David W. Humphrey

Comparison of high-performance liquid chromatography electrochemical detectors for the determination of aporphines, catecholamines and melatonin

Abstract A Bioanalytical Systems detector showed a greater sensitivity for low-level determinations of apomorphine, norepinephrine, epinephrine, dopamine, and melatonin compared to a Brinkmann Instruments system. Modifications of the Bioanalytical Systems flow cell, which have been developed in our laboratories, increase the sensitivity toward certain catecholic compounds, generally decrease baseline noise, and allow for serial coupling of detectors. 2

Determination of Apomorphine in Tablets Using High Performance Liquid Chromatography with Electrochemical Detection

Abstract A rapid and selective method using high performance liquid chromatography with electrochemical detection is described for the determination of apomorphine in tablets. Tablet mixes were dissolved in a standard volume of mobile phase containing the internal standard, N-n-propylnorapomorphine. Separation was achieved on a μ-phenyl column using methanol-acetonitrile-0.05M KH2PO4 (5:15:80) as mobile phase. The eluted compounds were detected with a sandwich-type electrochemical detector employing a glassy carbon working electrode and operated at 0.5V. Satisfactory accuracy and precision were obtained during analyses of tablets containing apomorphine.

Dynamics of Single Protein Polymers Visualized by Fluorescence Microscopy

Filamentous protein networks are one of the main structural elements in nature. This report describes novel approaches in video-enhanced fluorescence microscopy to visualize and analyze the molecular motions of single constituent filaments of these networks. Common examples of these biopolymer networks are the collagen matrix of connective tissue, cartilage and bones, fibrinogen networks with intercalated blood platelets, and the cytoskeleton of cells. The collagen matrix is a chemically cross-linked network of collagen fibers which consist of tropocollagen filaments. An in vitro example of a network of fibrinogen fibers with embedded platelets is displayed in Fig. 6.1. These fibrinogen gels, which form in wounds, are slowly contracted by the platelets facilitating wound closure during healing.