A pillar array column (PAC) is a micro column which is fabricated by reactive ion etching of a silicon substrate and has non-porous pillars with a high degree of order in narrow flow channels. Compared to conventional spherical particles randomly packed in an empty column, the order of pillars is systematically designed to provide a higher efficiency due to a smaller van Deemter A term and higher permeability (Kv) attributed to higher external porosity. Therefore, PACs are expected to have a higher resolution and are promising candidates for the next generation chromatography columns. However, retention capacity (contributing to resolution) with PACs is low because pillars have a non-porous structure resulting in a low surface area.

In order to achieve the same level of retention factor with PACs as with superficially porous particles which are currently drawing much attention in the market because of the high efficiency, electrochemical anodization was applied to grow porous shell layers of 300 nm (30 nm pores) on the surface of pillars with the diameter of 5 um and spacing (between pillars) of 2.5 um. A specific injection method (on-chip injection) was established, which enables a small amount of injection (a few nL) to minimize an influence of injection volume on a tiny PAC.
Uniformity of the porous PACs were assessed by determining local height equivalent to a theoretical plate (HETP) along the channels, which appeared to be constant. On measuring the retention time as an indicator of the surface area, an increase in the surface area by a factor of about 30 compared to that of non-porous pillars was found as expected. On measuring the efficiency of a PAC with a commercial HPLC instrument, theoretical plate of about 100,000 with a retention factor of 2.2 under an isocratic condition and peak capacity of about 500 under a gradient condition were obtained at an extremely low pressure with a 1 m long PAC, which are ascribed to the increase in surface area.
Original languageEnglish
Title of host publicationPresentation at the Pittcon 2015 conference
Publication statusPublished - 10 Mar 2015
EventPittcon conference & expo 2015 - New Orleans, United States
Duration: 8 Mar 201512 Mar 2015


ConferencePittcon conference & expo 2015
CountryUnited States
CityNew Orleans

    Research areas

  • HPLC Columns, Lab-on-a-Chip, Microfluidics

ID: 5101757