George R. Long

Thermal Lens Spectrophotometry in Agarose Gels

In this study, the application of thermal lens spectroscopy to detection of analytes in agarose gels was examined. It was found that a long-term refractive index gradient is produced in the sample, in addition to the thermally induced refractive index gradient, and gives rise to a long-term thermal lens signal. It is argued that the most likely source of the long-term signal is a concentration gradient formed in the sample. The long-term refractive index gradient results in a focusing lens, and is thus opposite to the thermal gradient. The formation of this gradient requires as much as 500 s to reach equilibrium during constant irradiation. The existence of the long-term refractive index gradient is verified by time-resolved Z-scan experiments. The signal resulting from this gradient is termed the long-term thermal lens and is shown to depend on temperature, is observed only for gelled agarose solutions, and is sensitive to anisotropies in the sample.

Thermal Lens Study of the Absorbance of Silver Colloid Solutions Produced by Photoreduction

The absorption of light by photolytically generated silver colloid solutions is studied by thermal lens spectrophotometry. It is found that absorbance by silver nitrate solutions at 488 nm is a result of colloid formation. The absorbance is related to the particle size distribution and varies substantially from measurement to measurement even within the same colloidal solution. The shot-to-shot variance of the thermal lens signal is minimized by producing the colloid in a flowing AgNO3 solution, but still varies significantly from solution to solution at equal concentrations.

On-Line Detection in Slab Gel Electrophoresis Using Thermal Lens Spectrophotometry

Thermal lens spectrophotometry was used to detect hemoglobin and cytochrome c within an acrylamide gel matrix both during electrophoresis and in static experiments in which each protein was incorporated in the matrix during polymerization. For cytochrome c, the detection limit was 0.02 mg/mL for static experiments (approximately 0.5 ng in the laser beam volume), while a detection limit of 180 ng (5 ng in the beam volume) was found for electrophoresis runs.

Computer assisted determination of the biological activity of polychlorinated biphenyls using gas chromatographic retention indices as molecular descriptors

Abstract Gas chromatographic retention indices of polychlorinated biphenyls (PCBs) on several different chromatographic columns are used as molecular descriptors to predict the toxicity of PCBs. Principal component and discriminant analysis are performed on the retention index data to classify a learning set of 27 PCB molecules of known toxicity. It was found that 25 of 27 PCBs were correctly classified using this method. The errors in classification are presumed to be a result of the varying degrees of toxicity of the PCB molecules. Further calculations using a set of 114 PCB congeners gave similar results. The predictions followed qualitative structure-activity relationships known for PCBs.

JCE LrnComOnline: Mission Statement

A new feature column, JCE LrnComOnline, aims to promote creation, dissemination, and utilization of well-crafted online instructional modules that span the chemistry curriculum. This brief mission statement outlines the goals and parameters for the column and includes instructions for submissions.