Desiccators are sealed containers that are used for drying samples under atmospheric pressure or vacuum pressure. These can also protect chemicals that are hygroscopic, as well as protect samples from dust and moisture in the air. Desiccators can be made of glass, polypropylene and polycarbonate, or acrylic in cabinet form. Below is a simple guide to desiccators.
- Glass – glass desiccators are made from borosilicate glass which makes the desiccator more robust. However, these desiccators can shatter and it is recommended that these desiccators are placed behind a screen when under vacuum.
- Polycarbonate and polypropylene – polycarbonate desiccators are shatterproof and implosion proof, giving them high impact resistance and allowing them to withstand high vacuum pressures.
- Vacuum – Vacuum desiccators can dry samples in two ways – under vacuum or by using a desiccant. Drying under vacuum uses a vacuum pump to remove any air from the system. Inert gases, such a nitrogen gas, can be used to achieve ultra-dry environments. Desiccants can help induce or sustain dry environments depending on the moisture content of the air and sample.
- non-vacuum – Non-vacuum desiccators can also dry samples in two ways – using desiccants or by purging. Purging of a desiccator uses either an inert gas, such as nitrogen, or compressed dry air to reduce oxygen levels. This desiccator uses atmospheric pressure to dry the chemicals.
- Acrylic cabinet – Cabinet desiccators can lower humidity levels and prevents moisture and [dust from damaging samples. These cabinets use a desiccant or an inert gas to remove moisture. The cabinet is preferred when drying bigger samples or a large quantity of samples at the same time. The shelves are adjustable to accommodate taller samples, and most cabinets are clear to easily see samples inside.
Desiccants are a hygroscopic substance which helps induce or sustain a dry environment by removing water from samples and air. It does this by capturing the water within its structure and preventing it from going back into the environment. The desiccant types are:
- Gel – Gel desiccant uses silica gel in pouches. This is the most common desiccant as it is inert, non-toxic, non-flammable and water-insoluble. Silica gel work as it is porous which absorbs and traps the water/liquids drying the air and sample out. This desiccant is reusable if heated around 85 degrees Celsius.
- Reusable cartridges that are made with a rugged polyester felt bag and mylar cover. The cartridge is filled with silica beads with a Natrasorb TI indicator that changes from blue to pink when saturated. These cartridges can be regenerated by heating the cartridge to 150 degrees celsius for 3 or more hours depending on the size.
- Disposable cartridges also use silica gel and can be regenerated or disposed of. To regenerate the cartridge can be gently heated overnight at 50 degrees celsius, or by removing the silica beads and placing it on glass or a porcelain dish. The beads are then heated to 150 degrees celsius for 1-2 hours. Some cartridges can come with a transparent polystyrene dish to allow you to see the silica beads to monitor the colour change.
Desiccator plates are used to hold crucibles/petri dishes etc. These come in stainless steel or polypropylene materials.
Stainless steel desiccator discs are heat resistant and rust-free, allowing for samples to be heated in the desiccator.
Polypropylene desiccator discs are semi-expanded discs that can only be used at room temperature
Stopcocks are used on vacuum desiccators to help evacuate the liquid or gas from inside the desiccator. This helps to reduce the chances of the desiccator from imploding as the stopcock can reduce the pressure inside the desiccator if opened.
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