Gradient Delay Volume in UHPLC
Kenneth Fountain, Waters Corporation, Milford, MA, USAAbstract The gradient delay volume is the volume between where the gradient is formed and the inlet of the column. This volume results in an unwanted isocratic hold at the beginning of the gradient that can differ from system to system. It is also a volume that needs to be flushed out at the end of the gradient in order to re-equilibrate the column prior to the next injection. The gradient delay volume impacts the throughput of a gradient separation as well as the transfer of a gradient method from one system to another. It does not impact the throughput and method transfer for isocratic separations.
Measuring the gradient delay volume of any LC system is essential to knowing when the sample that is injected will start to experience the real beginning of the gradient at the end of the isocratic hold. It is also important to know the gradient delay volume in order to properly design the gradient table. A general rule of thumb is that the gradient volume should be at least equal to the column void volume plus the gradient delay volume.
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