Liquid Chromatography

The Importance of Signal-to-Noise

In this technical article you will learn how the signal-to-noise ratio (S/N) is an important variable that may influence the performance of your method.

Measurement of S/N is fairly simple. First, expand the chromatogram sufficiently so that the baseline noise is readily apparent (it doesn’t matter if you cannot see the top of all the peaks). Now determine the noise by bracketing the baseline with two straight lines, one on the top edge of the noise and one on the bottom, roughly parallel to the noise. The vertical distance between the lines, converted to appropriate units, such as absorbance units (AU) is the baseline noise. This can be compared to the detector specifications to determine if the baseline noise is reasonable. If you can get the baseline noise to be within about 5-fold of the detector spec this is ideal. After all, detectors are specified in a controlled environment and typically with a dry cell, so obtaining the manufacturer’s specs in the lab may be a bit of an over-expectation. The signal is measured from the middle of the noise band to the top of the peak. The signal-to-noise ratio is simply the result of dividing the signal by the noise (same units).

By reading the full article you will see how important S/N is, especially for trace analysis and how by improving S/N, we can increase S, decrease N, or both.

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