Cyclohexane‐1,3‐dione as a derivatizing agent for the analysis of aldehydes by micelar electrokinetic chromatography with diode array detection

Aldehydes are important compounds in a large number of samples, especially food and beverages. In this work, for the first time, cyclohexane‐1,3‐dione (CHD) was used as a derivatizing reagent aiming aldehyde (formaldehyde, acetaldehyde, propionaldehyde, and valeraldehyde) analysis by MEKC‐DAD. The optimized separation of the derivates was performed using a voltage program (+20 kV, 0–15 min.; +23 kV, 15–17 min.) at a temperature of 26°C, and using as the running buffer a mixture containing 100 mmol/L of sodium dodecyl sulfate and 29 mmol/L of sodium tetraborate at pH 9.2, with maximum absorbance at 260 nm. CHD was compared with two other derivatizing agents: 3‐methyl‐2‐benzothiazolinone hydrazone and phenylhydrazine‐4‐sulfonic acid. The CHD‐aldehyde derivatives were also characterized by LC‐MS. The calibration curves for all aldehydes had r² above 0.999 and LODs ranged from 0.01 to 0.7 mg/L. The optimized methodology was applied in sugar cane brandy (cachaça) samples successfully. CHD showed to be an alternative derivatization reagent due to its stability, aqueous solubility, high selectivity and sensitivity, reduced impurities, and simple preparation steps.     

Simultaneous Determination of Nickel and Cobalt Using a Solid Bismuth Vibrating Electrode by Adsorptive Cathodic Stripping Voltammetry

A simple, fast, sensitive and greener voltammetric procedure for simultaneous analysis of nickel (Ni) and cobalt (Co) by square wave adsorptive cathodic stripping voltammetry (SW‐AdCSV) using a solid bismuth vibrating electrode is presented for the first time. The procedure enables to determine Ni together with Co, in ammonia buffer 0.1 M (pH 9.2) and in the presence of oxygen, and involves an adsorptive accumulation of metal‐dimethylglyoxime (Ni‐DMG and Co‐DMG) complexes on the electrode surface. For Ni and Co, the detection limits, obtained with 30 s of accumulation time, were 0.6 and 1.0 µg L^?1, respectively. The method was free of metals (Cd²⁺, Cr³⁺, Cr⁶⁺, Cu²⁺, Fe³⁺ and Pb²⁺ up to 50 µg L^?1, Al³⁺ and Mn²⁺ up to 500 µg L^?1; Zn²⁺ up to 300 µg L^?1) interferences up to the concentrations mentioned in brackets. The proposed method was validated for simultaneous determination of Ni and Co in a certified reference surface and river waters with good results.     

SALS,WAXS and mechanical properties of heat‐treated thermotropic polymers

The influence of heat treatment on the texture, microstructure and tensile mechanical properties of extruded thin films of a series of high‐performance thermotropic liquid crystal polymers (LCPs) was investigated. LCPs based on random units of hydroxybenzoic acid (B), hydroxynaphthoic acid (N), terephthalic acid (TA) and biphenol (BP) were kindly supplied by the former Hoechst Celanese Corp as 50 µm thick extruded tapes. The LCPs, denoted B‐N, COTBP and RD1000, have B and N as common comonomers and vary the other comonomers. Thus, this study also enables the investigation of the influence of monomer composition on microstructure and mechanical properties. Heat treatments were carried out at temperatures close to the solid‐to‐nematic transition (T_s→n) for periods up to 5 h, under dry air conditions. The thermal treatment produced either two endotherms or a small increase of T_s→n (B‐N and RD1000), or increased significantly T_s→n (COTBP). Moreover, when heat treatment was carried out approximately 40°C below the respective T_s→n, the mechanical Young's modulus, E, along the extrusion axis, increased for all LCPs. Strikingly, for COTBP, E increased over 100% relative to the as‐extruded film. The results also showed that the optimum treatment time for improving the Young modulus, under dry air atmosphere, was between 3 and 4 h. Wide‐angle X‐ray scattering showed a significant sharpening of crystalline reflections and concentration of the 002 meridional reflection as a result of thermal treatment, suggesting the elimination of defects and a better alignment of the molecular chains along the extrusion axis. This would explain the increase in tensile modulus. Copyright © 2013 John Wiley & Sons, Ltd.     

Stereoregular poly‐O‐methyl [m,n]‐polyurethanes derived from D‐mannitol

Novel linear carbohydrate‐derived [m,n]‐polyurethanes are successfully prepared using D ‐mannitol as renewable and low cost starting material. The key comonomer, 1,6‐di‐O‐phenylcarbonyl‐2,3,4,5‐tetra‐O‐methyl‐D ‐mannitol is polymerized with a diamine synthesized from D ‐mannitol or with alkylenediamines. These polymerization reactions afford, respectively, a [6,6]‐polyurethane entirely based on a carbohydrate derivative or [m,n]‐polyurethanes constituted by a poly‐O‐methyl substituted unit alternating with a polymethylene chain. All these polymers are stereoregular, as result of the C₂ axis of symmetry of mannitol. The optically active polyurethanes are characterized by standard methods (FTIR, RMN, GPC, TGA, and DSC). Thus, GPC analysis reveals weight‐average molecular weights between 18,000 and 25,000 Da. Thermal studies (DSC) indicate that the polymers obtained are amorphous materials with T_g values dependent on the structure and chain length of the diamine constituent. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Electrospray ionization mass spectrometry and partial least squares discriminant analysis applied to the quality control of olive oil

Direct infusion electrospray ionization mass spectrometry in the positive ion mode [ESI(+)‐MS] is used to obtain fingerprints of aqueous–methanolic extracts of two types of olive oils, extra virgin (EV) and ordinary (OR), as well as of samples of EV olive oil adulterated by the addition of OR olive oil and other edible oils: corn (CO), sunflower (SF), soybean (SO) and canola (CA). The MS data is treated by the partial least squares discriminant analysis (PLS‐DA) protocol aiming at discriminating the above‐mentioned classes formed by the genuine olive oils, EV (1) and OR (2), as well as the EV adulterated samples, i.e. EV/SO (3), EV/CO (4), EV/SF (5), EV/CA (6) and EV/OR (7). The PLS‐DA model employed is built with 190 and 70 samples for the training and test sets, respectively. For all classes (1–7), EV and OR olive oils as well as the adulterated samples (in a proportion varying from 0.5 to 20.0% w/w) are properly classified. The developed methodology required no ions identification and demonstrated to be fast, as each measurement lasted about 3 min including the extraction step and MS analysis, and reliable, because high sensitivities (rate of true positives) and specificities (rate of true negatives) were achieved. Finally, it can be envisaged that this approach has potential to be applied in quality control of EV olive oils. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of New Tetrazole Derivatives of α,α‐Trehalose

Five new nitrogen heterocycles, mono‐and disubstituted tetrazoles with potential synthetic and pharmacological interest, were synthesized from α, α‐trehalose via the alkylation of commercial tetrazoles. This method appears to have broad scope with respect to the variations at positions 1 and 2 of tetrazole.     

Analysis of PCBs in soils and sediments by microwave-assisted extraction,headspace-SPME and high resolution gas chromatography with ion-trap tandem mass spectrometry

A procedure for the determination of seven indicator PCBs in soils and sediments using microwave-assisted extraction (MAE) and headspace solid-phase microextraction (HS-SPME) prior to GC-MS/MS is described. Optimization of the HS-SPME was carried out for the most important parameters such as extraction time, sample volume and temperature. The adopted methodology has reduced consumption of organic solvents and analysis runtime. Under the optimized conditions, the method detection limit ranged from 0.6 to 1?ng/g when 5?g of sample was extracted, the precision on real samples ranged from 4 to 21% and the recovery from 69 to 104%. The proposed method, which included the analysis of a certified reference material in its validation procedure, can be extended to several other PCBs and used in the monitoring of soil or sediments for the presence of PCBs.     

Combined cysteine and homocysteine quantitation in plasma by trap and release membrane introduction mass spectrometry

Recently, a new and efficient method for total homocysteine (tHcy) quantitation in plasma using trap and release membrane introduction mass spectrometry (T&R-MIMS) with a versatile removable direct introduction membrane probe (DIMP) was described [R. Haddad, M. A. Mendes, N. F. Hoehr and M. N. Eberlin, Analyst, 2001, 126, 1212]. Herein we report on the use of the DIMP-T&R-MIMS technique for total cysteine (tCys) quantitation; hence combined tCys and tHcy quantitation in plasma or serum can be achieved. The method employs Cys and Hcy derivatization with ethyl chloroformate (after disulfide bond reduction with dithiothreitol and protein precipitation with trichloroacetic acid), preconcentration in a capillary silicone membrane, and their thermal desorption to the gas phase inside the ion source region of a mass spectrometer, at a point exactly between the two ionization filaments. Thermal desorption uses the uniform heat radiation provided by the two ionization filaments. The analytes are then ionized by electron ionization and both Cys and Hcy are quantitated by mass spectrometry using selected ion monitoring. For tCys quantitation, good linearity and reproducibility was observed for concentrations ranging from 5 to 350 microM, recovery was near 95%, and the limit of detection (LOD) was of 2 microM. This LOD is well below the mean Cys concentration in plasma, and serum samples from a large group of healthy people showed a mean tCys concentration of 132 +/- 45 microM.     

Electron impact mass spectrometry of some macrocyclic polyether lactones

Electron impact mass spectrometry has been used together with linked scans, exact mass measurements and mass-analysed ion kinetic energy spectrometry to study nine inacrocyclic polyether lactones in detail. The presence of abundant hydrogenated oxirane ions has been observed for all the compounds examined, and confirmed by kinetic energy release measurements.     

Amplified Chirality Transfer to Aromatic Molecules through Non-specific Inclusion by Amorphous,Hyperbranched Poly(fluorenevinylene) Derivatives

Optically active, hyperbranched, poly(fluorene-2,4,7-triylethene-1,2-diyl) [poly(fluorenevinylene)] derivatives bearing a neomenthyl group and a pentyl group at the 9-position of the fluorene backbone at various ratios acted as a chirality donor (host polymers) efficiently included naphthalene, anthracene, pyrene, 9-phenylanthracene, and 9,10-diphenyanthracene as a chirality acceptor (guest molecules) in their interior space in film as well as in solution, with the guest molecules exhibiting intense circular dichroism through chirality transfer with chirality amplification. The efficiency of the chirality transfer was much higher with higher-molar-mass polymers than lower-molar-mass ones as well as with hyperbranched polymers compared to the analogous linear ones. The hyperbranched polymers include the small molecules in their complex structure without any specific interactions at various stoichiometries. The included molecules may have ordered intermolecular arrangement that may be somewhat similar to those of liquid crystals. Naphthalene, anthracene, and pyrene included in the polymer exhibited efficient circularly polarized luminescence, where the chirality was remarkably amplified in excited states, and anthracene exhibited especially high anisotropies in the emission on the order of 10⁻².