Multiresidue method for the analysis of more than 140 pesticide residues in fruits and vegetables by gas chromatography coupled to triple quadrupole mass spectrometry

A new multiresidue method has been developed and validated for the determination of more than 140 pesticide residues in cucumber and orange by gas chromatography coupled to triple quadrupole mass spectrometry (GC-QqQ-MS/MS) in a single run of 25.50 min. The triple quadrupole (QqQ) analyzer simultaneously operated in the selected reaction monitoring (SRM) and selected ion monitoring (SIM) modes, acquiring two or three transitions per compound. Samples were extracted by the application of a single-phase extraction of 10 g of sample with acetonitrile containing 1% of acetic acid, followed by a liquid-liquid partition formed by the addition of 4 g of MgSO(4) and 1 g of NaOAc. A dispersive solid-phase extraction (D-SPE) with primary secondary amine (PSA) was applied to clean up the extracts. A final concentration step was included in order to increase sensitivity in the instrumental analysis. The method was properly validated in each matrix in a wide dynamic range (10-400 microg kg(-1)): this work relies on a new quantification strategy by the use of two calibration curves to increase the dynamic range, which permitted reduction of sample dilutions and increase in sample throughput. Recovery was studied at three concentration levels (11.5, 50.0, and 150.0 microg kg(-1)), yielding values in the range 70-110% with precision values, expressed as relative standard deviation (RSD), lower than 20 and 25% for the intraday and interday precision, respectively. Limits of quantification (LOQs) were established at 10 microg kg(-1), the lowest maximum residue level (MRL) value set by the European Union in vegetables. The method was successfully applied to the analysis of pesticide residues in real samples from the southeastern Spain. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Determination of linezolid in pharmaceutical dosage forms by liquid chromatography and ultraviolet spectroscopy

A liquid chromatographic (LC) method and a UV spectrophotometric method were developed and validated for quantitative determination of linezolid in tablets and injection. The isocratic LC analyses were performed on an RP18 column using a mobile phase composed of methanol-water-acetonitrile (40 + 40 + 20, v/v/v) at a flow rate of 1.0 mL/min. The UV spectrophotometric method was performed at 251 nm. The analytical methods were validated according to International Conference on Harmonization guidelines. The calibration graphs were linear (correlation coefficient > 0.999) in the studied concentration ranges of 0.1 to 10 microg/mL for LC and 2 to 16 microg/mL for UV spectrophotometry. The relative standard deviation values for intraday and interday precision studies were <2%, and the accuracy was >98% for both methods. The specificity of the LC method was proved using forced degradation. Statistical analysis showed no significant difference between the results obtained by the 2 methods. The proposed methods are precise and accurate and can be applied directly to the oral and parenteral pharmaceutical preparations of linezolid.     

Palladium-catalysed regioselective addition reaction of ethyl phenylphosphinate with terminal acetylenes: ligand- and solvent-dependent regioselectivity

Palladium-1,2-bis(diphenylphosphino)ethane complex catalyses regioselective Markovnikov addition of ethyl phenylphosphinate to terminal alkynes in toluene, while the use of tri-tert-butylphosphine as the ligand or ethanol as the solvent leads to regioselectivity reversal.     

Instability of confined thin liquid film trilayers

The instability of a system in which three stratified thin liquid films are confined in a channel with parallel walls and the interior film is subject to van der Waals-driven breakup is examined in this work. We derive a model based on lubrication theory and consisting of a pair of nonlinear partial differential equations describing the position of the two liquid interfaces. A linear stability analysis is carried out to show that the effects of varying the boundary film thicknesses can be understood in terms of several known limits, including a supported monolayer, confined bilayer, and supported bilayer. Variation of the boundary film viscosities is shown in many cases to eliminate the supported-bilayer limit. The parameter regimes in which squeezing and bending modes dominate the initial growth are determined, and nonlinear simulations are used to show that the mode always switches to squeezing near rupture. It is also found that a multi-modal dispersion relation may be created by asymmetries in thickness ratio, but not viscosity ratio, even in the absence of asymmetric interfacial tensions. The results of this study are expected to be relevant to multiphase microfluidic systems and the lithographic printing process.     

Structure elucidation of thermal degradation products of amlodipine

Thermal degradation of amlodipine base causes intramolecular reactions affording three cyclic products, referred to as AMLDEG-I, AMLDEG-II, and AMLDEG-III, respectively. AMLDEG-I is a cyclized product formed by intramolecular elimination of ammonia from amlodipine. AMLDEG-II is a positional isomer of AMLDEG-I. AMLDEG-III is also intramolecular cyclisation product. The three degradation products were isolated by column chromatography and characterized by FT-IR and 1H and 13C NMR spectroscopy data. The AMLDEG-III was crystallized and its structure was solved by single crystal X-ray diffraction (SXRD).     

Thermoelectric properties of Fe-substituted layered compound,LiCo<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

The layered compound LiCoO₂ belonging to the ABO₂ class exhibits a variety of interesting behaviors, and substitution adds a twist to the properties. Hence, the effect of partial substitution of Co⁺³ with Fe⁺³ on the high-temperature thermoelectric properties has been studied in detail. The X-ray diffraction patterns together with Rietveld refinement indicate formation of a single phase conforming to R\( \overset{-}{3} \)m space group in all the three cases, LiCo_1?x Fe _x O₂ with x = 0.01, 0.02, and 0.08. The electrical resistivity in all the compounds decreases by four orders of magnitude with increasing temperature from 300 to 1000 K, a semiconducting behavior. The Seebeck coefficient is found to be very high, >700 μV K^?1 in all the cases, and increases with increasing temperature and Fe⁺³ substitution. The thermal conductivity, on the other hand, has been found to decrease with temperature in all the compounds from 3.5 W m^?1 K^?1 at room temperature to 1 W m^?1 K^?1 at 973 K, a consequence of phonon-phonon scattering. High resistivity of the compounds limits power factor indicating that carrier concentration and mobility need to be increased to realize a high figure-of-merit.     

Substituent Effect on Absorption and Fluorescence Properties of Thieno[3, 2-<Emphasis Type="Italic">c</Emphasis>]Pyridine Derivatives

New substituted thieno[3,2-c]pyridine derivatives 5 were synthesized by the reaction of 3-bromo-4-chlorothieno[3,2-c]pyridine 1 with cyclic amine 2, which further on Suzuki reaction with boronic acids 4 converted to corresponding 3-arylthieno[3,2-c]pyridine 5. Substituent R³ has predominant effect on fluorescence properties of thienopyridines. However, the electron donor amine at C₄ has no effect on fluorescence properties of thienopyridines.

Open image in new window

Graphical Abstract New thieno[3,2-c]pyridine derivatives were synthesized from 3-bromo-4-chlorothieno[3,2-c]pyridine and cyclic amines, which by on Suzuki reaction with boronic acids converted to corresponding 3-arylthieno[3,2-c]pyridine. Substituent R3 has predominant effect on fluorescence properties of thienopyridines. However, the electron donor amine at C4 has no effect on fluorescence properties of thienopyridines

     

A Stability-Indicating LC Method for Analysis of Balsalazide Disodium in the Bulk Drug and in Pharmaceutical Dosage Forms

A novel, sensitive, stability-indicating gradient RP-LC method has been developed for quantitative analysis of balsalazide disodium and its related impurities both in the bulk drug and in pharmaceutical dosage forms. Efficient chromatographic separation was achieved on a C₁₈ stationary phase with a simple mobile-phase gradient prepared from methanol and phosphate buffer (10 mm potassium dihydrogen orthophosphate monohydrate, adjusted to pH 2.5 by addition of orthophosphoric acid). The mobile-phase flow rate was 1.0 mL min^?1. Quantification was achieved by use of ultraviolet detection at 240 nm. Under these conditions resolution of balsalazide disodium from its three potential impurities was greater than 2.0. Regression analysis resulted in a correlation coefficient greater than 0.99 for balsalazide disodium and all three impurities. This method was capable of detecting the three impurities at 0.003% of the test concentration of 0.3 mg mL^?1, using an injection volume of 10 μL. Inter-day and intra-day precision for all three impurities and for balsalazide disodium was within 2.0% RSD. Recovery of balsalazide disodium from the bulk drug (99.2–101.5%) and from pharmaceutical dosage forms (99.8–101.3%), and recovery of the three impurities (99.1–102.1%) was consistently good. The test solution was found to be stable in 70:30 (v/v) methanol–water for 48 h. When the drug was subjected to hydrolytic, oxidative, photolytic, and thermal stress, acidic and alkaline hydrolysis and oxidizing conditions led to substantial degradation. The RP-LC method was validated for linearity, accuracy, precision, and robustness.     

Stress Degradation Behavior of Entacapone and Development of LC Stability-Indicating Related Substances and Assay Method

A new, sensitive, stability indicating gradient RP-LC related substances and assay method has been developed for the quantitative determination of entacapone in bulk drugs. Efficient chromatographic separation was achieved on a C18 stationary phase with simple mobile phase combination of buffer and acetonitrile. Buffer consisted of 0.1% orthophosphoric acid, delivered in a gradient mode and quantitation was carried out using ultraviolet detection at 220 nm with a flow rate of 1.5 mL min^?1. In the developed LC method the resolution (R _s ) between entacapone and its three potential process impurities were found to be >2.0. Regression analysis showed an r ² value (correlation coefficient) >0.99 for entacapone and its three potential impurities. This method was capable to detect all three process impurities of entacapone at a level of 0.003% with respect to test concentration of 0.5 mg mL^?1 for a 20 μL injection volume. The inter- and intra-day precision values for all three impurities and for entacapone was found to be within 2.0% RSD. The method has shown good and consistent recoveries for entacapone in bulk drugs (99.2–101.5%) and its three impurities (99.5–102.2%). The test solution was found to be stable in diluent for 48 h. The drug substances were subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. Considerable degradation was found to occur in acid stress, base stress and oxidative conditions. The stressed test solutions were assayed against the qualified working standard of entacapone and the mass balance in each case was close to 99.7% indicating that the developed method was stability-indicating. The developed RP-LC method was validated with respect to linearity, accuracy, precision and robustness.     

Structure elucidation of an unexpected product from dehydration of a beta-hydroxyketone

The structure of an unexpected compound from the dehydration of an aldol addition product has been determined using 1-D and 2-D NMR techniques. This reaction is the last step in a new synthetic approach to the galanthan ring system. Complete 1H and 13C NMR assignments for two synthetic precursors are also reported.