Laboratory Glassware - Cleaning Laboratory Glassware

Cleaning Laboratory Glassware

There are many different methods of cleaning laboratory glassware. Most of the time, these methods are tried in this order:

• The glassware is soaked in a detergent solution to remove grease and loosen most contamination
• Gross contamination and large particles are removed mechanically, by scrubbing with a brush or scouring pad.
  • Alternatively, the first two steps may be combined by sonicating the glassware in a hot detergent solution
• Solvents known to dissolve the contamination are used to rinse the glassware and remove the last traces
• Acetone is often used for a final rinse of sensitive or urgently needed glassware as the solvent is miscible with water, and helps dilute and wash away remaining water from the glassware.
• Glassware is often dried by suspending it upside down to drip dry on racks; these can include a hot air fan to blow the internals dry. Another alternative is to place the glassware under vacuum, lower the boiling points of the remaining volatiles.

If the glassware are still dirty, more drastic methods may be needed. This includes soaking the piece in a saturated solution of sodium or potassium hydroxide in an alcohol ("base bath"), followed by a dilute solution of hydrochloric acid ("acid bath") to neutralize the excess base. Sodium hydroxide cleans glass by dissolving a tiny layer of silica, to give soluble silicates. Care should be taken using strongly alkaline solutions to clean fritted glassware, as this will degrade the frit over time.

More aggressive methods involving aqua regia (for removing metals from frits), piranha solution and chromic acid (for removing organics), and hydrofluoric acid baths are generally considered unsafe for routine use because of possible explosions and the corrosive/toxic materials involved.

Chromic acid is not a preferred method if the glassware is to be used for the biological sciences, as chromate ions can implant themselves in the glass and produce anomalous results when it is subsequently used for cell cultures; to which the ions are toxic. A proprietary alternative known as NoChromix is available, which is essentially a sachet of largely ammonium persulfate and a smaller amount of surfactant. This is poured into a bottle of concentrated sulfuric. Like concentrated hydrogen peroxide, ammonium and sodium persulfate are strong oxidisers, yet they are not hydroscopic and are more stable. This allows them to be more easily stored and used. When mixed with concentrated sulfuric, they begin releasing oxygen, which can oxidise the carbonaceous dehydration products formed from organic residues by the sulfuric to carbon dioxide; 'burning' them off the glass. The rate of effervescence is slower than that of strong piranha solution, allowing more time for deposits to mechanically break up and for the mixture to be used before fully decomposing. This same method is used in some PCB etching tanks, where sodium persulfate (fine etch crystals) are combined with sulfuric acid to oxidise the copper surface and then make it water soluble as it's sulfate.