Biomedical subjects

Robert E Santini

Publications and source records attributed to Robert E Santini.

4 recordsLinked to original sources

PubMed2006

Results with an apparatus for pressurized planar electrochromatography.

Pressurized planar electrochromatography (PPEC) is a fast and efficient planar chromatographic technique. The mobile phase is driven by electroosmotic flow, while the system is pressurized in a manner that allows heat to flow between the sorbent layer and the pressurizing medium. The reproducibility of solute retention was not satisfactory in the initial report describing PPEC. In the current report, this reproducibility is improved by better control of several experimental variables. The pressure at which PPEC is performed is now free of drift, and the temperature at which the layer is preconditioned is maintained to within +/-1 degrees C. The best reproducibility of retention is obtained when the plate is soaked in the mobile phase for a defined time before each run. In the original prototype, the temperature of the sorbent layer was not controlled. In the present apparatus, water, at a constant temperature between 3 and 60 degrees C, is circulated through channels in the two die blocks that pressurize the layer. The highest efficiency is obtained at an intermediate temperature. This behavior is ascribed to high resistance to mass transfer at the lower temperatures and increased diffusion at higher temperatures. Efficiency, as measured by the number of theoretical plates, increases with increasing migration distance. The height equivalent of a theoretical plate diminishes with increasing migration distance, and values as low as 0.0106 mm are obtained under appropriate conditions. This extrapolates to 94 000 plates/m. Manual spotting was used in this report. Evidence is presented that substantially better efficiency would be obtained if the initial spot size were smaller. The efficiency of PPEC in its current form is illustrated by a chromatogram showing the separation of nine solutes in 2 min. PPEC was also performed with TLC plates in a back-to-back configuration, and this doubles the number of samples that can be simultaneously separated.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2004

Apparatus and initial results for pressurized planar electrochromatography.

Pressurized planar electrochromatography (PPEC) is a new planar chromatographic technique in which the mobile phase is driven by electroosmotic flow, while the sorbent layer is pressurized in a manner that allows heat to flow from the layer through an electrically insulating, thermally conducting, sheet of aluminum nitride ceramic. A prototype apparatus for performing PPEC is described. Separation by PPEC is faster than by conventional TLC, and an example is presented of a 24-fold enhancement in the speed of separation. PPEC was performed on both regular and high-performance C18 layers, and the latter yield substantially faster separation. The sorbent layer requires conditioning at elevated temperature before use, and solute migration velocity increases with this temperature. The flow rate increases in a linear manner with increasing voltage and diminishes in a nonlinear manner with increasing pressure. Both electrical current and Joule heating diminish with increasing pressure, and the diminution of flow at high pressure can be compensated by an increase in voltage. PPEC is more efficient than classical TLC. Theoretical plate heights diminish with increasing Rf and are in the range 29-21 and 55-27 microm for the high-performance and regular plates, respectively. PPEC retains the advantages of classical TLC but has the ability to separate a substantially higher number of samples simultaneously. An example is presented on the separation of nine samples in 1 min on a 2.5 cm x 10 cm sorbent layer.

Journal Article↗

PubMed2004

NMR difference spectroscopy with a dual saddle-coil difference probe.

A new difference probe for nuclear magnetic resonance (NMR) spectroscopy is presented. The difference probe uses two saddle-shaped coils to excite and detect two samples simultaneously. The samples are held in a specially modified 3-mm NMR tube with an Ultem plastic disk to separate the samples. The probe's resonant circuit contains two crossed diodes that passively switch the relative phase of each coil during the NMR experiment. The result is a difference spectrum from the two samples. The degree of cancellation of common signals was determined to be approximately 90%, and the application of the probe to relaxation-edited difference spectroscopy for identifying protein-ligand interactions was demonstrated using glutathione and glutathione S-transferase binding protein.

Glutathione↗

PubMed2002

NMR difference probe: a dual-coil probe for NMR difference spectroscopy.

A unique probe designed to acquire nuclear magnetic resonance difference spectra of two samples is presented. The NMR Difference Probe contains two sample coils in a resonant circuit that switches between parallel excitation and serial acquisition to cancel common signals such as solvent peaks and impurities. Two samples containing a common analyte, acetonitrile, were used to demonstrate signal cancellation in a difference spectrum collected with a single pulse experiment. The cancellation was over 96% effective. The approach described has applications in the areas of solvent subtraction and spectral simplification.

Magnetic Resonance Spectroscopy↗