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Biomedical subjects

Isiah M Warner

Publications and source records attributed to Isiah M Warner.

42 records · Page 3Linked to original sources
PubMed2002

A colloidal graphite-coated emitter for sheathless capillary electrophoresis/nanoelectrospray ionization mass spectrometry.

A colloidal graphite-coated emitter is introduced for sheathless capillary electrophoresis/nanoelectrospray ionization time-of-flight mass spectrometry (CE/ESI-TOFMS). The conductive coating can be produced by brushing the capillary tip to construct a fine layer of 2-propanol-based colloidal graphite. The fabrication involves a single step and requires less than 2 min. Full cure properties develop in approximately 2 h at room temperature and then the tip is ready for use. The coated capillary tip is applied as a sheathless electrospray emitter. The emitter has proven to bear stable electrospray and excellent performance for 50 microm i.d. x 360 microm o.d. and 20 microm i.d. x 360 microm o.d. capillaries within the flow rate of 80-500 nL/min; continuous electrospray can last for over 200 h in positive mode. Baseline separation and structure elucidation of two clinically interesting basic drugs, risperidone and 9-hydroxyrisperidone, are achieved by coupling pressure-assisted CE to ESI-TOFMS using the described sheathless electrospray emitter with a bare fused-silica capillary at pH 6.7. It is found that the signal intensity of m/z in sheathless CE/ESI-TOFMS at pH 6.7 is approximately 50 times higher than that at pH 9.0 for the two analytes, although the electroosmotic flow (EOF) at pH 9.0 provides sufficient flow rate (approximately 150 nL/min) to maintain electrospray.

Colloids↗
PubMed2002

Enantiomeric separations using poly(L-valine) and poly(L-leucine) surfactants. Investigation of steric factors near the chiral center.

This study examined the effect of steric factors near the stereogenic center on polymerized surfactants, sodium N-undecyl-L-leucine, sodium N-undecyl-L-norleucine, sodium N-undecyl-L-tert.-butyl leucine, sodium N-undecyl-L-isoleucine. sodium N-undecyl-L-valine, sodium N-undecyl-L-norvaline. and sodium N-undecyl-L-proline. The effect of steric factors near the chiral center of the polymeric surfactants were examined using binaphthyl derivatives, aminoglutethimide, and 2,2,2-trifluoro-1-(9-anthryl)ethanol. In addition, fluorescence spectroscopy was used to determine the hydrophobicities of these surfactants using the environmentally-sensitive probe pyrene.

Hydrogen Bonding↗
PubMed2002

Analytical separations using molecular micelles in open-tubular capillary electrochromatography.

Open-tubular capillary electrochromatography (OT-CEC) is an alternative approach to conventional CEC. The primary advantage of OT-CEC is the elimination of problems associated with frits and silica particles in conventional CEC. This report is an investigation of the utility of using a polymeric surfactant (molecular micelle) for OT-CEC. In this approach, fused-silica capillaries coated with thin films of physically adsorbed charged polymers are developed by use of a polyelectrolyte multilayer (PEM) coating procedure. The PEM coating is constructed in situ by alternating rinses with positively and negatively charged polymers, where the negatively charged polymer is a molecular micelle. This can offer a number of advantages for separation of hydrophobic analytes. In this study, poly(diallyldimethylammonium chloride) was used as the cationic polymer and poly(sodium N-undecanoyl-L-glycinate) was used as the anionic polymer for PEM coating. The performance of the modified capillaries as a separation medium is evaluated by use of seven benzodiazepines as analytes. The run-to-run, day-to-day, week-to-week, and capillary-to-capillary reproducibilities of electroosmotic flow are very good with relative standard deviation values of less than 1% in all cases. In addition, the chromatographic performance of the monomeric form of the molecular micelle is compared for the separation of these analytes. The PEM-coated capillary was remarkably robust with more than 200 runs accomplished in this study. Strong stability against extreme pH values was also observed. The general utility of this approach is discussed in detail.

Benzodiazepines↗
PubMed2002

Depth of penetration of binaphthyl derivatives into the micellar core of sodium undecenoyl leucyl-leucinate surfactants.

Two different diastereomeric forms of sodium N-undecanoyl leucyl-leucinate (SULL) (both L,L and L,D) are used to examine the role of depth of penetration of chiral analytes into the micellar core of polymeric and monomeric surfactants on enantioselectivity. In this study, chiral separation of three binaphthyl derivatives, i.e. (+/-)-1,1'-bi-naphthyl-2,2'-diamine (BNA), (+/-)-1,1'-bi-2-naphthol (BOH), and (+/-)-1,1'-binaphthyl-2,2'-dihydrogen phosphate (BNP), are studied. Chromatographic results suggest that BNP interacts approximately the same with both the C- and N-terminal amino acid of poly SULL, while the preferential site of interaction of this analyte with the monomeric form of SULL (mono SULL) is at the C-terminal amino acid. This indicates that BNP enantiomers penetrate deeper into the micellar core of the poly SULL than that of the mono SULL. Varying the temperature resulted in a change in the depth of penetration of BNP into the micellar core of the poly SULL. However, the enantiomers of BNA and BOH always interact preferentially with the N-terminal amino acid of SULL surfactants (both polymer and monomer), independent of the temperatures studied.

Leucine↗
PubMedDate not supplied

Separation of benzodiazepines using capillary electrochromatography.

Benzodiazepines are often used for the treatment of epilepsy, convulsions, and many psychiatric disorders. The widespread use of this class of drugs has occasionally raised concern about recreational benzodiazepine abuse and has led to the erroneous impression that benzodiazepines have a relatively high abuse liability among recreational drug users. Therefore, the separation and identification of these compounds is of great interest. In general, the separation of benzodiazepines is performed using high-performance liquid chromatography (HPLC). Recently, capillary electrochromatography, which combines the high efficiency of capillary zone electrophoresis and the high selectivity of HPLC, has gained much attention. The focus of the work reported here is the use of a 40-cm packed bed of Reliasil 3- microm C(18) stationary phase to separate seven benzodiazepines. Optimal conditions are established by varying the mobile phase, amount of organic modifier, buffer concentration, applied voltage, and column temperature. A mobile phase composition of Tris-HCl (pH 8)-acetonitrile (60:40), an electrolyte concentration of 30mM, and a temperature of 15 degrees C with an applied voltage of 20 kV proves to be optimum. In addition, the method developed here is applied to the characterization of oxazepam in a standard urine sample.

Benzodiazepines↗