Baseline wander

Noise present in the detector signal may have two components, long-term noise and short-term noise. The former causes a slow baseline wander measured over a 1 h period and may be attributed to fluctuations in temperature, column stationary phase bleed, flow rate variation, or pneumatic leaks. Short-term noise is observed as small, sharp spikes of shorter duration than component peaks and usually arises in the detector. Most integrators smooth the signal so that noise is not apparent unless a direct plot mode is selected. It is important to establish the mean noise level, the baseline, in order to determine the limit of detection. The time period of a peak is most conveniently described by the peak width at half height and the noise, N, is measured as the variation between maxima and minima of the noise peaks over the time period. The contribution of noise to the total component signal should be less than 1% (Figure 5.17). 

FIGURE 17.33 (a) Electrocardiogram showing muscle noise and baseline wander, (b) The effect of introducing an analog 3-Hz (-3-dB) high-pass filter into the signal path. There is a marked reduction in baseline wander. 

When the baseline varies randomly over times similar to the peak width, it is called wander (Figure 5.2). Wander interferes most with interpreting a chart recording or the operation of an electronic integrator. It can come either from the detector or from extraneous sources, such as a small leak at a column fitting. 

The living nature of the dermis also creates an electrochemical potential called a skin battery. This battery is associated with the function of the sweat glands. It is very pressure-sensitive. Small movements or forces on the electrodes cause transient millivolt-order changes in the skin-battery magnitude. These changes appear as motion artifacts and wandering baselines on biopotential traces. 

Literally a wander of the baseline (see Eig. 3.13), this form of artefact can increase the difficulty of ECG interpretation. 

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