Good laboratory technique demands clean glassware, because the most carefully executed piece of work may give an erroneous result if dirty glassware is used. In all instances, glassware must be physically clean; it must be chemically clean; and in many cases, it must be bacteriologic ally clean or sterile. All glassware must be absolutely grease-free.

1. WASHING, DRYING AND STERILIZATION OF
GLASSWARE, DRYING OF SOLVENTS / CHEMICALS
PGS 504 Basic laboratory techniques (0+1)
K. Avinash
M.Sc. (Ag.) Soil Science
Department of Soil Science and Agricultural Chemistry
Tamil Nadu Agricultural University

2. • Good laboratory technique demands clean glassware, because the most carefully executed piece
of work may give an erroneous result if dirty glassware is used.
• In all instances, glassware must be physically clean; it must be chemically clean; and in many
cases, it must be bacteriologic ally clean or sterile.
• All glassware must be absolutely grease-free.
• The safest criteria of cleanliness are uniform wetting of the surface by distilled water.
• In pipettes and Burettes, the meniscus will be distorted and the correct adjustments cannot be
made. The presence of small amounts of impurities may also alter the meniscus.
Introduction

3.  Wash lab ware as quickly as possible after use. If a thorough cleaning is not possible
immediately, put glassware to soak in water. If lab ware is not cleaned immediately, it
may become impossible to remove the residue.
 Most new glassware is slightly alkaline in reaction. For precision chemical tests, new
glassware should be soaked several hours in acid water (a 1% solution of hydrochloric
or nitric acid) before washing.
 Brushes with wooden or plastic handles are recommended as they will not scratch or
abrade the glass surface.
Cleaning

4. • If the glassware isn’t clean after these initial steps you can go on to more
aggressive cleaning protocols.
• Scrape away any thick solid material from the glass if possible.
• Wipe away any grease from the glass joints with a solvent like acetone which
can be used to help remove the grease.
• Put the glassware in a warm cleaning solution of detergent and water.
• Use a brush or cleaning pad to clean any residue or contamination.
• Rinse with tap water first, followed by deionized water and allow to dry.
• Most new glass is slightly alkaline and should be washed upon receipt and
generally can be soaked in a 1% HCl or HNO3 solution before wash , rinse in tap
followed by DI water and allow to dry
Intial Glassware cleaning

5. • If the initial cleaning method fails try gentle solvents for long term
soaking.
• When dealing with the gentle aqueous solutions heat soaking or, in
some instances, mechanical agitation such as stirring, shaking, or
sonication can enhance its productivity.
• The common gentle aqueous cleaning mixtures like deionized water
Mild Cleaning Methods

6. Mixture uses examples
Deionized water For diluting out absorbed ions –
passive soaking
Deionized water
Dilute surfactants Solubilizing lipid material – agitation,
brushing, rubbing or sonication.
Soaps, detergents
Protein or saccharide hydrolyzing
enzymes
Breaking larger structures into
soluble molecules – passive soaking.
Protease, lipase, Amylase
Metal chelating compounds Insoluble salts become more so by
removing the metal ion – passive
soaking.
EDTA (Ethylenediaminetetraacetic
acid)
Dilute strong acids Insoluble salt’s anion is soluble as its
acid form – soak or agitation.
Phosphoric acid, nitric acid,
Concentrated weak acids Insoluble salt’s anion is soluble as its
acid form – soak, sonicate or brush.
Hydroxy acetic acid, citric acid, lactic
acid, gluconic acid
Dilute solutions of: Phosphates,
Carbonates or Ammonia
All create low levels of hydroxide
ions for solubilizing weak insoluble
acidic solids or hydrolyzing ester
bonds – soak, agitate or sonicate.
Phosphates, Carbonates or
Ammonia

7. Using Organic Solvents
• Organic solvents are often used to remove contaminants from glass.
• Basically, if it can be readily dissolved in an organic solvent it can be
removed by these means.
• The use of organic solvents is complicated due to their flammability
and toxicity.
• When working with solvents proper ventilation and appropriate PPE
(suitable glove compatibility with the solvent) are necessary.
• Moistening a cloth with solvent is good for easily accessed surfaces.
• Agitating solvent inside of a glass container is another method.
• E.g., Acetone, methyl ethyl ketone, toluene, isopropyl alcohol

8. Aggressive Cleaning Methods
• This method involve releasing the adhered material/contaminant by
removing the top layer of silicon oxide of the glass.
• It can also be done by oxiding the material itself from the glass surface.
• This can be achieved by soaking the glass in 2% hydrofluoric acid or a
base bath (sodium or potassium hydroxide in either ethanol or
isopropanol) before rinsing and cleaning in detergent.
• The aggressive method is achievable due to the borosilicate nature of
laboratory glassware as the acid will attach to the silica layer of the glass.

9. • Often the residue on glass is insoluble to organic solvents, surfactant solutions, or mildly
acidic solutions.
• At this point one of the common ways to clean glass is to oxidize the contaminant in order
to render it soluble.
• Oxidizing agents include aqua regia(nitric acid and HCl) ; Chromic acid which is a sulfuric
acid based agent ; Piranha solution (hydrogen peroxide based agent), fuming sulfuric acid
which contains pyrosulfuric acid
Oxidizing Contaminants from Glassware

10.  If dry glassware is not needed right away, it should be rinsed with distilled water and
allowed to dry overnight.
 If dry glassware is promptly needed, glassware can be rinsed with acetone and the
residual acetone allowed to evaporate.
 Evaporation of small amounts of residual acetone can be expedited by placing the
rinsed glassware in a warm oven for a short amount of time or by using suction from a
tube connected to the water aspirator.
Drying

11. • Glassware that appears "dry" actually contains a thin film of water
condensation on its surface. When using reagents that react with water, this
water layer needs to be removed. To evaporate the water film, glassware can
be placed at 1100C in oven overnight, or at the least for several hours.
• The water film can also be manually evaporated using a burner or heat gun, a
process called "flame drying". Both methods result in extremely hot glassware
that must be handled carefully with tongs or thick gloves.
• Regardless of the manner in which glassware is heated (oven or flame drying),
allow the glassware to cool in a water-free environment (in a desiccator, under
a stream of inert gas, or with a drying tube) before obtaining a mass or adding
reagents.
Oven and Flame Drying

12. • A drying tube is used when moderately but not meticulously dry conditions are desired in
an apparatus. If meticulously dry conditions are necessary, glassware should be oven or
flame dried, then the air displaced with a dry, inert gas.
• Drying tubes are pieces of glassware that can be filled with a drying agent (often
anhydrous CaCl2 or CaSO4 in the pellet form) and connected to an apparatus either
through a thermometer adapter or rubber tubing).
• Air passing through the tube is removed of water when it comes in contact with the drying
agent. Since it is important that air can flow through the drying tube, especially so the
apparatus is not a closed system, the drying agent should be fresh as used drying agents
can sometimes harden into a plug that restricts air flow.
• Drying tubes can also be filled with basic solids such as Na2CO3.to neutralize acidic gases.
Drying Tubes

13. • Exposure to hot dry air (130°-170°C) for 2-4 hr in a hot-air oven.
• Flame sterilization.
• Autoclaving is a method of sterilizing with water vapor under pressure.
Cotton plugs, gauze, labware, plastic caps, glassware, filters, pipettes,
water, and nutrient media can all be sterilized by autoclaving. Nearly all
microbes are killed by exposure to the super-heated steam of an
autoclave for 10-15 minutes. All objects should be sterilized at 121°C and
15 psi for 15-20 min.
Sterlization of Glassware

14. Drying Solvents/Chemicals
• The process of synthesizing and isolating an organic compound often results in an
organic compound or solution contaminated with traces of water. For instance, in
aqueous extractions some water will be transferred into the organic phase because of
the partial miscibility of the organic phase and water. This water must be removed
before the required compound can be properly characterized.
• The following two methods of drying solutions are commonly used:
 Saturated Aqueous Sodium Chloride
 Solid Drying Agents

15. Saturated Aqueous Sodium Chloride
• The bulk of the water can often be removed by shaking or "washing" the
organic layer with saturated aqueous sodium chloride.
• The salt water works to pull the water from the organic layer to the water
layer.
• This is because the concentrated salt solution wants to become more dilute
and because salts have a stronger attraction to water than to organic solvents.

16. • Final traces of water are removed by treating the organic solution with a drying agent. A drying agent is an inorganic
salt which readily takes up water to become hydrated.
Solid Drying Agents
Drying Agent Capacity Speed Applications
Calcium Chloride, Cacl2 High Medium Used For Hydrocarbons
Calcium Sulfate, Caso4 Low Fast Generally Useful
Magnesium Sulfate, Mgso4 High Fast
Not Used For Very Acid-sensitive
Compounds
Potassium Carbonate, K2CO3 Medium Medium Not For Acidic Compounds
Sodium Sulfate, Na2so4 High Slow Generally Useful

17. 1. Aldrich. Suggestion for cleaning glasswares.Corning,2009. AL-228 Technical Bulletin. 6000 N. Teutonia
Ave., Milwaukee, WI 53209. http://www.sigma-aldrich.com
2. University of Wisconsin-Madison. Office of Chemical safety. The chemical safety machanism: Laboratory
Glassware Cleaning. Environment, Health and Safety Department 30 East Campus Mall, Madison, WI
53715-1227 .
3. https://www.google.com/url?sa=t&source=web&rct=j&url=https://agriculture.az.gov/sites/default/files/
Surfactant%2520Cleaners.pdf&ved=2ahUKEwiQgZym27z-
AhWbTGwGHVASC1cQFnoECAMQBQ&usg=AOvVaw0pI8sJAvyG1LlL8Ibjd5Kg
4. https://chem.libretexts.org/Courses/SUNY_Oneonta/Chem_221%3A_Organic_Chemistry_I_(Bennett)/2
%3ALab_Textbook_(Nichols)/01%3A_General_Techniques/1.02%3A_Glassware_and_Equipment/1.2F%3
A_Drying_Glassware
Reference

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