The signal-to-noise ratio (S/N) in a liquid chromatography (LC) separation is usually defined as shown in Figure 1. The noise is measured between two lines bracketing the baseline and the signal is measured from the middle of the baseline to the top of the peak. S/N is merely the signal divided by the noise. There are some other ways to determine S/N, but that is not the point of the current discussion. My comments here will apply no matter what technique you use for measurement and calculation of S/N. As was discussed in an earlier instalment of LC Troubleshooting,1 S/N is of most concern when it makes a significant contribution to the error of chromatographic measurements. This usually occurs for S/N