Honey, I Shrunk the Columns: Recent Advances in the Design and Use of Narrow Internal Diameter UHPLC Columns

Abstract

The quest for increased sensitivity for low-concentration samples continues at an accelerated pace, especially in the pharmaceutical and clinical environments. High-end mass spectrometry instruments can enable the analyst to detect analytes at attomolar concentrations, but can be prohibitively expensive and require well-trained scientists to operate and interpret the data. Another approach to improve the sensitivity of high performance liquid chromatography (HPLC) assays is by decreasing the internal diameter (i.d.) of the column. Reducing the column’s internal diameter down from 4.6 mm to 2.1 mm has been in practice for several decades. However, extra caution is required when considering going down below 2.1-mm i.d. into the “capillary-flow” format. This paper describes advances in column design that enable the analyst to achieve high sensitivity and efficiency when reducing the internal diameter of the column. After an introduction outlining the theory of increased sensitivity with narrow and capillary-scale internal diameter columns, a novel 1.5-mm i.d. column format will be presented detailing how sensitivities comparable to capillary-like separations can be achieved with this column geometry. Application examples will demonstrate the performance benefits of utilizing a 1.5-mm i.d. column geometry.