NEW required reading from Waters — the Liquid Chromatography People
Purification of Synthesis Reaction Mixtures Describes use of Waters' High-Perfor mance Liquid Chromatograph, in RECY CLE mode to prepare milligrams to grams of purified, individual posi tional isomers from a synthesis reaction mix ture. CIRCLE 236 ON READER SERVICE CARD
Know More About Your Polymer A 28 pg. primer on Gel Permeation Chromato graphy (GPC). This booklet explains how GPC rapidly determines molecular weight dis tributions of polymers, and how it can be applied to solving real problems. CIRCLE 237 ON READER SERVICE CARD
High-Performance Liquid C h r o m a t o g r a p h s Illustrated 8 page, brochure gives com plete description of Waters' High-Performance Liquid Chro matographs for all modes of liquid chro matography.
CIRCLE 238 ON READER SERVICE CARD
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tered in trace analysis work, it is pos sible to operate an LCEC cell in the classical two-electrode mode. When three electrodes are used, the auxiliary electrode can be placed downstream as illustrated in Figure 2. This ar rangement, while convenient, does re sult in nonlinear behavior when large samples are injected (typ. >200 ng for compounds with small k') unless the ionic strength is very high or the gas ket very thick. Positioning the auxilia ry electrode opposite to the working electrode (i.e., across the flow stream) reduces the uncompensated resistance to a negligible value even when low ionic strength (6, indoleacetic acid, 5-hydroxytryptamine (26), tetrahydroisoquinoline alkaloids (27, 28), and the phenothiazines (11). Fig ure 4 illustrates the electrochemical detection of several aromatic amines and phenols. Once again, note the great selectivity which can be achieved by control of the electrode potential. Electronic Games Although constant-potential amperometry is the only LCEC approach which has been widely used in prac tice, it is possible to carry out more so phisticated experiments. Frequently, we are queried about the possibility of programming the potential during a chromatographic run using a triangu lar wave in the manner of cyclic voltammetry. There are several reasons why this idea is of no practical value. Steady-state hydrodynamic electroanalysis has the advantage of being relatively free of double-layer charg ing effects, and there is no point in
