Enantioselective analysis of zopiclone and its metabolites in plasma by liquid chromatography/tandem mass spectrometry

A high-performance liquid chromatographic method with triple-quadrupole mass spectrometry detection (LC-MS-MS) was developed and validated for the first time for the simultaneous quantification of zopiclone and its metabolites in rat plasma samples. The analytes were isolated from rat plasma by liquid-liquid extraction and separated using a chiral stationary phase based on an amylose derivative, Chiralpak ADR-H column, and ethanol-methanol-acetonitrile (50:45:5, v/v/v) plus 0.025% diethylamine as the mobile phase, at a flow-rate of 1.0 mL min(-1). Moclobemide was used as the internal standard. The developed method was linear over the concentration range of 7.5-500 ng mL(-1). The mean absolute recoveries were 74.6 and 75.7; 61.6 and 56.9; 72.5, and 70.7 for zopiclone enantiomers, for N-desmethyl zopiclone enantiomers and for zopiclone-N-oxide enantiomers, respectively, and 75.9 for the internal standard. Precision and accuracy were within acceptable levels of confidence (<15%). The method application in a pilot study of zopiclone kinetic disposition in rats showed that the levels of (+)-(S)-zopiclone were always higher than those of (-)-R-zopiclone. Higher concentrations were also observed for (+)-(S)-N-desmethyl zopiclone and (+)-(S)-N-oxide zopiclone, confirming the stereoselective disposition of zopiclone.

Electrospray MS-based characterization of beta-carbolines - mutagenic constituents of thermally processed meat

The beta-carbolines 1-methyl-9H-pyrido [3,4-b]indole and 9H-pyrido[3,4b]indole have been implicated as having causative roles in a number of human diseases, such as Parkinson`s disease and cancer. As they can be formed during the heating of protein-rich food, a number of analytical methodologies have been proposed for their detection and quantification in foodstuff For this purpose, LC-MS and LC-MS/MS have emerged as the most specific analytical methods, and the quantification is based on the occurrence of unusual ions, such as [M+H-(H(center dot))](+) and [M + H-2H](+). In this study, we have investigated the formation of these ions by accurate-mass electrospray MS/MS and demonstrated that these ions are formed from gas-phase ion-molecule reactions between water vapor present in the collision cell and the protonated molecule of 1-methyl-9H-pyrido [3,4-b]indole and 9H-pyrido[3,4b]indole. Although this reaction has been previously described for heterocyclic amine ions, it has been overlooked in the most of recent LC-MS and LC-MS/MS studies, and no complete data of the fragmentation are reported. Our results demonstrate that additional attention should be given with respect to eliminating water vapor residues in the mass spectrometer when analysis of beta-carbolines is performed, as this residue may affect the reliability in the results of quantification.

Enantioselective analysis of mirtazapine, demethylmirtazapine and 8-hydroxy mirtazapine in human urine after solid-phase microextraction

A selective and reproducible off-line solid-phase microextraction procedure was developed for the simultaneous enantioselective determination of mirtazapine (MRT), demethylmirtazapine and 8-hydroxymirtazapine in human urine. CE was used for optimization of the extraction procedure whereas LC-MS was used for method validation and application. The influence of important factors in the solid-phase microextraction efficiency is discussed, such as the fiber coatings, extraction time, pH, ionic strength, temperature and desorption time. Before extraction, human urine samples were submitted to enzymatic hydrolysis at 37 degrees C for 16 h. Then, the enzyme was precipitated with trichloroacetic acid and the pH was adjusted to 8 with 1 mol/L pH 11 phosphate buffer solution. In the extraction, the analytes were transferred from the aqueous solution to the polydimethylsiloxane-divinylbenzene fiber coating and then desorbed in methanol. The mean recoveries were 5.4, 1.7 and 1.0% for MRT, demethylmirtazapine and 8-hydroxymirtazapine enantiomers, respectively. The method was linear over the concentration range of 62-1250 ng/mL. The within-day and between-day assay precision and accuracy were lower than 15%. The method was successfully employed in a preliminary cumulative urinary excretion study after administration of racemic MRT to a healthy volunteer.

Development of Vegetable Oil Emulsions with Lamellar Liquid-Crystalline Structures

Emulsions containing vegetable oils and anisotropic phases have especially attractive properties in pharmaceutical technology. They are use as vehicle for different kind of drugs, especially those of topical application. Apart from that, many vegetable oil have pharmacological activity, increasing the necessity for the development of new delivery systems for them. We developed emulsions with vegetable oils at a fixed surfactant ratio and observed the formation of liquid crystalline phases. Nine vegetable oils: Andiroba, Apricot, Avocado, Brazil Nut, Buriti, Cupuassu, Marigold, Passion Fruit and Pequi and mineral oil were tested. Surfactant system was consisted by Steareth-2 and Ceteareth-5. Emulsions were prepared by the emulsion phase inversion (EPI) method, presenting high stability independent on the HLB value. Results indicate that this method could be employed to attain stable emulsions, even if the required HLB value is not known.

Rheological behavior, zeta potential, and accelerated stability tests of Buriti oil (Mauritia flexuosa) emulsions containing lyotropic liquid crystals

Background: It is well known that the Amazon region presents a huge biodiversity; therefore, countless natural resources are being employed in the production of phytocosmetics and phytomedicines. Objective: The purpose of this work was to obtain emulsions produced with Buriti oil and nonionic surfactants. Methods: Two surfactant systems were employed (Steareth-2 associated to Ceteareth-5 and to Ceteareth-20) to produce the emulsions using phase diagram method. Emulsions were obtained by echo-planar imaging method at 75 degrees C. Rheological behavior and zeta potential were evaluated, and accelerated stability tests were performed. Results: All emulsions analyzed presented pseudoplastic behavior. Zeta potential values were obtained between -14.2 and -53.3 mV. The formulations did not show changes in either physical stability, pH, or rheological behavior after accelerated stability tests. Significant differences were observed only after temperature cycling test. Conclusion: Based on these results, the emulsions obtained could be considered as promising delivery systems.

Novel and facile solution-phase synthesis of 2,5-diketopiperazines and O-glycosylated analogs

This work describes the synthesis in Solution of a series of related diketopiperazines with potential biological activities: cyclo(L-Pro-L-Ser), cyclo(L-Phe-L-Ser), cyclo(D-Phe-L-Ser) and the corresponding glycosylated analogs of the latter, cyclo[D-Phe-L-Ser(alpha GlcNAc)] and cyclo[D-Phe-L-Ser(beta GlcNAc)]. The synthetic approach involved coupling reactions of -OH or O-glycosylated serine benzyl esters with NFmoc-protected amino acids (Pro or Phe), followed by one-pot deprotection-cyclization reaction in the presence of 20% piperidine in DMF. (C) 2009 Elsevier Ltd. All rights reserved.

Methylmercury and inorganic mercury determination in blood by using liquid chromatography with inductively coupled plasma mass spectrometry and a fast sample preparation procedure

Despite the necessity to differentiate chemical species of mercury in clinical specimens, there area limited number of methods for this purpose. Then, this paper describes a simple method for the determination of methylmercury and inorganic mercury in blood by using liquid chromatography with inductively coupled mass spectrometry (LC-ICP-MS) and a fast sample preparation procedure. Prior to analysis, blood (250 mu L) is accurately weighed into 15-mL conical tubes. Then, an extractant solution containing mercaptoethanol, L-cysteine and HCI was added to the samples following sonication for 15 min. Quantitative mercury extraction was achieved with the proposed procedure. Separation of mercury species was accomplished in less than 5 min on a C18 reverse-phase column with a mobile phase containing 0.05% (v/v) mercaptoethanol, 0.4% (m/v) L-cysteine, 0.06 mol L(-1) ammonium acetate and 5% (v/v) methanol. The method detection limits were found to be 0.25 mu g L(-1) and 0.1 mu Lg L(-1) for inorganic mercury and methylmercury, respectively. Method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from the National Institute of Standards and Technology (NIST). The proposed method was also applied to the speciation of mercury in blood samples collected from fish-eating communities and from rats exposed to thimerosal. With the proposed method there is a considerable reduction of the time of sample preparation prior to speciation of Hg by LC-ICP-MS. Finally, after the application of the proposed method, we demonstrated an interesting in vivo ethylmercury conversion to inorganic mercury. (C) 2009 Elsevier B.V. All rights reserved.

A fast sample preparation procedure for mercury speciation in hair samples by high-performance liquid chromatography coupled to ICP-MS

A simple method for mercury speciation in hair samples with a fast sample preparation procedure using high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry is proposed. Prior to analysis, 50 mg of hair samples were accurately weighed into 15 mL conical tubes. Then, an extractant solution containing mercaptoethanol, L-cysteine and HCl was added to the samples following sonication for 10 min. Quantitative mercury extraction was achieved with the proposed procedure. Separation of inorganic mercury (Ino-Hg), methylmercury (Met-Hg) and ethylmercury (Et-Hg) was accomplished in less than 8 min on a C18 reverse phase column with a mobile phase containing 0.05% v/v mercaptoethanol, 0.4% m/v L-cysteine, 0.06 mol L(-1) ammonium acetate and 5% v/v methanol. The method detection limits were found to be 15 ng g(-1), 10 ng g(-1) and 38 ng g(-1), for inorganic mercury, methylmercury and ethylmercury, respectively. Sample throughput is 4 samples h(-1) (duplicate). A considerable improvement in the time of analysis was achieved when compared to other published methods. Method accuracy is traceable to Certified Reference Materials (CRMs) 85 and 86 human hair from the International Atomic Energy Agency (IAEA). Finally, the proposed method was successfully applied to the speciation of mercury in hair samples collected from fish-eating communities of the Brazilian Amazon.

Simultaneous Analysis of Tramadol, O-Desmethyltramadol, and N-Desmethyltramadol Enantiomers in Rat Plasma by High-Performance Liquid Chromatography-Tandem Mass Spectrometry: Application to Pharmacokinetics

Tramadol (T) is available as a racemic mixture of (+)-trans-T and (-)-trans-T. The main metabolic pathways are O-demethylation and N-demethylation, producing trans-O-desmethyltramadol (M1) and trans-N-desmethyltramadol (M2) enantiomers, respectively. The analgesic effect of T is related to the opioid activity of (+)-trans-T and (+)-M1 and to the monoaminergic action of (+/-)-trans-T. This is the first study using tandem mass spectrometry as a detection system for the simultaneous analysis of trans-T, M1, and M2 enantiomers. The analytes were resolved on a Chiralpak (R) AD column using hexane: ethanol (95.5:4.5, v/v) plus 0.1% diethylamine as the mobile phase. The quantitation limits were 0.5 ng/ml for trans-T and M1 and 0.1 ng/ml for M2. The method developed and validated here was applied to a pharmacokinetic study in rats. Male Wistar rats (n = 6 at each time point) received a single oral dose of 20 mg/kg racemic trans-T. Blood samples were collected up to 12 h after drug administration. The kinetic disposition of trans-T and M2 was enantioselective (AUC((+)/(-)) ratio = 4.16 and 6.36, respectively). The direction and extent of enantioselectivity in the pharmacokinetics of trans-T and M2 in rats were comparable to data previously reported for healthy volunteers, suggesting that rats are a suitable model for enantioselective studies of trans-T pharmacokinetics. Chirality 23: 287-293, 2011. (C) 2010 Wiley-Liss, Inc.

Analysis of the Phase Changes During Evaporation of Emulsions with Different Oil Phases

Emulsions surfer alterations in their microstructure after applied on the skin, because of the interaction with skin constituents and mainly by the evaporation of volatile components. These alterations are not even considered by cosmetic formulators, but they are extremely important because they can act on formulation stability, on delivery and on permeation of actives and also on the ability to build the occlusive film, responsible for skin`s moisturization. This research studied the phase changing during evaporation of emulsions made with three different oil phase: mineral oil, avocado oil, and isocethyl/stearoil stearate, as a function of the decrease on water ratio, using phase diagrams and evaporation test. It was observed the formation of liquid crystalline phases and their transition along the evaporation path for emulsions with the three different oil phases. It was also observed that these transitions occurred in different water ratios.

Analysis of Liquid Crystalline Nanoparticles by Small Angle X-Ray Diffraction: Evaluation of Drug and Pharmaceutical Additives Influence on the Internal Structure

The goal of this work was to study the liquid crystalline structure of a nanodispersion delivery system intended to be used in photodynamic therapy after loading with photosensitizers (PSs) and additives such as preservatives and thickening polymers. Polarized light microscopy and light scattering were performed on a standard nanodispersion in order to determine the anisotropy of the liquid crystalline structure and the mean diameter of the nanoparticles, respectively. Small angle X-ray diffraction (SAXRD) was used to verify the influence of drug loading and additives on the liquid crystalline structure of the nanodispersions. The samples, before and after the addition of PSs and additives, were stable over 90 days, as verified by dynamic light scattering. SAXRD revealed that despite the alteration observed in some of the samples analyzed in the presence of photosensitizing drugs and additives, the hexagonal phase still remained in the crystalline phase. (C) 2011 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100: 2849-2857, 2011

Quantification of carbamazepine, carbamazepine-10,11-epoxide, phenytoin and phenobarbital in plasma samples by stir bar-sorptive extraction and liquid chromatography

A sensitive and reproducible stir bar-sorptive extraction and high-performance liquid chromatography-UV detection (SBSE/HPLC-UV) method for therapeutic drug monitoring of carbamazepine, carbamazepine-10,11-epoxide, phenytoin and phenobarbital in plasma samples is described and compared with a liquid:liquid extraction (LLE/HPLC-UV) method. Important factors in the optimization of SBSE efficiency such as pH, extraction time and desorption conditions (solvents, mode magnetic stir, mode ultrasonic stir, time and number of steps) assured recoveries ranging from 72 to 86%, except for phenytoin (62%). Separation was obtained using a reverse phase C-18 column with UV detection (210 nm). The mobile phase consisted of water: acetonitrile (78:22, v/v). The SBSE/HPLC-UV method was linear over a working range of 0.08-40.0 mu g mL(-1) for carbamazepine, carbamazepine-10,11-epoxide and phenobarbital and 0.125-40.0 mu g mL(-1) for phenytoin, The intra-assay and inter-assay precision and accuracy were studied at three concentrations (1.0, 4.0 and 20.0 mu g mL(-1)). The intra-assay coefficients of variation (CVs) for all compounds were less than 8.8% and all inter-CVs were less than 10%. Limits of quantification were 0.08 mu g mL(-1) for carbamazepine, carbamazepine-10,11-epoxide and phenobarbital and 0.125 mu g mL(-1) for phenytoin. No interference of the drugs normally associated with antiepileptic drugs was observed. Based on figures of merit results, the SBSE/HPLC-UV proved adequate for antiepileptic drugs analyses from therapeutic levels. This method was successfully applied to the analysis of real samples and was as effective as the LLE/HPLC-UV method. (c) 2008 Elsevier B.V. All rights reserved.

Recognition of cyclic, acyclic, exocyclic, and spiro Acetals via structurally diagnostic ion/molecule reactions with the (CH3)(2)N-C+=O acylium ion

Reactions of the model acylium ion (CH3)(2)N-C+=O with acyclic, exocyclic, and Spiro acetals of the general formula (RO)-O-1-(CRR4)-R-3-OR2-upole mass spectrometry. Characteristic intrinsic reactivities were observed for each of these classes of acetals. The two most Characteristic intrinsic reactivities were observed for each of these classes of acetals. The two most common reactions observed were hydride and alkoxy anion [(RO-)-O-1 and (RO-)-O-2] abstraction. Other specific reactions were also observed: (a) a secondary polar [4(+) + 2] cycloaddition for acetals bearing alpha,beta-unsaturated R-3 or R-4 substituents and (b) OH- abstraction for exocyclic and spiro acetals. These structurally diagnostic reactions, in conjunction with others observed previously for cyclic acetals, are shown to reveal the class of the acetal molecule and its ring type and substituents and to permit their recognition and distinction from other classes of isomeric molecules.

Niobium to alcohol mol ratio control of the concurring esterification and etherification reactions promoted by NbCl5 and Al2O3 catalysts under microwave irradiation

Alcohols and acids can be switched to produce ethers or esters by varying the alcohol to catalyst mol ratio, in a new etherification and esterification method using NbCl5/Al2O3 catalyst under ""solvent free"" conditions and promoted by MW (microwave) irradiation. A ""two sites"" mechanism for the reaction is proposed, in an attempt to clarify the tendency of the catalyst to be dependent on the alcohol alone during the esterification process. (c) 2008 Elsevier B.V. All rights reserved.

Synthesis, characterization, and catalytic properties of a mesostructured lamellar xerogel tungsten oxide phase

Cetyltrimethylammonium bromide (CTAB) and n-hexadecylamine (HDA) have been used as template in the synthesis of a mesolamellar xerogel tungsten oxide phase (WO(3)/CTAB/HDA). The catalytic properties of the resulting material were investigated in the oxidation of cis-cyclooctene, styrene, and cyclohexane, using hydrogen peroxide (H(2)O(2)), terc-butyl hydroperoxide (t-BOOH), or m-chlorperbenzoic acid (m-CPBA) as oxygen transfer agent. In general, the catalytic results were comparable to those obtained with related systems, thus suggesting the potential application of this material as catalyst for epoxidation reactions. (C) 2011 Elsevier B.V. All rights reserved.