Development of sandwich HPLC microcolumns for analyte adsorption on the millisecond time scale.

A new class of columns is reported that uses only microgram quantities of active support and that provides for the retention of biological compounds and other analytes on the millisecond time scale. This was accomplished by packing standard HPLC supports into layers as small as 60 microm in length and using only 90 microg of support material. This provided columns with effective residence times in the millisecond time range when routine HPLC flow rates and pressures were used. The retention of analytes by such columns was examined under both adsorption- and diffusion-limited conditions. The RPLC adsorption of hemoglobin (a system with diffusion-limited retention) was found to give 95% binding in as little as 4 ms. The adsorption of fluorescein by an anti-fluorescein antibody column (an adsorption-limited system) gave 95% retention in 100-120 ms. One application examined for these columns was their use in a chromatographic-based competitive binding immunoassay. This used bovine serum albumin (BSA) as the model analyte, and fluorescein-labeled BSA was used for detection. The resulting approach had a contact time of 180 ms between the sample and an anti-BSA immunoaffinity microcolumn and provided a signal within 5-25 s after sample injection. The columns developed in this work should also be useful in other situations that involve a small amount of a stationary phase or that require short column residence times.