6-Phenylhexyl silane derivatized, sputtered silicon solid phase microextraction fiber for the parts-per-trillion detection of polyaromatic hydrocarbons in water and baby formula.

We report the fabrication of 6-phenylhexylsilane derivatized, sputtered silicon, solid phase microextraction fibers that show parts per trillion detection limits for polyaromatic hydrocarbons, and negligible carry over and phase bleed. Their fabrication involves sputtering silicon on silica fibers under various conditions. Six different fibers were evaluated by generating three different thicknesses of sputtered silicon at two different throw distances, which altered the morphologies of the silicon surfaces. All of the fibers were coated with similar thicknesses of 6-phenylhexylsilane (ca. 2 nm). These fibers were characterized with multiple analytical techniques. The optimum fiber configuration was then used to analyze polyaromatic hydrocarbons via direct immersion, gas chromatography mass spectrometry. Our best fiber for the extraction of low molecular weight polyaromatic hydrocarbons in water had similar performance to that of a commercial fiber. However, our fiber demonstrated ca. 3 times the extraction efficiency for higher molecular weight polyaromatic hydrocarbons. In addition, it outperformed the commercial fiber by showing better linearity, repeatability, and detection limits. A method for analyzing polyaromatic hydrocarbons in baby formula was developed, which showed very good linearity (0.5-125 ppb), repeatability (2-26%), detection limits (0.12-0.81 ppb), and recoveries (103-135%). In addition, our fiber showed much less (negligible) carry over and phase bleed than the commercially available fibers.

Mass spectral studies of silyl derivatives of partially hydrolyzed products of nitrogen mustards: Important markers of nitrogen mustard exposure.

RATIONALE: Nitrogen mustards (NMs) are vesicant class of chemical warfare agents. From the viewpoint of the Chemical Weapons Convention partially hydrolyzed products of nitrogen mustards (pHpNMs) are considered as important markers of nitrogen mustard exposure. The detection of pHpNMs from biological or environmental samples is highly useful for obtaining forensic evidence of exposure to NMs. METHODS: Gas chromatography interfaced with tandem mass spectrometry (GC/MS/MS) is a widely used tool for the identification and sensitive detection of metabolites of NMs in complex matrices. The pHpNMs were derivatized using silylating agents as they are highly polar and non-amenable to GC. The mass spectral studies of these silyl derivatives of pHpNMs were performed using GC/MS/MS in both electron ionization (EI) and chemical ionization (CI) mode. RESULTS: Various approaches have been proposed to assess the fragmentation pathways of the trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBDMS) derivatives of pHpNMs. All the proposed fragmentation pathways were based on the product and/or precursor ion scanning of corresponding ions in both EI and CI mode. In the case of EI, most of the fragmentation pathways involved either α-cleavage or inductive cleavage. CONCLUSIONS: This is the first report on the MS study of the silyl derivatives of pHpNMs. The study of the two different derivatives of pHpNMs using both EI- and CI-MS provides a reliable, unambiguous identification of pHpNMs in complex environmental and biomedical matrices (such as plasma and urine) during any verification activities.

The challenge of separating and determining biologically active electrostatically stabilized silanates using the high-performance liquid chromatography technique.

We present the results of research on the optimal conditions for the separation and determination of newly obtained hypercoordinated compounds, which belong to the group of electrostatically stabilized silanates. The research involved five stationary and four mobile phases. The best selectivity was obtained using the graphite phase and the mobile phase consisting of acetonitrile/water (80/20). The maximum selectivity of the determined electrostatically stabilized silanates was 1.13 and 1.06 for (1), (2), (3); 1.10 and 1.15 for (4), (5), (6); and 1.12 and 1.15 for (7), (8), (9). The octadecyl phase (which is recommended as standard) did not yield satisfactory results.

A Novel, Nonpeptidic, Orally Active Bivalent Inhibitor of Human ß-Tryptase.

ß-Tryptase is released from mast cells upon degranulation in response to allergic and inflammatory stimuli. Human tryptase is a homotetrameric serine protease with 4 identical active sites directed toward a central pore. These active sites present an optimized scenario for the rational design of bivalent inhibitors, which bridge 2 adjacent active sites. Using (3-[1-acylpiperidin-4-yl]phenyl)methanamine as the pharmacophoric core and a disiloxane linker to span 2 active sites we have successfully produced a novel bivalent tryptase inhibitor, compound 1a, with a comparable profile to previously described inhibitors. Pharmacological properties of compound 1a were studied in a range of in vitro enzymic and cellular screening assays, and in vivo xenograft models. This non-peptide inhibitor of tryptase demonstrated superior activity (IC50 at 100 pmol/L tryptase = 1.82 nmol/L) compared to monomeric modes of inhibition. X-ray crystallography validated the dimeric mechanism of inhibition, and 1a demonstrated good oral bioavailability and efficacy in HMC-1 xenograft models. Furthermore, compound 1a demonstrated extremely slow off rates and high selectivity against-related proteases. This highly potent, orally bioavailable and selective inhibitor of human tryptase will be an invaluable tool in future studies to explore the therapeutic potential of attenuating the activity of this elusive target.

Simultaneous detection of fluquinconazole and flusilazole in lettuce using gas chromatography with a nitrogen phosphorus detector: decline patterns at two different locations.

Method validations in addition to decline patterns of fluquinconazole and flusilazole in lettuce grown under greenhouse conditions at two different locations were investigated. Following the application of fluquinconazole and flusilazole at a dose rate of 20 mL/20 L water, lettuce samples were collected randomly for up to 7 days post-application, and simultaneously extracted with acetone, purified through solid-phase extraction, analyzed via gas chromatography with a nitrogen phosphorus detector, and confirmed through gas chromatography-mass spectrometry. The linearity was excellent, with determination coefficients (R(2) ) between 0.9999 and 1.0. The method was validated in triplicate at two different spiking levels (0.2 and 1.0 mg/kg) with satisfactory recoveries between 75.7 and 97.9% and relative standard deviations of <9. The limit of quantification was 0.01 mg/kg. Both analytes declined very quickly, as can be seen from the short half-life time of <4 days. Statistical analysis revealed significant differences between residues at different days of sampling, except at 7 days post-application (triple application). At that point, the decline patterns of fluquinconazole and flusilazole were independent of application rate, location, temperature and humidity. Copyright © 2015 John Wiley & Sons, Ltd.

Quantification of variable functional-group densities of mixed-silane monolayers on surfaces via a dual-mode fluorescence and XPS label.

The preparation of aminated monolayers with a controlled density of functional groups on silica surfaces through a simple vapor deposition process employing different ratios of two suitable monoalkoxysilanes, (3-aminopropyl)diisopropylethoxysilane (APDIPES) and (3-cyanopropyl)dimethylmethoxysilane (CPDMMS), and advances in the reliable quantification of such tailored surfaces are presented here. The one-step codeposition process was carried out with binary silane mixtures, rendering possible the control over a wide range of densities in a single step. In particular, APDIPES constitutes the functional silane and CPDMMS the inert component. The procedure requires only small amounts of silanes, several ratios can be produced in a single batch, the deposition can be carried out within a few hours and a dry atmosphere can easily be employed, limiting self-condensation of the silanes. Characterization of the ratio of silanes actually bound to the surface can then be performed in a facile manner through contact angle measurements using the Cassie equation. The reliable estimation of the number of surface functional groups was approached with a dual-mode BODIPY-type fluorescence label, which allows quantification by fluorescence and XPS on one and the same sample. We found that fluorescence and XPS signals correlate over at least 1 order of magnitude, allowing for a direct linking of quantitative fluorescence analysis to XPS quantification. Employment of synchrotron-based methods (XPS; reference-free total reflection X-ray fluorescence, TXRF) made the traceable quantification of surface functional groups possible, providing an absolute reference for quantitative fluorescence measurements through a traceable measurement chain.

Enhanced sensitivity of double gate junctionless transistor architecture for biosensing applications.

In the present work, we demonstrate the potential of double gate junctionless (JL) architecture for enhanced sensitivity for detecting biomolecules in cavity modulated field effect transistors (FETs). The higher values of body factor, achieved in asymmetric gate operation under impact ionization is utilized for enhanced sensing margin which is nearly five times higher than compared to symmetrical mode operation. The intrinsic detection sensitivity is evaluated in terms of threshold voltage change, and the ratio of drain current in the presence and absence of biomolecules in JL nanotransistors. It is shown that asymmetric mode JL transistor achieves a higher degree of detection sensitivity even for a partially filled cavity. The work demonstrates the potential of JL channel architecture for cavity based dielectric modulated FET biosensors.

Development of a Method for the Analysis of Multiclass Antibiotic Residues in Milk Using QuEChERS and Liquid Chromatography-Tandem Mass Spectrometry.

A precise and simplified method of sample preparation for the simultaneous quantification of the antibiotics ß-lactam, macrolide, tetracycline, sulfonamide, and quinolone in bovine milk was developed. The central composite design of response surface methodology was used to design and optimize the method for the determination of six different antibiotic residues in milk. The recovery of each antibiotic was studied using a quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. Octadecylsilane (C18), primary secondary amine (PSA), and sodium acetate (Na acetate) were the main factors affecting the recovery of each antibiotic. After optimization, the maximum predicted recovery rate was 84.18% for erythromycin under the optimized conditions of 101.20 mg C18, 52.00 mg PSA, and 1.01 g Na acetate. The recovery rates of the five other antibiotic residues ranged from 86.09% to 115.99%. The results suggested that modified QuEChERS could effectively be implemented in the analysis of antibiotic residues in milk.

Spectrophotometric determination of silicon tetrahydride in the air of workplace.

A new, simple and sensitive method was developed for the determination of silicon tetrahydride in the air of workplace in this study. The alkaline resin-based spherical activated carbon was used to collect sample of silicon tetrahydride at workplace. Silicon tetrahydride was then desorbed from active carbon in 100°C hot water. After reacting with ammonium molybdate, oxalic acid and 1,2,4-trichlorobenzene alpha-naphthol amino sulfonic acid under acid condition, silicon tetrahydride was transformed into silicon molybdenum blue. The absorbance of silicon molybdenum blue was quantitatively measured at the wavelength of 680 nm. The results showed that the average sampling efficiency and desorption efficiency were 97.53% and 94.94%, respectively by this method. Detection limits were 0.054 µg/mL for the spectrophotometric method and 0.14 mg/m(3) for the determination of silicon tetrahydride in the air of workplace (sampling volume was 7.5 L). The conversion rate of silicon tetrahydride gradually decreased when storage time of samples was extended. The descent rate of sample was less than 10% when the sample was sealed for 7 days in the room temperature. It was concluded that this spectrophotometric method can be successfully used to determine silicon tetrahydride in the worksites.

Using model-based screening to help discover unknown environmental contaminants.

Of the tens of thousands of chemicals in use, only a small fraction have been analyzed in environmental samples. To effectively identify environmental contaminants, methods to prioritize chemicals for analytical method development are required. We used a high-throughput model of chemical emissions, fate, and bioaccumulation to identify chemicals likely to have high concentrations in specific environmental media, and we prioritized these for target analysis. This model-based screening was applied to 215 organosilicon chemicals culled from industrial chemical production statistics. The model-based screening prioritized several recognized organosilicon contaminants and generated hypotheses leading to the selection of three chemicals that have not previously been identified as potential environmental contaminants for target analysis. Trace analytical methods were developed, and the chemicals were analyzed in air, sewage sludge, and sediment. All three substances were found to be environmental contaminants. Phenyl-tris(trimethylsiloxy)silane was present in all samples analyzed, with concentrations of ∼50 pg m(-3) in Stockholm air and ∼0.5 ng g(-1) dw in sediment from the Stockholm archipelago. Tris(trifluoropropyl)trimethyl-cyclotrisiloxane and tetrakis(trifluoropropyl)tetramethyl-cyclotetrasiloxane were found in sediments from Lake Mjøsa at ∼1 ng g(-1) dw. The discovery of three novel environmental contaminants shows that models can be useful for prioritizing chemicals for exploratory assessment.

Method for the analysis of total fluoride in fluoride-releasing dental varnishes.

Today's fluoride-releasing varnishes (F-varnish) contain a wide variety of ingredients which present analytical challenges for measuring their total fluoride content. This study reports improved methods to measure fluoride content in F-varnishes. Six different commercially available F-varnishes that contain difluorosilane (0.1% F) or NaF (2.26% F) alone or in combination with calcium-phosphates were analyzed. In a vial, 1-3 drops (0.05-0.15 g) of varnish product was dispensed, dissolved in chloroform, equilibrated in TISAB and analyzed via fluoride ion-selective electrode. The average weight percentage of fluoride for all F-varnishes containing NaF ranged from 2.03 to 2.24% F, which is within 90% of the declared label concentration of 2.26% F. Analysis of the difluorosilane-containing product required an additional hydrolysis step. ANOVA found no significant difference between the 5% NaF varnishes at p < 0.05. This method for fluoride analysis yields reliable and reproducible results and can be used for a wide variety of F-varnishes. The standard uncertainty for this method is ±4%. This method may become the basis for national and international standards that ensure the F-varnish products used in clinical practice have the fluoride content declared in the product literature.

Dissipation dynamic and residue distribution of flusilazole in mandarin.

In this paper, dissipation dynamic and terminal residue of flusilazole in mandarin and soil, as well as residue distribution of flusilazole in mandarin, were studied at three sites in China. Mandarin peel, mandarin pulp, whole mandarin, and soil samples were extracted by acetonitrile, cleaned up with dispersive solid-phase extraction, then analyzed by gas chromatography-mass spectrometry. The dissipation half-lives of flusilazole in mandarin and soil at all three experiment sites were 6.3-8.4 days and 5.5-13.4 days, respectively, with the exception of the soil dissipation at the Hunan site, which showed an increase-decrease process. Flusilazole residue levels in whole mandarin were all below 0.1 mg/kg on 14 days after the last application. Terminal residue study showed that flusilazole was mostly distributed in mandarin peel, which indicates minimal risk for eating mandarin pulp. These results could provide guidance for the proper and safe use of flusilazole on citrus fruits, and further our understanding of pesticide distribution in citrus fruits.

[Polyamidoamine dendrimer-functionalized silica nanocomposite with polydopamine coating for dispersive micro solid-phase extraction of benzoylurea insecticides in water samples].

Pesticides are used in the agricultural production process to ensure the yield and quality of agricultural products. However, in recent years, environmental pollution issues caused by pesticide residues have sparked widespread concern in society. It is important to develop convenient and efficient approaches to detect and monitor pesticide residues. In this study, targeting benzoylurea insecticides (BUs), polyamidoamine dendrimer-functionalized silica nanocomposite with polydopamine coating (SiO2-PAMAM-PDA) was designed and successfully synthesized. First, monodisperse silica nanoparticles were prepared by the hydrolysis of tetraethyl orthosilicate (TEOS) in mixed solution of ethanol, water and ammonia. The silane coupling agent (3-aminopropyl)triethoxysilane was then employed to introduce amino groups into the silica. Silica with the zeroth generation of polyamidoamine (PAMAM) modification (SiO2-PAMAM-G0) was obtained through Michael addition reaction of methyl acrylate. Ethylenediamine was added to polymerize with methyl acrylate using an amidation reaction to form the first-generation PAMAM (SiO2-PAMAM-G1). Finally, by polymerizing dopamine under alkaline conditions (pH=8.5), the SiO2-PAMAM-G1 was coated with PDA. Thus, the final product named SiO2-PAMAM-PDA was obtained. The composite was characterized using a transmission electron microscope (TEM) and an increase in surface roughness indicated the successful grafting of PDA coating. Dopamine structure contains abundant benzene rings and amino and hydroxyl groups. It could bind with BUs through multiple secondary interactions, such as hydrogen bond and π-π stacking interaction. Therefore, the introduction of PDA could effectively enhance the affinity of the material toward benzoylurea insecticides. The prepared nanocomposites were used as sorbents in a dispersive micro solid-phase extraction approach (D-µ-SPE). The established approach was employed to extract and enrich the BUs in water samples before high-performance liquid chromatography (HPLC) analysis. Diflubenzuron, triflumuron, hexaflumuron, and teflubenzuron were chosen as target analytes. The following was a typical D-µ-SPE procedure. The prepared adsorbents measuring 40 mg were first dispersed in an 8-mL sample solution containing 150 g/L NaCl. The dispersion was assisted by 120-s vortexing to ensure full contact between the SiO2-PAMAM-PDA and the targets. Next, the adsorbents were separated from the liquid phase by 4-min centrifugation (5000 r/min). Thereafter, the adsorbed benzoylureas were eluted using 1 mL acetonitrile as desorption solvent by 120-s vortexing. Separated by centrifugation, the eluate was dried under a mild nitrogen stream. The solid remains were redissolved in 0.1 mL of acetonitrile, filtered by filter membrane (0.22 µm), and then analyzed by HPLC. The experimental conditions in the D-µ-SPE process could have a great impact on the extraction efficiency. Experimental conditions were optimized using a single factor optimization approach to further enhance the extraction recoveries. The optimized conditions included adsorbent amount, extraction time, desorption solvent type, desorption solvent volume, desorption time, and NaCl addition amount. Under the optimal conditions, a linearity range of 10-500 µg/L and limits of detection (LODs, S/N=3) of 1.1-2.1 µg/L were obtained. The extraction recoveries and relative standard deviations (RSDs) of the four BUs were 82.8%-94.1% and 2.1%-8.0%, respectively. The established approach was compared with reported approaches targeting benzoylurea insecticides. It was discovered that this approach consumed less sample, material, organic solvent, and pretreatment time. It provided a more rapid and green choice for the determination of benzoylurea pesticides. To determine the applicability, the proposed approach was applied to analyze the four benzoylurea insecticides in three river water samples. The real water samples were pretreated using the developed approach ahead of instrumental analysis, and no benzoylurea pesticides residue was detected. Next, standard addition experiments were performed under three spiking levels, including 15, 50, and 200 µg/L. The established approach had good accuracy and feasibility with satisfactory recoveries (69.5%-99.4%) and RSDs (0.2%-9.5%).

Residue and dissipation dynamics of flusilazole in apple and soil.

A simple, quick and reliable residue analytical method for flusilazole in apple and soil was developed in this study. The samples were extracted with acetonitrile and determined by liquid chromatography with UV detection. The LOQ of the method was 0.02 mg/kg. The dissipation dynamic and final residues of flusilazole in apple and soil were studied using field trial method. The results of residual dynamics experiment showed that after the apple was treated by flusilazole at treble of recommended high dosage (3.75 g/kg H(2)O), the half-life times of flusilazole in apple and soil were 4.23-7.77 days and 3.04-5.14 days, respectively. Residues of flusilazole in apple at harvest time were all below 0.05 mg/kg at both recommended high dosage and 1.5 times of recommended high dosage.

Photonic crystal slab sensor with enhanced surface area.

In this work, we demonstrate improved molecular detection sensitivity for silicon slab photonic crystal cavities by introducing multiple-hole defects (MHDs), which increase the surface area available for label-free detection without degrading the quality factor. Compared to photonic crystals with L3 defects, adding MHDs into photonic crystal cavities enabled a 44% increase in detection sensitivity towards small refractive index perturbations due to surface monolayer attachment of a small aminosilane molecule. Also, photonic crystals with MHDs exhibited 18% higher detection sensitivity for bulk refractive index changes.

Development of a ceramic primer with higher bond durability for resin cement.

To increase the bond durability of resin to the CAD/CAM ceramic surface, two types of two-bottle type ceramic primers, consisting of Primer A1 or A2 and Primer B, were designed. Primer A1 was prepared by dissolving 25, 50, or 100 mg of gamma-methacryloxypropyltrimethoxysilane in 1 mL of ethanol. Primer A2 was prepared by dissolving 50 mg of mixed silanes, consisting of 1,2-bis(trimethoxysilyl)ethane to gamma-methacryloxypropyltrimethoxysilane, in 1 mL of ethanol. Mole fractions of 1,2-bis(trimethoxysilyl)ethane to gamma-methacryloxypropyltrimethoxysilane were 0, 10, 20, 30, 40 and 50 mol%. Primer B was prepared after dissolving 0.01, 0.05 or 0.1 mol L(-1) hydrochloric acid in ethanol by 50 vol%. Ceramic surface was silanated with a mixture of Primers A1 and B or Primers A2 and B for 1 min, and then air-dried. Commercial GC ceramic primer and Porcelain Liner M were utilized. Thereafter, dual-curing type resin cement was bonded to silanated ceramic surface through visible-light irradiation. Shear bond strength of resin to the ceramic surface was measured, before and after thermo-cycling. Addition of 0.01 or 0.05 mol L(-1) hydrochloric acid to the gamma-methacryloxypropyltrimethoxysilane allowed for significant increases in the bond strength. However, thermo-cycling resulted in significant decreases of approximately 5 MPa in the bond strength. Conversely, when the mixed silane, where 30 mol% of 1,2-bis(trimethoxysilyl)ethane dissolved in gamma-methacryloxypropyltrimethoxysilane, was utilized with 0.05 mol L(-1) hydrochloric acid, the reduction in the bond strength decreased to approximately 2 MPa. The designed ceramic primers exhibited higher ceramic bond durability than commercial ceramic primers.

Application of polydopamine functionalized magnetic graphene in triazole fungicides residue analysis.

In this work, a new analytical method based on polydopamine functionalized magnetic graphene (PDA@MG) adsorbent material has been developed to determine three triazole fungicides in water samples. As previous step, a novel polydopamine functionalized PDA@MG adsorbent material has been successfully prepared, which was characterized by fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). Based on this novel material, a new magnetic solid phase extraction (MSPE) method coupled with high performance liquid chromatography (HPLC) has been established for the determination of triazole fungicides in water samples. The main factors which could affect the experimental results were optimized. Under the optimal conditions, good linarites has been achieved in the range of 0.2-50 µg L-1, with the correlation coefficients (R2) were between 0.9962 and 0.9996. The limits of detections (LODs) were 0.0048-0.0084 µg L-1, and the relative standard deviations (RSDs) were between 1.7% and 4.8%. In addition, enrichment factors (EFs) were 572-916 times, which showed triazole fungicides residues could be accurately extracted and analyzed in this way. In the final experiment, the established method was applied to the detection of target analyzes in water samples. Satisfied results could be obtained for tebuconazole, propiconazole, and flusilazole. The recoveries of five water samples were between 69.4% and 106.4%, and the RSD were between 1.0% and 6.5%. The development method is more easy, effective, green and environmental-friendly, and has potential for application.

Visual observation of G-quadruplex DNA with the label-free fluorescent probe silole with aggregation-induced emission.

AIE molecule silole 1 could be used to detect G-quadruplex formation using an exonuclease I hydrolysis assay. This visual observation of G-quadruplexes has been successfully used in investigating multiple G-quadruplexes, including the one-stranded telomeric, c-myc, c-kit, VEGF G-quadruplexes, and a d(G(4)T(4)G(4)) inter-molecular G-quadruplex. The detection of G-quadruplex can be also applied to G-quadruplex isomers induced by small molecules.

X-ray photoelectron and infrared spectroscopies of quartz samples of contrasting toxicity.

An exploratory XPS and FTIR investigation of the surfaces of bulk quartz powders widely used in toxicological studies (DQ12 and Min-U-Sil 5) was carried with the aim of correlating surface features with toxicity as reflected by indicators of biological response. Some patches of amorphous silica were identified as well as varying amounts of calcium but none of these features correlated with biological response. No evidence of widely-quoted surface silanol (SiOH) structures was found in this investigation and the possibility that FTIR artefacts have been previously misidentified as silanol structures is discussed.

Characterization of the acidity of residual silanol groups in immobilized artificial membranes.

Residual silanol acidity and activity of one immobilized artificial membrane (IAM) column have been measured from the retention of LiNO(3) in the column with a methanol/buffer (1mM in Na(+)) (60:40, v/v) mobile phase buffered to different pH values. Just one type of silanol with pssK(a)=7.61 (near the pH limit recommended by the manufacturer) was found, although these silanols show large activity. The results obtained have been compared with those obtained previously for Resolve C18, Resolve Silica, Symmetry C18, Symmetry Silica, XTerra MS C18, underivatized XTerra, Lichrospher 100 RP-18, Purospher RP-18e, Luna C18 (2) and Chromolith Perfomance RP-18e, showing that the IAM column is similar to Luna C18 and Symmetry C18 in terms of silica quality, as measured by Li(+) retention. A warning about the use of IAM columns for emulation of biological systems at physiological pH 7 is given because the ionized silanols may contribute to the retention of some drugs at this pH.