Micro-HPLC 2: Producing Linear Gradients with the “Linear-Generator” Made from Connected Exponential-Diluters

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Abstract
A new approach is described for generating linear gradients in micro-HPLC. The “linear-generator” replaces a single-chamber exponential-diluter with several smaller exponential-diluters connected in series and having the same total volume. This linear-generator provides the advantages of the exponential-diluter: (a) Only one high-pressure, precision, low-flow pump is required, thus reducing costs (an inexpensive low pressure pump is used to flush the chamber between gradients). (b) Gradient formation is simple and reliable and nearly independent of flow. In addition, the linear-generator has several advantages over the exponential-diluter: (c) Nearly linear (vs. convex) gradients are formed, (d) The full 0–100% gradient range can be covered (vs. nearly linear segments over only part of the gradient. (e) Gradients have a gentle on-set that quickly attains the final 100% concentration (vs. an abrupt onset and a very slow aproach to the final composition with the exponential-diluter.)