8 Pulsed amperometric detection (PAD)
8.1 Introduction
The 3465 Detector can operate in pulsed amperometric detection (PAD) mode, in which the
working electrode (WE) is regenerated at a frequency of 0.5 to 3 Hz by the application of a series
of potential changes. This is particularly useful in applications where the working electrode is
rapidly fouled due to adsorption of insoluble reaction products. A well-known application area for
PAD is the analysis of carbohydrates.
Figure 8–1: Carbohydrate analysis in pulse mode
8.1.1 Pulse mode versus DC mode
Pulse mode is quite different than DC mode. Instead of a constant potential, a series of potential
steps is applied in a cyclic manner. The signal is sampled during a fraction of the total pulse
cycle. During the sampling time (ts) the signal is collected and the value is sent to detector
output. The frequency of data output is determined by the pulse duration: t1 + t2 + t3 + t4 + t5.
The duration is usually between 0.5 s and 2 s (data rate between 2 Hz and 0.5 Hz). The
background or cell current is usually considerably higher (100 nA to 1000 nA) than in DC mode.
Only nano- and micro-ampere ranges are available in pulse mode. The background current is
typically between 0.1 µA and 2 µA.
When the frequency of the data acquisition system (integrator) is higher than the pulse frequency,
a stepwise pattern may appear in the chromatogram. This is called “oversampling”, and the steps
December 16, 2021, 715007395 Ver. 00
Page 72
