Source: Vy M. Dong and Daniel Kim, Department of Chemistry, University of California, Irvine, CA
Organic synthesis is about transforming a readily available reagent into a more valuable product. Having clean glassware is crucial for the efficiency of this process. Dirty glassware can potentially affect the reaction and make isolation of the final product more challenging. Thus, a synthetic chemist must keep the glassware spotless. The methods described here will detail different glass cleaning techniques that are regularly used to remove organics, metals, grease, and salts.
General Considerations: While some of the below cleaning solutions are harmless to skin contact, it is always wise to wear chemical resistant gloves, a lab safety coat, and eye protection.
1. General Procedure for All Glassware
NOTE: This method applies to stir bars, spatulas, funnels, and other reusable equipment. It can also be used with any of the other washing methods described below.
2. General Acid Wash
NOTE: Some organic residues, metal salts, and stuck-on bases can be removed using a mild acid solution. When finished, non-oxidizing acids can be diluted and discarded down the drain (e.g., hydrochloric acid). Other acids like acetic acid, which is an organic acid, should be neutralized and added to water-based liquid waste containers. Usually sodium bicarbonate is used to quench and neutralize acids because it has its own visual indicator: the reaction of sodium bicarbonate and acid produces CO2 gas, and so bubbling indicates that there is still acid in solution. Once sodium bicarbonate is added and no bubbling is observed, then the solution is neutralized. This can all be placed in aqueous waste.
3. Base Bath
Note: In general, if there is a piece of glassware that cannot be cleaned by acid and soapy water, soaking the glassware in a base bath may help. The base bath is strongly basic and caustic. Care should be taken to prevent any spills. However, small amounts can be washed off completely using water. Serious spills can be neutralized with acetic acid and mopped up. The base bath should be neutralized and discarded with aqueous waste.
NOTE: Glass frits should not be cleaned using a base bath.
4. Aqua Regia
Note: Aqua regia is known for its properties in dissolving metals. This acid wash is strongly acidic, oxidizing, and caustic. Care should be taken to prevent any spills or skin contact. Small amounts that contact the skin will cause itching and must be washed off completely by rinsing the area under water for 15 min. Serious spills can be neutralized with NaHCO3 (sodium bicarbonate) and mopped up. Aqua regia produces fumes and should be handled inside of a fume hood. It can also corrode stainless steel. Aqua regia should be neutralized with sodium bicarbonate before adding to aqueous waste.
5. Cleaning Glass Ground Joints
Note: Ground joints can easily become stuck. One way to prevent this problem is to make sure all joints are clean. When clean, the ground glass joints are frosted white in appearance. Clear joints usually indicate small amounts of oils and grease that can contaminate spectroscopic data and the desired compound.
6. Removing Water
Note: Some reactions are very water sensitive. Even the moisture from the air can lead to a failed reaction. Therefore, it is important to drive off water and to keep outside air away from the inside of the glassware. Some glassware like reflux condensers are fragile and cannot be placed under vacuum; for this reason, an oven is preferred. Be aware that the keck-clamps that secure joints between two glass fittings are usually made of plastic and will melt if placed under heat.
Clean glassware is crucial for the efficacy and efficiency of chemical synthesis.
Organic synthesis is about transforming a readily available reagent into a more valuable product. Any source of contamination, such as dirty glassware, can potentially affect the reaction and make isolating the final product more challenging.
Just because a piece of glassware looks clean, does not mean that it is. When in doubt, clean it.
This video will illustrate many of the basic cleaning methods for glassware used in organic chemistry reactions.
We will begin our survey with a general method used for cleaning all glassware.
First, rinse the glassware with an organic solvent-such as acetone-to remove any excess organic oils. Deposit this rinsing into the appropriate safety container.
Next, mix warm tap water and soap. Using this and an appropriate brush, scrub the inside of the glassware. Then, rinse with warm tap water to remove the soapsuds.
Wash away the tap water with deionized water to avoid hard water stains. Lastly, rinse the glassware with acetone to remove the deionized water and expedite the drying process. This method on its own is sufficient when a specific residue removing technique is not required. When such a technique is called for this general method will still be used after the residue has been removed.
Some organic residues, metal salts, and stuck-on bases require a mild acid wash. Non-oxidizing acids can be poured down the drain when finished. Organic acids, on the other hand, must be neutralized and deposited in a water-based liquid waste container.
To begin, prepare a 1 M hydrochloric acid solution in deionized water. Then, inside a fume hood, add some of this acid solution to the glassware being cleaned. Make sure to swirl the solution to the dirty areas. When finished, depose of the acid solution appropriately. Finally, wash the glassware with soapy water, as outlined in the general procedure for all glassware.
Soaking glassware in a base bath may help when mild acid washes and soapy water are not enough. Care should be taken, as this bath is strongly basic and caustic, and can affect finely-calibrated glassware.
To begin, add a 2 M solution of potassium hydroxide in isopropyl alcohol to a designated cleaning bucket. Next, to prolong the life time of the base bath, clean the glassware using the general "soapy water" method. Then, carefully place the glassware in the base bath, making sure to remove as much air as possible.
Let the glassware soak overnight. After this, carefully remove the glassware from the bucket, pouring the base solution back into the bucket. Rinse with deionized water. The base bath can be used multiple times before replacing.
Finally, dry the glassware with acetone.
In situations with residual metals, aqua regia may be required. Care should be taken, as this acid wash is strongly acidic, oxidizing, and caustic-and can corrode stainless steel.
To begin, create a small batch of aqua regia by mixing nitric acid and hydrochloric acid in a 3 to 1 ratio. These acids are colorless, but when mixed will fume and turn dark orange.
Next, pipette the mixture into the dirty glassware. Swirl to dissolve residual metals. After this, pour the aqua regia into a separate container for treatment.
Neutralize the used aqua regia with sodium bicarbonate. Then, deposit the neutralized solution in an aqueous waste container. Using the general method, wash the glassware with soapy water.
Glass ground joints can easily become stuck if not cleaned properly. Clean glass joints are frosted in appearance. Dirty joints, on the other hand, are usually clear - indicating contamination with oil or grease.
First, clean the glassware using an appropriate method. Then, use a paper towel soaked in ethyl acetate and a small spatula to clean the inside, outside, and the edges of the joint.
After this, let the glassware dry.
In reactions that are water sensitive, it is important to drive off water and limit exposure to outside air. While there are several methods to remove water, using an oven is the safest, and preferred.
To begin, place the glassware into the oven. Turn the oven on, and leave the glassware inside for 30 to 60 min. After this, use oven gloves to remove the glassware.
Quickly cap with a septum. Flow nitrogen through the glassware while it is still hot. Once the glassware cools, it will be enriched with an inert atmosphere containing no water vapor. The glassware is now ready for use.
Now that we've surveyed the most common techniques used to clean laboratory glassware, we'll discuss some examples.
The successful synthesis of high purity product is reliant on properly cleaned glassware. In this example, metal nanoparticles are synthesized, and then encapsulated in various types of polymer.
First, gold nanoparticles are synthesized in glassware cleaned using the aqua regia process. After this, the nanoparticles are isolated by centrifugation.
The isolated nanoparticles are then transferred to a glass vial containing a solution of PSPAA for encapsulation.
Clean glassware is also important in many fields when attempting to quantify a compound of interest. For example, having clean instrumentation is important when investigating a crime scene. If not cleaned properly, contaminations could give rise to unreliable data.
You've just watched JoVE's introduction to cleaning glassware. You should now understand acid washes, base baths, and the general cleaning procedure for all glassware. Thanks for watching!
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