What is Delay Volume in HPLC? : Pharmaceutical Guidelines

What is Delay Volume in HPLC?

Delay volume, dead volume, dwell volume and void volume are well know terms in HPLC analysis. These are useful for an accurate analysis of pharmaceutical products by HPLC.
The delay volume in HPLC is often a topic where most people not only industry specialists in analytical chemistry but also other unrelated spheres seek clarification or seek to understand what it entails. This article, therefore, is aimed at enlightening anyone in need of having a solid understanding of the concept be it in the pharmaceutical aspect or the general public intending to have a basic understanding of the idea for knowledge purposes. Giving a concise and clear explanation of the delay volume in HPLC, therefore, will leave everyone who reads the article with a satisfactory and candid comprehension of the concept.

HPLC is an abbreviation for high-performance liquid chromatography. It is a technique used in analytical chemistry to separate, quantify and identify each component present in a mixture. Pumps are utilized in passing the pressurized solvent liquid with the sample mixture through a designated column which is filled with an adsorbent material which is substantial. The elements separate when flowing out due to their difference in their flow rates.

High-performance liquid chromatography is mainly used in manufacturing for example of pharmaceutical products, in legal issues to detect the presence of steroid drugs present in urine and for medical purposes, for example, testing for the levels of Vitamin D in blood serum among many others. The delay volume in HPLC comes about when gradient mixer instruments with low pressure are used.

The volume between the column inlet and the point of mixing the gradient brings about the delay volume in HPLC. The individual volumes include the tubing volume, the injector, the pump, and associated tubing. The volume therefore by which there is a time lag before the onset of any gradient translates to a delay volume in HPLC.

The delay volume in HPLC results in an isocratic hold when the gradient is beginning that differs from one system to another. To re-equilibrate the column before a subsequent injection, the delay volume is flushed out. The delay volume affects the throughput and also the transfer in a gradient method from one system to another. Worth noting is its impact does not affect isocratic separations of in HPLC.

The gradient volume should be equal to the column volume void plus the delay volume of the gradient. This is a general rule that helps one in knowing when the injected sample will start to have a real beginning of the gradient when the isocratic hold comes to an end.

In conclusion, advancements in technology have primarily revolutionized the design and thus the performance of HPLC machines with an impact on the delay volume of HPLC. As a result, the modern devices that have come up can mainly avoid or even completely prevent the delay volume in HPLC. This is achieved by delaying the injection period until the gradient rises to the level of the inlet of the injector. Shortening the column re-equilibration volume also ensures delayed injection. The gradient delay volume in HPLC, therefore, is consequently minimized significantly to near completion.

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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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