Geoffrey E. Barker

Binghamton University, Binghamton, New York, United States

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Publications (9)28.66 Total impact

  • Peng Sun, Adam Landman, Geoffrey E. Barker, Richard A. Hartwick
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    ABSTRACT: A capillary coating method was developed using a sodium-2-acrylamido-2-methylpropanesulfonate (NaAMPS) polymer. Capillaries coated with this anionic polymer exhibited pH-independent electroosmotic flows (EOFs). Capillaries with a particular EOF rate could be synthesized simply by changing the molar ratio of NaAMPS to neutral acrylamide in the polymer mixture. The pH-independent EOF of the coated capillary changed less than 1.5% over 20 days of routine, intermittent use. Capillary lifetime with a continuously applied electric field of 286 V cm−1 was about 60 h. Reproducibility of the coating procedure was 1.7% R.S.D, in observed EOF for independently synthesized capillaries. The pH-independent EOF of these capillaries as well as their selectable flow-rates (via synthesis) should prove useful in micellar electrokinetic capillary chromatography (MECC) at low pH values and for expansion of the separation window in MECC, as well as for more versatile separations of various species in the capillary zone electrophoresis mode.
    Journal of Chromatography A 11/1994; 685(2):303-312. DOI:10.1016/0021-9673(94)00635-0 · 4.26 Impact Factor
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    ABSTRACT: Chromatographic retention parameters of a series of 7 β-adrenolytics and of 12 antihistamine drugs were determined employing an α1-acid glycoprotein (AGP) high-performance liquid chromatographic (HPLC) column. For the group of antihistamines capillary electrophoretic (CE) retention was additionally measured in the presence of either AGP or human serum albumin (HSA). Two series of solutes hydrophobicity parameters were obtained by reversed-phase HPLC on an immobilized artificial membrane (IAM) column. The solutes studied were subjected to molecular modelling and the structural descriptors obtained were applied in studies of quantitative structure-retention (protein binding) relationships (QSRR). It was found that retention on AGP correlates well with the literature on physiological protein binding data. This retention was demonstrated to depend on hydrophobicity: to a lesser extent in the case of β-adrenolytics and strongly in the case of antihistamines. Hydrophobicity, along with molecular width and electron excess charge on aliphatic nitrogen was demonstrated to describe retention of antihistamines on AGP. The AGP column is recommended as a convenient reactor for studies of drug–protein interactions. Preliminary CE data do not correlate with the HPLC data.
    Biomedical Chromatography 05/1994; 8(3):125 - 129. DOI:10.1002/bmc.1130080306 · 1.66 Impact Factor
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    ABSTRACT: Micellar electrokinetic capillary chromatography (MEKC) is investigated for the separation and determination of caffeine and its analogues as a complementary method to high-performance liquid chromatography (HPLC). Separation efficiency, resolution, analysis time, sample recovery and reproducibility are examined by comparing MEKC and HPLC in parallel analysis. The results show that MEKC is a useful economic technique in pharmaceutical analysis, yielding high efficiency, resolution and short analysis times.
    Analytical Letters 03/1994; 27(5):927-937. DOI:10.1080/00032719408007362 · 0.98 Impact Factor
  • Nian Wu, Geoffrey E. Barker, Carmen W. Huie
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    ABSTRACT: The separation of six porphyrins having two to eight carboxylic acid side-chains by capillary electrophoresis using a combination of ionic surfactant and protein as a novel modifier in the run buffer is reported. Using sodium dodecyl sulfate (SDS) together with bovine serum albumin (BSA) as buffer additives, efficient and reproducible separation of mesoporphyrin, coproporphyrin, uroporphyrin, penta-, hexa- and heptacarboxylporphyrins was achieved at pH 7.4 whereas sodium taurodeoxycholate (bile salt) combined with BSA in the run buffer separated type I and III isomers of coproporphyrin as well. The presence of SDS or bile salt appeared to minimize protein-and/or porphyrins-inner capillary wall (untreated silica) interaction and to enhance solubilization and selectivity of porphyrins due to the formation of ionic surfactant-protein complex(es) in the run buffer.
    Journal of Chromatography A 01/1994; 659(2):435-442. DOI:10.1016/0021-9673(93)E1051-Z · 4.26 Impact Factor
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    ABSTRACT: A method for the chiral separation of dansyl-DL-amino acid mixtures using a dextran (M(r) 2,000,000) polymer network containing beta-cyclodextrin (beta-CD) in HPCE was developed. Mixtures of up to seven amino acids could be baseline resolved by this method under neutral pH conditions. Resolution was dependent on the dextran concentration in the polymer network. Temperature effects on the chiral separation were studied. Optimal efficiency and resolution of DL-enantiomeric pairs of amino acid samples were obtained at 25 degrees C. The resolution of different amino acids used in this work decreased with an increase in temperature.
    Electrophoresis 01/1994; 15(6):793-8. DOI:10.1002/elps.11501501111 · 3.16 Impact Factor
  • Peng Sun, Nian Wu, Geoffrey Barker, Richard A. Hartwick
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    ABSTRACT: A method utilizing dextran as a run buffer additive in addition to bovine serum albumin (BSA) for chiral separation by means of affinity capillary electrophoresis (ACE) has been developed. By adding different amounts of dextran to the run buffer, the net velocity of BSA can be adjusted to a desired rate. Enantiomers of some drugs [ibuprofen (IB) and leucovorin (LV)] and amino acids (dansyl-DL-leucine and dansyl-DL-norvaline) were separated on a capillary with 20 cm effective length by this method. The effect of dextran concentration on the retention of BSA and resolution of sample enantiomers was studied. Enantiomers of mandelic acid (MA), which have very weak affinity for BSA, were also resolved. Qualitative information pertaining to the binding interaction of the samples with BSA can be obtained by this method.
    Journal of Chromatography A 10/1993; 648(2):475-480. DOI:10.1016/0021-9673(93)80431-7 · 4.26 Impact Factor
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    ABSTRACT: An improvement in affinity capillary electrophoresis (ACE) was achieved by covalently linking bovine serum albumin (BSA) to a high-molecular- mass dextran (Mr 2 000 000) using cyanogen bromide. The efficiency of the binding reaction was greater than 99%, measured through quantitative separation of the protein and protein—dextran polymer network mixture on a bare capillary using capillary electrophoresis (CE). Baseline separation of leucovorin (LV) enantiomers was obtained under 9 min using a linear polyacrylamide-coated capillary (with an effective length of 20 cm) filled with the BSA—dextran polymer network. The present work offers several significant advantages over other approaches to ligand immobilization, and can be generally applied to a wide variety of ligand—substrate systems.
    Journal of Chromatography A 10/1993; 652(1):247-252. DOI:10.1016/0021-9673(93)80665-U · 4.26 Impact Factor
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    ABSTRACT: Naturally occurring 8- and 4-carboxylic porphyrin I and III isomers are separated using a run buffer consisting of bovine serum albumin (BSA) and phosphate as the electrolyte. The method requires the use of deactivated capillaries to minimize protein-wall interactions. The uroporphyrin isomers are resolved in 15 minutes while the separation of the coproporphyrin isomers requires 28 minutes. Retention times are largely characteristic of the number of carboxylic acid side chains as well as the relative affinity for BSA. The binding of porphyrins to BSA is supported by a wavelength maxima red shift in the soret region when using BSA in the run buffer.
    Journal of liquid chromatography 07/1993; 16:2089-2101. DOI:10.1080/10826079308019917
  • Geoffrey E. Barker, Paul. Russo, Richard A. Hartwick
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    ABSTRACT: A method for the determination of the (6R)- and (6S)-stereoisomers of leucovorin using electrokinetic chromatography (EKC) in the affinity mode has been developed. Bovine serum albumin (BSA) is used as a run buffer additive to incorporate enantiomeric selectivity into the system. Protein-wall interactions are minimized by using a poly(ethylene glycol) (PEG) coated capillary. Chiral resolution is obtained in 12.5 min with efficiencies greater than 200,000 theoretical plates using BSA as an additive, while no resolution is obtained in the absence of BSA. A general equation is derived to calculate the free energy of interaction between the leucovorin isomers and the BSA molecule. This method represents a new means of obtaining thermodynamic data for substrate binding interactions and for the general study of drug cross-reactions and interactions of drugs with serum and other proteins.
    Analytical Chemistry 01/1993; 64(23):3024-8. DOI:10.1021/ac00047a026 · 5.83 Impact Factor