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L A Colón

Publications and source records attributed to L A Colón.

11 recordsLinked to original sources
PubMed2000

Packing columns for capillary electrochromatography.

Considering the current interest in capillary electrochromatography (CEC), performed in packed columns, we present the different methods used to pack capillary columns for use in CEC. General considerations on column packing are given and the column fabrication process is discussed in sufficient detail to allow instruction to those who are not experienced in the field. Five different packing methods are discussed to deliver packing material into the capillary column from a practical view point: slurry pressure packing, packing with supercritical CO2, electrokinetic packing, using centripetal forces, and packing by gravity. Entrapment of particulate material by sintering and sol-gel technology is also mentioned. Although slurry pressure packing procedures are most common, higher separation efficiencies are obtained using other packing approaches. Electrokinetic packing seems to be the simplest technique to deliver the packing material into the capillary columns. Nevertheless, as with the other packing techniques, skill and experience are required to complete all the steps involved in the fabrication of packed columns for CEC.

Carbon Dioxide↗
PubMed2000

Recent progress in capillary electrochromatography.

Capillary electrochromatography (CEC) continues to captivate many separation scientists. A remarkable activity is apparent from the numerous publications in the literature using CEC. A review of the most recent progress in CEC is presented herein, covering an extensive fraction of the literature on CEC published from the year 1997 until the beginning of 2000. Most of the recent developments have concentrated on column technology.

Chromatography, High Pressure Liquid↗
PubMed1999

Capillary electrochromatography using a fluoropolymer as the chromatographic support material.

Fused-silica capillary columns were packed with ethylene chlorotrifluoroethylene (ECTFE) particles for use in capillary electrochromatography (CEC). Electroosmotic flow (EOF) was generated in these columns using acetonitrile-water mixtures as the mobile phase. Electroosmotic mobilities of 1.6 x 10(-4) cm2 V(-1) s(-1) (linear velocities of 1 mm s(-1)) were observed using a mobile phase without an electrolyte present. The EOF in the ECTFE-packed columns is enhanced when using trifluoroacetic acid (TFA) as a mobile phase additive; electroosmotic mobilities of 3.65 x 10(-4) cm2 (V-1) s(-1) (linear velocity of 2.5 mm s(-1)) were observed. This enhancement of EOF is attributed to dynamic coating of the ECTFE particles by TFA. Other electrolytes (i.e., Tris/Tris-HCl buffer and H3PO4) in the mobile phase did not have such an enhancement of EOF. However, a slight enhancement of EOF is observed, for example, if small quantities of TFA are added to the mobile phase containing Tris buffer. The potential of ECTFE for CEC is demonstrated by separating a mixture of amino acids.

Amino Acids↗
PubMed1999

A drying step in the protocol to pack capillary columns by centripetal forces for capillary electrochromatography.

Capillary columns have been packed for capillary electrochromatography (CEC) using centripetal forces. The packed columns were maintained under wet conditions or they were dried with nitrogen gas prior to forming the retaining frits. Upon fabrication of the retaining frits, the dried columns were resolvated with the mobile phase. The performance of the columns was evaluated to determine the effect of the drying step during the packing procedure. The columns submitted to the drying step showed improved separation efficiencies and stronger retention characteristics than those kept under wet conditions. The drying step allows the silica-based packing material to be better accommodated inside the capillary column. Upon solvation, the packing material "swells," resulting in a greater packing density, which allows for a stronger retention and improved separation efficiencies. The drying step led to a 13% increase in retention on columns packed with isopropanol. An increase of 15-20% in theoretical plates for the most retained compounds was also observed in such columns.

2-Propanol↗
PubMed1998

Determination of glucose by capillary electrophoresis/laser-induced fluorescence in transdermally collected samples.

Capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection has been used for the determination of glucose in samples collected by noninvasive means. The method uses an enzymatic reaction scheme that provides for the determination of small quantities of glucose with detection limits of 80 nM. This approach is used to evaluate passive transdermal diffusion as a noninvasive means to sample glucose in vivo. A simple sampling cell design is presented. Sample collection was performed on volunteer human subjects. Our experiments show that fluctuations in blood glucose concentration are reflected in the samples obtained by passive transdermal diffusion after glucose intake. The results indicate that glucose from the subcutaneous fluid can be accessed by passive diffusion.

Blood Glucose↗
PubMed1997

Advances in capillary electrochromatography.

Capillary electrochromatography (CEC) is a hybrid between capillary electrophoresis and high performance liquid chromatography (HPLC) that has gained popularity in recent years. CEC uses an electrically driven flow to transport the solutes through the chromatographic column. Separation can be achieved by differential partition between two phases, differential electromigration, or a combination of these two. Herein, the main features of CEC are presented, including basic principles and a literature overview on different practical approaches used.

Chromatography, High Pressure Liquid↗
PubMed1996

Hydrolytically stable amino-silica glass coating material for manipulation of the electroosmotic flow in capillary electrophoresis.

A hydrolytically stable amino-silica glass coating material was fabricated inside fused-silica capillaries, using sol-gel technology. Aminopropyltriethoxysilane was used as the precursor in the glass formation process. The net charge at the surface of the coating material depends on the degree of protonation of the amino groups and the degree of ionization of the silanol groups, thus enabling manipulation of the magnitude and direction of the electroosmotic flow (EOF). At low pH (< 6.0), the coating bears a net positive charge, which results in an electroosmotic flow from the cathode toward the anode and minimizes the wall-solute interactions of basic species. At high pH (> 6.5), the coating surface bears a net negative charge and the coated capillary behaves like an uncoated one, having an EOF in the cathodic direction. The amino-silica glass coating has also been shown to be extremely stable under both acidic and basic conditions. The reproducibility of the electroosmotic mobility of five different capillaries was found to be 7% R.S.D. The utility of the material is shown with the separation of basic proteins, peptides and basic compounds.

Acids↗
PubMed1996

Determination of carbohydrates as their dansylhydrazine derivatives by capillary electrophoresis with laser-induced fluorescence detection.

A mixture of mono- and disaccharides was derivatized with dansylhydrazine in a relatively fast chemical reaction (15 min) which is selective toward aldehydes and ketones. The products of the derivatization reaction were then separated by capillary electrophoresis (CE) using laser-induced fluorescence (LIF) as the detection mode. The smallest amount of carbohydrate derivatized and determined by CE/LIF was 10 pmol contained in 100 microL of the final reaction mixture. The CE/LIF method provided a linear response for the carbohydrates tested (over 2-3 orders of magnitude), with a limit of detection of 100 amol. Separation efficiencies over 250,000 theoretical plates were obtained. The procedure was used to analyze a tear fluid sample to demonstrate the applicability of the method for the glucose determination in small volumes of biological samples.

Dansyl Compounds↗
PubMed1995

Analysis of underivatized amino acids by capillary electrophoresis using constant potential amperometric detection.

A mixture of native (underivatized) amino acids is separated by capillary electrophoresis under alkaline conditions (pH approximately 12) and amperometrically detected with a copper-disk microelectrode. A simple design facilitates capillary-electrode alignment without the need for micropositioning equipment. The limits of detection for the amino acids are in the low microM concentration range, and the signal response is linear over 2-3 orders of magnitude. This procedure is applied to analyze the amino acid hydrolysis products from cytochrome c.

Amino Acids↗
PubMedDate not supplied

Analysis of tear fluid by CE/LIF: a noninvasive approach for glucose monitoring.

Nanoliter volumes of human tear fluid were collected by means of a capillary tube without inducing tearing and were analyzed for glucose content. The tear fluid was subjected to two enzymatic reactions to generate a fluorescent compound that is proportional to the concentration of glucose in the sample. CE with laser-induced fluorescence (LIF) detection was used to monitor the fluorescent species generated, hence glucose in the tear samples. The reproducibility of the method for six different preparations was < 9% relative standard deviation (RSD). The procedure was compared with the glucose dehydrogenase method for the determination of glucose in blood before using it to determine glucose in tear fluid. Blood and tear samples were collected from six healthy human subjects. The results showed that the higher glucose content in tear samples is consistent with the higher glucose content in blood samples. The glucose concentration of the tear samples analyzed ranged from 128 to 166 microM, and that of blood ranged from 3.3 to 4.3 mM.

Blood Glucose↗