Laboratory glassware cleaning

What is Laboratory Glassware?

Laboratory glassware refers to a variety of equipment, traditionally made of glass, used for scientific experiments and other work in science, especially in chemistry and biology laboratories. Some of the equipment is made of plastic for cost, ruggedness, and convenience reasons, but glass is still used for some applications because it is relatively inert, transparent, more heat-resistant than some plastics up to a point, and relatively easy to customize.

Borosilicate glasses, or formerly called Pyrex are often used to make laboratory glassware because they are less subject to thermal stress. For some applications quartz glass is used for its ability to withstand high temperatures or its transparency in certain parts of the electromagnetic spectrum. In other applications, especially some storage bottles, darkened brown glass is used to keep out much of the outside light so that the effect of light on the contents is minimized. Special-purpose materials are also used; for example, hydrofluoric acid is stored and used in polyethylene containers because it reacts with glass.

There are many different kinds of laboratory glassware items, the majority are covered in separate articles of their own. Such glassware is used for a wide variety of functions which include volumetric measuring, holding or storing chemicals or samples, mixing or preparing solutions or other mixtures, containing lab processes like chemical reactions, heating, cooling, distillation, separations including chromatography, synthesis, growing biological organisms, spectrophotometry, and containing a full or partial vacuum. When in use, laboratory glassware is often held in place with clamps made for that purpose, which are likewise attached and held in place by stands or racks. This article covers aspects of laboratory glassware which may be common to several kinds of glassware and may briefly describe a few glassware items not covered in other articles.

Beaker.
Borosilicate science lab glass beakers can be used for routine mixing, measuring and boiling. Similar to Pyrex beakers in chemical composition, they can be used for all the same basic aqueous measuring, mixing and heating applications where a glass lab beaker is required.

Boiling Flask
Borosilicate boiling flasks or Florence flask, a flat bottom boiling flask can be used on a wire mesh, a round bottom one need a clamp and boss head. Use instead of an Erlenmeyer flask if vigorous boiling is required.

Buret
Glass burets or burettes have a variety of applications and are used mainly where accurate amounts of liquid must be added in small amounts such as acid-base titrations and measuring.

Erlenmeyer flask
An Erlenmeyer flask is commonly used for simple measuring, storing and mixing of liquids. They can be used as wine or juice containers, culture chambers and brewing vats.

Graduated Cylinders
Graduated cylinders are handy for accurate measurements of small volumes of liquid that cannot be done with beakers and flasks. A borosilicate glass graduated cylinder should be used instead of other materials such as polypropylene and TPX if you are going to use oxidizing materials and certain hydrocarbons which can cause plastic to cloud.

Pipet.
measuring pipettes are accurate to 0.1% and are ideal for measuring small volumes for doing chemical titrations and serial dilutions for naturopathic medicine tinctures used in homeopathic remedies and other new age therapies.

Test Tubes
Test tubes are among the most common of requirements for lab supplies. The 18x150mm is considered the standard lab test tube size.

Volumetric Flasks
Volumetric flasks are used in analytical chemistry to produce accurate solutions.

Watch glasses
Watch glasses have all kinds of uses. They are concave "dishes" that can be used as beaker lids; to hold protists and other invertebrates for viewing under a microscope; or to dissolve materials such as crystals and powders.


General procedure for cleaning laboratory glassware before use in the analytical laboratory.NAIT Chemical Technology Laboratory Techniques Series.

Why we need to clean Laboratory Glassware ?

Clean glassware is essential in chemistry. Cleaning laboratory glassware isn't as simple as washing the dishes. Here's how to wash your glassware so that you won't ruin your chemical solution or laboratory experiment. The problem is that the tolerance for shmutz varies with the work you are doing, and sometimes a chemist does not know how important clean glassware is to an experiment until it has failed.

There are two broad degrees of clean in chemistry; quantitative and normal. Quantitatively clean glassware is required for the most demanding applications where a quantity is being measured at high precision, such in analytical or physical chemistry. At this level of cleanliness there are no residues such as grease or other impurities on the glassware. Normal clean glassware is free of most contamination but some contaminates like grease are tolerated. Glassware that has been cleaned normally is used where a high degree of precision is not required, such as in a synthesis.

What is the proper way of Laboratory glassware cleaning?

Health and Safety Considerations

Even a task as simple as washing glassware at the sink is potentially hazardous. You must wear eye protection, appropriate for the task, at all times. Gloves are recommended, even for general cleaning, if the glassware contained an irritant, lachrymator or toxic material. Before cleaning be sure that any excess reagent has been disposed of properly and the vessel in which it was contained has been triple rinsed into the waste container. Triple rinsing? Triple rinsing does not mean that you fill the vessel to the brim three times. This is a waste of solvent! Triple-rinsing is done in exactly the same as we rinse burets and pipets before using them. To triple-rinse a bottle or flask, simply place a small amount of solvent (2-5 mL) in the vessel and swirl to coat all of the inside surface. Then discard the wash in the appropriate waste bottle. Repeat as needed.

General Cleaning Tips

The key to cleaning is doing it a timely manner; letting dirty glassware sit for long periods of time guarantees a harder cleaning job. Therefore It is easier to clean glassware if you do it right away. Much of the time, detergent and tap water are neither required nor desirable. You can rinse the glassware with the proper solvent, then finish up with a couple of rinses with distilled water, followed by final rinses with deionized water.

The first step is to disassemble all your apparatus as soon as possible after you are finished with it. Remove all stopcocks and stoppers from addition funnels, separatory funnels and the like. Ground glass stopcocks and stoppers will freeze in place if certain reactants bases were used in them. Triple rinse all surfaces with an appropriate solvent to remove traces of solvents and reaction mixtures, place the rinses in the appropriate waste container.

Separate glassware that must be quantitatively clean from that which does not. In this way you do not waste time trying to quantitatively clean items that do not need to be.

How to Wash Out Common Lab Chemicals

Water Soluble Solutions(e.g., sodium chloride or sucrose solutions) Rinse 3-4 times with deionized water then put the glassware away.

Water Insoluble Solutions(e.g., solutions in hexane or chloroform) Rinse 2-3 times with ethanol or acetone, rinse 3-4 times with deionized water, then put the glassware away. In some situations other solvents need to be used for the initial rinse.

Strong Acids(e.g., concentrated HCl or H2SO4) Under the fume hood, carefully rinse the glassware with copious volumes of tap water. Rinse 3-4 times with deionized water, then put the glassware away.

Strong Bases(e.g., 6M NaOH or concentrated NH4OH) Under the fume hood, carefully rinse the glassware with copious volumes of tap water. Rinse 3-4 times with deionized water, then put the glassware away.

Weak Acids(e.g., acetic acid solutions or dilutions of strong acids such as 0.1M or 1M HCl or H2SO4) Rinse 3-4 times with deionized water before putting the glassware away.

Weak Bases(e.g., 0.1M and 1M NaOH and NH4OH) Rinse thoroughly with tap water to remove the base, then rinse 3-4 times with deionized water before putting the glassware away.

The following steps should be followed for glassware for which a simple solvent rinse is not sufficient. If you need quantitatively clean glassware, these should be the first steps toward this goal, and more aggressive cleaning methods may be required vide infra.

Degrease your glassware’s ground glass joints by wiping them with a paper towel soaked in a small amount of ether, acetone or other solvent. CAUTION! wear appropriate gloves and minimize your exposure to the vapors. Place the glassware in a warm concentrated aqueous solution of Alconox, or other detergent, and let it sit for several minutes then Scrub. Be sure that your brush is in good shape before scrubbing (not rusty, bristles are not matted down); replace it if necessary.

Rinse thoroughly with tap water and give a final rinse with deionized water. The water will sheet cleanly off the glass, if it is quantitatively clean. If water does not sheet off the glass, and you desire the glassware to be quantitatively clean, first repeat the above soaking and scrubbing steps. If, after a second cleaning, bits of solid still adhere to the glass, or if there is clearly a greasy residue on the glass, more aggressive action must be taken.

More Aggressive Cleaning Methods

The following cleaning methods are two of the more commonly used ways to remove contaminants from glassware. They are usually used after normal cleaning has failed, and they are often used together, because each is effective at removing different types of contaminants. Care must be taken using either one because of the corrosive nature of the solutions used.

If the contaminant is a metal-containing compound, soak the piece of glassware in a 6 M HCl solution. DANGER! this solution can cause severe burns! Wear appropriate gloves. Once the solid has dissolved, copiously rinse the item with tap water, and then repeat the general cleaning steps above. This method will also remove some organic residues (not grease).

If the contaminant is organic, submerge the item in a base bath (a saturated NaOH or KOH solution in ethanol, methanol or isopropanol). DANGER! the base bath will dissolve skin and alcohols are flammable! Wear butyl gloves and keep ignition sources away from the base bath. Be sure that the piece of glassware is completely filled with the solution and is sitting upright. After several minutes of soaking, carefully remove the item (it will be slippery), and rinse thoroughly. If the glassware is not quantitatively clean at this point, the general cleaning steps may need to be repeated, or a longer soaking time in the base bath, may be needed.

NEVER soak the following items in a base bath for prolonged periods:
-Glassware contaminated with metal-containing compounds
-Glass fritted funnels
-Cuvettes
-Volumetric glassware (pipettes, volumetric flasks)
-Any glassware contaminated by an oxidizing agent
-Anything that has not been washed according to the above steps first

Glass fritted funnels and volumetric glassware can be rinsed briefly with the base bath solution to remove small amounts of grease, but prolonged exposure to the caustic solution can damage these items.

Even More Aggressive Cleaning Methods

Sometimes 6 M HCl and a base bath are not sufficient, and even more aggressive methods must be employed. CAUTION! all of these methods will do severe damage to the eyes, skin, mucous membranes and lungs. Extreme caution should be exercised when using these methods. Wear butyl gloves (not latex or nitrile exam gloves), eye protection and a lab coat. Work in the hood.

Undergraduate students must check with their faculty supervisor before using these methods, and they must be under the direct supervision of a faculty member at all times when using these methods (no exceptions).
Aqua Regia This is an extremely powerful oxidizing solution prepared from 1 part concentrated HNO3 and 3 parts concentrated HCl (it is recommended that 1 part H2O be added if the aqua regia will be stored to minimize the generation of Cl2). It is the only acidic solution that will dissolve gold and will oxidize just about everything else. Extreme caution must be used when working with aqua regia because it generates Cl2 and NOx gases in addition to causing severe tissue damage. Clean the glassware before soaking in aqua regia and then rinse thoroughly with water.

Acidic Peroxide Solution This is most conveniently prepared by dissolving the commercially-available "NoChromix" mix in concentrated H2SO4 per the package directions. An alternative preparation is to prepare a solution by mixing equal proportions of concentrated H2SO4 and aqueous H2O2 solutions (remember to add the acid to the H2O2). A 3% H2O2 solution is usually sufficient, and under no circumstances should H2O2 solutions greater than 10% be used. The H2O2/H2SO4 solution is both a strong oxidant and a strong reductant, so care must be taken when using it. Another acidic peroxide cleaning solution can be prepared by dissolving 36 g (NH4)2S2O8 (ammonium peroxydisulfate) in 2.2 L of 98% H2SO4 (can be made right in the bottle of H2SO4, if the bottle is loosely stoppered). The procedure for these solutions is the same as for aqua regia as are the precautions for their use.

Chromic Acid This is a solution of CrO3 in concentrated H2SO4. A premeasured mix is available under the name "Chromerge", which should be treated in the same way as aqua regia or acidic peroxide solutions. Because high-valent chromium is carcinogenic, teratogenic and causes severe environmental damage, the use of chromic acid is not recommended.

Hydrofluoric Acid Concentrated solutions of HF will remove just about everything from glass and will even etch the surface of the glass itself. It should not be used on calibrated volumetrics. HF causes severe, painful burns that do not heal well, and prolonged or intense exposure can lead to a very slow, painful death. It is not to be used by any students at Truman under any circumstances.

Special Cases

Cuvettes Generally, you only need to rinse a cuvette in the appropriate solvent and wipe the outside with a Kimwipe immediately after use. If something has adhered itself to a cuvette, it is best to soak the cuvette in solvent first and gently coax the solid off the side with a cotton swab. Never use a brush on a cuvette! If this fails, one of the acidic cleaning solutions mentioned above can be used (but never HF!). It is not recommended that base bath be used on cuvettes, because it tends to etch glass surfaces.

Fritted Funnels These can generally be cleaned by inverting and allowing to solvent to flow by gravity through the frit in reverse (do not use vacuum to speed this process). Solvent can also be pulled through the frit (in the normal direction) under vacuum. Recalcitrant gunk can usually be removed by soaking in acid, followed by copious rinsing with water under vacuum. Because HF and the base bath solution etch glass, they should not be used on fritted funnels (a brief exposure to a base bath is not usually fatal to a frit, but prolonged soaking should be avoided).

Protein Contamination Usually proteins can be removed scrubbing with detergent, but occasionally protein defies removal. In that event, you can proceed to the more aggressive acidic solutions, or you can prepare a peptidase solution (an enzyme that degrades proteins). The enzymatic approach is a bit slower than the forcing methods, but it is gentler and so can be used in situations that the contaminated item is incompatible with acid.

Drying Glassware

Wet glassware can be dried by placing it on the drying rack or invert on a paper towel, placing it in the drying oven in which for items that are water-wet only and no flammable solvents, or rinsing with a solvent such as acetone, methanol or ethanol and then gently blowing compressed air into the vessel until it is dry. The first method is preferred for drying quantitatively clean glassware provided that the prongs of the drying rack are not inside the item, thus contaminating it. Volumetric glassware and cuvettes are never to be placed in drying ovens, even if they are not quantitatively clean. The third method is acceptable only when the compressed air supply is known to be free oil and other contaminants. An alternative to blowing air into the item is to use an aspirator, or house vacuum, to pull air into the item.

source:
Article written by Anne Marie Helmenstine, Ph.D., About.com
http://chemistry.about.com/od/chemistrylabexperiments/a/cleanglassware.htm
The Grasshopper's Guide to Cleaning Glassware - Author: J. M. McCormick Last Update: June 30, 2006
http://chemlab.truman.edu/Miscellaneous_files/Cleaning.htm