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R Kenneth Marcus

Publications and source records attributed to R Kenneth Marcus.

15 recordsLinked to original sources
PubMed2006

Characterization of capillary-channeled polymer fiber stationary phases for high-performance liquid chromatography protein separations: Comparative analysis with a packed-bed column.

Capillary-channeled polymer (C-CP) fibers are investigated as reversed-phase (RP) stationary phases for high-performance liquid chromatography of proteins. A comparative analysis of column characteristics for polypropylene and poly(ethylene terephthalate) C-CP fiber columns and a conventional packed-bed (C4-derivatized silica) column has been undertaken. Five proteins (ribonuclease A, cytochrome c, lysozyme, myoglobin, bovine serum albumin) were used to investigate the separation characteristics under typical RP gradient conditions. Column performance was compared under standard (identical) and optimized RP chromatographic conditions. The gradient compositions utilized with the C-CP fiber columns are similar to those used with conventional columns, employing flow rates in the 1-6 mL/min range and gradient rates of approximately 1%/min. The packed-bed column was operated as prescribed by the column manufacturer. The retention factor (k'), separation factor (alpha), resolution (Rs), asymmetry factor (As), elution order, and peak capacity values of a four protein separations performed on the C-CP fiber columns are compared to the same separation on the C4 column. One unique feature observed here is the lessening of the percentage of organic modifier necessary to elute the proteins from the fiber phases with increased linear velocity. The potential contribution of the different stationary phases to protein denaturation was evaluated through a spectrophotometric enzymatic activity assay. The repeatability of retention times under both sets of conditions for six consecutive injections of lysozyme on each C-CP fiber column is < or =1.5% RSD. The column-to-column reproducibility of retention times for three columns of each fiber type is also < or =1.5% RSD. The overall performance of the C-CP fiber columns was comparable to the conventional column used in these studies. Basic characteristics demonstrated here suggested further developments in the areas of ultrafast protein separations and preparative-scale protein chromatography.

Animals↗
PubMed2006

Electron-impact and glow-discharge ionization LC-MS analysis of green tea tincture.

A liquid chromatography-particle-beam mass spectrometer (LC-PB/MS) with interchangeable electron-impact (EI) and glow-discharge (GD) ion sources was evaluated for future application in analysis of botanical extracts. In this work a green tea tincture was characterized for a series of catechin components (catechin, epicatechin, epigallocatechin, and epigallocatechin gallate (EGCG)) and caffeine. Special emphasis was given to EGCG and caffeine, because they are important in determining the possible health effects of the green tea. The effects of instrument operating conditions were evaluated for the EI and GD ionization sources to determine their effect on analyte intensities and fragmentation patterns. These studies furnished information about the effects of these conditions in determining possible ionization pathways in the two ion sources. The mass spectra of these compounds obtained with the GD ion source are EI-like in appearance, with clearly identified molecular ions and fragmentation patterns that are easily rationalized. The absolute limits of detection for EGCG and caffeine were, respectively, 11 ng and 0.77 ng for the EI source and 3.2 ng and 0.61 ng for the GD source. The PB/EIMS and PB/GDMS combinations can be operated in a flow-injection mode, wherein the analyte is injected directly into the mobile phase, or coupled to high-performance liquid chromatography (HPLC), enabling LC-MS analysis of complex mixtures. A reversed-phase chromatographic separation of the green tea tincture was performed on a commercial C18 column using a gradient of water (containing 0.1% TFA) and ACN. Quantification of EGCG and caffeine was performed by the standard addition method. The amounts of EGCG and caffeine in the tested green tea tincture were each approximately 14 mg mL-1.

Caffeine↗
PubMed2006

Non-metal element detection by radio-frequency glow-discharge optical-emission spectrometry (rf-GD-OES) for determination of sol-gel-immobilized nucleotides.

A new method is presented for qualitative and quantitative determination of non-metal elements present in organic analyte species immobilized in a sol-gel matrix. Nucleic acids were chosen as well-defined relevant biomolecules for which element ratios could be used for detection and identification. Solid, lyophilized powders of ribose-form nucleotides (AMP, ADP, and ATP) were immobilized/entrapped in a methlytrimethoxysilane (mTMOS) sol-gel matrix and monitored for P (I) 214.9 nm, C (I) 193.0 nm, O (I) 130.2, and N (I) 149.3 nm emission by radio-frequency glow-discharge optical-emission spectroscopy (rf-GD-OES). Using the sol-gel method, analytical blanks were obtained by use of un-doped sol-gels. Empirical formula calculations by use of P (I) and C (I), P (I) and N (I), and P (I) and O (I) emission response ratios demonstrate the versatility of the technique as an element and species-specific detector. Results show there is high correlation between phosphorus and oxygen emission responses and the extent of phosphorylation, demonstrating the capacity of the method to produce vital qualitative and quantitative information for the specific nucleotide. Absolute sub-nanogram detection limits were achieved for all the elements studied.

Gels↗
PubMed2006

Capillary-channeled polymer fibers as a stationary phase for desalting of protein solutions for electrospray ionization mass spectrometry analysis.

Micropipet solid-phase extraction (SPE) tips have been used to desalt and purify proteins and peptides from mixtures of buffers and biological solutions. Removing salts and buffers prior to electrospray ionization mass spectrometry (ESI-MS) characterization improves the detection limits and the sensitivity of the protein analyses. Recently, capillary-channeled polymer (C-CP) fibers have been investigated as stationary phases for high-performance liquid chromatography separations of proteins. Polypropylene C-CP fibers incorporated as sorbent materials in micro-SPE tips are shown to effectively remove both inorganic and organic buffers from proteins in defined solutions. The architecture of the fibers provides large surface areas in comparison to conventional round fibers and is readily packed into capillaries that can be affixed to micropipet tips. Desalting of protein solutions is demonstrated for ESI-MS analysis through increased signal-to-noise ratios and reduced spectral complexity.

Chromatography, High Pressure Liquid↗
PubMed2005

Capillary-channeled polymer (C-CP) fibers as a stationary phase in microbore high-performance liquid chromatography columns.

Microbore columns utilizing polypropylene capillary-channeled polymer (C-CP) fibers as the stationary phase in high-performance liquid chromatography (HPLC) have been investigated. The polypropylene C-CP fiber diameter is approximately 50 microm, with eight channels along the periphery of the fiber ranging in diameter from approximately 12 to 35 microm. The polypropylene C-CP fibers were packed into fluorinated ethylene propylene (FEP) tubing, 1.3 mm inner diameter, with lengths of 500, 750, and 1,000 mm, to examine the effects of increased column length with regards to plate height, resolution and analysis time. The low backpressures characteristic of the C-CP fiber stationary phases allow the length of the column to be increased without significantly decreasing the specific permeability. The high specific permeability (approximately 5x10(-8) cm2) of the C-CP packed microbore columns yields a relatively low backpressure of 2.35 MPa at the highest flow rate of 17 microL/s (54 mm/s) for a 1,000 mm column. Radial compression of the soft-walled FEP tubing is accomplished by pulling the 1.7 mm o.d. column through a 1.4 mm diameter orifice. Reducing the inner diameter of the column from 1.3 to 1.0 mm lowered the interstitial fraction from 47% to 42%, decreased the A-term contributions to band broadening, resulted in a significant decrease in average plate height (approximately 30%), and increased resolution (approximately 36%) at identical linear velocities. Although the lower void volume of the radially compressed column increased the backpressure from 0.57 to 2.11 MPa at a linear velocity of approximately 20 mm/s, the specific permeability only decreased from approximately 7x10(-8) to 4x10(-8) cm2.

Chromatography, High Pressure Liquid↗
PubMed2005

Hydrodynamic flow in capillary-channel fiber columns for liquid chromatography.

The flow characteristics of capillary-channel polymer (C-CP) fiber liquid chromatographic (LC) columns have been investigated. The C-CP fibers are manufactured with eight longitudinal grooves (capillary channels) extending the length of the fibers. Three C-CP fiber examples were studied, with fiber dimensions ranging from approximately 35 microm to 65 microm, and capillary-channel dimensions ranging from approximately 6 microm to 35 microm. The influence of fiber packing density and column inner diameter on peak asymmetry, peak width, and run-to-run reproducibility have been studied for stainless steel LC columns packed with polyester (PET) and polypropylene (PP) C-CP fibers. The van Deemter A-term was evaluated as a function of fiber packing density (approximately 0.3 g/cm(3)-0.75 g/cm(3)) for columns of 4.6 mm inner diameter (i.d.) and at constant packing densities for 1.5 mm, 3.2 mm, 4.6 mm, and 7.7 mm i.d. columns. Although column diameter had little influence on the eluting peak widths, peak asymmetry increased with increasing column diameter. The A-terms for the C-CP fiber packed columns are somewhat larger than current commercial, microparticulate-packed columns, and means for improvement are discussed. Applications in the area of protein (macromolecule) separations appear the most promising at this stage of the system development.

Chromatography, Liquid↗
PubMed2004

Total protein determinations by particle beam/hollow cathode optical emission spectroscopy (PB/HC-OES) system III: investigation of carrier salts for enhanced particle transport.

Particle beam hollow cathode optical emission spectroscopy (PB/HC-OES) is evaluated as a generic tool for total protein determinations by monitoring the carbon atomic emission (C (I) 193.0 nm) resultant from dissociated analyte species. Previous studies demonstrated the capability of the PB/HC-OES system for total protein determinations with limits of detection for bovine serum albumin (BSA) samples being at the single-nanogram level for 200 microl injections. Non-linear behavior across the concentration range in the calibration curve was observed due to the poor transport of small particles (owing to low analyte concentrations) through the PB interface. The potential use of non-volatile salts as carrier agents is investigated in the determination of protein samples by PB/HC-OES. A range of chloride salts (different cations), potassium salts (different anions), and an organic modifier (ammonium acetate) is investigated here for possible use as carriers upon addition as sample injection matrices for protein samples. The analyte response curves of BSA samples with KCl added as the sample injection matrix show higher sensitivity, better linearity (R2) and subsequently lower detection limits in comparison to those obtained with water, HCl, KNO3 or ammonium acetate as carrier matrices.

Animals↗
PubMed2003

Total protein determinations by particle beam/hollow cathode optical emission spectroscopy.

A novel method for quantitative total protein determinations is presented. Total protein content is determined by particle beam/hollow cathode optical emission spectroscopy (PB/HC-OES) through monitoring of carbon atomic emission. The PB/HC-OES offers such advantages as ease of operation, exclusion of labor-intensive sample pretreatment processes, rapid analysis, high sensitivity, and low detection limit. The method could also be adapted to be integrated to current microfluidics devices. Parametric optimization for sample introduction, nebulization, desolvation, and hollow cathode source conditions is performed for the analysis of aqueous bovine serum albumin solutions. Response curves of C (I) 193.0-nm emission were obtained under the optimized conditions with both 10% HCl and 100 micromL KCl added to the sample matrix as potential carriers. The detection limit for triplicate injections of bovine serum albumin standards was found to be on the single-nanogram level with 200-microL injections. The addition of KCl significantly improved the sensitivity, supporting the proposed "carrier effect" of chloride salts in the particle transport process. Results obtained here suggest a range of applications for the use of the PB/HC-OES source for total protein determinations; emphasis here is future use in assessing protein quantification in microfluidic systems.

Electrodes↗
PubMed2003

Use of sol-gels as solid matrixes for simultaneous multielement determination by radio frequency glow discharge optical emission spectrometry: determinations of suspended particulate matter.

A new approach for the analysis of particulate matter by radio frequency glow discharge optical emission spectrometry (rf-GD-OES) is described. Dispersion of the particles in a sol-gel sample matrix provides a convenient means of generating a thin film suitable for sputter-sampling into the discharge. Acid-catalyzed sol-gel glasses synthesized from tetramethyl orthosilicate were prepared and spun-cast on glass substrates. The resultant thin films on glass substrates were analyzed to determine the discharge operating conditions and resultant sputtering characteristics while a number of optical emission lines of the film components were monitored. Slurries of powdered standard reference materials NIST SRM 1884a (Portland Cement) and NIST SRM 2690 (Coal Fly Ash) dispersed in the sols were cast into films in the same manner. Use of the sol-gels as sample matrixes allows for background subtraction through the use of analytical blanks and may facilitate the generation of calibration curves via readily synthesized, matrix-matched analytical standards in solids analysis. Detection limits were determined for minor elements via the RSDB method to be in the range of 1-10 microg/g in Portland Cement and Coal Fly Ash samples for the elements Al, Fe, Mg, S, and Si. Values for Ca were in the range of 15-35 microg/g. This preliminary study demonstrates the possibility of incorporating various insoluble species, including ceramics and geological specimens in powder form, into a solid matrix for further analysis by either rf-GD-OES or MS.

Journal Article↗
PubMed2003

Capillary-channeled polymer fibers as stationary phases in liquid chromatography separations.

A method utilizing capillary-channeled polymer (C-CP) fibers as stationary phases in high-performance liquid chromatographic separations has been investigated. Polymeric fibers of differing backbones (polypropylene and polyester) having nominal diameters of approximately 50 and approximately 35 microm and a channeled structure on their periphery were packed into stainless steel tubing (305 x 4.6 mm I.D.) for use in reversed-phase separations of various mixtures. The fibers have eight channels running continuously along the axis which exhibit very high surface activity. As such, solvent transport is affected through the channels through wicking action. Bundles of 1000-3000 fibers are loaded co-linearly into the tubing, providing flow channels extending the entire length of the columns. As a result, backing pressures are significantly lowered (approximately 50% reduction) in comparison to packed-sphere columns. In addition, the capital costs of the fiber material (< US$0.25 per column) are very attractive. Flow-rates of up to 5 ml/min can be used to achieve near baseline separation of related compounds in reasonable run times, indicating very fast mobile phase mass transfer (C-terms). The polymer stationary phases demonstrate high selectivity for a wide variety of analytes with gradient elution employed successfully in many instances. Specifically, separations of three polyaromatic hydrocarbons (benzo[a]pyrene, chrysene, pyrene), mixtures of both organic and inorganic lead compounds [chlorotriethyllead, chlorotriphenyllead, lead nitrate, lead(II) phthalocyanine], and a lipid standard of triglycerides were accomplished on the polymeric stationary phases. Other species of biological interest, including groups of aliphatic and aromatic amino acids have also been effectively separated. The reversed-phase nature of the fiber surfaces is supported through atomic force microscopy measurements using hydrophilic and hydrophobic functionalized polystyrene beads as the probe tips. Separations of the various analytes demonstrate the feasibility of utilizing C-CP fibers as stationary phases in reversed-phase LC. It is envisioned that columns of this nature would be particularly useful in prep-scale separations as well as for immobilization matrices for organic constituents in aqueous environments.

Chromatography, High Pressure Liquid↗
PubMed2003

Particle beam glow discharge mass spectrometry: spectral characteristics of nucleobases.

Use of a particle beam glow discharge (PB-GD) source for mass spectrometric determinations of deoxy- and ribonucleosides and nucleotides is described. Use of this combination of sample introduction and ion source decouples the vaporization and ionization steps, leading to very simple spectral structure. The mass spectra of these compounds are EI-like in nature, with clearly identified molecular ions and fragmentation patterns that are easily rationalized. The PB-GDMS combination can be operated in a flow injection mode wherein the analyte is injected directly into the solvent flow, or can also be coupled to a high-performance liquid chromatography (HPLC) system allowing LC/MS analysis of mixtures. Mass spectra obtained for nucleic acid bases, nucleosides, and nucleotides are readily obtained with injections of low-nanomole quantities. Representative PB-GDMS spectra for deoxy- and ribonucleosides, nucleotides, and mixed-base oligonucleotides are presented to demonstrate the capabilities of the GD source. Characteristic fragmentation peaks from the spectra of adenine, cytosine, guanine, and thymine were identified in 22-base sequences of single-stranded DNA. The PB-GD source is capable of producing spectra that may be used to identify the individual bases present in mixed-base DNA and RNA fragments.

Mass Spectrometry↗
PubMed2003

A novel stationary phase: capillary-channeled polymer (C-CP) fibers for HPLC separations of proteins.

A novel stationary phase is demonstrated for the separation of proteins. Capillary-channeled polymer (C-CP) fibers provide a stationary phase that is characterized by a high surface activity (yielding strong wicking action) and drastically reduced back pressures. Columns prepared by pulling approximately 1200 50- micro m diameter polypropylene C-CP fibers through stainless steel tubing with column dimensions of 4.6-mm i.d. and 306-mm length exhibit reversed-phase characteristics in the separation of the proteins. A gradient method [95:5 water-acetonitrile (ACN)/propanol (1:1) to 35:65 water-ACN/propanol] with trifluoroacetic acid added as an ion-pairing agent yields high-quality separations of superoxide dismutase, hemoglobin, hemocyanin, and myoglobin. It is believed that the C-CP fiber stationary phase holds a number of promising traits for applications in both analytical and prep-scale separations of diverse organic species, including a wide range of biomolecules.

Chromatography, High Pressure Liquid↗
PubMed2002

Radio frequency glow discharge optical emission spectroscopy: a new weapon in the depth profiling arsenal.

While the array of analytical methods routinely applied for depth profile analysis was fairly static over the decades of the 1980s and 1990s, there appears to be an emerging technique that has a number of very positive and complementary attributes, and warrants serious consideration by the thin film community. Radio frequency glow discharge optical emission spectroscopy (rf-GD-OES) is a technique that provides depth-resolved elemental composition information on a wide variety of sample types. In a manner very much like most depth profiling methods, the rf-GD plasma utilizes an ion sputtering step to ablate sample material in a layer-by-layer fashion. Different from the more commonly applied methods, the device operates at elevated pressures [2-10 Torr Ar (266-1,330 Pa)] and has the inherent capability of sputtering electrically insulating materials directly, without any auxiliary means of charge compensation. In addition, sputtering rates on the order of 1 micro m/min provide rapid analysis, with depth resolving powers that are comparable to high-vacuum sputtering methods. Three examples of the use of the rf-GD-OES method are presented as examples of its analytical potential: (1) boron-implanted silicon wafer, (2) a barrier-type alumina film, and (3) a porous-type alumina film. It is believed that the method holds a great deal of promise as part of the arsenal of weapons in the thin films laboratory.

Festschrift↗