Simultaneous determination of eight pesticide residues in coconut using MSPD and GC/MS

A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed to determine dimethoate, malathion, lufenuron, carbofuran, 3-hydroxycarbofuran, thiabendazole, difenoconazole and trichlorfon in coconut pulp using gas chromatography-mass spectrometry with selected ion monitoring (GC/MS, SIM). Different parameters of the method were evaluated, such as type of solid-phase (C(18), alumina, silica-gel and Florisil), the amount of solid-phase and eluent (dichloromethane, acetone, ethyl acetate, acetonitrile, n-hexane and n-hexane:ethyl acetate (1:1, v/v)). The best results were obtained using 0.5 g of coconut pulp, 1.0 g of C(18) as dispersant sorbent, 1.0 g of Florisil as clean-up sorbent and acetonitrile saturated with n-hexane as eluting solvent. The method was validated using coconut pulp samples fortified with pesticides at different concentration levels (0.25-1.0 mg kg(-1)). Average recoveries (four replicates) ranged from 70.1% to 98.7%, with relative standard deviations between 2.7% and 14.7%, except for lufenuron and difenoconazole, for which recoveries were 47.2% and 48.2%, respectively. Detection and quantification limits for coconut pulp ranged from 0.02 to 0.17 mg kg(-1) and from 0.15 to 0.25 mg kg(-1), respectively.     

The nonadiabatic deactivation paths of pyrrole

Multireference configuration interaction (MRCI) calculations have been performed for pyrrole with the aim of providing an explanation for the experimentally observed photochemical deactivation processes. Potential energy curves and minima on the crossing seam were determined using the analytic MRCI gradient and nonadiabatic coupling features of the COLUMBUS program system. A new deactivation mechanism based on an out-of-plane ring deformation is presented. This mechanism directly couples the charge transfer 1pipi* and ground states. It may be responsible for more than 50% of the observed photofragments of pipi*-excited pyrrole. The ring deformation mechanism should act complementary to the previously proposed NH-stretching mechanism, thus offering a more complete interpretation of the pyrrole photodynamics.     

Diverging pathways to topologically complex polycyclic bis-acetals and their ring system interchange

Carbinol-tethered octalin-diols (1), which differ only by the C11 configuration at the angular position, were transformed selectively to three types of structurally unrelated original scaffolds such as unsymmetrical octahydroanthracenes (5/7), furofuranes (6), or spirans (8/9) via a two-step protocol. The 11S* configuration ensures a C13-C4 Friedel-Crafts type C-C bonding (through an unprecedented oxidative cleavage-triggered domino process) while the 11R* configuration allows for a C13-C2 Marson-type Friedel-Crafts C-C bonding (through a nucleophilic acetal opening).     

Regioselective entry to bromo-gamma-hydroxybutenolides: useful building blocks for assemblying natural product-like libraries

[reaction: see text] We report a regioselective entry to 3-bromo- and 4-bromo-5-hydroxy-5H-furan-2-ones by photooxidation of 3-bromofuran with a singlet oxygen in the presence of a suitable base. By this procedure, a variety of 3-substituted gamma-hydroxybutenolides have become for the first time easily accessible. Strategies employing these highly functionalized building blocks for the preparation of focused libraries of natural-like molecules are also discussed.     

Effect of ethanol in the organic phase on liquid-liquid extraction in monosegmented flow analysis. Determination of zinc in drugs

In liquid-liquid extraction performed by monosegmented flow analysis (MSFA), the aqueous sample is introduced between two air bubbles and flows, under restricted dispersion, through a glass extraction tube where the analyte is retained, usually at pH higher than 8. The retained analyte is removed to a small volume of an organic phase containing a ligand which is introduced after the second air bubble. In this work, the effect of the organic phase composition on the extraction of Cu(II), Zn(II) and Cd(II) in MSFA systems was investigated by changing the ethanol content (0.1-4% v/v) in toluene, chloroform and carbon tetrachloride. The extracting efficiency of the organic phases containing ethanol was evaluated by using dithizone (DT), 1-2-pyridylazo-2 naphthol (PAN) and sodium diethyldithiocarbamate (DDTC) as ligands for the metals. The MSFA extraction system was improved by introducing a new syringe-based device for organic phase delivery. The presence of ethanol in the organic phase shows a remarkable (up to ten times) effect on the extraction efficiency of the flow system when DT is employed. Its presence is mandatory if DDTC is used, as it accounts for ligand solubility in the organic phase. The extraction efficiency also increases with the pH of the aqueous phase as a consequence of higher ionisation of the glass silanols, where the analytes are adsorbed before extraction. The system has been evaluated for determination of Zn(II) in drugs showing a mean R.S.D. of 2.2% and mean relative accuracy of 4.4%, when compared with atomic absorption spectrometry results. Typical sample frequency, sample and organic phase consumption are 30 samples per hour, 200 and 100 mul, respectively.     

Acid properties of the HZSM-12 zeolite with different Si/Al ratio by thermo-programmed desorption

In this work was studied the acid properties of a series of HZSM-12 zeolites with different Si/Al molar ratio. The samples of ZSM-12 were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na₂O:xAl₂O₃:100SiO₂:200H₂O, where: x=2, 1, 0.67 and 0.50, respectively. After the synthesis, the samples of ZSM-12 were ion-exchanged NH₄Cl solution to obtain zeolite in the acid form (HZSM-12). The acid properties were evaluated by n-butylamine thermodesorption in a TG equipment at three different heating rates. The model-free kinetic model was applied in the TG integral curves to estimate the apparent activation energy (E _a) of the n-butylamine desorption process. The results obtained showed that the HZSM-12 zeolite presents two kinds main of acid sites: one with E _a in the range of 115-125 kJ mol^-1 classified as weak and other kind with E _a varying of 230-250 kJ mol^-1 classified as strong. This revised version was published online in July 2006 with corrections to the Cover Date.     

Coke removal of the HZSM-12 zeolite with different silica/alumina ratio

The coke removal of HZSM-12 zeolite deactivated in the reaction of n-heptane cracking was studied by thermogravimetry using two multiple heating rate integral kinetics models proposed by Ozawa-Flynn-Wall and Vyazovkin to obtain the activation energy of process of thermoxidation of coke. The results obtained by both models presented excellent accordance with the related literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of synthetic 19-norsteroids trenbolone, tetrahydrogestrinone and gestrinone by gas chromatography-mass spectrometry

Tetrahydrogestrinone, gestrinone and trenbolone are synthetic 19-norsteroids with androgenic properties sharing a labile conjugated ketotrienyl motif. Their LC-MS analyses tend to overcome classical derivatization problems, a shortcoming to the use of GC-MS. Therefore, alternative derivatization procedures were evaluated. The procedure with methoxylamine: pyridine followed by TMSImid: MSTFA gave the best results. This is attributed to the stability of the MO-TMS derivatives hindering the formation of artifacts and tautomerism. A full method is presented including SPE, hydrolysis and liquid-liquid extraction. It was possible to confirm the analytes below 2 ng/mL in urine, being the method robust and cost effective also for screening proposes.