Search results for "Onium"
showing 10 items of 2091 documents
Sub- and supercritical fluid extraction of trichloropyridinol from soil prior to immunoassay
1997
A comparative study on the extraction of TCP (3,5,6-trichloro-2-pyridinol, a metabolite of chlorpyrifos) from soil with CO2 and H2O is reported. The polarity of the analyte requires the presence of both a cosolvent (methanol) and an ion-pair reagent [(1R)-(-)-10-camphorsulfonic acid ammonium salt] for 95% extraction in 30 min when supercritical CO2 at 40 degrees C and 383 bar is used as extractant. Subcritical water (250 degrees C and 200 bar) enables complete extraction within 15 min without additives. Quantitation of the target analyte is performed by specific immunoassay using a non-commercial monoclonal antibody which provides a linear determination range between 0.005 and 5 micrograms/…
Quantitative electron probe microanalysis of metallic oxide mixtures applying an empirical calibration technique
1997
Abstract An analytical procedure is proposed for the independent quantitative chemical analysis of each element in the presence of other elements in the matrix of a sample by Energy Dispersive Electron Probe Microanalysis. For this purpose, an empirical calibration technique (which we shall call here the JABO method), which studies the variation of the X-ray intensities in terms of the analyte concentration in a chemical system with a complex matrix, is established. The methodology consists of the modification of the unknown sample by addition of a diluent, an internal standard and the analyte itself (dilution-addition method). A mathematical model is proposed to calculate the K parameters …
Comparison between micellar liquid chromatography and capillary zone electrophoresis for the determination of hydrophobic basic drugs in pharmaceutic…
2007
[EN] The determination of highly hydrophobic basic compounds by means of conventional reversed-phase liquid chromatographic methods has several drawbacks. Owing to the characteristics of micellar liquid chromatography (MLC) and capillary electrophoresis (CE), these techniques could be advantageous alternatives to reversed-phase chromatographic methods for the determination of these kinds of compounds. The objective of this study was to develop and compare MLC and CE methods for the determination of antipsychotic basic drugs (amitryptiline, haloperidol, perphenazine and thioridazine) in pharmaceutical preparations. The chromatographic determination of the analytes was performed on a Kromasil…
A taylor series model to evaluate the interelemental effects in X-ray fluorescence analysis, applied to the iron-zirconium-diluent system
1995
A semi-empirical model has been developed to quantify the interelemental effects in X-ray fluorescence analysis. The measured X-ray fluorescence intensity has been expressed as a function of the different fluorescence elements composing the sample. this complex function has become an operative function via a Taylor series development. An explication has been given for the significance of the different terms of the series. These terms respond to mathematical functions known as characteristic functions for each chemical system. A parameter (B) has been defined which makes it possible to quantify the influence of the interelemental effect as a function of the analyte concentration (C) and that…
From attraction to repulsion : anion–π interactions between bromide and fluorinated phenyl groups
2011
Anion–π interactions in crystals of fluorobenzyl ammonium salts depend on the degree of fluorination at the aromatics.
Self-assembly of 3,5-bis(ethoxycarbonyl)pyrazolate anions and ammonium cations of β-phenylethylamine or homoveratrylamine into hetero-double-stranded…
2009
Hydrogen-bonded double-stranded hetero-helices are formed when reacting sodium 3,5-bis(ethoxycarbonyl)pyrazolate with beta-phenethylammonium or homoveratrylammonium chloride, in which one of the strands is defined by the ammonium cations and the other one by the pyrazolate anions.
CH-Directed Anion-π Interactions in the Crystals of Pentafluorobenzyl-Substituted Ammonium and Pyridinium Salts
2010
Simple pentafluorobenzyl-substituted ammonium and pyridinium salts with different anions can be easily obtained by treatment of the parent amine or pyridine with the respective pentafluorobenzyl halide. Hexafluorophosphate is introduced as the anion by salt metathesis. In the case of the ammonium salt 4, water co-crystallisation seems to suppress effective anion-pi interactions of bromide with the electron-deficient aromatic system, whereas with salts 5 and 6 such interactions are observed despite the presence of water. However, due to asymmetric hydrogen-bonding interactions with ammonium side chains, the anion of 5 is located close to the rim of the pentafluorophenyl group (eta(1) interac…
Bis(5-tert-butyl-2-hydroxy-3-methylbenzyl)(6-hydroxyhexyl)ammonium chloride monohydrate, an anion receptor complex
2007
In the title compound, C(30)H(48)NO(3)(+) x Cl(-) x H(2)O, the cation acts with a water molecule as a chloride ion receptor. The chloride ion forms three strong intramolecular hydrogen bonds. The water molecule forms both an intramolecular bridge between one phenol H atom and the chloride ion, and an intermolecular link to the aliphatic alcohol O atom. Weak intermolecular C-H...Cl and C-H ...O hydrogen bonds provide additional packing interactions.
Anion-Exchange Properties of Trifluoroacetate and Triflate Salts of N-Alkylammonium Resorcinarenes
2016
The synthesis of N-benzyl- and N-cyclohexylammonium resorcinarene trifluoroacetate (TFA) and triflate (OTf) salt receptors was investigated. Solid-state analysis by single-crystal X-ray diffraction revealed that the N-alkylammonium resorcinarene salts (NARSs) with different upper substituents had different cavity sizes and different affinities for anions. Anion-exchange experiments by mixing equimolar amounts of N-benzylammonium resorcinarene trifluoroacetate and N-cyclohexylammonium resorcinarene triflate, as well as N-benzylammonium resorcinarene triflate and N-cyclohexylammonium resorcinarene trifluoroacetate showed that the NARS with flexible benzyl groups preferred the larger OTf anion…
Recent advances in electrochemical meso- and β-functionalization of porphyrins and electrografting of diazonium porphyrins
2020
Abstract Recent studies on electrochemical meso- and β-functionalization of porphyrins and electrografting of diazonium porphyrin are presented. First, the electrochemical oxidative C–C coupling between porphyrins will be presented, followed by the intermolecular and intramolecular meso- and β-substitutions of porphyrins. Then, the latest results on diazonium porphyrin electrografting will be reviewed.