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F Zarrin

Publications and source records attributed to F Zarrin.

8 recordsLinked to original sources
PubMed1997

DNA analysis using an electrospray scanning mobility particle sizer.

A scanning mobility particle sizer (SMPS) allows size separation of gas phase particles according to their electrophoretic mobilities. The addition of an electrospray source (ES) recently allowed extension of SMPS analysis to the macromolecular range. We demonstrate here the application of ES-SMPS to nucleic acids analysis. Single- and double-stranded DNA molecules ranging from 6.1 kDa (single-stranded DNA 20 nucleotides in length) to 300 kDa (500 base-pair double-stranded DNA) were separated and detected by ES-SMPS at the picomole to femtomole levels. The measured electrophoretic mobility diameters were found to correlate with the analytes' molecular weights, while the peak areas could yield quantitative information. No fragmentation of DNA was observed under the conditions employed. Different apparent densities were observed for single-stranded and double-stranded DNAs, showing a different behavior for each type of biomolecule. The total analysis time was about 3 min/spectrum. Further optimization of ES-SMPS is expected to make it a fast and sensitive technique for biopolymer characterization.

DNA↗
PubMed1995

Particle size distribution is not the major factor explaining variable analyte transmission efficiency in liquid chromatography/particle beam/mass spectrometry.

We characterized the particle size distribution and the analyte transmission efficiency of a liquid chromatography/particle beam/mass spectrometry (LC/PB/MS) system as a function of experimental variations normally used to optimize the LC/PB/MS system. The particle size distribution was evaluated using an electrical differential mobility particle sizer (DMPS) and both the DMPS and the mass spectrometer were used to evaluate transmission. The latter results were correlated to provide evidence related to mechanisms which contribute to poor sample transmission. Addition of ammonium acetate buffer did not increase the aerosol particle mean diameter. However, it did lead to significant increases in caffeine transmission efficiency observed in both the DMPS and the mass spectrometer. Our results were interpreted to suggest a possible electrostatic cause for quantitative anomalies in LC/PB/MS rather than simple mass discrimination in the particle beam momentum separator.

Aerosols↗
PubMed1994

Electrospray-condensation particle counter: a molecule-counting LC detector for macromolecules.

A new detector for macromolecular separations is described. The detector counts individual macromolecules (molecular weights greater than about 10,000) and reports counts per second. The chromatographic effluent is electrosprayed, neutralized, and swept to the detector by a stream of air. The detector is a condensation particle counter that detects individual particles by light scattering from droplets condensed on the particles. When used as the detector for a size exclusion separation of proteins, the detector has a linear range of 4 orders of magnitude with detection limits as low as 0.1 microgram/mL. The detector can be directly interfaced (no makeup flow) with effluent flows as low as 10 nL/min. A Monte Carlo model based on size measurements of the electrosprayed droplets correctly predicts the observed detector behavior.

Biopolymers↗
PubMed1988

Measurement of protein rotational motion using frequency domain polarized fluorescence depletion.

Polarized fluorescence depletion (PFD) methods (Yoshida, T. M. and B. G. Barisas. Biophys. J. 1986. 50:41-53) are approximately 10(3)-10(4) fold more sensitive than other techniques for measuring protein rotational motions in cell membranes and other viscous environments. Proteins labeled with fluorophores having a high quantum yield for triplet formation are examined anaerobically in a fluorescence microscope. In time domain PFD experiments a several-microsecond pulse of linearly polarized light produces an orientationally-asymmetric depletion of ground state fluorescence in the sample. Monitoring the decay of ground state depletion with a probe beam alternatively polarized, parallel, and perpendicular to the depletion pulse permits the triplet lifetime and rotational correlation time to be resolved and evaluated. We have now explored fluorescence depletion methods in the frequency domain to see whether such measurements could provide simpler and more efficient routine measurements of protein rotational relaxation than previous time domain PFD methods. An acousto-optic modulator (AOM) modulates the intensity of a 514.5 nm argon ion laser beam and a Pockels cell (PC) rotates its plane of polarization. These devices are driven by sinusoidal or square waves in fixed frequency relation, and rigidly phase locked, one to another. The fluorescence emitted from a sample then contains various overtones and combinations of the AOM and PC frequencies. The magnitude and phase of individual fluorescence signal frequencies are measured by a lock-in amplifier using a reference also phase-locked to both the AOM and PC. Specific frequencies permit evaluation of the rotational correlation time of the macromolecule and of the fluorophore triplet state lifetime, respectively. Measurement of bovine serum albumin rotation in glycerol solutions by this method is described.

Mathematics↗