A laboratory makes use of several glassware items such as volumetric flasks, burettes, pipettes, beakers, watch glasses, specific gravity bottles,vials,petri dishes, graduated cylinders, etc. Such items are not disposables and are used repeatedly. However, the quality of analytical results is dependent to a large extent on their cleanliness and freedom from contamination.
Laboratory glassware cleaning practices covered briefly the adopted glassware cleaning practices.The present article offers suggestions for cleaning of different types of glassware and their cleaning practices after handling of different classes of chemicals.
Cleaning of different categories of glassware
Glassware for laboratory applications should be inspected carefully before use. They should be free from spots and visibly clean, free from chemical contamination and also free from bacteria,ie,sterile before being used in microbiological applications. A simple method adopted for checking freedom from oil or grease contamination is uniform wetting by a stream of distilled water. Presence of grease or oil will prevent uniform wetting and result in formation of minute droplets.
After use immediately soak in warm soap water. Clean any stubborn deposits with a soft brush. Rinse with tap water followed by 3 – 4 rinses with deionised water. Hot air oven drying should be avoided as this can affect the volumetric calibration of glassware. In case glassware is urgently required rinse 2- 3 times with acetone and apply vacuum to remove the residual acetone. Air blowing should be avoided as it can contaminate the cleaned flask.
Wash with soap water. Use long handle soft brush if necessary. and finally rinse 2 – 3 times with deionised water. Remove the joint and boil in a weak solution of sodium carbonate to remove grease. Apply a thin film of grease after cleaning and re-insert into the burette.
Insert pipettes gently into a jar filled with tap water for some time. After removal dip in a jar of dissolved detergent or chromic acid and after soaking for sufficient time (several hours) run deionised water both outside and inside. Wipe outside with lint free tissue. Allow to dry.
Culture tubes and Petri dishes
Microbiological studies required use of culture tubes and Petri dishes. Sterilize before cleaning in the autoclave for 20 – 30 minutes at 121 degrees centigrade and 15 psi pressure. Empty the contents and adopt general cleaning practices as for other glassware.
Cleaning after use of different types of chemicals
Commonly you would encounter aqueous or non-aqueous samples in laboratory analysis.After using aqueous solutions you should wash glassware with tap water followed by rinsing 3 to 4 times with deionised water.In case of non-aqueous samples rinsing with ethanol or acetone is sufficient followed by 3 – 4 rinses with deionised water.
Strong acids and bases
Wear gloves and safety glasses for the cleaning operation. Rinse with several volumes of tap water in a fume hood followed by 3 to 4 rinses with deionised water
Weak acids and bases
Glassware used for handling weak acids or bases or dilute solutions of strong acids or bases can be rinsed with tap water followed by 3-4 rinses with deionised water
Steam autoclaving for sterilization requires essential precautions:
- Remove closure caps, if any, before autoclaving
- Inspect glassware carefully for cracks. Autoclave crack free glassware only as cracked or chipped glassware can break during the process of sterilization.
- Allow the glassware to attain room temperature after autoclaving so as to avoid handling injuries or breakages.
- Only borosilicate glass items should be autoclaved. Bottles which are usually made from soda lime glass do not withstand the autoclave temperatures.
- The autoclave should be provided with auto cut-off in case there is accidental increase in temperature or pressure.
Take adequate precautions when cleaning laboratory glassware. Protection of eyes, hands and dress is essential so as to avoid cut injuries due to breakages, soap solution entry into eyes and causing irritation. Other harsh cleaning agents can cause skin burns or even produce toxicity through skin penetration.