Glassware Cleaning in Laboratory

The cleaning of analytical glassware is an essential procedure for the successful carrying out of laboratory assays and tests without interference from the residues of previous analyses. It is necessary to assure the quality of future products handled in the equipment, to prevent cross-contamination, and as a Good Laboratory Practices (GLP) requirement.

Personal Protective Equipment Required
Lab coat, safety glasses or goggles, nitrile gloves, heavy-duty (gauntlet neoprene) gloves. Safety apron may be worn on top of the lab coat. Face shield advised for acid and base baths along with aqua regia and piranha solutions.

To provide a clear explanation for proper cleaning of laboratory glassware.

Ground glass is commonly used in laboratories. Any abrasion reduces the strength of glass, making it more susceptible to breakage. Additionally, thermal shock may result from sudden changes in temperature. To avoid accidents, follow these tips for safely cleaning glassware.

General Precautions
  1. Careful handling and storage should be used to avoid damaging glassware.
  2. Inspect the glassware before each use and discard if scratched on inner surfaces, chipped, cracked or damaged in any way.
  3. Use only plastic core brushes that have soft non-abrasive bristles or soft, clean sponges/rags. Use brushes to clean inside of deep glassware.
  4. Do not reach inside of glassware while cleaning to prevent cuts should the glassware break.
  5. Rubber sink and counter mats can help reduce the chance of breakage and resultant injury.
  6. Do not overload sinks or soaking bins.
  7. Do not place metal or other hard objects, such as spatulas, glass stirring rods, or brushes with metal parts, inside the glassware. This will scratch the glass and cause eventual breakage and injury.
  8. Never use strong alkaline products and hydrofluoric acid as cleaning agents. These materials dissolve glass, leading to damage and eventual breakage.
  9. Do not use any abrasive cleansers, including soft cleansers (e.g., Ajax, Comet, Old Dutch, Soft Scrub, etc.), as these will scratch the glass and cause eventual breakage and possible injury. Scotch Brite and similar scouring pads will scratch glass and should not be used.
  10. Do not use heat as a method to remove carbon residues. Heating glassware to temperatures > 800 °F will cause permanent stresses in the glass and eventual breakage.
  11. Use proper drying racks for fully cleaned glassware.
  12. Tongs, a dust pan, and a broom are the best tools for cleaning up broken glass. If hands are used to pick up glass, only handle large pieces of glass and wear heavy leather gloves to protect the hands. Broken glass must be packaged in labeled, rigid, and sealed containers before disposal.
  13. Proper instruction should be provided in the use of glass equipment designed for specialized tasks, which can represent unusual risks for the first-time user.

  1. Both the acid and base baths are flammable and corrosive; contact with skin will cause burns. Their fumes might irritate your airways.
  2. Piranha solution and aqua regia are corrosive and may cause severe burns.
  3. You are handling large amounts of glassware that is many times slippery from the cleaning solutions – be extra careful to avoid breaking anything and cutting yourself. This is particularly important when the glassware isn’t clean – chemicals could get in the wounds.

Glassware Cleaning
  • The routine procedure will be outlined first. Extra steps may be necessary in some cases; those are described after the general cleaning methods.
  • All glassware/spatulas/frits/etc. must be spotless before going into any cleaning bath. In most cases, this can be achieved using one or more solvents. If this is not the case, refer to the “what to do…” section below. Once this is achieved, move on to the next steps:

General Glassware (except volumetric material and fritted glass)
  • First let the glassware soak in the base bath for at least 3 hours (usually overnight). When putting glassware in the base bath make sure the glassware is completely filled with base bath and no air bubbles are seen. For oversized items, it may be necessary to flip them and let them soak for another period before taking them out of the base bath. Then, take items out of the base bath (be careful not to spill base everywhere!!!), rinse with DI water 3 times (make sure you rinse both the inside and the outside surface). 
  • After this, transfer the glassware to the acid bath and let it soak (3 h – overnight; take care to avoid air bubbles). Once this is done, rinse with DI water 3 times, and finally leave soaking in DI water. After the allotted time (3 h – overnight) rinse 3 times with DI water and allow to dry on drying rack.

For test tubes
  • Do not leave them on the drying rack; put them in the oven to dry overnight (wrap tubes together with aluminum foil before putting them in the oven).

Volumetric glassware (flasks, pipets, graduated cylinders) and anything with fritted glass (frits, columns)
  • The procedure is similar to what’s described for general glassware, with the exception that two acid baths are used instead of a base bath and an acid bath. Fritted glass can trap impurities; air bubbles left in the glassware are detrimental to the cleaning process. 
  • Make sure no air bubbles are present when putting frits in the acid or DI water baths. When rinsing frits with DI water, attach the hose to the stem and fill the frit with water from the bottom up. Frits may get airborne when doing this: be careful and fill them slowly.
  • Frits are to be dried in the oven overnight after soaking in DI water.
  • Do not put volumetric material in the oven. Ever.

  • Soak in an Alconox bath overnight, rinse with DI water and then soak in DI water. Let them air dry.

Stir Bars
  • These can be cleaned along with the general glassware. However, it’s convenient to clean them in a personal acid bath kept in the hood (it’s easy to lose stir bars in the big buckets).

What to Do if all the Above isn’t Enough
Do not despair. Do not ignore the problem or hide the glassware away. More options are described below:

This is a mild detergent that can effectively clean some items. It is a good first approach.

Stronger Base Bath
We have a KOH/isopropanol base bath in addition to all the NaOH/ethanol ones. Avoid putting frits in it; if you must do it (because nothing else has worked), don’t leave them for longer than an hour.

Aqua Regia
This is a good option when there are metallic contaminants. Mainly used for stir bars and frits.

Piranha Solution
An all-time favorite. Eats through most stuff. Great (albeit dangerous) option for fritted glass.

Before using Aqua Regia, Piranha or other severe cleaning solutions for the first time, consult with more experienced labmates to ensure proper safety measures are followed.

Waste Disposal
  • For waste generated during cleaning before the base and acid baths, dispose of in proper waste container.
  • Aqua Regia and Piranha waste must be disposed of in separate waste containers and submitted for pick-up immediately.

Description of Cleaning Solutions/Baths
Acid Bath: 3 M hydrochloric acid in ethanol
Base Bath: 3 M sodium hydroxide in ethanol
Strong Base Bath: 3 M potassium hydroxide in isopropanol
Aqua Regia: One part concentrated nitric acid to three parts concentrated hydrochloric acid. Add nitric acid to hydrochloric acid. See note below.
Piranha: 3:1 concentrated sulfuric acid/hydrogen peroxide. Add hydrogen peroxide to sulfuric acid. Mixing is extremely exothermic, so allow solution to cool before using. All containers that contain Piranha should be made of glass. 
When handling large amounts of aqua regia or piranha (>500 mL), use neoprene gloves. All handling of aqua regia and piranha MUST be done inside a fume hood. Perform all work in a secondary container that is clean and free of organics.

Warning: NEVER add any organic solvents to an aqua regia or piranha solution, as it could cause an explosion. Even small amounts of organics could make the aqua regia or piranha solution unstable. Only make small, fresh batches of aqua regia and piranha for each use.

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