Selection Guide: JG Finneran’s Microplate & 96-Well Plate Sealing Options

Molded elastomeric mats have individual plugs made of ethylene vinyl acetate (EVA), silicone, or PTFE-faced silicone. These plugs apply localized friction and tension on individual wells, thereby isolating them and preventing vapor from transferring across the plate.

• EVA: EVA mats are flexible and economical. They perform reliably with mild alcohols and aqueous solutions, and are a popular choice for general room-temperature storage. The downside of EVA is its lack of resistance to dichloromethane, tetrahydrofuran, and other harsh organic solvents.

• Silicone and PTFE-Faced Silicone: These materials are the gold standard for analytical chemistry. Pure silicone is known for its elastomeric memory, which allows it to re-seal even after multiple needle punctures. Combining it with a chemically inert polytetrafluoroethylene (PTFE) facing shields against aggressive solvents, preventing samples from interacting with the underlying elastomer.

Rather than employing individual well plugs, film-based closures involve the application of a continuous planar barrier over the top surface of the microplate. This method uses chemical adhesives or heat-induced fusion to isolate all of the plate's contents when the plate is being stored or subjected to thermal processing.

• Adhesive Films: These films require manual application using a rubber roller. They are ideal for short-term incubation, bioassays, and even cold storage. The catch is that the organic adhesives they use can leach into solvent matrices and therefore introduce unwanted interference peaks during LC-MS or GC-MS runs.

• Heat Seals: Heat sealing melts a polymer or foil layer onto the plate rim, providing a permanent cover. These seals are single-use only, require a separate heat-sealing device, and are recommended for use in thermal cycling and deep-freeze storage at up to -80°C.

Polypropylene 96-well plates are commonly used in life science labs. However, they tend to skew results. For instance, using these plates normally results in lower quantitative yield, as hydrophobic analytes and proteins stick to polypropylene walls. It also leads to unexpected ghost peaks in chromatograms because solvents extract trace antioxidants, oligomers, and additives from molded polypropylene.

To bypass plastic interference without sacrificing 96-well automation compatibility, labs shift to modular systems that embed vials into microplate footprints. A leading example of this design is the JG Finneran Multi-Tier™ Microtiter Plate System, which uses a 96-well footprint base frame that holds individual glass or plastic vials ranging from 0.5 mL to 2.0 mL.

Why is the Modular Approach Better?

• Samples make contact only with Type I Borosilicate Glass, preventing plastic binding and solvent leaching.

• Open-bottom base plate configuration enables direct contact with heating or cooling blocks.

• Works well with matching PTFE-faced silicone mat caps, pre-slit for high-speed liquid handlers.