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1.1
Overview
The Thermo Scientific Dionex
current resulting from the application of potential (voltage) across electrodes in
flow-through cells. Depending on the method by which the potential is applied
and the current measured, several different properties of the flowing solution can
be determined. These measurements help answer the major questions analytical
chemists ask: What's in it, and how much is there?
Of course, other detectors are used in high performance liquid chromatography
(HPLC). The UV-visible absorbance detector dominates all other forms of
detection. Sensitivity is excellent for many analytes, especially aromatic species,
and transparent mobile phases are readily available. However, there are numerous
analytes that have very poor absorbance and are not detected with sufficient
sensitivity by UV absorbance. Most of these nonchromophoric molecules are
aliphatic organic molecules and inorganic ions. Low wavelength UV detection
can be used, but at a loss in selectivity. Refractive index detection can also be
used. However, maintaining a stable baseline can be difficult, and RI detection is
less sensitive and substantially less selective than UV detection.
Fortunately, a wide variety of nonchromophoric molecules can be detected with
good or excellent sensitivity by one of several forms of electrochemical detection.
These molecules include carboxylic, sulfonic, and phosphonic acids; alcohols,
glycols, aldehydes, and carbohydrates; primary, secondary, tertiary, and
quaternary amines; sulfates, sulfoxides, thiols, sulfides, and mercaptans; and
inorganic anions and cations. In addition, when compared to UV absorbance
detection, electrochemical detection provides substantial improvements in
sensitivity and selectivity for amine and hydroxy-substituted aromatics such as
catecholamines.
Several forms of electrochemical detection have become popular for certain
HPLC applications. Conductivity is the workhorse detection method in ion
chromatography, just as UV detection is for HPLC. DC amperometry is the
preferred method for neurochemical analyses. Pulsed amperometry is now
established as the superior detection method for carbohydrates. For most of the
numerous analytes listed in the previous paragraph, detection by UV-visible
absorbance is poor, while one of the three main techniques of electrochemical
Doc. 065551-01 6/13
1 • Introduction
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ED50A Electrochemical Detector measures
1-1
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