Picoliter injector

Reichmuth, D.S., Shepodd, T.J., Kirby, B.J., On-chip high-pressure picoliter injector for pressure-driven flow through porous media Anal. Chem. 2004, 76, 5063-5068. 

Several modules had to be developed before a functional microfluidic HPLC system could be assembled. In a series of papers, the Sandia National Laboratory group demonstrated high-pressure connectors for introduction of liquids, fabrication of integrated polymer checking microvalve elements, on-chip high-pressure picoliter injector, and eventually a complete HPLC chip. ... 

The high-pressure picoliter injector also consists of a moving monolithic plug similar to that used for valving, thus significantly reduced in size. The injection volume is controlled by pressure difference between sample and mobile phase channels and by time. For example, a 0.25 s long injection afforded a sample volume of 180 pL. 

Application of a potential between reservoirs 1 (sample) and 4 (injection waste) electrokinetically pumps sample solution as indicated in Fig. 3. In this way, a geometrically defined 150 pm (90 pi) section of the separation channel can be filled [19]. If the injection potential is applied long enough to ensure that even the slowest sample component has completely filled the injection volume, a representative aliquot of sample can be analyzed (so-called volume defined injection). This is in contrast to electrokinetic sample injection in conventional capillaries, which is known to bias the sample according to the respective ionic mobilities [61]. These characteristic differences are shown schematically in Fig. 4. It should be noted that this picoliter sample injector is exclusively controlled by the application of electric fields and does not require any active elements with moving parts such as valves and external pumps. The reproducibility of the peak height of the injected sample plugs has been reported to be within 2 % RSD (relative standard deviation) and less [19,23]. 

Kinetic sample injection is a method which employs electroosmotic flow to load and separate the samples for chemical and biomedical analysis in many bio- or chemical Lab-on-a-Chip. It is one of the injection techniques used for the microfluidic injector within microfluidic devices. The typical volume delivered by kinetic injection is about htmdreds of picoliters. 

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