RESUMO
This study describes the development of an analytical methodology for the separation of quaternary amines using non-aqueous microchip electrophoresis (NAME) coupled with capacitively coupled contactless conductivity detection (C4D). All experiments were performed using a commercial microchip electrophoresis system consisting of a C4D detector, a high-voltage sequencer and a microfluidic platform to assemble a glass microchip with integrated sensing electrodes. The detection parameters were optimized and the best response was reached applying a 700-kHz sinusoidal wave with 14Vpp excitation voltage. The running electrolyte composition was optimized aiming to achieve the best analytical performance. The mixture containing methanol and acetonitrile at the proportion of 90:10 (v:v) as well as sodium deoxycholate provided separations of ten quaternary amines with high efficiency and baseline resolution. The separation efficiencies ranged from 8.7×104 to 3.0×105 plates/m. The proposed methodology provided linear response in the concentration range between 50 and 1000µmol/L and limits of detection between 2 and 27µmol/L. The analytical feasibility of the proposed methodology was tested in the determination of quaternary amines in corrosion inhibitor samples often used for coating oil pipelines. Five quaternary amines (dodecyltrimethylammonium chloride, tetradecyltrimetylammonium bromide, cetyltrimethylammonium bromide, tetraoctylammonium bromide and tetradodecylammonium bromide) were successfully detected at concentration levels from 0.07 to 6.45mol/L. The accuracy of the developed methodology was investigated and the achieved recovery values varied from 85 to 122%. Based on the reported data, NAME-C4D devices exhibited great potential to provide high performance separations of hydrophobic compounds. The developed methodology can be useful for the analysis of species that usually present strong adsorption on the channel inner walls.
Assuntos
Aminas/química , Eletroforese em Microchip/métodos , Aminas/isolamento & purificação , Condutividade Elétrica , Eletrodos , Eletroforese em Microchip/instrumentaçãoRESUMO
A new sample preparation procedure to determine six heterocyclic aromatic amines (3-Amino-1,4-dimethyl-5H-pirido[4,3-b]indole, 3-Amino-1-methyl-5H-pirido[4,3-b]indole, 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine, 2-amino-9H-pyrido-[2,3-b] indole, 2-amino-3-methyl-9H-pyrido-[2,3-b] indole and 2-Amino-1,6-dimethylimidazo [4,5-b]-pyridine) in cooked beefburguers by using a combination of microwave-assisted solvent extraction and dispersive liquid-liquid microextraction with an ionic liquid generated in situ was used. The optimized microwave extraction procedure consisted of a clean-up step with n-heptane and a subsequent dissolution step in basic media to desorb the analytes from the matrix. Next, an aqueous solution of the ionic liquid 1-octyl-3-methylimidazolium tetrafluorborate and sodium hexafluorphosphate was added and a water-insoluble 1-octyl-3-methylimidazolium hexafluorphosphate was formed within the matrix sample. The amines were analyzed by liquid chromatography with fluorescence and diode-array detection by using a typical C18 column. Peak identities were confirmed by absorbance spectral matching. Repeatability (RSD%) between 5.4% and 10.9%, enrichment factors between 19 and 30, limits of detection between 0.35 and 2.4 ng mL(-1) and recoveries between 69% and 100% were achieved. The extraction methodology is simple, rapid (about 40 min/sample) cheap and green since small amounts of non-toxic solvents are necessary.
Assuntos
Aminas/isolamento & purificação , Microextração em Fase Líquida/métodos , Produtos da Carne/análise , Aminas/química , Animais , Bovinos , Cromatografia Líquida de Alta Pressão , Microextração em Fase Líquida/instrumentação , Micro-OndasRESUMO
The complete stereostructures of xestoproxamines A-C, from the Bahamian sponge Neopetrosia proxima, were assigned from spectroscopic analysis, including MS, 2D NMR, and integrated degradation-CD analysis. Two new CD application protocols are described for defining absolute configuration: one for allylic methyl groups in branched chains and a second for the heterocyclic core bis-piperidine with specific applicability to other members of this class alkaloids--known for their stereoheterogeneity--and tertiary cyclic amines in general.