Bio


Received PhD from University of Texas at Austin, Department of Chemistry with Marye Anne Fox
NIH Postdoctoral Fellow at Stanford University in Richard N. Zare's research lab, Department of Chemistry

Academic Appointments


All Publications


  • Selective and sensitive detection of pathogens with pathogen-imprinted polymers Dulay, M. AMER CHEMICAL SOC. 2018
  • Taking back my power: My story of sexual harassment Dulay, M. AMER CHEMICAL SOC. 2018
  • Polymer-spray mass spectrometry for rapid analysis of drugs in biofluids Dulay, M. AMER CHEMICAL SOC. 2018
  • Polymer-spray mass spectrometric detection and quantitation of hydrophilic compounds and some narcotics. Rapid communications in mass spectrometry : RCM Dulay, M. T., Zare, R. N. 2017; 31 (19): 1651–58

    Abstract

    High-throughput screening of biofluids is essential in monitoring concentration of a variety of drugs to determine their efficacy and toxicity. Organosiloxane polymers prepared by sol-gel chemistry as sample supports, and electrospray ionization emitters in a single material and as an alternative to paper substrates, is described in this study.Hydrophobic drugs and hydrophilic streptomycin were analyzed by polymer-spray mass spectrometry with an LTQ-Orbitrap mass spectrometer. Drug samples in urine (1-2 μL) were deposited on an OSX polymer, allowed to dry, then electrosprayed from the polymer tip into the mass spectrometer without sample pretreatment. The OSX polymers, whose polarity and porosity can be controlled, were prepared by sol-gel chemistry where methyl-substituted alkoxysilanes were hydrolyzed in the presence of a pore template and an acid catalyst.Five nanograms each of seven narcotic drugs were detected in <1 min (relative standard deviation (RSD) of response <1% for each drug). Calibration curves of cocaine and streptomycin in urine were used to establish the performance of the polymer. For sample 1 (n = 2), the mean recovery for cocaine was 81% with paper and 90% with polymer. Streptomycin is detected with polymer, not with paper; for samples 1 and 2 (n = 3), mean recovery was 97% and 95%, respectively.Organosiloxane polymers achieve more sensitive analysis than paper, allowing for more accurate quantitation of both hydrophobic and hydrophilic drug compounds. The ability to tailor the polymer polarity and porosity allows for the synthesis of a wide range of polymers, and thus opens many possibilities for further development and applications.

    View details for PubMedID 28792093

    View details for PubMedCentralID PMC5591076

  • Monitoring Enzymatic Reactions in Real Time Using Venturi Easy Ambient Sonic-Spray Ionization Mass Spectrometry ANALYTICAL CHEMISTRY Jansson, E. T., Dulay, M. T., Zare, R. N. 2016; 88 (12): 6195-6198

    Abstract

    We developed a technique to monitor spatially confined surface reactions with mass spectrometry under ambient conditions, without the need for voltage or organic solvents. Fused-silica capillaries immersed in an aqueous solution, positioned in close proximity to each other and the functionalized surface, created a laminar flow junction with a resulting reaction volume of ∼5 pL. The setup was operated with a syringe pump, delivering reagents to the surface through a fused-silica capillary. The other fused-silica capillary was connected to a Venturi easy ambient sonic-spray ionization source, sampling the resulting analytes at a slightly higher flow rate compared to the feeding capillary. The combined effects of the inflow and outflow maintains a chemical microenvironment, where the rate of advective transport overcomes diffusion. We show proof-of-concept where acetylcholinesterase was immobilized on an organosiloxane polymer through electrostatic interactions. The hydrolysis of acetylcholine by acetylcholinesterase into choline was monitored in real-time for a range of acetylcholine concentrations, fused-silica capillary geometries, and operating flow rates. Higher reaction rates and conversion yields were observed with increasing acetylcholine concentrations, as would be expected.

    View details for DOI 10.1021/acs.analchem.6b01246

    View details for Web of Science ID 000378470200019

    View details for PubMedID 27249533

  • Protein Analysis by Ambient Ionization Mass Spectrometry Using Trypsin-Immobilized Organosiloxane Polymer Surfaces ANALYTICAL CHEMISTRY Dulay, M. T., Eberlin, L. S., Zare, R. N. 2015; 87 (24): 12324-12330

    View details for DOI 10.1021/acs.analchem.5b03669

    View details for Web of Science ID 000366871500053

    View details for PubMedID 26567450

  • Droplet Spray Ionization from a Glass Microscope Slide: Real-Time Monitoring of Ethylene Polymerization ANALYTICAL CHEMISTRY Jiang, J., Zhang, H., Li, M., Dulay, M. T., Ingram, A. J., Li, N., You, H., Zare, R. N. 2015; 87 (16): 8057-8062

    Abstract

    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.

    View details for DOI 10.1021/acs.analchem.5b02390

    View details for Web of Science ID 000359892100005

  • Droplet spray ionization from a glass microscope slide: real-time monitoring of ethylene polymerization. Analytical chemistry Jiang, J., Zhang, H., Li, M., Dulay, M. T., Ingram, A. J., Li, N., You, H., Zare, R. N. 2015; 87 (16): 8057–62

    Abstract

    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.

    View details for PubMedID 26204485

  • Visible light-induced photopolymerization of an in situ macroporous sol-gel monolith JOURNAL OF SEPARATION SCIENCE Dulay, M. T., Choi, H. N., Zare, R. N. 2007; 30 (17): 2979-2985

    Abstract

    A one-step, in situ, photopolymerization of a mixture of methacryloxypropyltrimethoxysilane in the presence of an acid catalyst, water, and toluene is accomplished in a 75 microm id polyimide-coated capillary using visible light (460 nm) for a 15 min irradiation time. The mixture is a two-component photosystem comprising Irgacure 784 photosensitizer and diphenyliodonium chloride photoinitiator. The visible photopolymerized sol-gel (vis-PSG) column shows RP chromatographic behavior. The analytical potential of these columns is demonstrated with the isocratic separation of small, neutral alkyl phenyl ketones. Operational parameters, such as mobile phase composition, field strength, and column temperature were varied to assess how they affect the separation performance of the monolith.

    View details for DOI 10.1002/jssc.200700328

    View details for Web of Science ID 000251461500024

    View details for PubMedID 17960846

  • On-line biological sample cleanup for electrospray mass spectrometry using sol-gel columns JOURNAL OF CHROMATOGRAPHY B-ANALYTICAL TECHNOLOGIES IN THE BIOMEDICAL AND LIFE SCIENCES Johannesson, N., Pearce, E., Dulay, M., Zare, R. N., Bergquist, J., Markides, K. E. 2006; 842 (1): 70-74

    Abstract

    Using a slight overpressure, a urine sample is loaded onto a monolithic photopolymerized sol-gel column that has been derivatized with hydrophobic carbon chains and then the complex urine matrix is washed with aqueous solution. A buffer containing organic solvent is used to elute the adsorbed peptides by an applied voltage and the sample is then introduced into a mass spectrometer by sheath flow electrospray. The importance of desalting this type of sample is demonstrated by an experiment that shows that the signal intensity of a test solution with neurotensin, sprayed directly into the mass spectrometer, decreased from 4.5x10(4) cps to no detectible signal when just 10% urine is added to the sample solution. We suggest that this procedure may find general application for desalting biological samples prior to mass spectrometric analysis.

    View details for DOI 10.1016/j.jchromb.2006.05.012

    View details for Web of Science ID 000240712700011

    View details for PubMedID 16814621

  • Enhanced proteolytic activity of covalently bound enzymes in photopolymerized sol gel. Analytical chemistry Dulay, M. T., Baca, Q. J., Zare, R. N. 2005; 77 (14): 4604-4610

    Abstract

    Trypsin is covalently linked to a photopolymerized sol-gel monolith modified by incorporating poly(ethylene glycol) (PSG-PEG) for on-column digestion of N(alpha)-benzoyl-l-arginine ethyl ester (BAEE) and two peptides, neurotensin and insulin chain B. The coupling of the enzyme to the monolith is via room-temperature Schiff chemistry in which an alkoxysilane reagent (linker) with an aldehyde functional group links to an inactive amine on trypsin to form an imine bond. The proteolytic activity of the immobilized trypsin was measured by monitoring the formation of N alpha-benzoyl-L-arginine (BA), the digestion product of BAEE. The BA is separated from BAEE by capillary electrophoresis and detected downstream (18.5 cm from the microreactor) by absorption (254 nm). Using the Bradford assay, we determined that 97 ng of trypsin is bound to the 1-cm microreactor located at the entrance of capillary column. The bioactivity of the trypsin-PSG-PEG microreactor at 20 degrees C for the digestion of BAEE was found to be 2270 units/mg of immobilized trypsin. The bioactivity of trypsin bound to the capillary wall in the open segment upstream from the monolith was 332 units/mg of immobilized trypsin under the same conditions. In contrast, the activity of free trypsin could not be observed for the digestion of BAEE at 20 degrees C after 16 h of incubation time.

    View details for PubMedID 16013879

  • Enhanced proteolytic activity enzymes in photopolymerized of covalently bound sol gel ANALYTICAL CHEMISTRY Dulay, M. T., Baca, Q. J., Zare, R. N. 2005; 77 (14): 4604-4610

    View details for DOI 10.1021/ac0504767

    View details for Web of Science ID 000230530300042

  • Capillary electrophoretic and micellar electrokinetic separations of asymmetric dimethyl-L-arginine and structurally related amino acids: Quantitation in human plasma JOURNAL OF SEPARATION SCIENCE Trapp, G., Sydow, K., Dulay, M. T., Chou, T., Cooke, J. P., Zare, R. N. 2004; 27 (17-18): 1483-1490

    Abstract

    We report the development of efficient electrophoretic methods for the separation and quantification of L-arginine and six naturally occurring derivatives that are structurally and functionally related. Capillary electrophoresis (CE) employing a concentrated borate buffer at pH 9.4 achieves the separation of mixtures containing dimethyl-L-arginine, NG-monomethyl-L-arginine, L-arginine, L-homoarginine, L-ornithine, and L-citrulline as 4-fluoro-7-nitrobenzofurazan derivatives. In addition, the separation of the isomeric dimethyl-L-arginine derivatives (symmetric and asymmetric) is attained with baseline resolution by micellar electrokinetic chromatography (MEKC) when a high concentration of deoxycholic acid is added as a surfactant to the same running buffer. The influence of buffer type, concentration, and pH on the separation was studied to optimize separation conditions. The limit of quantitation (LOQ) for asymmetric dimethyl-L-arginine in aqueous solution was determined to be 20 microM using UV absorption in a CE separation and 0.1 microM using laser induced fluorescence (LIF) detection in an MEKC separation. This newly developed method was successfully applied for the quantitation of asymmetric dimethyl-L-arginine and L-arginine in human plasma samples at levels that might be used as a clinical diagnostic for cardiovascular disease (0.125 microM LOQ).

    View details for DOI 10.1002/jssc.200401918

    View details for PubMedID 15638156

  • Integration of on-line protein digestion, peptide separation, and protein identification using pepsin-coated photopolymerized sol-gel columns and capillary electrophoresis/mass spectrometry ANALYTICAL CHEMISTRY Kato, M., Sakai-Kato, K., Jin, H. M., Kubota, K., Miyano, H., Toyo'oka, T., Dulay, M. T., Zare, R. N. 2004; 76 (7): 1896-1902

    Abstract

    A miniaturized pepsin reactor was prepared inside a fused-silica capillary (i.d. 75 microm) by coating a pepsin-containing gel on a photopolymerized porous silica monolith. The pepsin-encapsulated film was prepared by a sol-gel method. The sol-gel reaction was optimized so that the sol solution containing pepsin forms a thin film on the photopolymerized sol-gel (PSG) monolith that was initially fabricated at the inlet of the capillary. Pepsin was encapsulated into the gel matrix without losing its activity. The large surface area of the PSG monolith enabled the immobilized pepsin to achieve a high catalytic turnover rate, and the porous nature of the PSG promotes penetration of large molecular proteins into the column. The immobilized pepsin-digested peptides and proteins, and the resulting mixture of peptide fragments, could be directly separated in the portion of the capillary where no PSG monolith exists. The durability and repeatability of the fabricated pepsin-coated column was tested and found to be satisfactory. An acidic solution consisting of 0.5 M formic acid was used as the running buffer, because it suppresses the adsorption of proteins or peptides on the inner surface of the capillary as well as enables direct connection of the output of the capillary electrophoresis column to a mass spectrometer. The on-line digestion of insulin chain beta and lysozyme provides identification of the proteolytic peptides. Recovery was achieved for 100% of the insulin chain beta amino acid sequence and 73% of the lysozyme amino acid sequence.

    View details for DOI 10.1021/ac035107u

    View details for Web of Science ID 000220618400022

    View details for PubMedID 15053649

  • Determination of glutamine and serine in rat cerebrospinal fluid using capillary electrochromatography with a modified photopolymerized sol-gel monolithic column JOURNAL OF CHROMATOGRAPHY A Kato, M., Jin, H. M., Sakai-Kato, K., Toyo'oka, T., Dulay, M. T., Zare, R. N. 2003; 1004 (1-2): 209-215

    Abstract

    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).

    View details for DOI 10.1016/S0021-9673(03)00451-5

    View details for Web of Science ID 000184296600023

    View details for PubMedID 12929975

  • Toward sol-gel electrochromatographic separations on a chip JOURNAL OF SEPARATION SCIENCE Morishima, K., Bennett, B. D., Dulay, M. T., Quirino, J. P., Zare, R. N. 2002; 25 (15-17): 1226-1230
  • Capillary electrophoresis separation and native laser-induced fluorescence detection of metallotexaphrins JOURNAL OF SEPARATION SCIENCE Quirino, J. P., Dulay, M. T., Fu, L., Mody, T. D., Zare, R. N. 2002; 25 (13): 819-824
  • Effect of preparatory conditions on the performance of photopolymerized sol-gel monoliths for capillary electrochromatography International Symposium on High Performance Liquid Phase Separations and Related Techniques (HPLC Kyoto) Kato, M., Sakai-Kato, K., Toyo'oka, T., Dulay, M. T., Quirino, J. P., Bennett, B. D., Zare, R. N. ELSEVIER SCIENCE BV. 2002: 45–51

    Abstract

    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.

    View details for Web of Science ID 000177061200006

    View details for PubMedID 12186390

  • Genetic screening using the colour change of a PNA-DNA hybrid-binding cyanine dye NUCLEIC ACIDS RESEARCH Wilhelmsson, L. M., Norden, B., Mukherjee, K., Dulay, M. T., Zare, R. N. 2002; 30 (2)

    Abstract

    As the relationship between human genes and various malfunctions and diseases becomes revealed at an ever-increasing pace, the need arises for the development of rapid genetic screening methods for diagnostic purposes. Genetic diseases show great diversity. Some are caused by a few characteristic localised mutations, while others arise from a large number of variations. Hence, it is unlikely that a single, general diagnostic method that applies to all cases will ever exist. Instead, a combination of methods is frequently applied. Here we propose the use of a dramatic colour change that a cyanine dye, 3,3'-diethylthiadicarbocyanine, displays upon binding to DNA-PNA duplexes. This method could become an inexpensive, fast and simple genetic screening test by visual inspection, with no need for complicated equipment. Our results demonstrate that this diagnostic method may be sufficiently sensitive to discriminate between even a fully complementary and a single mutation DNA sequence.

    View details for Web of Science ID 000173551200027

    View details for PubMedID 11788729

  • Bonded-phase photopolymerized sol-gel monoliths for reversed phase capillary electrochromatography JOURNAL OF SEPARATION SCIENCE Dulay, M. T., Quirino, J. P., Bennett, B. D., Zare, R. N. 2002; 25 (1-2): 3-9
  • Strategy for on-line preconcentration in chromatographic separations ANALYTICAL CHEMISTRY Quirino, J. P., Dulay, M. T., Bennett, B. D., Zare, R. N. 2001; 73 (22): 5539-5543

    Abstract

    In chromatographic separations, the heights of peaks are proportional to the concentrations of sample components present in an injected mixture. In general, an increase in the peak height cannot be achieved by simply increasing the injection time or the sample plug length. An exception occurs if some form of on-line preconcentration is possible. We present a new strategy for achieving on-line preconcentration by the use of a porous chromatographic material that acts as a solid-phase extractor as well as a stationary-phase separator. We are able to realize significant on-line preconcentration using capillary columns filled with a photopolymerized sol-gel (PSG). More than 2-cm plugs of sample solution can be loaded into the capillary and concentrated using a running buffer that is the same as the injection buffer (to avoid solvent gradient effects). As a demonstration, mixtures of three different polycyclic aromatic hydrocarbons, eight different alkyl phenyl ketones, and five different peptides in solutions of aqueous acetonitrile have been injected onto the PSG column and separated by capillary electrochromatography. The preconcentration is marked in terms of peak heights, with up to 100-fold increase for the PAH mixture, 30-fold for the alkyl phenyl ketone mixture, and 20-fold for the peptide mixture. Preconcentration takes place because of the high mass-transfer rates possible in the highly porous structure, and the extent of preconcentration follows the retention factor k for a given analyte.

    View details for DOI 10.1021/ac015522r

    View details for Web of Science ID 000172209400027

    View details for PubMedID 11816585

  • On-line preconcentration in capillary electrochromatography using a porous monolith together with solvent gradient and sample stacking ANALYTICAL CHEMISTRY Quirino, J. P., Dulay, M. T., Zare, R. N. 2001; 73 (22): 5557-5563

    Abstract

    Preconcentration effects of solvent gradient and sample stacking are investigated on a photopolymerized sol-gel (PSG) in capillary electrochromatography. The porous PSG monolith has a high mass-transfer rate. This characteristic promotes preconcentration of dilute samples. Plugs of samples more than 2 cm in length prepared in the separation solution (nongradient condition) are injected onto the PSG column. The extent of preconcentration is quite significant, showing up to a 100-fold increase in peak heights of the separated analytes. Even larger preconcentrations are achieved under gradient conditions by dissolving the sample in a matrix with a higher concentration of noneluting solvent (water). For eight alkyl phenyl ketones and four polycyclic aromatic hydrocarbons that serve as neutral test analytes, improvements in peak heights obtained under gradient conditions can be more than a 1000-fold. Indeed, injection of a 91.2-cm plug, which is more than 3 times the total length of the capillary, was possible with only a minor loss in resolution. Five peptides serve as charged test analytes. Nongradient conditions in which the sample is hydrodynamically injected onto the PSG column show sizable preconcentration because of sample stacking. The use of a solvent gradient with the same ionic strength, however, does not appear to have practical value because of destacking caused by the changing organic composition that affects the conductivity. As an alternative preconcentration method, we demonstrate that electric field-enhanced sample injection on the PSG yielded up to a 1000-fold improvement in detection sensitivity for the test peptides.

    View details for Web of Science ID 000172209400030

    View details for PubMedID 11816588

  • Photopolymerized sol-gel monoliths for capillary electrochromatography ANALYTICAL CHEMISTRY Dulay, M. T., Quirino, J. P., Bennett, B. D., Kato, M., Zare, R. N. 2001; 73 (16): 3921-3926

    Abstract

    A solution of methacryloxypropyltrimethoxysilane in the presence of an acid catalyst, water, toluene, and a photoinitiator was irradiated at 365 nm for 5 min in a 75-microm i.d. capillary to prepare a porous monolithic sol-gel column by a one-step, in situ, process. The photopolymerized sol-gel (PSG) column shows reversed-phase behavior. Using this column, a variety of low-molecular-weight neutral compounds, including polycyclic aromatic hydrocarbons, alkyl benzenes, alkyl phenyl ketones, and steroids are separated from mixtures. Various different operational parameters, such as buffer composition, field strength, and column temperature, were varied to assess their influence on column performance. Use of PSG as a stationary phase for a pressure-driven separation is also demonstrated.

    View details for DOI 10.1006/ac0100749

    View details for Web of Science ID 000170482800019

    View details for PubMedID 11534717

  • Photopolymerized sol-gel frits for packed columns in capillary electrochromatography 14th International Symposium on Microscale Separations and Analysis Kato, M., Dulay, M. T., Bennett, B. D., Quirino, J. P., Zare, R. N. ELSEVIER SCIENCE BV. 2001: 187–95

    Abstract

    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.

    View details for Web of Science ID 000170359200018

    View details for PubMedID 11521865

  • Enantiomeric separation of amino acids and nonprotein amino acids using a particle-loaded monolithic column ELECTROPHORESIS Kato, M., Dulay, M. T., Bennett, B., Chen, J. R., Zare, R. N. 2000; 21 (15): 3145-3151

    Abstract

    A solution is prepared of 5 microm 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 microm inner diameter capillary column and heated for 1 h at 120 degrees 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).

    View details for PubMedID 11001212

  • Softening of fused-silica capillaries during particle packing ELECTROPHORESIS Chen, J. R., Dulay, M. T., Zare, R. N. 2000; 21 (7): 1430-1431

    Abstract

    When a semipreparative capillary electrochromatography (CEC) capillary is packed with silica particles and exposed to solvent, its mechanical strength is markedly reduced. In our studies, a fused-silica capillary (internal diameter > 200 microm and wall thickness < 150 microm) was packed under pressure (approximately 200 psi) with spherical silica particles (1.5-5 microm) suspended in water or various common organic solvents. After one hour of exposure, the capillary can be readily deformed, and it keeps its deformed shape upon release of the force causing deformation. It is suggested that capillary softening is promoted through the propagation of internal microcracks that have been caused by action of the particles during packing in the presence of solvent. Application of a protective coating to the inside of the capillary is found to reduce or eliminate capillary softening.

    View details for PubMedID 10826691

  • Macroporous photopolymer frits for capillary electrochromatography ANALYTICAL CHEMISTRY Chen, J. R., Dulay, M. T., Zare, R. N., Svec, F., Peters, E. 2000; 72 (6): 1224-1227
  • Preparation and characterization of monolithic porous capillary columns loaded with chromatographic particles ANALYTICAL CHEMISTRY Dulay, M. T., Kulkarni, R. P., Zare, R. N. 1998; 70 (23): 5103-5107

    Abstract

    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.

    View details for Web of Science ID 000077278700046

    View details for PubMedID 21644688

  • Evidence for the extraterrestrial origin of polycyclic aromatic hydrocarbons in the Martian meteorite ALH84001 General Discussion on Chemistry and Physics of Molecules and Grains in Space Clemett, S. J., Dulay, M. T., Gillette, J. S., Chillier, X. D., Mahajan, T. B., Zare, R. N. ROYAL SOC CHEMISTRY. 1998: 417–436

    Abstract

    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.

    View details for Web of Science ID 000076353800024

    View details for PubMedID 9809015

  • The template synthesis and X-ray characterization of pyrrole-derived hexadentate uranyl(VI) Schiff-base macrocyclic complexes INORGANICA CHIMICA ACTA Sessler, J. L., Mody, T. D., Dulay, M. T., ESPINOZA, R., Lynch, V. 1996; 246 (1-2): 23-30
  • Automated capillary electrochromatography: Reliability and reproducibility studies JOURNAL OF CHROMATOGRAPHY A Dulay, M. T., Yan, C., Rakestraw, D. J., Zare, R. N. 1996; 725 (2): 361-366

    Abstract

    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.

    View details for PubMedID 8900577