distillate had the highest concentration of S and were, therefore, the best candidates for GC–PFPD analysis. GC–PFPD methods were developed to separate the S species adequately enough for those peaks to be analyzed by GC–MS which matched fragmentation patterns identified by the MS chemical library as tetrahydrothiophenes, dithiolanes, and thiophenes. MS fragmentation patterns were used to identify other, larger, S‐bearing species as sulfides and disulfides cross‐linking between two FAME molecules. The results obtained from this study provide a foundation for developing effective purification methods to remove S‐containing impurities from waste grease‐derived biodiesel.

Determination of Aromatic Arsines in Environmental Solids by Direct Thermal Desorption Gas Chromatography

ABSTRACTTo quantify aromatic arsines in the environment, such as World War I era chemical warfare agents and degradation products of arsenicals used in agriculture, a sensitive, selective, and direct method is needed. We describe the development and optimization of a method for the measurement of trace levels of triphenylarsine used as a model aromatic arsenic compound. Triphenylarsine was determined at low µg/g levels in sand, soil, and lake sediment by thermal desorption before gas–liquid chromatography (GC) with mass spectrometric and pulsed flame photometric detection. The dithiol derivative of phenylarsonic acid was used as an internal standard, thereby significantly improving the precision of the method. The desorption conditions were studied and found to be optimal at 350°C for 15 min. Significant improvement in precision was realized by preparing the solid samples as slurries in acetone and by inserting a small (∼100 mg) quartz wool plug into the sample vial. The method was applied to determine triphenylarsine in authentic soil and sediment samples that had been fortified with triphenylarsine and aged for at least 15 days. Recoveries for soil samples ranged from 84.3 ± 2.3 to 87.7 ± 1.3%, while lower recoveries were obtained for sediment samples (75.1 ± 3.0%). The detection limit for triphenylarsine in soil was 3.14 ng with a precision of 7.10% (n = 4). Using these optimized conditions, the performance of the direct thermal desorption GC method for sample introduction was greatly improved compared to methods that have been reported in the literature.

English

This study investigates the impact of clarification process on the nutritional, mineral and vitamin composition of the cashew apple juice. The proximate composition in percentage for moisture, dry matter, ash, crude fibre, ether extract, crude protein and carbohydrate were determined in line with the recommended methods of Association of Official Analytical Chemist (AOAC), and vitamin profile was analysed using Gas Chromatography coupled with the Pulsed Flame Photometric Detector (GC-FPD). The mineral analysis also followed the recommendation of AOAC. The clarified cashew apple juice had values in mg/100 of 10.1, 6.1, 2.2, 28.8, 10.2 and 0.22 for calcium, magnesium, sodium, potassium, phosphorus and iron, respectively. The study showed that cashew apple juice is rich in nutrient and contains a good level of trace elements necessary for healthy living. Rice gruel as a natural sourced clarifying agent can better replace industrial clarification agents for a safer drink production. ords: Clarification process, nutritional composition, mineral composition, vitamin composition, cashew apple juice.

Headspace solid-phase microextraction and gas chromatographic analysis of low-molecular-weight sulfur volatiles with pulsed flame photometric detection and quantification by a stable isotope dilution assay.

Low-molecular-weight volatile sulfur compounds such as thiols, sulfides, disulfides as well as thioacetates cause a sulfidic off-flavor in wines even at low concentration levels. The proposed analytical method for quantification of these compounds in wine is based on headspace solid-phase microextraction, followed by gas chromatographic analysis with sulfur-specific detection using a pulsed flame photometric detector. Robust quantification was achieved via a stable isotope dilution assay using commercial and synthesized deuterated isotopic standards. The necessary chromatographic separation of analytes and isotopic standards benefits from the inverse isotope effect realized on an apolar polydimethylsiloxane stationary phase of increased film thickness. Interferences with sulfur-specific detection in wine caused by sulfur dioxide were minimized by addition of propanal. The method provides adequate validation data, with good repeatability and limits of detection and quantification. It suits the requirements of wine quality management, allowing the control of oenological treatments to counteract an eventual formation of excessively high concentration of such malodorous compounds.

Health risks due to consumption of pesticides in ready-to-eat vegetables (salads) in Kumasi, Ghana

BackgroundPesticide residue levels were determined in ready-to-eat vegetables collected from 16 sites along the food chain; which is, farms, markets, cafeterias and street food vending sites in Kumasi, Ghana. The aim of the study was to determine the concentrations of pesticides residues in two ready-to-eat vegetables and assess the health risks due to consumption of these contaminated vegetables.MethodsPesticide residues in ready-to-eat vegetables or salads were extracted by means of the QuEChERS method. Synthetic pyrethroid and organophosphorus pesticides residues in samples were determined using Gas Chromatography with Electron Capture Detector and Pulsed Flame Photometric Detector respectively. Consumption data of ready-to-eat vegetables were obtained from a questionnaire-based dietary survey in the study area. The hazard index and the relative potency factor (RPFs) approaches were used to assess the health risk from chronic cumulative dietary exposure to pesticides.ResultsThere were six synthetic pyrethroid residues detected in the ready-to-eat samples at varying concentrations. They were bifenthrin, permethrin, cypermethrin, deltamethrin, lambda-cyhalothrin and fenvalerate. Also, two organophosphates were detected in the samples; which were chlorpyrifos and diazinon. Lambda-cyhalothrin residues was present in all the samples in the study, with the mean concentration of 4.5 × 10−2 mgkg−1. The mean concentration of diazinon in all the samples (0.040 mgkg−1) exceeded the EU MRLs (0.01 mgkg−1), chlopyrifos exceeded its MRL in one sample from the street food vending site and cafeteria each. Deltamethrin, Fenvalerate and Permethrin exceeded their respective MRL in samples from Asafo (Street food vending sites) and Adum (Cafeteria) and KNUST (Farm) respectively. However, the health index of all pesticides residues detected were below the permissible limit. The cumulative intake from the RPF approach for the pesticides were relatively lower than the ADI of the index chemicals.ConclusionThe concentrations of chlorpyrifos, deltamethrin, fenvalerate, diazinon and permethrin exceeded their respective EU MRLs in some ready-to-eat vegetable samples in the study. The health index and comparison of cumulative intake from RPF with ADI of the index chemicals suggest that pesticide residues in ready-to-eat vegetables could not be considered a major public health problem.

Investigation of 2-Sulfanylethyl Acetate Cysteine-S-Conjugate as a Potential Precursor of Free Thiols in Beer

The compounds 2-sulfanylethyl acetate (2SEA, roasted- or burnt-like flavor) and 3-sulfanylpropyl acetate (also with roasted- or burnt-like flavor), mainly issued from the Ehrlich pathway (in this case, the catabolism by yeast of cysteine and homocysteine, leading to the formation of 2-sulfanylethan-1-ol and 2-sulfanylpropan-1-ol, which are subsequently acetylated), are found in all fresh beers, at levels strongly depending on the yeast strain used in fermentation. Yet, even in the absence of yeast, their production is still seen to occur in the bottle during the first months of storage. As for other thiols, S-cysteine adducts have been suspected to be hydrolyzed during beer aging. The commercially unavailable S-cysteine conjugate of 2SEA (Cys-2SEA, 93% purity), never described before in the literature, was synthesized by acetylation of the S-cysteine conjugate of 2-sulfanylethan-1-ol (Cys-2SEol). Cys-2SEA was solubilized in model aqueous media (pH 4.2) and in beer before aging. 2SEA was further extracted and analyzed by gas chromatography coupled to a pulsed flame photometric detector (GC-PFPD), and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI(+)-MS/MS) allowed us to quantify the undegraded Cys-2SEA (specific m/z ions at 120, 148, and 191). Cys-2SEA was shown to be relatively stable in both media, although some beer constituents were noted as being able to slightly facilitate the chemical degradation (molar conversion into free thiol up to 0.3% at room temperature). A modified “Strecker degradation” mechanism is proposed here, explaining the release of thiols from the Schiff bases created between the cysteine adducts and beer diketones. Up to now, tests have failed to reveal evidence for the presence of Cys-2SEol and Cys-2SEA in hops by direct HPLC-ESI(+)-MS/MS analyses, although 2SEol was released from cysteine-S-conjugate extracts in the presence of apotryptophanase.

Determination of organotin compounds in sediment samples by dispersive liquid-liquid microextraction followed by gas chromatography – Pulsed flame photometric detection (DLLME-GC-PFPD)

Dispersive liquid-liquid microextraction (DLLME) was evaluated for the simultaneous determination of butyl-, phenyl- and octyltin compounds in sediment samples. The most significant factors in DLLME procedure were type and volume of extraction and disperser solvents, and the optimal conditions were reached when 413 and 34μL of methanol and tetrachloroethylene, respectively, were used. Under optimal conditions, the limit of detection and the relative standard deviation ranged between 0.3 and 1.0ngL−1 and 2–6%, respectively. The developed method was validated for the analysis of a certified reference material and spiked seawater and marine sediment samples, with satisfactory results. Finally, harbor sediment samples collected from the Chilean coastal region were analyzed to demonstrate the applicability of the developed method in the determination of organotin compounds in the environment.