Syringe pumps, valve pumps and peristaltic pumps are classified as positive-displacement pumps.
When a solenoid valve opens or closes, there is usually a small amount of liquid moved. This effect can be deliberately used as a pump. There are solenoid valves that are also specified for use as precision pumps, but they have to be at least 2-way (3-port) valves since you need a source to aspirate from and a destination to dispense into. They are very precise but you can’t control the volume of the dispense except by making multiple dispenses.
Syringe pumps as you know use the motion of a piston in a cylinder to aspirate or dispense a fluid. They can be extremely precise and accurate if built properly. I used to work with some that were accurate below 10 microliters and precise, IIRC to within about a microliter. However, they were also very expensive. Syringe pumps are generally slow moving as high speed can cause the pump to cavitate, which reduces precision and introduces air into the fluid path. Cavitation is a release of dissolved gas (air) into the pumped fluid when the fluid pressure drops below the vapor pressure of the gas. This causes the gas to be released as small bubbles.
One common technique that I saw when I was involved in the medical device industry is to build a motorized fixture that a syringe can fit into and and use that to control the piston. It gives a high precision and also solves the problem of contamination: just throw the syringe away when you’re done.
Peristaltic pumps are also an option for a positive-displacement pump, but they are typically an order of magnitude less accurate than syringe pumps. They have the advantage that material compatibility is mainly an issue of the what the tubing is made from.
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