Axial heterogeneities in capillary ultrahigh pressure liquid chromatography columns: Chromatographic and bed morphological characterization.

•Systematic axial heterogeneities depicted for 75 μm i.d. capillary UHPLC columns.•Kinetic performance study complemented by bed morphological analysis.•Highest separation efficiency and bed homogeneity observed towards column outlet.•Enhanced band broadening contributions from wall effects towards column inlet.•Constant-pressure mode causes axial gradients in packing rate and bed morphology.