Cleaning Glassware

Cleaning glassware is an important part of synthetic chemistry. Chemists must be able to rely on clean glassware for their reaction. Assessing glassware by eye is not enough to confirm whether the glassware is clean. If unsure about the nature of the glassware, clean it. It is always better to take a few extra minutes to have clean glassware than to spend hours removing contaminants or have irreproducible results.

How clean the glassware needs to be is also an important factor. The level of cleanliness of the glassware depends on the type of work being done. Over cleaning can waste time and money. Understanding the chemistry can assist in evaluating how much cleaning is required for the glassware. Covered here are the most basic cleaning steps necessary for most organic chemistry reactions.

One basic principle is that "like" dissolves "like". Polar solutions dissolve polar materials and non-polar solutions dissolve non-polar grease. There is no single step that can clean any glassware in any condition. Instead, a basic understanding of the method and what it can clean is important.

One recommendation is to clean the glassware just after its use. Chemists are busy and are generally balancing many tasks, but cleaning glassware between reactions or while a reaction is running is usually a good use of time.

For safety reasons, each item of glassware should be inspected. Broken glassware is dangerous and should be repaired or discarded. Flasks and other glassware that are commonly put under vacuum or pressure should be inspected for star cracks. These are weak points on the glass that could create sudden explosions or implosions if placed under pressure. It is good practice to use eye protection even when cleaning glassware with simple soap and water. Gloves provide good protection, too, especially when handling harsh cleaning solutions.

For waste disposal, all organic solutions, organic reagents, and any organic contaminated paper or solid should not be discarded in the sink or trash. Dispose of all organic material in safety bins, which are handled by the site's Environmental Health & Safety (EH&S) team; all organic liquids should be placed in an appropriately labeled liquid container (which is also picked up by EH&S). Water used for washing the glassware and scrubbing with soap can go down the drain.

Removing grease from the joints of glassware is important. Most organic greases can be removed by non-polar solvents like hexanes or ethyl acetate. Since ethyl acetate is a much greener solvent (i.e., safer, less toxic, lower environmental impact), it is the preferred choice. If the grease still remains, then a base bath will remove most greases from joints or stopcocks.

Before using any water-based products, all glassware should be rinsed with organic solvent that is then disposed of in an organic waste container. Using a green polar solvent like acetone is preferred. This will help to remove most organic residues from a flask before washing. When using organic solvents, remember that like dissolves like. Hexanes are an example of a nonpolar solvent that is commonly used. Frequently used polar solvents include: isopropanol (rubbing alcohol), acetone, ethyl acetate, and methylene chloride (dichloromethane).

Once the glassware is removed, make soapy water by mixing powdered or liquid glassware cleaning reagents with tap water. Different sized brushes will help to reach and clean the inside of curved glassware. If glassware is not cleaned right away, a small tub of this soapy water can be used for long-term soaking. Using warmer water helps to dissolve and remove salts and stuck-on grease. Soapy water can be rinsed off with tap water, follow by deionized water. Then the water can be removed with acetone.

Ultrasonic cleaners are great for extremely stuck-on grease or residue. If traditional scrubbing with a brush fails, then filling the glassware with warm soapy water and placing in a sonicator will help to loosen dirt particles.

A base bath can be prepared and used to remove grease. In addition to glassware, a base bath can be used for other dirty objects like stir bars or spatulas. Since a base bath is caustic and can strip away glass, finely calibrated glassware should not be cleaned by this method. Materials like volumetric flasks, vacuum parts like vacuum stopcocks, or glass frits should not be cleaned by this method.

Acids and oxidizers can remove salts, metals, and organic reagents. All acids should be used inside of a well ventilated fume hood. Items that cannot be cleaned by a base bath like volumetric flasks or glass frits can be used by this method.

Finally, some reactions require water-free conditions. In these cases, it is important to remove any trace water from inside of the reaction flask. Even if it appears dry, there can be a small thin coating from air moisture. This can be removed with high heat either by placing the glassware in an oven or by heating under a vacuum.

Glassware cleaning is a multi-step process. The most common procedure that will be effective against most dirty glassware will be to first rinse with an organic solvent, and then second, to wash and scrub with warm, soapy water. Then the glassware needs to be rinsed with tap water, deionized water, and finally with acetone before placing on a rack to air dry. When this fails to clean the glassware, depending on the experiment and the type of glassware, additional steps to clean with acid or base (or both) might need to be executed. Cleaning glassware is an art, and developing the knowledge of what solvents or cleaning solutions to use will improve with experience and time.

Clean glassware is simple and fundamental in organic chemistry practice. The knowledge of how to remove tough stains, residues, and contaminates provides the confidence to use glassware without worry of contamination.

By following the guidelines to cleaning glassware, the chemist can focus on the chemistry and worry less about contamination from glassware. The above protocol demonstrated how to clean glassware using warm, soapy water, acid wash, base bath, and aqua regia, and how to dry glassware, as well as advice for cleaning glass ground joints. Disposal of cleaning solutions were also discussed briefly. These glass cleaning procedures work for all kinds of glassware including, but not limited to: round-bottom flasks, Erlenmeyer flasks, separatory funnels, chromatography columns, stir bars, spatulas, funnels, filters, graduated cylinders, beakers, Schlenk flasks, and test tubes.

Ensuring clean glassware can enforce good practices beyond the organic chemist's bench. Having clean equipment in general is important for all types of applications within and outside of chemistry and science. In each case, it is important to consider the material of the item being cleaned and the tools required for cleaning.

We use simple acid and base solutions to clean materials in everyday life. For example, chefs need clean pots and pans, and while these pots and pans do not need acetone for finishing, usually warm, soapy water can remove sticky grease. Interestingly, some people suggest boiling a dirty pot with vinegar to achieve a strong clean, and it is not too surprising that acetic acid is the major ingredient in vinegar. Additionally, baking soda is sodium carbonate and a common house-hold cleaning tool.

Another example of an application where having clean equipment and glassware is essential is quantification analysis for those in an analytical field. Cross-contamination or dirty instrumentation can give rise to unreliable data, affecting many different areas of work; this could be in hospitals, clinics, a crime scene, or on a manufacturing line.

Finally, cleaning products are sold on the market for everyday use for glassware, with the added purpose of cleaning bathroom tiles, windows, and mirrors. These are sometimes filled with organics and may be mildly acidic or basic. This combination can remove grease and water stains.