Production Ganoderma lucidum extract nanoparticles by expansion of supercritical fluid solution and evaluation of the antioxidant ability.

Due to the growing human tendency to treat with natural substances, fungi such as Ganoderma lucidum can be a good source to meet this need. Effectiveness, ease of use and a rich source of active ingredients such as ganoderic acids have caused G. lucidum to be considered in the pharmaceutical and food industries. In this project, G. lucidum was applied to extraction using supercritical carbon dioxide. Then expansion of supercritical fluid solution (ESS) was used as, novel, repeatable and green method to yield nanoparticles from G.lucidum extract. The response surface method was used to improve the Extraction efficiency, antioxidant activity, and improving the nanoparticles production status. Optimal conditions were observed at the extraction step by setting pressure at 27.5 MPa, dynamic time of 46 min, and modifier volume of 162 µL. The optimum point for the production of nanoparticles was obtained as follows: pressure drop at 25 MPa, 20 min for collection time, and 40° C for temperature. Under these conditions, the size and count were 86.13 nm, and 98, respectively. Nanoparticles were analyzed by FESM and, the DPPH was used for antioxidant activity evaluation. The LC-MS identified various ganoderic acids from G.lucidum that are famous to be highly oxygenated triterpenoids.

Micronization of Thebaine Extracted from Papaver bracteatum Lindl. Using Supercritical Fluid Technology.

BACKGROUND: Thebaine, as a main opiate alkaloid extracted from Papaveraceae plants, is widely used in the synthesis of many pharmaceutical ingredients such as buprenorphine, naltrexone, naloxone, and hydrocodone. Nevertheless, thebaine and related derivatives are often insoluble in aqueous media and have low bioavailability in digestive systems. OBJECTIVE: Reducing particle size and changing the morphology can mitigate the mentioned problem. In this study, extraction of thebaine from the capsule, stem, and root of Papaver bracteatum L. was optimized and micronization of extract components was developed to study solubility. METHODS: The extraction process was performed using supercritical carbon dioxide. Experimental central composite design was employed to determine the optimal conditions. Analysis of extract was done using a validated high performance liquid chromatography method and mass spectrometry. The micronization process was performed using an inhouse developed supercritical technique. The nanoparticles were characterized using field emission scanning electron microscopy (FESEM) and ImageJ software. The effect of micronization was explored on the solubility of extract components via ultraviolet spectroscopy. RESULTS: The percentage of thebaine in dried capsule, stem, and root powder was about 1.05, 0.31, and 0.83% respectively. The extraction results indicate that supercritical pressure has the greatest effect on the extraction yield. Analysis of FESEM images revealed that nanoparticles of extract components with particle size distribution of 5-100 nm were collected successfully. CONCLUSION: The extraction results indicate that pressure has the greatest effect on the extraction yield. In vitro studies illustrated that the solubility of extract components increased up to 1.7 times during the micronization process. HIGHLIGHTS: Expansion of supercritical methods as an effective method was performed for extracting and preparing alkaloid nanoparticles. This process led to improved oral bioavailability of alkaloids.

Development of a bimetal-organic framework-polypyrrole composite as a novel fiber coating for direct immersion solid phase microextraction in situ supercritical fluid extraction coupled with gas chromatography for simultaneous determination of furfurals in dates.

A new, simple, hyphenated technique couples supercritical fluid extraction and direct immersion SPME with GC-FID (SFE-DI-SPME-GC-FID) for the determination of 2-furaldehyde (2-F) and 5-hydroxymethylfurfural (5-HMF) in solid foods. A bimetal-organic framework-polypyrrole composite was grown in situ on stainless steel wire in solution and used as a novel solid phase microextraction (SPME) fiber coating. A central composite design based on a 2n-1 fractional factorial experimental design was employed to optimize the SFE conditions for 2-F and 5-HMF at a pressure of 325 atm, temperature of 35 °C, dynamic extraction time of 15 min, and modifier volume of 150 µL. Also, the factors related to the solid-phase microextraction method including ionic strength, desorption time and temperature together with extraction time and temperature were optimized prior to the gas chromatography analysis. Under the optimal conditions, the limits of detection were in the range of 1.28-5.92 µg kg-1. This method showed good linearity for 2-F and 5-HMF in the ranges of 40-50 000 and 4540-500 000 µg kg-1, respectively, with coefficients of determination more than 0.9995. Single fiber repeatability and fiber-to-fiber reproducibility were less than 6.76% and 9.12%, respectively. The new method was successfully utilized to determine the amounts of 2-F and 5-HMF in the real solid food matrix without the need for tedious pretreatments.

Simultaneous extraction and fractionation of petroleum biomarkers from tar balls and crude oils using a two-step sequential supercritical fluid extraction.

In this study a novel sustainable method based on supercritical fluid extraction (SFE) method was developed for simultaneous extraction and fractionation of petroleum biomarkers. We herein proposed a two-step supercritical fluid extraction method for crude oil and tar ball to separate the petroleum biomarkers into aliphatic and aromatic fractions. In the first step, pure scCO2 was used, while scCO2 modified was used as a solvent in the subsequent step. CO2 SFE can serve as an environmental-friendly alternative to common column chromatography method for petroleum biomarker or compositional analysis by GC-MS. The extraction process was shown to be selective, according to the polarity of the solvent, providing fractionation of aliphatic and aromatic hydrocarbons. Yet the total extraction procedure in SFE was significantly faster than column chromatography methods (~80 min vs. 8 h). We will discuss the implications of this SFE method as a novel sustainable alternative to the existing extraction techniques.

Preparation of Withaferin A nanoparticles extracted from Withania somnifera by the expansion of supercritical fluid solution.

INTRODUCTION: Withania somnifera (L.) Dunal. is a plant with several important medicinal properties that have long been used in traditional therapy to treat some diseases. OBJECTIVE: Micronisation reduces the particle size, which increases the bioavailability. In this study, due to the great potential of Withaferin A in the treatment of diseases, the nanoparticle formation of Withaferin A extracted from Withania somnifera, was considered. METHODOLOGY: In the first step, the experimental parameters of supercritical fluid extraction of W. somnifera were optimised by central composite design (CCD). Then, the herbal extract was micronised using a new, repeatable, and robust method in terms of the expansion of carbon dioxide supercritical solvent. Also, the parameters of the experiment were optimised with the Draper-Lin small composite designs. Moreover, we identified Withaferin A nanoparticle in the extracted samples by utilising liquid chromatography-mass spectrometry (LC-MS) and the obtained precipitates were characterised using field emission scanning electron microscopy (FESEM). RESULTS: The optimal conditions of the experiment were as follows: pressure drop 254 atm, at the temperature of 53°C, equilibrium time 23 min, and collection time 57 min. Based on the observed results, the optimum points for the size and number of Withaferin A nanoparticles were predicted as 5 and 5842 nm, respectively. CONCLUSION: The nanoparticle production was accomplished through the expansion of supercritical solution, while the speed of expansion was much lower compared to the ordinary rapid expansion of supercritical solution (RESS) methods. Also, the nanonisation conditions, especially the pressure drop, significantly affected the formation of nanoparticles.

Supercritical fluid extraction followed by supramolecular solvent microextraction as a fast and efficient preconcentration method for determination of polycyclic aromatic hydrocarbons in apple peels.

In this work, reverse micelle-based supramolecular solvent microextraction method coupled with supercritical fluid extraction and used for determining trace amounts of polycyclic aromatic hydrocarbons in apple peels. The extract was analyzed by high-performance liquid chromatography equipped with a fluorescence detector. Coupling supramolecular solvent microextraction with supercritical fluid extraction method, resolve low preconcentration factor of supercritical fluid extraction method, improved limit of detection of polycyclic aromatic hydrocarbons and allow the use of supramolecular solvent microextraction in solid matrices. The effective parameters on the supramolecular solvent microextraction and supercritical fluid extraction efficiency were optimized using one variable at a time and face centered design methods, respectively. Under the optimum condition, the limits of detection and limits of quantifications were in the range of 0.34-1.27 and 1.03-3.82 µg/kg, respectively. Analysis of polycyclic aromatic hydrocarbons in apple peels showed that the supercritical fluid extraction/ supramolecular solvent microextraction method provide great potential for trace analysis of polycyclic aromatic hydrocarbons in fruit samples (RSDs < 7.7%).

Preparation of Curcuma Longa L. Extract Nanoparticles Using Supercritical Solution Expansion.

Nanoparticles of Curcuma longa Linn (turmeric) rhizome extract were prepared using supercritical carbon dioxide (SC-CO2). The SC-CO2 was used for sample pre-treatment, including lipophilic compounds removal and extraction, as well as particle production. The particle formation process was based on the expansion of supercritical solution of plant extract into a secondary chamber. In the course of the expansion of supercritical solution process, the herbal extract changed from dissolved mode at higher pressures to precipitated mode at lower pressures, as long as the pressures were higher than the critical pressure. The particle growth via coagulation was limited by a large number of unsuccessful collisions between CO2 molecules and primary nuclei due to the presence of pressurized CO2 molecules where the particle formation occurs. The presence of curcumin derivatives in nanoparticles was confirmed by liquid chromatography-mass spectrometry results. Irregular to quasi-spherical particles with average diameter of 47 ± 20 nm (n = 300) were prepared at a pre-expansion pressure of 35 MPa, pressure drop of 24 MPa, temperature of 50°C, equilibration time of 30 min, collection time of 60 min, extract volume of 30 µL, and feeding solution concentration of 2 mg mL-1.

Low-voltage electrochemically stimulated stir membrane liquid-liquid microextraction as a novel technique for the determination of methadone.

In the present work, for the first time, a new portable setup was designed, developed and presented for the extraction of methadone, as a basic drug model from biological fluid samples using a low-voltage electrically stimulated stir membrane liquid-liquid microextraction technique (LV-ESSM-LLME), followed by high-performance liquid chromatography with ultraviolet detection. This new approach combines the advantages of stir membrane liquid-liquid microextraction and electrokinetic migration in the same unit under soft electrochemical conditions in a portable device, allowing for the isolation and preconcentration of the target analyte in a simple and efficient manner under three-phase mode. To investigate the influence of external stirring and the application of electrical potential as the driving force, a comparative study of all variables involved in the extraction process was carried out using the low-voltage electromembrane extraction (LV-EME) and LV-ESSM-LLME methods. Under soft electrokinetic migration conditions, methadone was transported from an acidic sample solution (pH 4.0), through the NPOE immobilized in the pores of the porous polypropylene sheet membrane, and into 25µL of 10mmolL-1 HCl acceptor solution with a stirring rate of 1000rpm and 700rpm after 15min and 20min for LV-ESSM-LLME and LV-EME, respectively. Under the optimized conditions, preconcentration factors in the range of 17-24 and 21.5-29 for LV-EME and LV-ESSM-LLME, respectively, were considered, and satisfactory repeatability (4.5<[RSD]<7.5) was obtained in different matrices. The obtained relative recoveries of the target analyte were in the range of 87-94% and 93-101% for LV-EME and LV-ESSM-LLME, respectively, which indicated the excellent capability of the developed methods to extract methadone from complex matrices.

Application of response surface methodology for the optimization of supercritical fluid extraction of essential oil from pomegranate (Punica granatum L.) peel.

Essential oils and volatile components of pomegranate (Punica granatum L.) peel of the Malas variety from Meybod, Iran, were extracted using supercritical fluid extraction (SFE) and hydro-distillation methods. The experimental parameters of SFE that is pressure, temperature, extraction time, and modifier (methanol) volume were optimized using a central composite design after a (24-1) fractional factorial design. Detailed chemical composition of the essential oils and volatile components obtained by hydro-distillation and optimum condition of the supercritical CO2 extraction were analyzed by GC-MS, and seventy-three and forty-six compounds were identified according to their retention indices and mass spectra, respectively. The optimum SFE conditions were 350 atm pressure, 55 °C temperature, 30 min extraction time, and 150 µL methanol. Results showed that oleic acid, palmitic acid and (-)-Borneol were major compounds in both extracts. The optimum extraction yield was 1.18 % (w/w) for SFE and 0.21 % (v/w) for hydro-distillation.

Optimization of supercritical fluid extraction of essential oils and fatty acids from flixweed (Descurainia Sophia L.) seed using response surface methodology and central composite design.

Essential oils and fatty acids of Descurainia sophia L. seed were obtained by supercritical CO2 extraction and steam distillation methods. The effect of different parameters such as pressure, temperature, modifier volume, dynamic and static extraction timeon the extraction yield were optimized using a central composite design after a 2 (n-1) fractional factorial design. The results showed that under the pressure of 355 bar, temperature of 65 °C, methanol volume of 150 µL, dynamic and static extraction times of 35 and 10 min, respectively, the major components were methyl linoleate (18.2 %), camphor (12.32 %), cis-thujone (11.3 %) and trans-caryophyllene (9.17 %). The results indicated that by using the proper conditions, the supercritical fluid extraction is more selective than the steam distillation method. Extraction yields based on supercritical fluid extraction varied in the range of 0.68 to 17.1 % (w/w), and the extraction yield based on the steam distillation was 0.25 % (v/w).

Development of a particle-trap preconcentration-soft ionization mass spectrometric technique for the quantification of mercury halides in air.

Measurement of oxidized mercury, Hg(II), in the atmosphere poses a significant analytical challenge as Hg(II) is present at ultra-trace concentrations (picograms per cubic meter air). Current technologies are sufficiently sensitive to measure the total Hg present as Hg(II) but cannot determine the chemical speciation of Hg(II). We detail here the development of a soft ionization mass spectrometric technique coupled with preconcentration onto nano- or microparticle-based traps prior to analysis for the measurement of mercury halides in air. The current methodology has comparable detection limits (4-11 pg m(-3)) to previously developed techniques for the measurement of total inorganic mercury in air while allowing for the identification of HgX2 in collected samples. Both mercury chloride and mercury bromide have been sporadically detected in Montreal urban and indoor air using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). We discuss limitations and advantages of the current technique and discuss potential avenues for future research including quantitative trace measurements of a larger range of mercury compounds.

Porous-membrane-protected polyaniline-coated SBA-15 nanocomposite micro-solid-phase extraction followed by high-performance liquid chromatography for the determination of parabens in cosmetic products and wastewater.

A SBA-15/polyaniline para-toluenesulfonic acid nanocomposite supported micro-solid-phase extraction procedure has been developed for the extraction of parabens (methylparaben, ethylparaben, and propylparaben) from wastewater and cosmetic products. The variables of interest in the extraction process were pH of sample, sample and eluent volumes, sorbent amount, salting-out effect, extraction and desorption time, and stirring rate. A Plackett-Burman design was performed for the screening of variables in order to determine the significant variables affecting the extraction efficiency. Then, the significant factors were optimized by using a central composite design. The optimum experimental conditions found at 50 mL sample solution, extraction and desorption times of 40 and 20 min, respectively, 500 µL of 3% v/v acetic acid in methanol as eluent, 0.01 M salt addition, and 10 mg of the sorbent. Under the optimum conditions, the developed method provided detection limits in the range of 0.08-0.4 ng/mL with good repeatability (RSD% < 7) and linearity (r(2) = 0.997-0.999) for the three parabens. Finally, this fast and efficient method was employed for the determination of target analytes in cosmetic products and wastewater, and satisfactory results were obtained.

Carrier mediated transport solvent bar microextraction for preconcentration and determination of dexamethasone sodium phosphate in biological fluids and bovine milk samples using response surface methodology.

In the current study, a fast and simple preconcentration and sample clean up procedure was developed based on carrier mediated three phase solvent bar liquid phase microextraction (TPSB-LPME) method prior to high performance liquid chromatography (HPLC) equipped with an ultraviolet (UV) absorbance detector for simultaneous extraction and determination of trace amounts of dexamethasone sodium phosphate (DSP) in human plasma, human urine and bovine milk. According to this procedure, dexamethasone sodium phosphate was extracted from an acidic aqueous sample (SP, 7.5mL with pH=6) into the organic solvent 1-octanol (containing 5%, w/v of Aliquat-336 as carrier) residing in the pores of a hollow fiber and then back extracted into an alkali receiving phase (RP, 5µL of 0.65M NaClO4 with pH=10) was located inside the lumen of the fiber. After the extraction period, the receiving phase was directly injected into HPLC. The effect of different extraction conditions (i.e., pH of source and receiving phases, ionic strength, stirring rate, counter-ion concentration and extraction time) on the extraction efficiency of DSP was investigated and optimized using central composite design (CCD) as a powerful tool. Under the optimal conditions, preconcentration factor of 320, extraction recovery of 23%, dynamic linear range of 1-1000ngmL(-1) (r(2)=0.997) and limit of detection of 0.1ngmL(-1) were obtained. Eventually, applicability of the proposed method was successfully confirmed by extraction and determination of drug in plasma and urine samples and bovine milk with R.S.D.s<8%. Comparing to the traditional methods, the proposed method exhibits high sensitivity and high preconcentration factors as well as good precision. The extraction setup is simple and due to active transport of analytes, high cleanup effect and good selectivity are obtained in the extraction process. This extraction technique is also the most economical sample preparation and preconcentration technique as compared to traditional extraction techniques.

Comparison of supercritical fluid extraction and ultrasound-assisted extraction of fatty acids from quince (Cydonia oblonga Miller) seed using response surface methodology and central composite design.

Fatty acids of Cydonia oblonga Miller cultivated in Iran were obtained by supercritical (carbon dioxide) extraction and ultrasound-assisted extraction methods. The oils were analyzed by capillary gas chromatography using mass spectrometric detections. The compounds were identified according to their retention indices and mass spectra (EI, 70eV). The experimental parameters of SFE such as pressure, temperature, modifier volume, static and dynamic extraction time were optimized using a Central Composite Design (CCD) after a 2(5) factorial design. Pressure and dynamic extraction time had significant effect on the extraction yield, while the other factors (temperature, static extraction time and modifier volume) were not identified as significant factors under the selected conditions. The results of chemometrics analysis showed the highest yield for SFE (24.32%), which was obtained at a pressure of 353bar, temperature of 35°C, modifier (methanol) volume of 150µL, and static and dynamic extraction times of 10 and 60min, respectively. Ultrasound-assisted extraction (UAE) of Fatty acids from C. oblonga Miller was optimized, using a rotatable central composite design. The optimum conditions were as follows: solvent (n-hexane) volume, 22mL; extraction time, 30min; and extraction temperature, 55°C. This resulted in a maximum oil recovery of 19.5%. The extracts with higher yield from both methods were subjected to transesterification and GC-MS analysis. The results show that the oil obtained by SFE with the optimal operating conditions allowed a fatty acid composition similar to the oil obtained by UAE in optimum condition and no significant differences were found. The major components of oil extract were Linoleic, Palmitic, Oleic, Stearic and Eicosanoic acids.

Optimization of supercritical fluid extraction combined with dispersive liquid-liquid microextraction as an efficient sample preparation method for determination of 4-nitrotoluene and 3-nitrotoluene in a complex matrix.

Supercritical fluid extraction (SFE) combined with dispersive liquid-liquid microextraction (DLLME) followed by gas chromatography with flame ionization detector (GC-FID) was developed for the extraction and determination of 4-nitrotoluene and 3-nitrotoluene in soil sample. The effects of different SFE experimental parameters on the extraction recovery were studied simultaneously using a central composite design (CCD) after a 2(n-1) fractional factorial experimental design. The variables of interest in SFE were pressure, temperature, modifier volume, and dynamic extraction time. From this statistical evolution the pressure, dynamic extraction time, and modifier volume were found to have significant effects on the results achieved from SFE-DLLME-GC-FID, while temperature was not statistically significant at a 95% confidence level. The optimal SFE conditions for 4-nitrotoluene and 3-nitrotoluene were a pressure of 350 atm, temperature of 35°C, dynamic extraction time of 30 min and modifier volume of 150 µL. Under the optimal conditions, the extraction calibration plots were linear in the range of 0.25-25 mg kg(-1) and the limits of detection (LODs) were 0.12 mg kg(-1) for both of the analytes. Performance of the present method was evaluated for extraction and determination of 4-nitrotoluene and 3-nitrotoluene in soil samples, and satisfactory results were obtained (RSDs<6.5%).

Central composite design for the optimization of supercritical carbon dioxide fluid extraction of fatty acids from Borago officinalis L. flower.

UNLABELLED: In the present study, fatty acids and essential oils of the flower of borage (Borago officinalis L.) were obtained by supercritical carbon dioxide fluid extraction under different conditions. The extracts obtained were compared to oils of borage flower oil isolated by hydrodistillation. The obtained oils were analyzed by gas chromatography mass spectrometry. The compounds were identified according to their retention indices and mass spectra. The experimental parameters of supercritical fluid extraction (SFE) were optimized using a central composite design after a full factorial experimental design. Extraction yields based on SFE varied in the range of 0.02% to 1.96% (w/w), and the oil yield based on the hydrodistillation was 0.05% (v/w). The optimum conditions of SFE were obtained at a pressure of 350 atm, a temperature of 65 °C, a methanol modifier volume of 100 µL, and static and dynamic extraction time of 10 min. Main components of the extracts under optimum SFE conditions were palmitic acid, linoleic acid, γ-linolenic acid, and oleic acid. The results indicated that by using the suitable extraction conditions, SFE is more effective than the conventional hydrodistillation method in the extraction of fatty acids and the preservation of its quality. PRACTICAL APPLICATION: SFE is a good technique for the extraction of oils from plants. The extraction yields by SFE are more than the conventional method. SFE is used on a large scale for production of essential oils and pharmaceutical products from plants.

Simultaneous speciation and preconcentration of ultra traces of inorganic tellurium and selenium in environmental samples by hollow fiber liquid phase microextraction prior to electrothermal atomic absorption spectroscopy determination.

A simple and effective speciation and preconcentration method based on hollow fiber liquid phase microextraction (HF-LPME) was developed for simultaneous separation of trace inorganic tellurium and selenium in environmental samples prior to electrothermal atomic absorption spectroscopy (ETAAS) determination. The method involves the selective extraction of the Te (IV) and Se (IV) species by HF-LPME with the use of ammonium pyrrolidinecarbodithioate (APDC) as the chelating agent. The complex compounds were extracted into 10 microL of toluene and the solutions were injected into a graphite furnace for the determination of Te (IV) and Se (IV). To determine the total tellurium and selenium in the samples, first Te (VI) and Se (VI) were reduced to Te (IV) and Se (IV), and then the microextraction method was performed. The experimental parameters of HF-LPME were optimized using a central composite design after a 2(n-1) fractional factorial experimental design. Under optimum conditions, enrichment factors of up to 520 and 480 were achieved for Te (IV) and Se (IV), respectively. The detection limits were 4 ng L(-1) with 3.5% RSD (n=5, c=2.0 microg L(-1)) for Te (IV) and 5 ng L(-1) with 3.1% RSD for Se (IV). The applicability of the developed technique was evaluated by application to spiked, environmental water and soil samples.

Effects of relative humidity and CO(g) on the O3-initiated oxidation reaction of Hg0(g): kinetic & product studies.

Ozone is assumed to be the predominant tropospheric oxidant of gaseous elemental mercury (Hg0(g)), defining mercury global atmospheric lifetime. In this study we have examined the effects of two atmospherically relevant polar compounds, H2O(g) and CO(g), on the absolute rate coefficient of the O3-initiated oxidation of Hg0(g), at 296 +/- 2 K using gas chromatography coupled to mass spectrometry (GC-MS). In CO-added experiments, we observed a significant increase in the reaction rate that could be explained by pure gas-phase chemistry. In contrast, we found the apparent rate constant, k(net), varied with the surface-to-volume ratio (0.6 to 5.5 L flasks) in water-added experiments. We have observed small increases in k(net) for nonzero relative humidity, RH < 100%, but substantial increase at RH > or = 100%. Product studies were performed using mass spectrometry and high resolution transmission electron microscopy coupled to an electron dispersive spectrometer (HRTEM-EDS). Our results give evidence for enhanced chain growth of HgO(s) on a carbon grid at RH = 50%. A water/surface/ozone independent ozone oxidation rate is estimated to be (6.2 +/- (1.1; tsigma/ radicaln) x 10(-19) cm3 molecule(-1) s(-1). The total uncertainty associated with the ensemble of experiments amount to approximately < or = 20%. The atmospheric implications of our results and the effect of an added reaction partner in homogeneous and heterogeneous atmospheric chemistry will be discussed.

Biological and chemical redox transformations of mercury in fresh and salt waters of the high arctic during spring and summer.

It is well-established that atmospheric deposition transports Hg to Arctic regions, but the postdepositional dynamics of Hg that can alter its impact on Arctic food chains are less understood. Through a series of in situ experiments, we investigated the redox transformations of Hg in coastal and inland aquatic systems. During spring and summer, Hg reduction in streams and pond waters decreased across a 4-fold increase in salinity. This alteration of Hg reduction due to chloride was counterbalanced by the presence of particles, which favored the conversion of oxidized Hg to its elemental form. In saline waters, biogenic organic materials, produced by algae, were able to promote oxidation of Hg(O) even under dark conditions. Overall these results point to the vulnerability of marine/ coastal Arctic systems to Hg, compared to inland systems, with oxidation processes enhancing Hg residence times and thus increasing its potential to enter the food chain.

Product study of the gas-phase BrO-initiated oxidation of Hg0: evidence for stable Hg1+ compounds.

Mercury is a key toxic environmental pollutant, and its speciation affects its bioavailability. BrO radicals have been identified as key oxidants during mercury depletion events observed in Arctic and sub-Arctic regions. We report the first experimental product study of BrO-initiated oxidation of elemental mercury at atmospheric pressure of ca. 0.987 bar and T= 296+/-2 K. We used chemical ionization and electron impact mass spectrometry, gas chromatography coupled to a mass spectrometer, a MALDI-TOF mass spectrometer, a cold vapor atomic fluorescence spectrometer, and high-resolution transmission electron microscopy coupled to energy dispersive spectrometry. BrO radicals were formed using visible and UV photolysis of Br2 and CH2Br2 in the presence of ozone. We have analyzed the products in the gas phase, on suspended aerosols and on wall deposits, and identified HgBr, HgBrO/HgOBr, and HgO as reaction products. Mercury aerosols with a characteristic width of ca. 0.2 microm were observed as products. We herein discuss the implications of our results to the chemistry of atmospheric mercury and its potential implications in the biogeochemical cycling of mercury.