Search results for "liquid"
showing 10 items of 4351 documents
Ionic liquids as precatalysts in the highly stereoselective conjugate addition of α,β-unsaturated aldehydes to chalcones.
2014
Imidazolium-based ionic liquids (ILs) serve both as recyclable reaction media and as precatalysts for the N-heterocyclic carbene-catalyzed conjugate addition of α,β-unsaturated aldehydes to chalcones. The reaction produces a broad scope of 1,6-ketoesters incorporating an anti-diphenyl moiety in high yields and with high stereoselectivity. In recycling experiments, the IL can be reused up to five times with retained reactivity and selectivity. Moreover, the 1,6-ketoesters form self-assembled organogels in aliphatic hydrocarbons. The reaction protocol is robust, easily operated, scalable and highly functionalized compounds can be obtained from inexpensive and readily accessible starting mater…
Use of green alternative solvents in dispersive liquid‐liquid microextraction: A review
2021
Dispersive liquid-liquid microextraction is one of the most widely used microextraction techniques currently in the Analytical Chemistry field, mainly due to its simplicity and rapidity. The operational mode of this approach has been constantly changing since its introduction, adapting to new trends and applications. Most of these changes are related to the nature of the solvent employed for the microextraction. From the classical halogenated solvents (e.g., chloroform or dichloromethane), different alternatives have been proposed in order to obtain safer and non-pollutants microextraction applications. In this sense, low density solvents, such as alkanols, switchable hydrophobicity solvent…
Uncommon perspectives in palladium- and copper-catalysed arylation and heteroarylation of terminal alkynes following Heck or Sonogashira protocols: I…
2013
Abstract Conjugated alkynes are recurring building blocks in natural products and in a wide range of important compounds, such as pharmaceuticals, agrochemicals, or molecular materials. The palladium-catalysed cross-coupling reaction between the sp 2 -hybridized carbon atoms of aryl, heteroaryl, and vinyl halides with the sp -hybridized carbon atoms of terminal alkynes is one of the most important developments in the field of alkyne chemistry over the past 50 years. Room for improvement still exists in these important reactions of direct arylation of terminal alkynes. In this prospect, the present authors have developed several strategies aiming at improving the reactivity, the selectivity,…
Analysis of pharmaceutical preparations containing antihistamine drugs by micellar liquid chromatography
2005
Rapid chromatographic procedures for analytical quality control of pharmaceutical preparations containing antihistamine drugs, alone or together with other kind of compounds are proposed. The method uses C18 stationary phases and micellar mobile phases of cetyltrimethylammonium bromide (CTAB) with either 1-propanol or 1-butanol as organic modifier. The proposed procedures allow the determination of the antihistamines: brompheniramine, chlorcyclizine, chlorpheniramine, diphenhydramine, doxylamine, flunarizine, hydroxyzine, promethazine, terfenadine, tripelennamine and triprolidine, in addition to caffeine, dextromethorphan, guaifenesin, paracetamol and pyridoxine in different pharmaceutical …
Inter-laboratory validation of procedures for measuring 8-oxo-7,8-dihydroguanine/8-oxo-7,8-dihydro-2’-deoxyguanosine in DNA.
2002
The aim of ESCODD, a European Commission funded Concerted Action, is to improve the precision and accuracy of methods for measuring 8-oxo-7,8-dihydroguanine (8-oxoGua) or the nucleoside (8-oxodG). On two occasions, participating laboratories received samples of different concentrations of 8-oxodG for analysis. About half the results returned (for 8-oxodG) were within 20% of the median values. Coefficients of variation (for three identical samples) were commonly around 10%. A sample of calf thymus DNA was sent, dry, to all laboratories. Analysis of 8-oxoGua/8-oxodG in this sample was a test of hydrolysis methods. Almost half the reported results were within 20% of the median value, and half …
Nickel(II) inhibits the repair of O 6 -methylguanine in mammalian cells
1999
Nickel compounds are widespread carcinogens, and although only weakly mutagenic, interfere with nucleotide excision repair and with the repair of oxidative DNA base modifications. In the present study we investigated the effect of nickel(II) on the induction and repair of O6-methylguanine and N7-methylguanine after treatment with N-methyl-N-nitrosourea (MNU). We applied Chinese hamster ovary cells stably transfected with human O6-methylguanine-DNA methyltransferase (MGMT) cDNA (CHO-AT), and compared the results with the MGMT-deficient parental cell line. As determined by high-performance liquid chromatography/electrochemical detection (HPLC/ECD), there was a slight but mostly not significan…
Biomarkers, matrices and analytical methods targeting human exposure to chemicals selected for a European human biomonitoring initiative
2020
E-mail addresses: kvo@envs.au.dk (K. Vorkamp), Castano@isciii.es (A. Castaño), Jean-Philippe.Antignac@oniris-nantes.fr (J.-P. Antignac), Luis.Boada@ulpgc.es (L.D. Boada), ECequier@quimica.udl.cat (E. Cequier), Adrian.Covaci@uantwerpen.be (A. Covaci), M.Esteban@isciii.es (M. Esteban López), LineSmastuen.Haug@fhi.no (L.S. Haug), Kasper@ipa-dguv.de (M. Kasper-Sonnenberg), Koch@ipa-dguv.de (H.M. Koch), Octavio.Perez@ulpgc.es (O. Pérez Luzardo), Agnese.Osite@lu.lv (A. Osīte), Loic.Rambaud@santepubliquefrance.fr (L. Rambaud), mtpin@ticino.com (M.-T. Pinorini), Gabriele.Sabbioni@bluewin.ch (G. Sabbioni), Cathrine.Thomsen@fhi.no (C. Thomsen).; International audience; The major purpose of human biom…
Computer Aided Evaluation of HPLC (High Pressure Liquid Chromatography) with Fluorometric Detection
1982
A program system for automated HPLC measurements of vitamin A concentration is reported. This system provides for guidance of operators, for control of apparatus and for supervision of quality measurements.
Paediatric oral formulations: comparison of two extemporaneously compounded suspensions from tacrolimus capsules
2011
Study objectives: The objective of this study was to determine the stability of tacrolimus in extemporaneously compounded liquid formulations. Methods: Two sets of liquid formulations were prepared using two different vehicles: one set in sterile water and in simple syrup (1:1) and one set using equal volumes of commercially available suspending agent (Ora-Plus) and simple syrup. The concentration of tacrolimus in each formulation was 0.5 mg/mL. The preparations containing Ora-Plus were stored at 25°C, the formulations that were prepared with sterile water and simple syrup were stored under refrigeration at 4°C. Results: Samples were collected at regular time intervals over a period of 56 d…
Fast simultaneous determination of prominent polyphenols in vegetables and fruits by reversed phase liquid chromatography using a fused-core column
2015
A reversed-phase high-performance liquid chromatography method with photodiode array detection has been developed enabling the joint determination of 17 prominent flavonoids and phenolic acids in vegetables and fruits. A multi-segmented gradient program using a fused-core column for the separation of several phenolic classes (phenolic acids and flavonoids) has been optimised. The influence of extraction conditions (sample freeze-drying, ultrasound extraction, solvent composition and extraction time) has been also optimised using response surface methodology with tomato samples as a model. Complete recoveries (76-108%) were obtained for the phenolic compounds present in tomato. The developed…