Biomedical subjects

Lane C Sander

Publications and source records attributed to Lane C Sander.

33 records · Page 2Linked to original sources

PubMed2005

Dynamically coated capillaries for enantioselective separations by capillary electrophoresis.

The level of variability in migration times and peak areas often encountered in capillary electrophoresis (CE) has restricted its use for routine analysis. Cationic analytes also tend to interact with the capillary wall, resulting in skewed peak shapes and reduced efficiency. We investigated a dynamic coating procedure that involves a two-step process to modify the capillary and that results in a higher but stable electro-osmotic flow (EOF) at low pH. We compared enantioselective separations of several basic compounds on unmodified and dynamically coated capillaries. A derivatized cyclodextrin was used as the chiral additive. When the dynamic coating was used, peak symmetry improved, and migration times were significantly shorter. The dynamic coating procedure also resulted in improved migration time and peak area precision.

Journal Article↗

PubMed2004

Selectivity of long chain stationary phases in reversed phase liquid chromatography.

A series of commercial monomeric and polymeric C(18), C(27), and C(30) stationary phases were compared with immobilized poly(ethylene-co-acrylic acid) stationary phases synthesized in-house. The columns were characterized on the basis of methylene selectivity, silanol activity, metal activity, pore size, shape selectivity, and the ability to separate tocopherol isomers and carotenoid isomers. Monomeric and polymeric C(30) phases were shown to yield excellent separations of the tocopherol isomers while the polymeric C(30) and polyethylene phases were more appropriate to the separation of carotenoids.

Acrylic Resins↗

PubMed2004

Two new marine sediment standard reference materials (SRMs) for the determination of organic contaminants.

Two new marine sediment standard reference materials (SRMs), SRM 1941b Organics in Marine Sediment and SRM 1944 New York/New Jersey Waterway Sediment, have been recently issued by the National Institute of Standards and Technology (NIST) for the determination of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl (PCB) congeners, and chlorinated pesticides. Both sediment SRMs were analyzed using multiple analytical methods including gas chromatography/mass spectrometry (GC/MS) on columns with different selectivity, reversed-phase liquid chromatography with fluorescence detection (for PAHs only), and GC with electron capture detection (for PCBs and pesticides only). SRM 1941b has certified concentrations for 24 PAHs, 29 PCB congeners, and 7 pesticides, and SRM 1944 has certified concentrations for 24 PAHs, 29 PCB congeners, and 4 pesticides. Reference concentrations are also provided for an additional 58 (SRM 1941b) and 39 (SRM 1944) PAHs, PCB congeners, and pesticides. SRM 1944, which was collected from multiple sites within New York/New Jersey coastal waterways, has contaminant concentrations that are generally a factor of 10-20 greater than SRM 1941b, which was collected in the Baltimore (Maryland) harbor. These two SRMs represent the most extensively characterized marine sediment certified reference materials available for the determination of organic contaminants.

Environmental Monitoring↗

PubMed2003

Chemometric studies of polycyclic aromatic hydrocarbon shape selectivity in reversed-phase liquid chromatography.

The molecular shape recognition differences between monomeric and polymeric C18 stationary phases in the reversed-phase liquid chromatography (RPLC) separation of unsubstituted polycyclic aromatic hydrocarbons (PAHs) and methyl-substituted polycyclic aromatic hydrocarbons (MPAHs) are examined through the use of partial least squares (PLS) analysis techniques. The resulting PLS models are able to describe the enhanced shape selectivity of the polymeric phase for recognizing subtle structural differences among planar and nonplanar isomers. PLS component analyses of these models reveal that spatial and topological descriptors are primarily used to rank structural differences among the PAHs (i.e., fused-ring patterns, molecular length and breadth) that control such shape-selective chromatographic processes. This is consistent with the view that polymeric alkyl chain stationary phases contain size- and shape-specific "slots" that promote the separation of structurally-related solutes. In contrast, the monomeric phase model is limited in resolving both the isomer classes and the nonplanarity shape differences among the PAHs. However, an improvement of shape recognition on the monomeric phase was elucidated by the PLS model for two PAHs (phenanthro[3,4-c]phenanthrene and dibenzo[g,p]chrysene) exhibiting the most extreme nonplanarity. These results suggest that a limited amount of space between alkyl chains may exist within the higher-density polymeric phase to recognize shape differences among the bulkier and nonplanar solutes.

Journal Article↗

PubMed2003

Liquid chromatographic method for the determination of enantiomeric composition of amphetamine and methamphetamine in hair samples.

Interest in hair analysis as an alternative or complementary approach to urinalysis for drug abuse detection has grown in recent years. Hair analysis can be particularly advantageous for drugs such as amphetamine and methamphetamine that are rapidly excreted. Confirmation of abuse of these stimulants is complicated by the fact that some forms are found in legitimate medications. Examination of the enantiomeric composition of amphetamine and methamphetamine in hair samples can provide valuable assistance in interpreting drug testing results. In this work, we developed a liquid chromatographic method for the separation of amphetamine and methamphetamine enantiomers isolated from human hair samples. The drug enantiomers were separated on a chiral stationary phase after derivatization with an achiral fluorescent agent. The methodology was evaluated with a Standard Reference Material that contained several drugs of abuse including amphetamine and methamphetamine.

Amphetamine↗

PubMed2003

Synthesis and characterization of C13 to C18 stationary phases by monomeric, solution polymerized, and surface polymerized approaches.

A series of bonded phases were synthesized from consecutive length alkylsilanes ranging from C13 through C18, with three different bonding chemistries (monomeric, solution polymerized, and surface polymerized) at each phase length. The phases were characterized in terms of methylene selectivity, shape selectivity, and band broadening. No significant chromatographic differences were found to result from the synthetic routes, except that the different bonding chemistries provide a different range of bonding densities. For bonding densities ranging from 2 to 8 micromol/m2, a linear increase in methylene selectivity was observed with increasing bonding density. Over the narrow range of bonded phase lengths investigated, shape selectivity is more dependent on density than phase length.

Polymers↗

PubMed2003

Structure-function relationships in high-density octadecylsilane stationary phases by Raman spectroscopy. 3. Effects of self-associating solvents.

Raman spectroscopy is used to examine the subtle effects of polar, hydrogen-bonding solvents; temperature; and the surface grafting method (surface- or solution-polymerized) on alkyl chain rotational and conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2. Rotational and conformational order is assessed using the intensity ratio of the antisymmetric to symmetric v(CH2) modes as well as the frequencies at which these Raman bands are observed. Alkyl rotational and conformational order decreases with decreasing surface coverage in these polar solvents, consistent with the behavior of these materials in air. For homogeneously distributed, high surface coverage materials, these polar solvents induce rotational ordering that is proposed to be due to the self-association of these solvents through hydrogen bonding or other dipole interactions at the alkylsilane-solvent interface. From these observations, molecular pictures of these solvent-stationary-phase interfaces are proposed in which solvent interaction with the stationary phase occurs primarily at the distal methyl group of the alkyl chains.

Journal Article↗

PubMed2003

Structure-function relationships in high-density octadecylsilane stationary phases by Raman spectroscopy. 4. Effects of neutral and basic aromatic compounds.

The effects of aromatic compounds (toluene, benzene, p-xylene, anisole, aniline, and pyridine), temperature, and surface grafting method (surface- or solution-polymerized) on alkyl chain rotational and conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2 are examined by Raman spectroscopy. Rotational and conformational order are assessed using the intensity ratio of the antisymmetric to symmetric v(CH2) modes as well as the frequency at which the symmetric v(CH2) band is observed. Alkyl rotational and conformational order decrease with decreasing surface coverage in these aromatic compounds, which is consistent with the behavior of these materials in air and in other solvents. In addition, order of the alkyl chains is dependent on solvent hydrophobicity, hydrogen-bonding ability, and basicity. The most hydrophobic compounds impart disorder to the stationary phase; the hydrogen-bonding aromatics increase the rotational order of homogeneously distributed, high-surface-coverage materials; and basic aromatic compounds increase the conformational order of high- and low-coverage materials as the basic compounds undergo silanophilic interactions with exposed surface silanols. From these observations, molecular pictures of the chromatographic interface that display interactions between the alkyl chains and these aromatic compounds are proposed.

Journal Article↗

PubMed2003

Additive concentration effects on enantioselective separations in supercritical fluid chromatography.

Polar additive concentration effects in supercritical fluid chromatography were studied on chiral stationary phases having either a macrocyclic glycopeptide or a derivatized polysaccharide as the chiral selector. Two basic additives, isopropylamine and triethylamine, were incorporated into the methanol modifier at various concentrations and the effects on retention, selectivity, and resolution were monitored. Many of the analytes failed to elute from the macrocyclic glycopeptide stationary phase in the absence of an additive and the most noticeable effect of increasing additive concentration was a significant decrease in retention. On the derivatized polysaccharide stationary phase the additives had little effect on retention, but they did foster significant improvements in peak shape and resolution.

Journal Article↗

PubMed2003

Enantioselective separations in capillary electrophoresis with dextran sulfate as the chiral selector.

Dextran sulfate, a polyanionic polysaccharide, was evaluated as a chiral additive in capillary electrophoresis. Structurally related compounds having a variety of functional groups were utilized to probe the selectivity of the chiral selector. The effects of pH, chiral selector concentration, and chiral selector composition on resolution were also studied. At low pH, the reversed polarity mode was employed to achieve separation of the probe compounds. The electrophoretic results provided insight into the chiral recognition of dextran sulfate in capillary electrophoresis. Several factors, including hydrophobic, steric, and electrostatic interactions, appeared to play a role in the observed enantioseparations.

Dextran Sulfate↗

PubMed2003

Determination of polycyclic aromatic hydrocarbons with molecular weight 300 and 302 in environmental-matrix standard reference materials by gas chromatography/mass spectrometry.

An analytical approach based on gas chromatography/ mass spectrometry (GC/MS) is presented for the measurement of polycyclic aromatic hydrocarbons with molecular weight (MW) 300 and 302 in environmental samples. Three different GC stationary phases [5% and 50% phenyl methylpolysiloxane and dimethyl (50% liquid crystalline) polysiloxane] were compared, and retention indexes (RI) are given for 23 individual MW 302 isomers. Identification of MW 300 and 302 isomers in four environmental-matrix Standard Reference Materials (SRMs) (SRM 1597, coal tar extract; SRM 1648 and SRM 1649a, air particulate matter; and SRM 1941, marine sediment) was based on the comparison of RI data and mass spectra from authentic standards. Dibenzo[a,l]pyrene, which is of considerable interest because of its high carcinogenicity, was identified and quantified in the four environmental-matrix SRMs. A total of 23 isomers of MW 302 and four isomers of MW 300 were quantified in four different environmental-matrix SRMs, and the results are compared to previously reported results based on liquid chromatography with fluorescence detection.

Environmental Pollutants↗

PubMed2002

Structure-function relationships in high-density octadecylsilane stationary phases by Raman spectroscopy. 1. Effects of temperature, surface coverage, and preparation procedure.

Raman spectroscopy is used to examine the effects of temperature, surface coverage, nature of the alkylsilane precursor (octadecyltrichlorosilane, methyloctadecyldichlorosilane, or dimethyloctadecylchlorosilane), and surface grafting method (surface or solution polymerized) on alkyl chain conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2. Conformational order is assessed using the intensity ratio of the antisymmetric and symmetric v(CH2) modes as well as the frequency at which these Raman bands are observed. Conformational order increases with surface coverage. Temperature-induced surface phase changes are observed between 258 and 343 K for this homologous series of stationary phases that are demonstrated to adhere to the Clapeyron equation for a simple first-order transition. Phase changes are discussed in terms of variation of the molar enthalpy, molar entropy, and molar volume of the stationary phase, all of which depend on surface coverage. For the limited range of systems investigated, a correlation between stationary-phase preparation (surface versus solution polymerized and nature of the silane precursor) and extent of alkyl chain order is not clearly observed.Instead, akyl chain order is largely dependent on bonding density. A molecular picture of temperature-induced disorder in octadecylsilane stationary phases is proposed, with disorder originating at the distal carbon and propagating toward the proximal carbon.

Molecular Conformation↗

PubMed2002

Structure-function relationships in high-density octadecylsilane stationary phases by Raman spectroscopy. 2. Effect of common mobile-phase solvents.

Raman spectroscopy is used to examine the effects of solvent, temperature, and surface grafting method (surface or solution polymerized) on alkyl chain rotational and conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2. Rotational and conformational order is assessed using the intensity ratio of the antisymmetric to symmetric v(CH2) modes as well as the frequency at which these Raman bands are observed. Solvents studied include perdeuterated hexane, toluene, chloroform, tetrahydrofuran, benzene, methanol, acetone, acetonitrile, and water. Stationary-phase order was investigated at temperatures between 258 and 323 K. Alkyl chain rotational and conformational order, and hence, solvation of the stationary phase, is dependent on solvent parameters (polarity, size, etc.), temperature, and stationary-phase properties (polymerization method and surface coverage). Information on stationary-phase conformational order allows solvent-stationary-phase interactions to be described in terms of a combination of adsorption and partitioning models for reversed-phase liquid chromatography. Finally, a distinct interplay between solvent- and temperature-induced ordering of these stationary phases is documented that is also a function of solvent and stationary-phase properties.

Molecular Conformation↗

PubMed2002

Chiral recognition of functionalized cyclodextrins in capillary electrophoresis.

The chiral recognition of hydroxypropylated, dimethylated, and sulfated cyclodextrins was evaluated by utilizing them as chiral additives in capillary electrophoresis. Although each selector yielded enantiomeric separations of most of the target analytes, differences were observed in the electrophoretic results for the different derivatized cyclodextrins and for additives having varying degrees of substitution. The results for the sulfated cyclodextrins also highlighted the importance of knowing the degree of substitution as well as the location of the substituents when comparing chiral selectors.

Chromatography, Micellar Electrokinetic Capillary↗

PubMedDate not supplied

Preparation and characterization of a suite of ephedra-containing standard reference materials.

The National Institute of Standards and Technology, the U.S. Food and Drug Administration, Center for Drug Evaluation and Research and Center for Food Safety and Applied Nutrition, and the National Institutes of Health, Office of Dietary Supplements, are collaborating to produce a series of Standard Reference Materials (SRMs) for dietary supplements. A suite of ephedra materials is the first in the series, and this paper describes the acquisition, preparation, and value assignment of these materials: SRMs 3240 Ephedra sinica Stapf Aerial Parts, 3241 E. sinica Stapf Native Extract, 3242 E. sinica Stapf Commercial Extract, 3243 Ephedra-Containing Solid Oral Dosage Form, and 3244 Ephedra-Containing Protein Powder. Values are assigned for ephedrine alkaloids and toxic elements in all 5 materials. Values are assigned for other analytes (e.g., caffeine, nutrient elements, proximates, etc.) in some of the materials, as appropriate. Materials in this suite of SRMs are intended for use as primary control materials when values are assigned to in-house (secondary) control materials and for validation of analytical methods for the measurement of alkaloids, toxic elements, and, in the case of SRM 3244, nutrients in similar materials.

Alkaloids↗