ABSTRACT
This chapter reviews the development of high-performance liquid chromatography (LC) instrumentation for gradient elution with packed microbore columns, i.e., columns of 2 mm inside diameter or less. It discusses flows and gradient volumes for different column sizes, the expected reproducibility of retention, times and peak areas with gradients, and the measurement and causes of gradient deviations. Other piston displacement isocratic microbore pumps might use the new methods of connected exponential mixers or breakthrough curves to provide gradients for submillimeter and even open-tubular systems. Even with the new-generation syringe pumps, flow precision and flow accuracy decrease at the extremely low flow rates required for micro- and open-tubular LC. Gradients to simplify sample injection and to cover a wide sample polarity range, coupled with long (inexpensive) fused silica microbore columns to provide many plates, should show that gradient microbore LC can make an important contribution to separations of sample-limited and complex biological samples.
