Ronald E. Shoup

Simultaneous multiple electrode liquid chromatographic—electrochemical assay for catecholamines, indoleamines and metabolites in brain tissue

To enhance the selectivity of liquid chromatographic-electrochemical assays for biogenic amines and metabolites in brain tissue, multiple electrode transducers were investigated. Two configurations of dual working electrodes were examined: parallel-adjacent and series arrangements. Using the raw detector currents with each configuration, peak-height ratios from simultaneously generated chromatograms were calculated to assess the selectivity of the instrument for direct injections of brain tissue supernatant. Ratios were consistent with injections of standards. Nearly coeluting peaks such as norepinephrine and 3-methoxy-4-hydroxyphenylglycol were resolved by using dual detector electrodes in series; only the catecholamines were detected at the downstream electrode owing to their electrochemical reversibility. The scheme was applicable to the assay of norepinephrine, 3,4-dihydroxyphenylacetic acid, dopamine, homovanillic acid, serotonin, 5-hydroxytryptophan and 5-hydroxyindole-3-acetic acid in brain tissue in less than 15 min.

I. Minireview: Neurochemical applications of liquid chromatography with electrochemical detection

Abstract Liquid chromatography with electrochemical detection (LCEC) has been shown to have unique advantages for the determination of many substances of neurochemical interest. The technique is rapid, sensitive, and relatively inexpensive. In addition, it avoids the need for radiolabelled substances, the formation of volatile derivatives, or reactions which generate fluorescent products. LCEC is widely used for the measurement of the catecholamines and their metabolites and has recently gained acceptance for determination of the neurochemically important tryptophan metabolites. The method is also capable of assessing the activity of a number of neurologically important enzymes. The review which follows is intended to provide a brief overview of the LCEC technique and a guide to recent literature exemplifying its neurochemical applications.

A Versatile Thin-Layer Detector Cell for High Performance Liquid Chromatography

ABSTRACT A thin-layer electrochemical cell constructed from engineering plastics is described. The sandwich design can accommodate carbon or metal electrodes embedded in the wall of a rectangular channel. Miniature grid electrodes can be placed across the channel. The new transducer has been used in both static and hydrodynamic experiments including amperometric detection in liquid chromatography.

A simple liquid chromatography procedure for p-aminohippuric acid in blood serum and urine.

Abstract An extremely simple procedure for determining p-aminohippuric acid (PAH) is described based on liquid chromatographic separation followed by detection via direct electrochemical oxidation in a thin-layer cell. The detection limit for PAH is approximately 100 pg and quantitation is possible with 500 pg injected. Absolute recovery is 100% as no loss of sample occurs at any point in the assay. The precision for a 0.5 mg/ml pooled serum sample was 1.7% relative standard deviation. No deproteinization, extraction, or reagents are required. The assay procedure is highly selective for PAH and eliminates the need for nonspecific colorimetric reagents presently in use.

Detectors for Trace Organic Analysis by Liquid Chromatography: Principles and Applications

Although liquid column chromatography (LC) had been used as a means of chemical separation for many years prior to 1969, it was not accepted as a method useful for rapid, routine analysis, due to the relatively long times required to achieve resolution. Significant theoretical and technological advances have since been made in this field, and excellent separations can now be achieved within a few minutes using high-efficiency LC column packings. Liquid chromatography offers many advantages over gas-liquid chromatography (GLC) in that no restrictions are placed on the size, volatility, or thermal stability of the sample molecules. In addition, LC offers tremendous flexibility in the choice of mobile and stationary phases such that most sample components can be conveniently resolved using some appropriate combination of mobile and stationary phases.