Quantification of free and total bisphenol A and bisphenol B in human urine by dispersive liquid-liquid microextraction (DLLME) and heart-cutting multidimensional gas chromatography-mass spectrometry (MD-GC/MS)

A novel method combining dispersive liquid-liquid microextraction (DLLME) and heart-cutting multidimensional gas chromatography coupled to mass spectrometry was developed for the determination of free and total bisphenol A (BPA) and bisphenol B (BPB) in human urine samples. The DLLME procedure combines extraction, derivatization and concentration of the analytes into one step. Several important variables influencing the extraction efficiency and selectivity such as nature and volume of extractive and dispersive solvents as well as the amount of acetylating reagent were investigated. The temperature and time to hydrolyze BPA and BPB conjugates with a β-glucuronidase and sulfatase enzyme preparation were also studied. Under the optimized conditions good efficiency extraction (71-93%) and acceptable total DLLME yields (56-77%) were obtained for both analytes. Matrix-matched calibration curves were linear with correlation coefficients higher than 0.996 in the range level 0.1-5 μg/l, and the relative standard deviations (%RSD) were lower than 20% (n = 6). The limits of detection were 0.03 and 0.05 μg/l for BPA and BPB, respectively. The applicability of the proposed method for determining urinary free and total BPA and BPB was assessed by analyzing the human urine of a group of 20 volunteers. Free BPA was detected in 45% of the sample whereas total BPA was detected in 85% of the samples at concentrations ranging between 0.39 and 4.99 μg/l. BPB was detected in conjugated form in two samples.     

Evaluation of the Alpo-11 Crystallinity by Thermogravimetry

The evaluation of the crystallinity of several samples of ALPO-11 was performed by X-ray diffraction and thermogravimetry. Through XRD, the degrees of crystallinity of the samples were determined by the measurement of the area of the peaks at 2γ ranging from 20.7 to 24.1 degrees. The sample that presented the largest area was considered as 100% crystalline and the areas of the other samples were normalized in relation to this. From TG, the degree of crystallinity was determined considering the mass loss in the temperature range from 453 to 653 K that is related to remotion of di-isopropylamine molecules used during the synthesis procedure. The quantity of diisopropylamine on the material is proportional to the degree of crystallinity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Analysis Applied to Solid Catalysts Acidity,Activity and Regeneration

The use of catalysts in numerous important processes is widespread throughout the chemical and petroleum-processing industries. Thermal analytical techniques can be used to evaluate important properties and processes associated with solid catalysts. This paper presents examples carried out in our laboratory of the general application of TG and DSC to the acidity, activity and regeneration of solid catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Acid Properties of SiMCM-41 Mesoporous Molecular Sieve

The SiMCM-41 mesoporous molecular sieve was synthesised by the hydrothermal method. The physicochemical characterisation by infrared spectroscopy, X-ray diffraction and thermogravimetry, showed that the material presents a well-defined structure. In this study, the determination of the total acidity and relative strength of the acid sites of the SiMCM-41,was performed by desorption of adsorbed n-butylamine combined with thermogravimetric measurements. The total acidity, determined by means of the amount of amine desorbed normalised by mass of solid, was equivalent to 0.927 mmol g^–1, in the temperature range from 96 to 235°C. By using the Flynn and Wall integral kinetic model, at 5, 10 and 20°C min^–1 heating rates, it was determined that the activation energy to desorb n-butylamine was 90.7 kJ mol^–1, in the same temperature range, evidencing that SiMCM-41 presents only weak acid sites on its surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of histamine in port wines and grape juices by ion-pair extraction and stable isotope dilution GC-MS

Summary An isotope dilution, GC-MS method for the quantitation of histamine in wines and grape juices was assayed. This method includes isolation of histamine and its, deuterated analogue [α,α,β,β-²H₄]histamine, used as the labelled internal standard, by ion-pair extraction with bis-2-ethylhexylphosphate, conversion to the volatile derivative: tris-pentafluorobenzyl-histamine, capillary GC separation and measurement of the abundance ratio of the (M-181)⁺ ions from labelled and unlabelled derivatives. The method was successfully applied to the determination of histamine in several samples of Port wine, red and white table wine and grape juice. Data are given on detectability, linearity, repeatability and recovery.     

Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion

A flow injection system for the automatic determination of total phosphorus in beer is described. The developed manifold uses a two-stage photooxidation/thermal digestion procedure together with oxidizing and hydrolyzing reagents to convert all forms of phosphorus compounds to orthophosphate. Polyphosphates are hydrolyzed by acid and heat, and organo-phosphates are digested by UV-catalyzed peroxodisulfate oxidation. The orthophosphate formed is then spectrophotometrically determined by the phosphomolybdenum blue reaction, using stannous chloride as reducing agent. The results obtained for a set of 19 beer samples (with concentrations from 120 to 735 mg P/L) were in good agreement with the reference method, the maximum relative deviation found being 4.7%. Relative standard deviations for ten consecutive determinations were lower than 1.5%, and a detection limit of 1 mg P/L was achieved. Received: 18 May 1999 / Revised: 5 July 1999 / Accepted: 7 July 1999     

Analysis of Rotenoids by High Temperature High Resolution Gas Chromatography-Mass Spectrometry

A short glass capillary column coated with PS-090 (20% phenyl–80% methylpolysiloxane, of 10 m × 0.30 mm i.d.; with 0.1 μm film thickness) was used to analyze samples from Tephrosia candida; eighteen rotenoids were separated and identified without derivatization by HT-HRGC and HT-HRGC-MS. The mass spectra show the typical fragmentation pattern for rotenoids, with the base peaks either at M⁺, or originating from RDA (Retro Diels-Alder) rearrangements. HT-HRGC and HT-HRGC-MS were shown to be extremely valuable and neglected techniques for structural studies as well as the routine analysis of rotenoids in crude extracts. Possible applications to other classes of aromatic natural products, e.g. flavonoids, are envisaged.     

Synthesis of 6-Membered-Ring Fused Thiazine-Dicarboxylates and Thiazole-Pyrimidines via One-Pot Three-Component Reactions

A facile and efficient one-pot three-component reaction method for the synthesis of thiazine-dicarboxylates is reported. Reaction of an isocyanide and dialkyl acetylenedicarboxylate with 2-amino-4H-1,3-thiazin-4-one derivatives containing both an acidic proton and an internal nucleophile gave the products in good yields of 76–85%. The reactivity of dialkyl acetylenedicarboxylates was further tested in the synthesis of thiazole-pyrimidines where a two-component reaction of 2-aminothiazole with dialkyl acetylenedicarboxylates was successfully converted to a more efficient three-component reaction of a thiourea, α-haloketone and dialkyl acetylenedicarboxylate (DMAD/DEtAD) to give thiazole-pyrimidines in good yields of 70–91%.     

Intermolecular Hydrogen Bonds and the Supramolecular Structure of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-Bis(<Emphasis Type="Italic">p</Emphasis>-tolylsulfonyl)diethylenetriamine

Abstract  The title compound N,N′-bis(p-tolylsulfonyl)diethylenetriamine (1) was synthesized and its crystal structure determined by X-ray diffraction. Adjacent molecules of 1, symmetrically related through a c-glide, are linked by alternating hydrogen bonds that form molecular chains along [0 0 1]. Two molecular chains occur in each unit cell and pack to form alternating layers in a three-dimensional supramolecular structure. The compound crystallizes in the Pca2₁ space group stabilized by the inclusion of solvent dichloromethane molecules in structural voids between molecules of 1. The dichloromethane molecules are related through a twofold screw rotation axis and are not disordered. Index Abstract  Intermolecular hydrogen bonds involving sulfonamide moieties of title compound afford a supramoleular structure that accommodates the inclusion of dichloromethane in alternating layers.      

Free glycerol determination in biodiesel samples using palladium nanoparticles modified glassy carbon electrode associated with solid phase extraction

Journal of Solid State Electrochemistry - In this work, we developed a method for the quantification of free glycerol in biodiesel using electrochemical detection and solid phase extraction (SPE)....