Maria T. Dulay

Preparation and characterization of monolithic porous capillary columns loaded with chromatographic particles.

Using sol-gel technology, a porous glass matrix (xerogel) is formed in a capillary column and acts as a support for a stationary phase of chromatographic particles used in capillary electrochromatography. Preparation of the sol-gel matrix and immobilization of the octadecylsilica (ODS) stationary phase occur in a single step. The presence of the particles in the column greatly reduces matrix cracking caused by internal pressure differentials within the pores of the sol-gel matrix. Good electroosmotic flow is achieved in part because of the inherent negative charge of both the particles and the sol-gel matrix. The performance of these sol-gel/ODS capillary columns was evaluated with a mixture of aromatic and nonaromatic organic compounds. Efficiencies of up to 80 000 plates/m were observed in columns with immobilized 3-μm ODS particles. The efficiency and resolution are enhanced when 3-μm ODS particles are used in place of the 5-μm particles.

Automated capillary electrochromatography: reliability and reproducibility studies

The routine application of capillary electrochromatography (CEC) is demonstrated by incorporating 75 microns I.D. capillaries packed with 3 microns octadecylsilica (ODS) particles into a commercial CZE instrument. A mixture of several neutral compounds is separated into its components with an average efficiency up to 181 000 plates/m in less than 8 min. Hundreds of consecutive runs are performed over a period of weeks from which it is concluded that the reproducibility of the capacity factors is better than 2% and that CEC separations can be achieved in a reliable and routine manner.

Enantiomeric separation of amino acids and nonprotein amino acids using a particle-loaded monolithic column.

A solution is prepared of 5 μm silica particles modified with (S)‐N‐3,5‐dinitrobenzoyl‐1‐naphthylglycine (particle 1) or (S)‐N‐3,5‐dinitrophenylaminocarbonyl‐valine (particle 2) suspended in liquid tetraethylorthosilicate, ethanol, and aqueous hydrochloric acid. This solution is injected under pressure into a 30 cm long, 75 μm inner diameter capillary column and heated for 1 h at 120°C after which the modified particles are embedded in a monolithic column of sol gel. The packed column measures approximately 15 cm from the inlet to the window used to view the laser‐induced fluorescence. Thirteen different amino acids and three nonprotein amino acids are derivatized with the fluorogenic reagent 4‐fluoro‐7‐nitro‐2,1,3‐benzoxadiazole (NBD‐F) before injection onto the column for capillary electrochromatographic separation. The enantiomeric separation of the monolithic column packed with particle 1 results in a resolution ranging from 1.14 to 4.45, whereas that packed with particle 2 results in a resolution ranging from 0.79 to 1.17. On the basis of resolution and amount of chiral packing material the enantiomeric separation obtained by capillary electrochromatography is judged to be superior to that obtained previously with high performance liquid chromatography (HPLC).

Photopolymerized sol-gel frits for packed columns in capillary electrochromatography.

Porous sol-gel frits are fabricated in a capillary column by filling it with a solution of 3-(trimethoxysilyl)propyl methacrylate, hydrochloric acid, water, toluene (porogen), and a photoinitiator (Irgacure 1800) and exposing it to UV light at 365 nm for 5 min. The separation column (30 cm x 75 microm I.D.) contains between the inlet and outlet frits a 15-cm packed segment filled with 5-microm silica particles modified with the chiral compound (S)-N-3,5-dinitrobenzoyl-1-naphthylglycine. A detection window (1 mm long) is placed immediately after the outlet frit. To demonstrate the performance of this chiral separation column, mixtures of 16 different amino acids (three of which are not naturally occurring) derivatized with the fluorogenic reagent 4-fluoro-7-nitro-2,1,3-benzoxadiazole were separated by capillary chromatography. The enantiomeric separation of the column results in a resolution ranging from 1.21 to 8.29, and a plate height ranging from 8.7 to 39 microm.

Effect of preparatory conditions on the performance of photopolymerized sol-gel monoliths for capillary electrochromatography

We prepared different photopolymerized sol-gel (PSG) columns by varying the amount of monomer (methacryloxypropyltrimethoxysilane), porogen (toluene) and catalyst (hydrochloric acid) in the reaction solution containing a photoinitiator (Irgacure 1800). The effects of these variations on the chromatographic behavior of the PSG columns were studied. All of the columns studied exhibited reversed-phase character. The concentration of hydrochloric acid was important for the rigidity of the columns, although it did not affect the separation property. The ratio of monomer solution to porogen was a critical factor in controlling the through-pore size and the surface area of PSG, which were found to significantly affect the separation properties, such as permeability, theoretical plate number, retention time, and separation efficiency, of a mixture of test analytes-thiourea, benzene, and naphthalene. There was no change in the retention order for the test analytes. Short separation times were achieved on PSG columns made from a 10% monomer stock solution and 90% porogen with 1 M hydrochloric acid. Mixtures of polycyclic aromatic hydrocarbons and alkylbenzenes were separated with theoretical plate numbers greater than 100 000 plates/m.

Evidence for the extraterrestrial origin of polycyclic aromatic hydrocarbons in the Martian meteorite ALH84001

Possible sources of terrestrial contamination are considered for the observation of polycyclic aromatic hydrocarbons (PAHs) in the Martian meteorite ALH84001. Contamination is concluded to be negligible.

Bonded-phase photopolymerized sol-gel monoliths for reversed phase capillary electrochromatography

A porous chemically modified photopolymerized sol-gel (PSG) monolith enhanced the capillary electrochromatographic separations of two test mixtures, one containing eight alkyl phenyl ketones and the other containing thiourea and three polyaromatic hydrocarbons. Derivatization of the PSG surface with silane coupling reagents resulted in bonded phases of pentafluorophenylpropyldimethyl, pentafluorophenyl, 3,3,3-trifluoropropyl, n-octadimethyl, perfluorohexyl, and aminopropyl. The fabrication of the bonded-phase PSG column is easy to do with the silanization reaction proceeding at room temperature for not longer than 60 minutes. The hydrophobicity of the PSG was altered without degrading its chromatographic performance. The bonded-phase PSG monoliths have higher stability at pH values below 4 as compared to the parent (underivatized) PSG. Separations of different mixtures containing nucleosides, positively charged peptides, and taxol derivatives illustrate the potential of bonded-phase PSG columns for the analyses of biologically and pharmaceutically important compounds. We report column efficiencies of up to 180 000 plates/meter and retention factors as large as 28.6 for decanophenone.

Toward sol-gel electrochromatographic separations on a chip

A porous photopolymerized sol-gel (PSG) monolith was synthesized in the separation channel of a borosilicate glass chip via UV irradiation (5 min) of a mixture of 3-methacryloxypropyltrimethoxysilane, an acid catalyst, a porogen, and a photoinitiator. The PSG monolith adhered strongly to the chemically untreated channel walls. The chip was fabricated using standard lithography procedures to give channels that are 35-μm deep and 90-μm wide. Masking the other channels defined the 4.7-cm PSG section in the separation channel. Two dyes Coumarin 314 and 510 were successfully separated within baseline resolution in 225 s when fluorescent detection occurred immediately after the PSG section. The separation time was reduced to 80 s with little loss in resolution by detecting the dyes 1.2 cm from the front of the PSG monolith.

Droplet spray ionization from a glass microscope slide: real-time monitoring of ethylene polymerization.

Ambient ionization mass spectrometry is achieved in a simple manner by loading a sample solution onto a corner of a microscope cover glass positioned in front of the inlet to a mass spectrometer and applying a high voltage to the sample. The resulting stream of charged droplets is stable, has no contamination from the substrate platform, and can be used repeatedly. The utility of droplet spray for in situ analysis and real-time monitoring of chemical reactions was demonstrated by the bis(cyclopentadienyl)zirconium dichloride (zirconocene dichloride)/methylaluminoxane, Cp2ZrCl2/MAO, homogeneously catalyzed polymerization of ethylene in various solutions. Reaction times ranged from seconds to minutes, and catalytically active species and polymeric products of ethylene were acquired and identified by tandem mass spectrometry.

Determination of glutamine and serine in rat cerebrospinal fluid using capillary electrochromatography with a modified photopolymerized sol-gel monolithic column

Capillary electrochromatographic separations of amino acid mixtures were studied using two modified porous photopolymerized sol-gel monolithic columns. One was modified with dimethyloctadecylchlorosilane (DMOS), and the other was modified with DMOS, followed by chlorotrimethylsilane to end-cap residual silanol groups. Prior to separation, amino acids were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole using as a mobile phase 50 mM phosphate (pH 2.5), water, and acetonitrile in the ratio of 1:1:8. Five derivatized amino acids (Asn, Phe, Ala, Ile, and Leu) were separated within 7 min. Theoretical plate numbers varied between 58700 and 105000/m. This separation method with the end-capped monolithic column was applied to rat cerebrospinal fluid. The dominant amino acid found was Gln at a concentration of 420 microM along with small quantities of Ser (54 microM).