Laboratory Glassware Cleaning Practices

Use of clean laboratory glassware is critical for high accuracy and precision of your results. Cleanliness of glassware up to the required degree prior to start of analytical work is often underestimated and some analysts feel the job can be entrusted to laboratory support staff. A dedicated analyst on the other hand is never ashamed of washing laboratory glassware to his or her own satisfaction.

Breakages can be frustrating and lead to loss of valuable time. A few precautions taken can avoid such embarrassing situations

• Prevent breakage by exercising care by avoiding hitting of burettes, pipettes or measuring cylinder tips to tap or washbasin walls
• Measuring cylinders, Centrifuge tubes, flasks, etc should be dried on wooden or plastic pegs mouth downwards
• Only soft brushes should be used if necessary. Never clean absorption cells with brushes as scratches will lead to wrong absorbance readings and result in optical mismatch of the cell pair
• Volumetric flask should never be dried in the drying oven with temperatures exceeding 65°C. Always un stopper cover before placing in the oven

Cleaning Agents

Used laboratory glassware should be soaked in water even if immediate cleaning is not possible. Most commonly available detergents can be used for subsequent cleaning. An oxidizing agent such as Potassium dichromate in sulphuric acid is a good choice. The solution becomes green on continued use due to loss of its oxidizing power and should be discarded. A mixture of 3N HCL and 1 volume of methyl alcohol is useful for cleaning of stains in absorption cells. This mixture should not be shaken in closed vessels due to generation of heat.

Grease can be removed from the joints and stoppers by boiling in a weak solution of sodium bicarbonate and subsequently soaked in a solution of potassium dichromate or acetone prior to rinsing with distilled water.

New laboratory glassware is slightly alkaline. Soak in 1% HNO3 or HCl solution for about an hour and then wash with distilled water before drying.