The portion of the chromatogram recording the detector response when only the mobile phase emerges from the column.
Source:
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 834 (https://doi.org/10.1351/pac199365040819)
See also:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2176 (https://doi.org/10.1351/pac199062112167)