Solid Handling

Solid dispensing is ubiquitous in synthetic chemistry, and scientists spend hours on the scale, performing manual weighing tasks. While ideal, automating this task is challenging because solids can exhibit a wide range of properties, from density to particle size distribution and flowability.

Currently, there are two main types of solid dispensing modules used in chemical automation, and both rely on gravimetric dispensing: the first involves hopper/feeder modules, and the second involves volumetric modules. Hopper/feeder modules are gravimetric solid dispensing tools that consist of a hopper into which solids are loaded, with an opening at the bottom. Various types of feeders direct the flow of solids to a bottom port. Typically, the port opening is controlled by a rotary valve, and the feeder action is controlled by various mechanical devices. In some cases, the solid flow can be additionally controlled by a knocking or vibrating action.

Existing automated weighing uses hopper-based modules that control the flow of solids by rotating the dispensing. Hopper/feeder modules are best suited for dispensing solids in milligram to gram quantities. Additionally, hopper/feeder modules are best suited for dispensing free-flowing solids, as interruptions in the solids flow can cause the equipment to time out.

Liquid Handling

Liquid handling modules are relatively simple to assemble, but achieving reliability and robustness can be a challenge. Liquid handling modules may need to be calibrated for small volume dispensing of various liquid types, such as low viscosity organic solvents. High viscosity liquids may present unique challenges that cannot be overcome using common liquid handling modules. These liquids are best handled with volumetric pipettes. Clogging and air bubbles are other common challenges in liquid handling. When aspirating and dispensing from capped vials, a vent is required to achieve pressure equalization. Some solutions to this problem include using special needles with additional grooves for pressure equalization and using pre-slit septum caps.

Liquid handling modules include aspiration and dispensing of solvents, liquid reagents, and stock mixtures. The simplest liquid handling system includes a pump for liquid displacement, valves to direct the flow, various tubes, and a dispensing head equipped with a pipette or needle.

The two most common types of pumps observed in chemical automation systems are peristaltic pumps and syringe pumps. Peristaltic pumps expel liquids through pressure waves generated by rollers mounted on a rotor compressing tubing. Peristaltic pumps are relatively inexpensive and can be used for continuous dispensing of larger volumes in the milliliter range. Syringe pumps contain syringes and plungers (usually driven by stepper motors) equipped with dispensing or non-dispensing valves for flexible flow path planning. These pumps are programmable for small and precise dispensing volumes in the microliter range.

Valves are usually used to enable different flow paths. Ports and positions are the main features of valves. Ports are tubing connection points, and positions are the directional states that valves can reach. Two-position rotary valves can have a large number of ports (usually six), where the fluid connection between adjacent ports is switched by position. Selector valves work in a similar way, but in this case one common port is connected to various optional ports by switching positions.

The tip of the liquid handling system plays an important role in the quality and accuracy of the dispensing. The dispensing head can be equipped with a needle and a pipette. The advantage of the needle is the ability to pierce a vial with a septum. The dispensing head can be equipped with a needle and a pipette. The advantage of the needle is the ability to pierce a vial with a septum.

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