Search PubMed⌕ Search

Biomedical subjects

Luis A Colón

Publications and source records attributed to Luis A Colón.

10 recordsLinked to original sources
PubMed2006

Surface confined ionic liquid as a stationary phase for HPLC.

Trimethoxysilane "ionosilane" derivatives of room temperature ionic liquids based on alkylimidazolium bromides were synthesized for attachment to silica support material. The derivatives 1-methyl-3-(trimethoxysilylpropyl)imidazolium bromide and 1-butyl-3-(trimethoxysilylpropyl)imidazolium bromide were used to modify the surface of 3 microm diameter silica particles to act as the stationary phase for HPLC. The modified particles were characterized by thermogravimetric analysis (TGA) and (13)C and (29)Si NMR spectroscopies. The surface modification procedure rendered particles with a surface coverage of 0.84 micromol m(-2) for the alkylimidazolium bromide. The ionic liquid moiety was predominantly attached to the silica surface through two siloxane bonds of the ionosilane derivative (63%). Columns packed with the modified silica material were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic carboxylic acids as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic interaction, and other electrostatic interactions.

Journal Article↗
PubMed2006

Evaluation of poly{-N-isopropylacrylamide-co-[3-(methacryloylamino)propyl]trimethylammonium} as a stationary phase for capillary electrochromatography.

A cationic polyacrylamide-based stationary phase was synthesized and characterized for CEC. The stationary phase was prepared by radical copolymerization of N-isopropylacrylamide (NIPAAm) and (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTA), producing a copolymer attached to 5 microm porous silica particles. Fourier transform infrared spectroscopy and thermogravimetric analysis were used to characterize the copolymer. Under capillary electrochromatographic conditions, the poly-NIPAAm-co-MAPTA stationary phase showed to be stable in a wide pH range. The amino groups in the MAPTA provided an anodic EOF for CEC separation. The electroosmotic mobility changed less than 10% when the pH of the mobile phase was changed from 2 to 12. The run-to-run RSD of analyte migration time was less than 1.5% (n = 3), and the RSD of peak area was less than 3% (n = 3). The day-to-day RSD for migration time was less than 2% (n = 3). The polar groups present in the stationary phase contributed to the selectivity of the phase providing for hydrophilic interactions. In the separation of a series of neutral and acidic compounds, the stationary phase shows a mixed-mode separation mechanism with both hydrophobicity and hydrophilicity contributing to the separation.

Acrylamides↗
PubMed2005

Injection valve for ultrahigh-pressure liquid chromatography.

The increased interest in HPLC at elevated pressures, beyond the conventional 6000 psi (400 bar), has created a demand for injection systems capable of withstanding pressures beyond the 20,000 psi (1380 bar). To achieve high-resolution separations, an appropriate length of columns packed with sub 2-microm packing materials, a 30,000-40,000 psi (2070-2760 bar) pressure range is desirable. A new air-actuated needle valve injection system rated to withstand pressures of up to 40,000 psi (2760 bar) has been evaluated. Under isocratic chromatographic conditions, injecting 200 nL and operated at approximately 20,000 psi (1380 bar), the system showed a peak area reproducibility of approximately 2.5% RSD, contrasting the 5% RSD of a pressured-balanced injection system operated under similar conditions. Programmed for partial loop injections using injection times of 300-700 ms (injection volumes in the range of 1-2.5 microL) and operated at pressures close to 30,000 psi (2070 bar), the reproducibility in peak area for the amounts injected was approximately 1.5% RSD or lower, while an injection time of 100 ms resulted in a reproducibility of 3-4% RSD. The new injection system did not show any significant carryover, and after thousands of injections, the system has not shown sign of wear, loss of pressure during injection, or loss in chromatographic performance.

Journal Article↗
PubMed2005

Metal oxide monolithic columns.

Metal oxide monoliths composed of ZrO2 and HfO2 have been synthesized in situ inside capillary columns. The material shows globular-like structure and through pores. Capillary electrochromatography and capillary liquid chromatography were performed in a monolithic column with the HfO2 material. Separation of a simple sample mixture showed the potential of the new metal oxide monolithic columns.

Chromatography, Liquid↗
PubMed2005

Very high-pressure capillary liquid chromatography assisted by voltage.

Capillary liquid chromatography at moderately high pressures and capillary electrochromatography (CEC) have been combined to drive the mobile phase through capillary columns packed with small diameter particles. In a column packed with 1.5 microm nonporous particles, linear velocities near 3mm/s were observed when combining inlet pressures of 690 bar (10,000 psi) and an applied voltage of 25 kV. Optimum linear velocity for the column was achieved using a pressure-voltage combination of 350 bar (5000 psi) and 5 kV. Separation efficiencies at near optimum linear velocity agreed with those predicted by the van Deemter equation for liquid chromatography. Retention factors were observed to decrease under pressure-voltage combination as the voltage was increased; such a behavior has been attributed to Joule heating effects.

Chromatography, High Pressure Liquid↗
PubMed2005

Allyl-functionalized hybrid silica monoliths.

A hybrid organosilica monolith was synthesized containing an allyl functionality. This provided a viable platform for producing silica-based, chromatographic, monolithic columns with the stationary phase bonded through a surface silicon-carbon bond rather than a conventional siloxane bond.

Journal Article↗
PubMed2004

Very high pressure HPLC with 1 mm id columns.

Theoretical calculations and experimental data indicate that very high pressure HPLC can be performed using 1 and 1.5 mm id columns, and contrary to previous beliefs, the frictional heating generated does not appear to be detrimental to the separation.

Chromatography, High Pressure Liquid↗
PubMed2002

Joule heating in packed capillaries used in capillary electrochromatography.

Effective heat dissipation is critical for reproducible and efficient separations in electrically driven separation systems. Flow rate, retention kinetics, and analyte diffusion rates are some of the characteristics that are affected by variation in the temperature of the mobile phase inside the column. In this study, we examine the issue of Joule heating in packed capillary columns used in capillary electrochromatography (CEC). As almost all commonly used CEC packings are poor thermal conductors, it is assumed that the packing particles do not conduct heat and heat transfer is solely through the mobile phase flowing through the system. The electrical conductivity of various mobile phases was measured at different temperatures by a conductivity meter and the temperature coefficient for each mobile phase was calculated. This was followed by measurement of the electrical current at several applied voltages to calculate the conductivity of the solution within the column as a function of the applied voltage. An overall increase in the conductivity is attributed to Joule heating within the column, while a constant conductivity means good heat dissipation. A plot of conductivity versus applied voltage was used as the indicator of poor heat dissipation. Using theories that have been proposed earlier for modeling of Joule heating effects in capillary electrophoresis (CE), we estimated the temperature within CEC columns. Under mobile and stationary phase conditions typically used in CEC, heat dissipation was found to be not always efficient. Elevated temperatures within the columns in excess of 23 degrees C above ambient temperature were calculated for packed columns, and about 35 degrees C for an open column, under a given set of conditions. The results agree with recently published experimental findings with nuclear magnetic resonance (NMR) thermometry, and Raman spectroscopic measurements.

Buffers↗
PubMed2002

Organo-silica nano-particles used in ultrahigh-pressure liquid chromatography.

A simple one-step process was used to synthesize uniform, spherical organosilica nano-particles containing octadecyl moieties. These nano-particles, having a diameter of 670 nm, were slurry packed into fused-silica capillary tubes of 50 microm internal diameter and tested for use in ultrahigh-pressure liquid chromatography (UHPLC) at inlet pressures of about 50,000 psi (approximately 3,500 bar), providing for the use of HPLC with nano-particle packed columns. The retention characteristics of a column packed with the organo-nano-particles were shown to be stable under acidic (pH < 1) and basic (pH > 11) conditions. Fast analysis times and relatively high separation efficiencies (approximately 500,000 plates m(-1)) were obtained under the conditions used.

Chromatography, High Pressure Liquid↗