Pipetting and Dispensing in High-Density Plates

Today s HTS and uHTS systems support two basic types of liquid-handling functions pipetting and dispensing. This section describes pipetting and dispensing techniques used in HTS and uHTS. It also discusses their precision and provides quality criteria and benchmarks for state-of-the-art liquid handling in high-density plates. 

Pipettors make use of three methods to overcome the surface tension, which tends to retain the expelled aliquot volume at the tip orifice  

Contact-free dispensing of submicroliter volumes does not allow for an air gap in the tip. The flexibility of the air gap diminishes the deceleration of the liquid column in front of the air gap and makes contact-free dispensing of nanoliter aliquots impossible. 

In HTS, the dispensing function stands for a repetitive unidirectional transport of equal volume aliquots from one (or a few) reservoirs to a series of wells in a plate. Dispensers enable the contact-free transfer of assay reagents and biological materials without immersion of the dispensing nozzle into the liquid in the target well. Contact-free dispensing is based on a fast ejection of a liquid jet through a nozzle 

The accuracy of liquid-handling operations in HTS is analyzed by three key parameters derived from test experiments in which equal volume aliquots are pipetted or dispensed over the plate. The trueness over the plate is a measure of the deviation of the average of the actual volume dispensed over a plate from the intended volume. It is measured gravimetrically and is defined as 

---