Accurate washing of glassware is important as Good laboratory technique demands clean glassware, because the most carefully executed piece of work may give an erroneous result if dirty glassware is used. The residue from previous analysis will cause inaccuracies, low sensitivity and lack of precision.
Different types of glassware washing techniques:
- Manual washing: Manual cleaning is typically defined as the direct cleaning of equipment by a trained labor using a variety of hand tools and cleaning agents.
- Glassware washer: An equipment designed to wash the laboratory glassware employed along with dryer system. Used glassware shall be kept in the compartment provided with the supply of cleaning agent. Only a trained lab technician can operate the equipment. This is the most reliable and efficient technique for glassware washing.
Prepare cleaning solution daily at the start of work shift or as when required by following procedure :
- Preparation of 0.5 % Teepol : 5 ml of Teepol in 1000 ml Purified Water.
- Preparation of 1% Labolene : 10 ml of Labolene in 1000 ml Purified Water.
- Preparation of 1% Extran: 10 ml of Extran in 1000 ml of Purified Water.
Washing of common laboratory glassware’s:
- Collect used glassware kept in trays labeled as ‘TO BE WASHED ‘.Carry the trays and take in to washing area.
- Empty the contents of the glassware into the washbasin and run water.
- Wipe outer surface of glass ware with tissue paper dipped in IPA/ Acetone to remove any previous information written on Glass ware.
- Rinse the used glassware with running tap water.
- Immerse the glassware in cleaning solution and allow to soak for 15 minutes.
- Rub the inside and outside of glassware with a suitable nylon brush and wash with tap water.
- If required sonicate the glassware in a detergent/hot detergent solution which is a alternate to both a detergent solution and scrubbing.
- Check whether all stains are removed or not. If not, repeat the operation twice to ensure Cleaning.
- Further, rinse the glassware twice with purified water , drain the water.
- Keep the washed glassware on the racks provided in the hot air oven at 60°C. Dry It for 1 hour.
- Acetone may be used for a final rinse of urgently needed glassware as the solvent is miscible with water and helps dilute and wash away remaining water from the glassware and evaporate easily.
- Glassware which do not get cleaned with the above procedure , clean the glassware with 1% nitric acid or more concentrated nitric acid followed by plenty of tap water and finally rinsing with tap water.
- Check the final rinse water for pH it should be between 5.0 – 7.0 .
Washing of pipettes
- Place pipettes, tips down, in a cylinder or tall jar of water immediately after use.
- Do not drop them into the jar. This may break or chip the tips and render the pipettes useless for accurate measurements.
- Be certain that the water level is high enough to immerse the greater portion or all of each pipette.
- The pipettes may then be drained and placed in a cylinder or jar of cleaning solution for 1 hour
- If required soaking shall be for several hours, or overnight, drain the pipettes and run tap water over and through them until all traces of dirt are removed.
- Rinse the pipettes in running purified water and allow the water to out and dry in the hot air oven at 60°C. Dry it for 1 hour.
Washing of Burette
- Remove the stopcock and wash the burette with cleaning solution and water. Rinse with tap water until all the content is removed.
- Then rinse with purified water and dry and wash the stopcock separately.
- Keep the empty cleaned burettes in inverted position.
Washing of cuvettes or other optical glassware
- Glasswares used for optical measurements cylinders, optical cells and cuvettes should be washed by the analysts themselves.
- After each use, cuvettes should be washed well with water and rinsed with methanol, then dry and store in cuvette box.
- When cuvettes develop a buildup on the interior walls, they can be cleaned with acid solutions like dilute acetic acid solution first: soak overnight in 3M acetic acid, rinse well. Do not use the basic solution for washing them.
Washing of silica crucible
- Fill the silica crucible with nitric acid and heat it over the burner under fuming hood.
- Wash with tap water.
- Ignite the crucible at 700 °C temperature in a muffle furnace and then cool it.
Washing of platinum crucible
- Immerse crucible in a Hydrochloric acid or nitric acid followed by copious rinse with Tap water followed by purified water and dry.
Washing of new glasswares
- Most new glassware is slightly alkaline in reaction. For precision chemical tests, new glassware of should be soaked for 2 hours in acid water (a 1% solution hydrochloric or nitric acid) before washing.
- Wash with excess quantity of tap water and then rinse with purified water.
Precaution
- Wash glassware as quickly as possible after use. If a thorough cleaning is not possible immediately, put glassware to soak in water. If glassware is not cleaned immediately, it may become impossible to remove the residue.
- Never soak the glassware for long period in strong alkaline solution as it will damage the glass.
- To prevent breakage when rinsing or washing pipettes, burettes, be careful not to let tips hit the sink or the water tap.
- Use of chromic acid or highly alkaline solution is avoided.
- Do not allow acid to come in contact with a piece of glassware before the detergent is thoroughly removed, if this happens a film of grease may be formed.
- Dispose off any of the remaining corrosive or hazardous material used in the analysis, before giving the glassware for washing.
- All glassware must be scrupulously clean and if it has been standing for any length of time, must be rinsed with purified water before use.
- Protect clean glassware from dust.
- The analysts should wash optical cells and cuvettes themselves.
Safety precaution : When cleaning glassware, wear goggle and gloves.
