A desiccator, an airtight container, used to dry samples and store hygroscopic materials under atmospheric or vacuum pressure. Sometimes it is referred to as dehumidifiers or dehydrators. It is also used to cool heated samples and objects like crucibles. It uses a suitable drying agent (desiccant).
Desiccator plays a crucial role in cooling and storing hygroscopic materials as they tend to absorb moisture if left outside in the working environment.
The hygroscopic substance known as desiccant present inside the desiccators is responsible to absorb water molecules from samples. Desiccant captures water molecules within its structure and prevents them from escaping back to the environment. Commonly used desiccants are:
- Silica gel: Silica gel is an inert, non-toxic, non-flammable, and porous material that traps water molecules within its structure. It is the most commonly used desiccant. Reusing it is possible if heated up to 85°C.
- Montmorillonite clay– Montmorillonite clay is a least expensive, naturally occurring desiccant that works well as a desiccant below 50°C and within the relative humidity range but at a higher temperature, it gives up moisture rather than absorbing it.
- Molecular sieve– Molecular sieve is a synthetic porous crystalline aluminosilicate having uniform pore size. It is the best desiccant that can even remove water molecules trapped within a fully saturated silica gel
- Calcium sulfate– Calcium sulfate is a general-purpose desiccant catered for laboratory use. It is chemically stable, non-disintegrating, nontoxic, and non-corrosive. It also does not release adsorbed water easily even when exposed to ambient temperature.
Desiccator vs Desiccant
The difference between a desiccator and a desiccant are:
|1.||A desiccator is an airtight container used to dry samples and store hygroscopic materials under atmospheric or vacuum pressure.||Desiccant is a hygroscopic substance (such as calcium oxide or silica gel) that is used as a drying agent because of its high affinity to water|
|2.||It is available as a round chamber or cubic cabinet.||It is available as powders or beads or clay.|
|3.||It allows the proper functioning of the desiccant by creating an airtight space.||It is the main component of a desiccator that absorbs water molecules.|
Types of Desiccators
There are four types of desiccators. They are:
This desiccator type requires manual operation and monitoring. It is flexible as any type of desiccant can be employed (silica gel beads, activated charcoal, clay molecular sieves, etc) based on economics and convenience. The desiccant is placed below or on any shelf to remove moisture from the chamber. Continuous desiccation saturates the desiccant with the water molecules. The saturated desiccant should be regenerated via heating or replaced. It is economic and convenient to use. It is portable.
Gas Purge Desiccator
A slow steady flow of inert gas (dry nitrogen) is supplied to achieve a low humidity level much faster than desiccants. It works by removing the wet air and replacing it with dry gas, therefore named a gas purge desiccator. It is flexible as it provides the option to close stopcocks and use regular desiccants instead of inert gas.
The wall of the gas purge desiccator consists of a gas inlet and outlet allowing the movement of gas. They can reach the desired humidity level much quicker than standard and automated desiccators and provide a dust-free environment.
This desiccator requires minimal manual monitoring than the standard desiccator because of its ability to regenerate the desiccants. The electric fans and heaters present it continuously regenerate the desiccant by preventing saturation and automatically maintaining a low-humidity environment. It uses silica gel beads as desiccants. These desiccants last for thousands of regeneration cycles. It operates on a set schedule of desiccation followed by a regeneration period.
A vacuum desiccator removes air and moisture through the use of a vacuum pump. The use of a vacuum pump reduces humidity which helps to evacuate air from the chamber and also reduces oxygen level. Stopcock on vacuum desiccators helps to evacuate the liquid or gas from inside. It can also be operated using desiccants. Vacuum desiccator cabinets are available in round/jar or cubic form.
It is best for long-term storage of the materials that air can damage. Its other use is for degassing techniques. It is flexible since the stopcock is removable to disconnect the vacuum pump to use regular desiccants in it.
The desiccator consists of various parts which include:
- Desiccator Cabinet/Chamber: A desiccator cabinet can be round or in cubic form. Round-style desiccators typically have one shelf and a domed top to provide extra vertical space. Cabinet-style desiccators provide easier accessibility, greater storage capacity, and stacking ability. They often have multiple shelves. Its construction can be of glass, polypropylene, polycarbonate, or acrylic cabinets. The design of this type of desiccator is in a way to maintain a low-humidity atmosphere which is useful in drying hot objects and storing samples for the long term without any damage due to chemical reactions caused by moisture or fungal growth. They can be vacuum and non-vacuum cabinets with different configurations and various height and width options.
- Lid: The material for the lid is the same as that of the chamber. It is placed on the top of the chamber. Silicone grease applied on the interface of the lid and chamber maintains an airtight seal.
- Desiccator plate: A pair of mesh or sieves is placed inside the chamber. The upper perforated plate holds crucibles, Petri plates, and other materials along with the samples to be dried or stored. A lower plate holds the desiccant. The plates can be of stainless steel or polypropylene materials.
- Stopcock: It is present in vacuum desiccators which helps to remove the air and moisture from the chamber.
- Vacuum pump: It pumps the air and moisture out of the chamber, and accelerates the process of drying. It is present only in vacuum desiccators.
Uses of Desiccator
- To remove moisture from chemicals, used to make standard solutions like NaCl, KCl, and oxalic acid.
- For the storage of materials that require constant weighing under dry conditions like soil, dissolved solids, etc.
- For cooling and long-term storage of hygroscopic chemicals like sodium chloride, and sodium hydroxide crystals.
- For determining the dry weight of compounds like proteins, sugars, etc.
- For drying heat-labile substances like drying proteins and drying bacteria (usually starter culture).
Operating the Equipment
Using a round-style desiccator:
- To open the desiccator, slide the lid gently. The lid is placed with an airtight seal so, opening and closing of the lid required precaution.
- Grasp the knob with one hand and the base with another hand. Lifting the lid should be avoided.
- Place the crucible/ samples on the desiccator plate. Don’t keep the lid open for a long time.
- To close the equipment , place the lid gently on top and close slowly by applying a mild force till it closes. The lid should be rotated to ensure that an airtight seal is created.
- Rub a small amount of silicon grease around the flat surface of the lid to make it airtight.
- Leave it undisturbed. Open the lid only if it is necessary for a short period.
Using a vacuum-sealed round-style desiccator:
- Open stop-cock on top to release the vacuum inside at the time of opening.
- Try sliding the lid. If not possible, use a spatula to create a rift between the lid and the body.
- On hearing the hissing sound of vacuum release, slide the top cover by holding the bottom firmly with the other hand.
- Avoid keeping hot substances directly in the desiccator. The hot substances heat the air inside the chamber which creates a vacuum later which makes opening the lid difficult. Therefore, an ignited crucible or another very hot object should be cooled before being placed into it.
- Do not place a wet crucible or other wet materials into the equipment as it can hamper the desiccant.
- Avoid placing any substances that rapidly lose moisture leading to the loss of their efficacy.
- Store the chemicals that are compatible with the chemical composition of the chamber/cabinet. For example:
- Some chlorinated solvents degrade plastics;
- Hydroxide solutions dissolve aluminum and etch glass;
- Hydrofluoric acid dissolves glass
- Avoid storing materials that are highly reactive with water such as sodium metal. Contact with humid air, while opening the lid can lead to a violent reaction.
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About the author
Padma Shrestha is from Kathmandu, Nepal. She is currently pursuing a Masters degree in Medical microbiology at Tribhuvan University . She has great interest in Microbiology and Molecular Biology