Simultaneous determination of sulfonamides and metabolites in manure samples by one-step ultrasound/microwave-assisted solid–liquid–solid dispersive extraction and liquid chromatography–mass spectrometry

An in-line matrix cleanup method was used for the simultaneous extraction of 15 sulfonamides and two metabolites from manure samples. The ultrasound/microwave-assisted extraction (UMAE) combined with solid–liquid–solid dispersive extraction (SLSDE) procedure provides a simple sample preparation approach for the processing of manure samples, in which the extraction and cleanup are integrated into one step. Ultrasonic irradiation power, extraction temperature, extraction time, and extraction solvent, which could influence the UMAE efficiency, were investigated. C₁₈ was used as the adsorbent to reduce the effects of interfering components during the extraction procedure. The extracts were concentrated, and the analytes were analyzed by liquid chromatography–tandem mass spectrometry (LC–MS/MS) without any further cleanup. The isotopically labeled compounds sulfamethoxazole-d ₄, sulfamethazine-d ₄, sulfamonomethoxine-d ₄, and sulfadimethoxine-d ₆ were selected as internal standards to minimize the matrix effect in this method. The recoveries of the antibiotics tested ranged from 71 to 118 % at the three spiking levels examined (20, 200, and 500 μg?·?kg^-1). The limits of detections were 1.2–3.6 μg?·?kg^-1 and the limits of quantification were 4.0–12.3 μg?·?kg^-1 for the sulfonamides and their metabolites. The applicability of the method was demonstrated by analyzing 30 commercial manure samples. The results indicated that UMAE–SLSDE combined with LC–MS/MS is a simple, rapid, and environmentally friendly method for the analysis of sulfonamides and their metabolites in manure, and it could provide the basis for a risk assessment of the antibiotics in agricultural environments.     

A double-stage tube furnace—acid-trapping protocol for the pre-concentration of mercury from solid samples for isotopic analysis

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1–20 ng/g) by wet chemistry is challenging. Combustion–trapping techniques have been shown to be an appropriate alternative [1]. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O₂ stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into H₂O, CO₂, SO₂, etc. The O₂ carrier gas, including combustion products and elemental Hg, is then purged into a 40 % (v/v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO₃/1HCl (v/v), 25 mL/min O₂ flow rate, and a dynamic temperature ramp rate (15 °C/min for 25–150 and 600–900 °C; 2.5 °C/min for 150–600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81–102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80–120 %. This protocol has the advantages of a short sample processing time (～3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis.     

Solid-phase preconcentration of cadmium(II) using amino-functionalized magnetic-core silica-shell nanoparticles, and its determination by hydride generation atomic fluorescence spectrometry

We report on the synthesis and evaluation of aminated-CoFe₂O₄/SiO₂ nanoparticles that can serve as a selective solid-phase sorbent for the extraction of cadmium ion. The nanoparticles consist of a magnetic CoFe₂O₄ core and an amino-modified silica shell. They can efficiently extract cadmium(II) ion and then can be isolated from the sample solution due to the magnetic nature of the core. The effects of the experimental conditions on the extraction process were optimized. Cadmium was then quantified by hydride generation atomic fluorescence spectrometry. The resulting calibration curve is linear in the concentration range of 0.01–10 μg?L^?1, the instrumental detection limits (3σ) is 3.15 ng?L^?1 and the relative standard deviation is 4.9 % at the 1.0 μg?L^?1 level (for n?=?11). The enrichment factor is 50 (for 50 mL samples), and the adsorbent can be used for at least 45 cycles of preconcentration and elution. The method was applied to the determination of cadmium in environmental water samples, and successfully validated by analyzing two certified reference materials.

Thermal degradation and evolved gas analysis of N,N′-bis(2 hydroxyethyl) linseed amide (BHLA) during pyrolysis and combustion

The thermal degradation of N,N′-bis(2 hydroxyethyl) linseed amide (BHLA) was investigated by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy (TG–FTIR–MS). Thermogravimetric analysis revealed that the thermal degradation process can be subdivided into three stages: sample drying (<200 °C), main decomposition (200–500 °C), and further cracking (>500 °C) of the polymer. The compound reached almost 800 °C during pyrolysis and combustion. The activation energy at the second step during combustion was slightly higher than that of pyrolysis emissions of carbon dioxide, aliphatic hydrocarbons, carbon monoxide, and hydrogen cyanide, and other gases during combustion and pyrolysis were detected by FTIR and MS spectra. It was observed that the intensities of CO₂, CO, HCN, and H₂O were very high when compared with their intensities during pyrolysis, and this was attributed to the oxidation of the decomposition product.     

On-line packed magnetic in-tube solid phase microextraction of acidic drugs such as naproxen and indomethacin by using Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@layered double hydroxide nanoparticles with high anion exchange capacity

The authors describe a 3-component nanoparticle system composed of a silica-coated magnetite (Fe₃O₄) core and a layered double (Cu-Cr) hydroxide nanoplatelet shell. The sorbent has a high anion exchange capacity for extraction anionic species. A simple online system, referred to as "on-line packed magnetic-in-tube solid phase microextraction" was designed. The nanoparticles were placed in a stainless steel cartridge via dry packing. The cartridge was then applied to the preconcentration acidic drugs including naproxen and indomethacin from urine and plasma. Extraction and desorption times, pH values of the sample solution and flow rates of sample solution and eluent were optimized. Analytes were then quantified by HPLC with UV detection. Under optimal conditions, the limits of detection range from 70 to 800 ng L^?1, with linear responses from 0.1–500 μg L^?1 (water samples), 0.6–500 μg L^?1 (spiked urine), and 0.9–500 μg L^?1 (spiked plasma). The inter- and intra-assay precisions (RSDs, for n?=?5) are in the range of 2.2–5.4%, 2.8–4.9%, and 2.0–5.2% at concentration levels of 5, 25 and 50 μg L^?1, respectively. The method was applied to the analysis of the drugs in spiked human urine and plasma, and good results were achieved.

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Graphical abstract Fe₃O₄@SiO₂@CuCr-LDH magnetic nanoparticles were synthesized and packed in to a stainless steel column. The column was applied to solid phase microextraction of acidic drugs from biological samples.

     

Oxygen isotope exchange in praseodymium nickelate

Oxygen surface exchange kinetics and diffusion were studied in Pr₂NiO_4?+?δ (PNO) by the isotope exchange method with gas phase equilibration in the temperature range of 600–800 °C and oxygen pressure range of 0.33–1.62 kPa. The oxygen heterogeneous exchange rate (r_H), oxygen diffusion coefficient (D), rates of oxygen dissociative adsorption (r_a), and oxygen incorporation (r_i) were calculated along with the apparent activation energies of oxygen surface exchange and diffusion processes. The temperature dependence of r_H was found to benon-linear in Arrhenius coordinates. The apparent activation energy changed from 1.4?±?0.2 eV at T?>?700 °C to 2.0?±?0.1 eV. This might be attributed to the change in the rate-determining stage of oxygen exchange for Pr₂NiO_4?+?δ at T ~?700 °C, because of a shift in the ratio between r_a and r_i caused by the difference in their activation energies. Possible reasons for the observed changes in the rate-determining stage are discussed.     

Magnetic Solid Phase Extraction Based on Modified Magnetite Nanoparticles Coupled with Dispersive Liquid–Liquid Microextraction as an Efficient Method for Simultaneous Extraction of Hydrophobic and Hydrophilic Drugs

In this work, surfactant-coated Fe₃O₄@decanoic acid nanoparticles was synthesized as a viable nanosorbent for coextraction of drugs with different polarities (hydrophobic, hydrophilic). To reach desirable enrichment factors, efficient clean-up and low limits of detection (LODs), the method was combined with dispersive liquid–liquid microextraction (DLLME). The coupling of these extraction methods with GC-FID detection was applied to simultaneous extraction and quantification of venlafaxine (VLF) as a hydrophilic model drug and desipramine (DESI) and clomipramine (CLO) as hydrophobic model drugs in urine samples. The effect of sample pH, nanosorbent amount, sorption time, surfactant concentration, eluent type, eluent volume, salt content, elution time in magnetic solid phase extraction step and extraction solvent and its volume along with sample pH in DLLME step were optimized. Under the selected conditions, linearity was achieved within the range of 5–5000 µg L^?1. The LOD values were obtained in the range of 1.5–3.0 µg L^?1 for DESI, 1.2–2.5 µg L^?1 for VLF and 2.0–4.0 µg L^?1 for CLO, respectively. The percent of extraction recoveries and relative standard deviations (n?=?5) were in the range of 82.4–95.9 and 6.1 for DESI, 60.5–92.8 and 6.9 for VLF and 57.2–58.0 and 5.5 for CLO, respectively. Ultimately, the applicability of the new method was successfully confirmed by the extraction and quantification of DESI, VLF and CLO from human urine samples.     

Determination of phthalate esters in edible oils by use of QuEChERS coupled with ionic-liquid-based dispersive liquid–liquid microextraction before high-performance liquid chromatography

A selective and low organic-solvent-consuming method of sample preparation combined with high-performance liquid chromatography with diode-array detection is introduced for analysis of phthalic acid esters in edible oils. Sample treatment involves initial liquid–liquid partitioning with acetonitrile, then QuEChERS cleanup by dispersive solid-phase extraction with primary secondary amine as sorbent. Preconcentration of the analytes is performed by ionic-liquid-based dispersive liquid–liquid microextraction, with the cleaned-up extract as disperser solvent and 1-hexyl-3-methylimidazolium hexafluorophosphate as extraction solvent. Under the optimized conditions, correlation coefficients (r) were 0.998–0.999 and standard errors (S _y/x ) were 2.67–3.37?×?10³ for calibration curves in the range 50–1000 ng g^?1. Detection limits, at a signal-to-noise ratio of 3, ranged from 6 to 9 ng g^?1. Intra-day and inter-day repeatability, expressed as relative standard deviation, were in the ranges 1.0–6.9 % and 2.4–9.4 %, respectively. Recovery varied between 84 % and 106 %. The developed method was successfully used for analysis of the analytes in 28 edible oils. The dibutyl phthalate content of four of the 28 samples (14 %) exceeded the specific migration limit established by domestic and international regulations.

Chitosan-poly(m-phenylenediamine)@Fe3O4 nanocomposite for magnetic solid-phase extraction of polychlorinated biphenyls from water samples

A extraction medium based on chitosan-poly(m-phenylenediamine) (CS-PPD) @Fe₃O₄ nanocomposite was synthesized by chemical polymerization of m-phenylenediamine in the presence of chitosan coated magnetic nanocomposite, and for the first time, used as the sorbent for the magnetic solid-phase extraction (MSPE) of seven polychlorinated biphenyls (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, and PCB180) at trace levels in water samples. Gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) was used for PCBs quantification and detection. Several factors related to MSPE efficiencies, such as type and amount of sorbent, extraction time, sample pH, and desorption conditions were investigated. Under the optimized conditions, an excellent linearity was observed in the range of 1.0–200 ng L^–1 for PCB180, 0.5–200 ng L^–1 for the other six PCBs with the correlation coefficients ranging from 0.9954 to 0.9993. The good recoveries at spiked levels of 10.0, 20.0, and 50.0 ng L^–1 were obtained in the range of 94 %–108 %, and the coefficients of variations were less than 6 %. The proposed method was feasible, rapid, and easy to operate for the trace analysis of the PCBs in local aquaculture water, livestock breeding water, and sewage water samples. Graphical Abstract

Fig. 1 Schematic diagram for the preparation of chitosan–poly(m-phenylenediamine) @Fe₃O₄ nanocomposite.     

Determination of sulfadiazine in phosphate- and DOC-rich agricultural drainage water using solid-phase extraction followed by liquid chromatography-tandem mass spectrometry

Trace levels of the veterinary antibiotic compound sulfadiazine (SDZ) can be determined in agricultural drainage water samples with this new method. Optimized sample pretreatment and solid-phase extraction was combined with liquid chromatography coupled to tandem mass spectrometry (SPE LC-MS/MS) using positive electrospray ionization. The linear dynamic range for the LC-MS/MS was assessed from 5 μg/L to 25 mg/L with a 15-point calibration curve displaying a coefficient of correlation r ²?=?0.9915. Agricultural drainage water spiked at a concentration of 25 ng/L gave recoveries between 63 and 98 % (relative standard deviation 15 %), while at 10 ng/L, it showed a lower recovery of 32 % (relative standard deviation 47 %). The final SPE LC-MS/MS method had a limit of detection (LOD)_Method and a limit of quantification (LOQ)_Method of 7.5 and 23 ng/L agricultural drainage water, respectively. Determination of SDZ, spiked at a realistic concentration of 50 μg/L, in artificial drainage water (ADW) containing common and high levels of phosphate (0.05, 0.5, and 5 mg/L) gave recoveries between 70 and 92 % (relative standard deviation 7.4–12.9 %). Analysis of the same realistic concentration of SDZ in ADW, spiked with common and high levels of dissolved organic carbon (2, 6, and 15 mg/L) confirmed the possible adaptation of a tandem solid-phase extraction (strong anion exchange (SAX)-hydrophilic-lipophilic balance (HLB)) followed by liquid chromatography-tandem mass spectrometry methodology. Recoveries obtained ranged from 104 to 109 % (relative standard deviation 2.8–5.2 %). The new methods enable determination of the veterinary antibiotic compound SDZ in agricultural drainage water from field experiments and monitoring schemes for phosphate- and dissolved organic carbon (DOC)-rich water samples in intensive farming areas.

Magnetic molecularly imprinted polymer nanoparticles for the solid-phase extraction of paracetamol from plasma samples,followed its determination by HPLC

We are presenting magnetic molecularly imprinted polymer nanoparticles (m-MIPs) for solid-phase extraction and sample clean-up of paracetamol. The m-MIPs were prepared from magnetite (Fe₃O₄) as the magnetic component, paracetamol as the template, methacrylic acid as a functional monomer, and 2-(methacrylamido) ethyl methacrylate as a cross-linker. The m-MIPs were then characterized by transmission electron microscopy, FT-IR spectroscopy, X-ray diffraction and vibrating sample magnetometry. The m-MIPs were applied to the extraction of paracetamol from human blood plasma samples. Following its elution from the column loaded with the m-MIPs with an acetonitrile-buffer (9:1) mixture, it was submitted to HPLC analysis. Paracetamol can be quantified by this method in the 1 μg L^?1 to 300 μg L^?1 concentration range. The limit of detection and limit of quantification in plasma samples are 0.17 and 0.4 μg L^?1. The preconcentration factor of the m-MIPs is 40. The HPLC method shows good precision (4.5 % at 50 μg L^?1 levels) and recoveries (between 83 and 91 %) from spiked plasma samples. Figure

We are presenting magnetic molecularly imprinted polymer nanoparticles (m-MIPs) for solid-phase extraction and sample clean-up of paracetamol. The m-MIPs were applied to the extraction of paracetamol from human blood plasma samples     

Orchids as Sources of Novel Nanoinsecticides? Efficacy of <Emphasis Type="Italic">Bacillus sphaericus</Emphasis> and <Emphasis Type="Italic">Zeuxine gracilis</Emphasis>-Fabricated Silver Nanoparticles Against Dengue,Malaria and Filariasis Mosquito Vectors

Mosquitoes are the most critical group of insects in the context of public health, since they transmit key parasites and pathogens, causing millions of deaths annually. Insecticides from natural products may boost the effectiveness of vector control programs. In this study, we tested silver nanoparticles (AgNPs) fabricated using the leaf extract of the orchid Zeuxine gracilis as reducing agent, and the microbial pesticide Bacillus sphaericus, against the mosquitoes Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus. The synthesis of AgNP was confirmed analyzing the excitation of surface Plasmon resonance using ultraviolet–visible (UV–Vis) spectrophotometry. SEM and TEM showed the irregular shapes of AgNPs. EDX spectroscopy, FTIR spectroscopy, X-ray diffraction and dynamic light scattering analysis were carried out. AgNPs were highly effective against the larvae of An. stephensi (LC₅₀ = 8.48 µg/mL), Ae. aegypti (LC₅₀ = 10.39 µg/mL) and Cx. quinquefasciatus (LC₅₀ = 13.21 µg/mL), respectively. Combined treatments testing B. sphaericus with AgNPs were also effective against An. stephensi (LC₅₀ = 12.32 µg/mL), Ae. aegypti (LC₅₀ = 14.78 µg/mL) and Cx. quinquefasciatus (LC₅₀ = 19.19 µg/mL). Overall, this study suggests that the orchid-synthesized AgNPs can be a rapid, environmentally safer bio-pesticide to be used in synergy with B. sphaericus to control mosquito vectors.     

Development of a microwave-assisted-extraction-based method for the determination of aflatoxins B1, G1, B2, and G2 in grains and grain products

This article describes the use of microwave-assisted extraction (MAE) as a pretreatment technique for the determination of aflatoxins B₁, G₁, B₂, and G₂ in grains and grain products. The optimal operation parameters, including extraction solvent, temperature, and time, were identified to be acetonitrile as the extraction solvent at 80 °C with 15 min of MAE. The extracts were cleaned up using solid-phase extraction followed by derivatization with trifluoroacetic acid and were determined by liquid chromatography–fluorescence detection. A Sep-Pak cartridge was chosen over Oasis HLB and Bond Elut cartridges. By the use of aflatoxin M₁ as an internal standard, relative recoveries of the aflatoxins ranged from 90.7 to 105.7 % for corn and from 88.1 to 103.4 % for wheat, with relative standard deviations between 2.5 and 8.7 %. A total of 36 samples from local markets were analyzed, and aflatoxin B₁ was found to be the predominant toxin, with concentrations ranging from 0.42 to 3.41 μg/kg.

An oligosorbent-based aptamer affinity column for selective extraction of aflatoxin B<Subscript>2</Subscript> prior to HPLC with fluorometric detection

The article describes an aptamer affinity column for selective solid-phase extraction of aflatoxin B₂ (AFB₂). Amino-modified aptamer against AFB₂ was immobilized on CNBr-activated Sepharose through a covalent bond. The effects of oligosorbents based on 3′- or 5′-amino-modified sequences with a C6 or a C7 spacer arm were evaluated by UV spectroscopy at 260 nm. The extraction recovery was evaluated by HPLC with fluorometric detection. The extraction of AFB₂ was optimized. Under the optimum conditions, the aptamer affinity column has a linear response to AFB₂ in the range of 0.5–80 ng, with a capacity of 84.6 ng. Control supports without immobilized aptamers and a nonspecific oligosorbent immobilized with a negative control oligonucleotide were studied in order to demonstrate selectivity. The method was tested with spiked peanut sample (0.5–50 μg·kg^?1 AFB₂) and gave average recoveries of 80.9% and a mean relative standard deviation of 1.9%. The limit of detection is 25 pg·mL^?1. This is much lower than the maximum residue limits suggested by the European Union. The columns can be re-used up to five times without any loss of performance. The oligosorbent was also applied to clean-up of AFB₂ from peanut sample extracts before HPLC analysis. Results were further confirmed by ultra-fast liquid chromatography with tandem mass spectrometry. Conceivably, the method may also be applied to other samples, such as food, agricultural products, and traditional Chinese medicines.

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Graphical abstract Schematic illustration of the fabrication procedures of aptamer affinity column, AAC (a), its principle of aptamer bound to aflatoxin B₂ (b) and the obtained AAC (c).

     

Synthesis,structural, and electrochemical properties of NaCo(PO<Subscript>3</Subscript>)<Subscript>3</Subscript> cathode for sodium-ion batteries

A new Co-base sodium metaphosphate compound, NaCo(PO₃)₃, has been synthesized here by solid-state method. The crystal structure is refined by the Rietveld method, and the results reveal that NaCo(PO₃)₃ has an orthorhombic structure with the space group of P2 ₁ 2 ₁ 2 ₁ and lattice parameters of a = 14.2453(2) Å, b = 14.2306(1) Å, and c = 14.2603(2) Å. Its typical morphology and chemical composition are confirmed by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). The valence states of all elements and the internal/external vibrational modes of NaCoP₃O₉ compound are measured by X-ray photoelectron and vibrational spectrum, where a typical feature of the (PO₃)^? polyanion group is observed. Meanwhile, the electrochemical properties of NaCo(PO₃)₃ cathode for sodium-ion batteries are also elevated and an initial discharge capacity of 33.8 mAh/g can be obtained at 0.05 C within 1.5–4.2 V. After 20 cycles, a discharge capacity of 26.7 mAh/g can be obtained and a well-kept oxidation–reduction plateau is still observed for NaCo(PO₃)₃ cathode, indicating the good reversibility of this metaphosphate electrode.     

A comparison of the structure and bonding in the aliphatic boronic R–B(OH)<Subscript>2</Subscript> and borinic R–BH(OH) acids (R=H; NH<Subscript>2</Subscript>, OH,and F): a computational investigation

Boronic acids, R–B(OH)₂, play an important role in synthetic, biological, medicinal, and materials chemistry. This investigation compares the structure and bonding surrounding the boron atoms in the simple aliphatic boronic acids, R–B(OH)₂ (R=H; NH₂, OH, and F), and the analogous borinic acids, R–BH(OH). Geometry optimizations were performed using second-order Møller–Plesset perturbation theory (MP2) with the Dunning–Woon aug-cc-pVTZ, aug-cc-pVQZ, and aug-cc-pV5Z basis sets; single-point CCSD(FC)/aug-cc-pVTZ//MP2(FC)/aug-cc-pVTZ level calculations were used to generate a QCI density for natural bond orbital analyses of the bonding. The optimized boron–oxygen bond lengths for the X–B–O_t–H trans-branch of the endo-exo form of the boronic acids and for the X–B–O–H cis-branch of the boronic and borinic acids (X=N, O, and F, respectively) decrease as the electronegativity of X increases. The boron–oxygen bond lengths are generally longer in the endo-exo or anti forms of the boronic acids than in the corresponding borinic acids. NBO analyses suggest the boron–oxygen bond in H₂BOH is a double bond; the boron–oxygen bonding in the remaining boronic and borinic acids in this study has a significant contribution from dative pπ–pπ bonding. Values for Δ\({\text{H}}_{298}^{0}\) for the highly balanced reaction, R–B(OH)₂ + R–BH₂ → 2 R–BH(OH), suggest that the bonding surrounding the boron atom is stronger in the borinic acid than in the corresponding boronic acid.     

Development of monolith-based stir bar sorptive extraction and liquid chromatography tandem mass spectrometry method for sensitive determination of ten sulfonamides in pork and chicken samples

A highly sensitive method was developed for the simultaneous determination of ten sulfonamides in pork and chicken samples by monolith-based stir bar sorptive extraction (SBSE) coupled to high-performance liquid chromatography tandem mass spectrometry. The samples were freeze-dried and extracted by acetonitrile, then enriched and further extracted by SBSE which was based on poly(vinylphthalimide-co-N,N-methylenebisacrylamide) monolith (SBSE-VPMB) as coating. To achieve optimum extraction performance of SBSE for sulfonamides, several parameters, including pH value and ionic strength in the sample matrix and extraction and desorption time, were investigated in detail. Under the optimal conditions, the limits of detection (S/N?=?3) for target sulfonamides were 1.2–6.1 ng/kg in pork and 2.0–14.6 ng/kg in chicken, respectively. Real samples spiked at the concentration of 0.5 and 5.0 μg/kg showed recoveries above 55 % and relative standard deviations below 12 %. At the same time, the extraction performances of target sulfonamides on SBSE-VPMB were compared with other SBSE based on porous monolith and commercial SBSE.

Calix[4]arene-bis(t-octylbenzo-18-crown-6) as an extraordinarily effective macrocyclic receptor for the univalent thallium cation

From extraction experiments and $ \gamma $ -activity measurements, the exchange extraction constant corresponding to the equilibrium Tl⁺ (aq) + 1·Cs⁺ (org) ? 1·Tl⁺ (org) + Cs⁺ (aq) taking place in the two-phase water–phenyltrifluoromethyl sulfone (abbrev. FS 13) system (1 = calix[4]arene-bis(t-octylbenzo-18-crown-6); aq = aqueous phase, org = FS 13 phase) was evaluated as log K _ex (Tl⁺, 1·Cs⁺) = 1.7 ± 0.1. Further, the extraordinarily high stability constant of the 1·Tl⁺ complex in FS 13 saturated with water was calculated for a temperature of 25 °C: log β _org(1·Tl⁺) = 13.1 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1·Tl⁺ was derived. In the resulting 1·Tl⁺ complex, the “central” cation Tl⁺ is bound by eight bond interactions to six oxygen atoms from the respective 18-crown-6 moiety and to two carbons of the corresponding two benzene rings of the parent receptor 1 via cation–π interaction.     

Occupational exposure to complex mixtures of volatile organic compounds in ambient air: desorption from activated charcoal using accelerated solvent extraction can replace carbon disulfide?

A desorption study of 57 volatile organic compounds (VOCs) has been conducted by use of accelerated solvent extraction (ASE) and gas chromatography–mass spectrometry. Different solvents were tested to extract activated charcoal tubes with the objective of replacing carbon disulfide, used in official methods, because of its highly toxic health and environmental effects. Extraction conditions, for example temperature and number of cycles, were investigated and optimized. The definitive extraction procedure selected was use of acetone at 150 °C and two consecutive extraction cycles at a pressure of 1,500 psi. Considering a sample volume of 0.005 Nm³, corresponding to a sampling time of 8 h at a flow rate of 0.01 L?min^?1, the method was validated over the concentration range 65–26,300 μg?Nm^?3. The lowest limit of quantification was 6 μg?Nm^?3, and recovery for the 93 % of analytes ranged from 65 to 102 %. For most of the compounds, relative standard deviations were less than 15 % for inter and intra-day precision. Uncertainty of measurement was also determined: the relative expanded uncertainty was always below 29.6 %, except for dichlorodifluoromethane. This work shows that use of friendlier solvent, for example acetone, coupled with use of ASE, can replace use of CS₂ for chemical removal of VOCs from activated charcoal. ASE has several advantages over traditional solvent-extraction methods, including shorter extraction time, minimum sample manipulation, high reproducibility, and less extraction discrimination. No loss of sensitivity occurs and there is also a salutary effect on bench workers’ health and on the smell of laboratory air.

Comparison of the Active Species in the RF and Microwave Flowing Discharges of N<Subscript>2</Subscript> and Ar–20 %N<Subscript>2</Subscript>

We report a detailed comparison between RF and microwave (HF) plasmas of N₂ and Ar–20 %N₂ as well as in the corresponding afterglows by comparing densities of active species at nearly the same discharge conditions of tube diameter (5–6 mm), gas pressure (6–8 Torr), flow rate (0.6–1.0 slm) and applied power (50–150 W). The analysis reveals an interesting difference between the two cases; the length of the RF plasma (~25 cm) is measured to be much longer than that of HF (6 cm). This ensures a much longer residence time (10^?2 s) of the active species in the N₂ RF plasma [compared to that (10^?3 s) of HF], providing a condition for an efficient vibrational excitation of N₂(X, v) by (V–V) climbing-up processes, making the RF plasma more vibrationally excited than the HF one. As a result of high V–V plasma excitation in RF, the densities of the vibrationally excited N₂(X, v > 13) molecules are higher in the RF afterglow than in the HF afterglow. Destruction of N₂(X, v) due to the tube wall is estimated to be very similar between the two system as can be inferred from the γ_v destruction probability of N₂(X, v > 3–13) on the tube wall (2–3 × 10^?3 for both cases) obtained from a comparison between the density of N₂(X, v > 3–9) in the plasmas to that of the N₂(X, v > 13) in the long afterglows. Interestingly enough, densities of N-atoms and N₂(A) metastable molecules in the afterglow regions, however, are measured to be very similar with each other. The measured lower density of N₂ ⁺ ions than expected in the HF afterglow is rationalized from a high oxygen impurity in our HF setup since N₂ ⁺ ions are very sensitive to oxygen impurity .