When the columns are set up and mobile phase is allowed to flow at a certain condition before
injecting samples, the ECD monitors the current, which is called background current (BGC). Generally speaking, lower background current allows higher sensitivity, assuming the signal peak height is the same for the analyte of interest. This is because there is less background noise and more stability (higher signal to noise ratio). When you run the system after setting up a new condition, the BGC typically will initially spike to a high level and settle down over time (sometimes hours or overnight depending on the application). The BGC tends to go lower over time as the column equilibrates.
The background current is decided by several factors including the condition of the mobile phase, precolumn, separation column, or working electrode.
The typical BGC reading (the values normally obtained after a few hours running mobile phase through the column with the ECD on):
PP-ODS for DA, 5-HT, 0.1 to 2.0 nA.
AC-GEL for Ach, 4.0-10 nA. If it is too low, polish the platinum with diamond paste (DM-10). It takes overnight to be stable of new columns and working electrode.
CA-5ODS for NE, 0.1-0.5 nA. CA-5ODS has lower back ground than other columns.
SC-5ODS for monoamines, 0.5-5.0 nA
SC-3ODS for monoamines, 0.5-5.0 nA
CAX column under 5 nA
However, if you are getting an unusually low background current, it could be due to problems, especially if the signal peak height is also lower. If it has been more than a few months since the working electrode has been cleaned, please see the following article on care and use of electrodes.