Cleaning Glassware

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.

1. To remove any excess organic oils, rinse glassware briefly with an organic solvent such as acetone. Acetone rinsing should go into organic waste.
2. With warm tap water, use an appropriate brush and soapy water to scrub the inside of curved glassware.
3. Remove soapsuds using warm tap water.
4. To avoid hard water stains, use deionized water or reverse osmosis water to wash away tap water.
5. Rinse again with acetone to remove water. This step helps to expedite the glass drying process.

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.

1. Make a 1 M HCl (aq.) solution or a 5% v/v acetic acid in deionized or reverse osmosis water.
2. Inside of a fume hood, add some of the acid cleaning solution to the glassware and swirl the solution to cover the dirty areas. It is sometimes useful to use a cleaning brush, pipet, spatula, or sonication.
3. Neutralize the acid wash before adding to aqueous waste (a sodium bicarbonate solution will neutralize the acid).
4. Clean the glassware according to the general method above.

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.

1. In a designated cleaning bucket (e.g., 6-gallon paint bucket), add an approximately 2 M solution of KOH (potassium hydroxide) in IPA (isopropyl alcohol; 2-propanol). IPA can be substituted with methanol or ethanol. Use a cap to retard evaporation.
2. Clean the glassware according to the general method above.
3. Carefully soak the glassware in the base bath making sure to remove as much air as possible (it is best to soak overnight).
4. When removing the glassware from the bucket, pour back into the bucket any of the base bath solution inside of the glassware. Then take the glassware and rinse off any remaining base solution in the sink with deionized or reverse osmosis water.
5. Dry with acetone.

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.

1. Make small batches of aqua regia using a 3:1 ratio of nitric acid to hydrochloric acid (HNO₃:HCl).
   NOTE: Both acids are clear but upon mixing will fume and turn dark orange.
2. Add aqua regia by pipette or by careful pouring, and swirl to dissolve residual metals.
3. Remove most aqua regia by pouring it into a second container that will be treated and disposed of in aqueous waste.
4. Clean glassware according to the general method as described above.

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.

1. Clean the ground glass joints after cleaning the glassware by one of the methods above.
2. Clean the inside of ground glass joints (this can be tricky). The best way is to use a paper towel soaked in ethyl acetate (EtOAc) and a small spatula.
3. Easily clean the outside of ground glass joints by using a paper towel soaked in ethyl acetate.
4. Wet the tip of a paper towel with EtOAc and use the spatula to reach the edges of the joint.
5. Observe that the ethyl acetate evaporates in seconds and reveals a frosted white ground glass joint.
   NOTE: Any other volatile solvent will work, such as hexanes. However, ethyl acetate is much greener and safer to use than hexanes.

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.

1. Use one of the three methods to heat glassware sufficiently enough to remove water:
   a. An oven (this is used for glassware)
   b. A heat gun
   c. Over a hot flame
2. If heating using a heat gun or a flame, place the glassware under vacuum (with the stir bar). This pulls the water vapor out of the flask while drying.
3. If using an oven, place the glassware with the stir bar in the oven and leave for roughly 30-60 min (or longer). When removing, use oven gloves, and quickly cap the glassware with a septum and flow nitrogen through the glassware while it is still hot. The nitrogen helps to remove any outside air, which contains a small amount of water vapor; it is important to perform this step while the glassware is hot because water vapor will still be in the gas phase. If allowed to cool down, the water vapor will condense on the glass surface.
4. Safely handle the glassware for reaction setup once the glassware cools down to touch (at this point, the inside of the glassware will be enriched in an inert gas and should contain no water).