How to make a zero dead volume (ZDV) connection
Ensuring a low swept volume within tubing connections is highly important in HPLC & UHPLC systems to preserve chromatography peak shapes, as well as in capillary tubing applications where the internal tubing volumes are very small. This is often referred to as ZDV or zero dead volume, although the connection actually may contribute with a small but acceptable volume.
True zero dead volume (ZDV) unions are designed so that the two joined pieces of tubing butt perfectly together as shown in the left image below. These products have no swept volume contained within the union body. The fluid moves directly from one tube into another in this type of connector. When using true ZDV unions, it is crucial to ensure that the connecting tubing has burr-free 90-degree ends. To make sure that the two tubing ends meet in the centre of a true ZDV union, a gauge plug should be inserted to one end while the first tubing is being assembled. This serves as a hard stop for the tubing to bottom out against as it is connected to the opposite port. The gauge plug is then removed, and the second piece of tubing is connected, using the first piece of tubing to bottom out against, resulting in the two tubes joined together in the centre of the union. However, if the tubing ends are not made to meet perfectly during assembly, there is a risk of introducing a rather large dead volume, alternatively resulting in a poor seal and thus a leaking connection.
The installation issues posed by a true zero dead-volume (ZDV) union are solved by designing the union body to include a thin web of material in the centre, see right image below. A small thru-hole (matching the ID of the intended tubing) is drilled through the centre of the web allowing fluid to flow from the tubing on one side of the web into the tubing on the other side. Even though this is not a true ZDV union, it is a practical solution and a generally accepted alternative, and manufacturers may still call them ZDV unions. Note, however, that it is important to choose a union with a through-hole that match the dimension of the fluid path, to avoid introducing excessive dead volumes that may affect the performance of the fluidic system.
In summary, low dead volume connections are important in HPLC & UHPLC as well as in capillary systems. A practical way of achieving this is by using so-called ZDV unions that have a small diameter hole through a thin web of material, which introduce a limited but acceptable dead volume into the liquid flow path.
Visit the product pages for HPLC & UHPLC connectors to learn more about the different component options for joining fluidic paths, or contact Biotech Fluidics to discuss your requirements.
