Effects of organoclay modifiers on the flammability, thermal and mechanical properties of polycarbonate nanocomposites filled with a phosphate and organoclays

Polycarbonate was melt blended with solid bisphenol A bis(diphenyl phosphate), and a series of organoclays. Effects of the organoclay modifiers on the flammability, thermal and mechanical properties of the nanocomposites were studied by limiting oxygen index, UL-94 burning test, thermogravimetric analysis, differential scanning calorimetry, tensile test and dynamic mechanical analysis. Although all the nanocomposites exhibit an intercalated-exfoliated morphology, they vary in the magnitude of intercalation revealed by X-ray diffraction and transmission electron microscopy. Flammability of the nanocomposites is strongly related to the thermal stability rather than the morphology. Glass transition temperature (T_g) and mechanical properties are controlled by both the morphology and the affinity of the organoclays with the matrix. The modifier containing hydroxyl moiety has stronger interactions with the matrix but it can promote its degradation, thus the corresponding nanocomposite exhibits a better intercalated morphology, higher T_g, superior strength and modulus however a worse thermal stability and flame retardancy. An additional silane within the organoclays would make the organoclays more compatible with the matrix but be a steric obstacle to the intercalation of the matrix chains; however, flame retardancy of the corresponding nanocomposite is enhanced due to the flame retardant nature of the silane. Similarly, the modifier bearing two long alkyl tails shows stronger affinity with the matrix than the one bearing a single tail, but it would hinder the intercalation due to the steric effect. These establishments between organoclay modifiers and the properties of nanocomposites might be guidance for developing materials with practical applications.     

Influence of char residues on flammability of EVA/EG, EVA/NG and EVA/GO composites

Graphite (expanded graphite(EG), natural graphite (NG) and graphite oxide (GO)) flame retardant poly(ethylene-co-vinyl acetate) copolymer (EVA) composites (EVA/EG, EVA/NG and EVA/GO) have been prepared by melt compounding. The flammability, the combustion process, the quantity of the residual char, the morphology of the residual chars and the thermal stability of the chars were investigated by cone calorimeter, SEM and TGA. The results indicate that heat release rate (HRR), total heat released (THR) and total smoke release (TSR) of EVA/EG (EG 30 phr) composite decrease to about 21%, 42% and 28% of that of pure EVA, respectively. The orders of the three kinds of graphite on the reduction effect of THR and TSR are EG > NG > GO. The higher the quantity, the higher is the thermal stability of the char residue and the more compact and porous char structure may be the main reasons for the phenomenon above. It has been found that the flame retardance of EVA vulcanisates is improved and the fire jeopardizing is dramatically reduced due to the addition of the graphite, especially for EG, which can give some advice to design formulations for practical applications as the jackets of cables.     

Quantification of Diaminomaleonitrile Using High Performance Liquid Chromatography with UV and Electrospray Ionization Mass Spectrometric Detection

Abstract

A method was developed to quantify diaminomaleonitrile (DAMN) in complex aqueous matrices using high performance liquid chromatography with UV and electrospray ionization mass spectrometric (ESI-MS) detection. The method is rapid (analytical times <10 min), able to quantify DAMN against complex backgrounds, and achieved with part per billion detection limits. Given the central role of DAMN in generating heterocycles of known biological significance, this study provides a rapid and sensitive method for quantifying DAMN in complex solutions.     

Determination of Gold by Flame Atomic Absorption Spectrometry with Hollow Fiber Liquid Phase Microextraction Using Room Temperature Ionic Liquids

A novel method to preconcentrate gold was developed employing a synergistic enhancement of a room temperature ionic liquid combined with hollow fiber liquid phase micro-extraction with flame atomic absorption spectrometry detection. The method is based on the complexation of gold with dithizone. The formed hydrophobic complex was subsequently extracted into the lumen of a hollow fiber. The organic phase was siphoned into FAAS for the determination. A room temperature ionic liquid and dithizone were used the enhancement reagent and chelating reagent, respectively. The addition of a room temperature ionic liquid led to a five-fold improvement in the extraction of gold. The 1-octanol was immobilized in the pores of the polypropylene hollow fiber as the liquid membrane and was also used as the acceptor solution. Some parameters that influenced extraction and determination were evaluated in detail, such as concentrations of the ionic liquid and dithizone, pH of samples, stirring rates, extraction time, and interferences. Under optimized conditions, a detection limit of 0.9 ng mL^?1 and an enrichment factor of 130 were achieved. The relative standard deviation (RSD) was 3.7% for Au (40 ng mL^?1, n = 5). The proposed method was successfully applied to the determination of gold in certified reference environmental samples and ore samples with satisfactory results.     

Determination of Copper by Faas After Preconcentration with Lead-4-Methylpiperidinedithiocarbamate on Microcrystalline Naphthalene By Solid Phase Extraction

ABSTRACT

By using the Pb-4-methylpiperidinedithiocarbamate complex (Pb(4-MPDC)₂) on microcrystalline naphthalene in a column a method was developed for the preconcentration of copper in water samples prior to its determination by FAAS. In this method, copper in liquid phase quantitatively replaces lead on the Pb(4-MPDC)₂-naphthalene solid phase in the column, forming solid Cu(4-MPDC)₂ complex.

Afterwards, copper on Cu(4-MPDC)₂-naphthalene can be easily eluted by potassium cyanide into the aqueous phase, and the Cu is measured by FAAS. The optimum experimental parameters such as pH, flow rate, sample volume, Pb(4-MPDC)₂-naphthalene ratio, concentration of the potassium cyanide solution and effect of matrix ions for the preconcentration of copper were investigated. The obtained recovery was nearly 100 %, when the enrichment factor was 100 for standard solutions and spiked water samples. The proposed method has been employed for the determination of copper in various standard metal alloys and natural water samples.     

Tunable Selectivity of an Alkali Aerosol Flame Ionization Detector Towards Organobromine and Organoiodide Species for Gas Chromatography

Abstract

The performance of a halogen selective aerosol alkali flame ionization detector (AFID) is presented. A constant delivery of desolvated alkali salt aerosol is introduced into the detector in the form of dual hydrogen gas flames. The problems of enhancement-source vaporization and contamination, which occur in fixed alkali salt versions, do not occur with the presented aerosol design. Detection limits range from 321 pgI/sec to 450 pgI/sec and 6.7 ngBr/sec to 15 ngBr/sec. Selectivity ratios were 10³ gI/gC and 10² gBr/gC using an 100 ppm potassium chloride as the alkali salt solution.     

Application of high‐resolution ESI and MALDI mass spectrometry to metabolite profiling of small interfering RNA duplex

We investigated the application of a high‐resolution Orbitrap mass spectrometer equipped with an electrospray ionization (ESI) source and a matrix‐assisted laser desorption/ionization‐time‐of‐flight (MALDI‐TOF) mass spectrometer to the metabolite profiling of a model small interfering RNA (siRNA) duplex TSR#34 and compared their functions and capabilities. TSR#34 duplex was incubated in human serum in vitro, and the duplex and its metabolites were then purified by ion exchange chromatography in order to remove the biological matrices. The fraction containing the siRNA duplex and its metabolites was collected and desalted and then subjected to high‐performance liquid chromatography (HPLC) equipped with a reversed phase column. The siRNA and its metabolites were separated into single strands by elevated chromatographic temperature and analyzed using the ESI‐Orbitrap or the MALDI‐TOF mass spectrometer. Using this method, the 5' and/or 3' truncated metabolites of each strand were detected in the human serum samples. The ESI‐Orbitrap mass spectrometer enabled differentiation between two possible RNA‐based sequences, a monoisotopic molecular mass difference which was less than 2 Da, with an intrinsic mass resolving power. In‐source decay (ISD) analysis using a MALDI‐TOF mass spectrometer allowed the sequencing of the RNA metabolite with characteristic fragment ions, using 2,4‐dihydroxyacetophenone (2,4‐DHAP) as a matrix. The ESI‐Orbitrap mass spectrometer provided the highest mass accuracy and the benefit of on‐line coupling with HPLC for metabolite profiling. Meanwhile, the MALDI‐TOF mass spectrometer, in combination with 2,4‐DHAP, has the potential for the sequencing of RNA by ISD analysis. The combined use of these methods will be beneficial to characterize the metabolites of therapeutic siRNA compounds. Copyright © 2012 John Wiley & Sons, Ltd.     

Identification of isomeric 5‐hydroxytryptophan‐ and oxindolylalanine‐containing peptides by mass spectrometry

Cells continuously produce reactive oxidative species that can modify all cellular components. In proteins, for example, cysteine, methionine, tryptophan (Trp), and tyrosine residues are particularly prone to oxidation. Here, we report two new approaches to distinguish two isomeric oxidation products of Trp residues, i.e. 5‐hydroxytryptophan (5‐HTP) and oxindolylalanine (Oia) residues, in peptides. First, 2‐nitrobenzenesulfenyl chloride, known to derivatize Trp residues in position 2 of the indole ring, was used to label 5‐HTP residues. The mass shift of 152.98 m/z units allowed identifying 5‐HTP‐ besides Trp‐containing peptides by mass spectrometry, whereas Oia residues were not labeled. Second, fragmentation of the Oia‐ and 5‐HTP‐derived immonium ions at m/z 175.08 produced ions characteristic for each residue that allowed their identification even in the presence of y₁ ions at m/z 175.12 derived from peptides with C‐terminal arginine residues. The pseudo MS³ spectra acquired on a quadrupole time‐of‐flight hybrid mass spectrometer displayed two signals at m/z 130.05 and m/z 132.05 characteristic for Oia‐containing peptides and a group of six signals (m/z 103.04, 120.04, 130.04, 133.03, 146.04, and 148.04) for 5‐HTP‐cointaining peptides. In both cases, the relative signal intensities appeared to be independent of the sequence providing a specific fingerprint of each oxidative modification. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of amino acid‐derived betaines by electrospray ionization tandem mass spectrometry

Betaines belong to the naturally occurring osmoprotectants or compatible solutes present in a variety of plants, animals and microorganisms. In recent years, metabolomic techniques have been emerging as a fundamental tool for biologists because the constellation of these molecules and their relative proportions provide with information about the actual biochemical condition of a biological system. Therefore, identification and characterization of biologically important betaines are crucial, especially for metabolomic studies. Most of the natural betaines are derived from amino acids and related homologues. Although, theoretically, all the amino acids can be converted to corresponding betaines by simple methylation of the amine group, only a few of the amino acid‐derived betaines were fully characterized in the literature. Here, we report a combined electrospray ionization tandem and high‐resolution mass spectrometry study of all the betaines derived from amino acids, including the isomeric betaines. The decomposition pathway of protonated, sodiated and potassiated molecule ions that enable unambiguous characterization of the betaines including the isomeric betaines and overlapping ionic species of different betaines is distinctive. Copyright © 2012 John Wiley & Sons, Ltd.     

Dereplication of known pregnane glycosides and structural characterization of novel pregnanes in Marsdenia tenacissima by high‐performance liquid chromatography and electrospray ionization‐tandem mass spectrometry

In the search for novel natural products in plants, particularly those with potential bioactivity, it is important to efficiently distinguish novel compounds from previously isolated, known compounds, a process known as dereplication. In this study, electrospray ionization‐multiple stage tandem mass spectrometry (ESI‐MSⁿ) was used to study the behaviour of 12 pregnane glycosides and genins previously isolated from Marsdenia tenacissima, a traditional Chinese medicinal plant, as a basis for dereplication of compounds in a plant extract. In addition to [M + Na]⁺ and [M + NH₄]⁺ ions, a characteristic [M‐glycosyl + H]⁺ ion was observed in full‐scan mode with in‐source fragmentation. Sequential in‐trap collision‐induced dissociation of [M + Na]⁺ ions from 11,12‐diesters revealed consistent preferred losses of substituents first from C‐12, then from C‐11, followed by losses of monosaccharide fragments from the C‐3 tri‐ and tetrasaccharide substituents. A crude methanol extract of M. tenacissima stems was analysed using high‐performance liquid chromatography coupled to ESI‐MS. Several previously isolated pregnane glycosides were dereplicated, and the presence of an additional nine novel pregnane glycosides is predicted on the basis of the primary and fragment ions observed, including two with a previously unreported C₄H₇O C‐11/C‐12 substituent of pregnane glycosides. This study is the first report of prediction of the structures of novel pregnane glycosides in a crude plant extract by a combination of in‐source fragmentation and in‐trap collision‐induced dissociation and supports the usefulness of LC‐ESI‐MSⁿ not only for dereplication of active compounds in extracts of medicinal plants but also for detecting the presence of novel related compounds. Copyright © 2012 John Wiley & Sons, Ltd.